Micromachines doi: 10.3390/mi17111292

Authors: Miao Zhang Zhi Xiong Xiaodong Li Ling Zhang

With the rapid development of smart wearable devices and autonomous systems, high-precision and highly robust positioning in GNSS-denied environments—such as indoor spaces, underground areas, and tunnels—has become a critical engineering requirement. Nevertheless, several key challenges remain in practical applications. This paper establishes an adaptive and robust visual-inertial pedestrian navigation algorithm framework. For the inertial sensor, an online error compensation model is constructed, and IMU preintegration is employed to achieve pedestrian motion propagation. For visual observations, a lightweight front-end is designed to reduce computational burden. By introducing the Huber robust kernel function, the quality of visual observation information is evaluated in real time, and anomalous residuals are down-weighted or even rejected, thereby preventing abnormal observation data from degrading the state estimation and significantly enhancing the stability of the system in complex environments. Validation in real-world scenarios demonstrates that the proposed algorithm achieves a positioning error of less than 0.4% in normal environments while maintaining a positioning error within 1.5% in visually degraded scenarios, exhibiting excellent anti-degradation capability and good engineering applicability.

Micromachines doi: 10.3390/mi17111291

Authors: Zhaozhi Wu Aosong Cui Jianxin Zhou Jianxun Lu Xiangfu Chen Yuanji Li Cheng Deng Ri Chen

Micro-electrochemical machining (micro-ECM) is a non-contact subtractive process in which material is removed by anodic dissolution. This review examines 150 publications from 1992 to 2026 on hybrid and assisted machining, tool electrode design and fabrication, and electrolyte flow control. The literature was drawn from major scientific databases and includes journal articles, conference papers, and book chapters, with an emphasis on precision machining of difficult-to-machine materials. In contrast to previous reviews, this work compares the reported performance ranges, limitations, and application scenarios of five principal micro-ECM strategies: vibration-assisted, laser-assisted, jet-based, magnetic-field-assisted, and through-mask machining. It also evaluates tool electrode materials, structural designs, and fabrication methods, including abnormal wear mechanisms in silicon electrodes. Different electrolyte systems and approaches to controlling the inter-electrode flow field are discussed. The review highlights unresolved challenges, including limited understanding of multiphysics interactions, the trade-off between machining localization and mass transport, wear of non-metallic conductive electrodes, and the limited maturity of industrial applications. Priorities for future research include multiscale modeling, in situ measurement, closed-loop process control, and the development of more sustainable electrolytes. These insights may support further advances in micro-ECM and its industrial implementation.

Micromachines doi: 10.3390/mi17111290

Authors: Lingye Kong Jiaming Li Zhixiang Zou Jiangwen Liu

High-reinforcement-fraction SiCp/Al metal matrix composites (MMCs) are difficult to machine efficiently because large, electrically nonconductive reinforcement particles can accumulate in the inter-electrode gap and destabilize discharge and debris evacuation. This study proposes a grooved hollow abrasive electrode for grinding-aided electrochemical discharge machining (G-ECDM). Straight axial grooves are introduced on a hollow abrasive electrode to create enlarged debris-removal pathways without increasing the diamond-grit protrusion beyond the critical discharge gap. Multiphysics simulations and machining observations show that the enlarged pathways redirect electrolyte flow outward, reduce debris residence and local accumulation, and promote the evacuation of large debris particles. Under identical comparison conditions, the proposed electrode achieved a material removal rate (MRR) of 2.14 g/min, compared with 1.41 g/min for the hollow abrasive electrode and 0.07 g/min for the hollow round electrode; the corresponding tool-wear ratio (TWR) was 0.13, compared with 0.28 and 1.01, respectively. Single-factor experiments further show that peak current, pulse width, spindle speed, and flushing pressure affect the trade-off between MRR and tool wear. The results demonstrate that deliberately engineering the debris-evacuation path is an effective means of improving discharge stability and machining performance in G-ECDM of high-reinforcement-fraction SiCp/Al composites.

Micromachines doi: 10.3390/mi17111288

Authors: Hopewell Mnyandu Precious Mahlambi Mun’delanji Vestergaard

Abacavir sulphate residues reported in South African water resources highlight the need for monitoring pharmaceutical contaminants to assess wastewater treatment efficiency and protect aquatic ecosystems. This study aimed to determine whether combining molecularly imprinted polymers (MIPs) with a carbon paste electrode (CPE) could improve the selectivity and sensitivity of abacavir detection while providing a cost-effective alternative to conventional methods. The optimized MIP-CPE sensor was applied to determine abacavir sulphate in real water matrices. The MIP was attained by bulk polymerization and coupled with CPE. The MIP had thermal stability of greater than 300 °C. Using differential pulse voltammetry (DPV), it was possible to quantify abacavir sulphate using a redox probe; a linear response in a range of 2 to 14 µM with a correlation coefficient (R2) of 0.991 was observed, with lower limits of detection (LOD) and quantification (LOQ) of 1.47 µM and 4.47 µM, respectively. Thus, the developed MIP-CPE sensor can be used to detect analyte residues present at trace levels. The developed sensor demonstrated satisfactory accuracy and precision in real water matrices, achieving recoveries of 82.2–101.2% with RSD values of 1.27–7.34% for spiked abacavir sulphate concentrations of 8 and 12 µM. The presence of abacavir sulphate was only detected in uMhlathuzana wastewater effluent samples, with a concentration of 7.19 µM (RSD 7.40%, n = 3). The MIP-CPE showed high selectivity for abacavir sulphate when tested alongside common interferents (lamivudine, ibuprofen, nevirapine, and trimethoprim). Abacavir sulphate gave the lowest peak current (DPV) of the group (489 µA), due to the ferricyanide peak falling when the target rebinds and blocks the probe. A lower current for abacavir therefore means more rebinding, which is evidence of selectivity. The MIP-CPE sensor demonstrated rapid rebinding and strong affinity for abacavir sulphate, even in complex matrices. This study offers wastewater treatment plants as a cost-effective, sensitive, and selective analytical method for routine monitoring of antiretroviral contaminants before effluent discharge into environmental waters.

Micromachines doi: 10.3390/mi17111289

Authors: Laura Ionel Iulia Anghel Cristian Viespe

Spatiotemporal couplings are defined by non-separable spatial and temporal or spectral dependences of the optical field. They must be distinguished from the kinematic conversion between pulse duration and longitudinal spatial extent, s = cτ, which applies to a rigidly translating profile in vacuum under specified observation conditions. This review examines theoretical and experimental frameworks developed to describe such regimes, where diffraction–dispersion analogies coexist with angular dispersion, pulse-front tilt, space-dependent spectra, and structured spatiotemporal wave packets and discusses their influence on peak intensity, nonlinear absorption, energy deposition, ablation, heat-affected zones, processing resolution, surface quality, and reproducibility, while highlighting the emerging role of MEMSs and micromachine-based optical systems in enabling precise control of these processes for advanced laser micromachining. Particular attention is devoted to the fundamental concepts of spatiotemporal analogies, spatiotemporal couplings in ultrashort pulses, and the corresponding spatiotemporal effects relevant to petawatt laser systems. The influence of these effects in ultrashort and ultra-intense laser systems is discussed, where spatiotemporal distortions impact focal intensity and pulse duration. We highlight how spatiotemporal structuring of ultrashort and ultra-intense laser pulses, combined with tailored micro- and nanostructured targets, enables control of field localization, energy deposition, and laser–matter coupling. By proceeding beyond a direct space–time equivalence, spatiotemporal analogies provide essential insight for both fundamental understanding and practical optimization of ultrashort and ultra-intense laser–target interactions.

Micromachines doi: 10.3390/mi17111287

Authors: Kailiang Zhang Wei Xiang Anbin Hu

Many biochemical reactions performed in microfluidic systems, such as nucleic acid amplification and enzymatic assays, require precise, compact, portable, and programmable temperature control. However, existing platforms are often limited by high cost, bulkiness, and poor integration with real-time visualization. Here, we present a portable microfluidic platform that integrates a high-precision thermal regulation module with a smartphone-based imaging interface, enabling real-time sample monitoring under programmable temperature protocols. An STM32 microcontroller with a positional PID algorithm achieves a steady-state temperature accuracy of ±1.5 °C and adjustable heating and cooling rates of 0.1–5 °C/s, supporting both constant-temperature and thermal-cycling modes. As a representative application, we use this platform to evaluate the thermal stability of water-in-oil single-emulsion droplets under programmable heating. In this system, the oil phase was a mixture of silicone oil and RSN-749, and the mass ratio of the two components was varied to examine its effect on droplet stability. Our results suggest that, under the tested conditions, droplet coalescence tended to be more pronounced during temperature ramping than during isothermal holding. For this oil–surfactant formulation, the coalescence ratio remained below 4% across 20–95 °C. Therefore, this low-cost, user-friendly platform offers a practical analytical tool for temperature-controlled microfluidic reactions and thermal stability assessment, with potential for future point-of-care diagnostic workflows.

Micromachines doi: 10.3390/mi17111286

Authors: Morteza Bayareh Minseok Kim

In a microchannel, a gas bubble can occupy much of the available cross-section. Its shape and motion then depend closely on the channel walls and the thin liquid layer between them. This review examines how such confinement governs gas–liquid flow and its momentum, mass, and heat transport. It first considers the forces and flow regimes that arise in different channel geometries, then examines how surface tension and wettability affect bubble formation, deformation, breakup, and coalescence. It focuses on squeezing, dripping, and jetting in T-junction and flow-focusing devices. The review connects these interfacial processes to pressure drop and to transport through bubble caps, liquid films, and recirculating slugs. It also assesses what experimental measurements and numerical methods can reveal about these processes. Across the studies considered, bubble size, void fraction, film thickness, and wall conditions help explain why similar flow rates can produce different hydraulic and transport responses. Progress in prediction will require more complete measurements of interface behavior and models tested across multiple fluids, geometries, and flow regimes.

Micromachines doi: 10.3390/mi17111285

Authors: Yerui Feng Chuanhe Du Yanbo Shi Xiaolong Jiang Hongyan Li

ZrB2–SiC ultra-high-temperature ceramics have important aerospace applications, but their high hardness and brittleness make conventional machining difficult. This study investigated micro-hole electrical discharge machining (micro-EDM) of ZrB2–SiC ceramics using a resistance–capacitance relaxation pulse generator. Single-factor experiments examined the effects of capacitance, voltage, and resistance on the material removal rate (MRR), relative electrode wear ratio, and taper angle. Scanning electron microscopy was used to characterize the machined surfaces. A three-factor, five-level orthogonal design was subsequently employed, and signal-to-noise ratio analysis, range analysis, and analysis of variance were used to quantify the effects and percentage contributions of the machining parameters. Entropy weighting was combined with grey relational analysis to identify a parameter combination that balanced machining efficiency, electrode wear, and hole taper. The selected combination was a capacitance of 10,000 pF, a voltage of 156 V, and a resistance of 500 Ω. Compared with the combination predicted from the factor-level means, this combination reduced the relative electrode wear ratio by 10.34% and the taper angle by 9.11%, with an 11.24% decrease in MRR. Because the orthogonal array was based on single-run experiments (n = 1), the S/N ratios and ANOVA p-values are used for factor ranking and descriptive contribution analysis rather than for formal significance testing. These results provide an experimental basis for selecting process parameters for micro-EDM of ZrB2–SiC ceramics.

Micromachines doi: 10.3390/mi17111284

Authors: Xinxue Pan Haowen Liao Xiangyang Chen Yuxuan Zhou Fangyan Zheng

Trains traveling through rail transit tunnels generate bidirectional, alternating, and intermittent piston-like airflow. Traditional wind energy collectors have problems such as poor bidirectional airflow adaptability and high starting wind speed. This paper proposes a microminiaturized bidirectional differential triboelectric–electromagnetic hybrid generator (BR-TEG). The device adopts a vertical coaxial layered configuration, integrating a triboelectric generator (TEG) and an electromagnetic generator (EMG). The upper and lower layers are assembled with wind cups facing in opposite directions, forming a differential counter-rotating structure that can adapt to the bidirectional reciprocating piston airflow in tunnels and achieve continuous wind capture from all directions. The top layer is equipped with a slip ring transmission mechanism, which resolves issues such as lead wire entanglement and unstable power generation during bidirectional rotation. Experimental results show that the BR-TEG has a minimum startup wind speed of 0.8 m/s, and at a wind speed of 9 m/s, the total peak power reaches 679.02 mW. The device, in conjunction with the energy management circuit, can stably power low-power monitoring devices such as LED arrays and Bluetooth temperature and humidity sensors. Additionally, the frequency of the device’s electrical output exhibits a strong linear correlation with wind speed, enabling it to serve both as a wind energy harvester and a tunnel wind speed monitor. In summary, the BR-TEG provides a new technical solution for the utilization of wind energy in rail transit tunnels and the construction of distributed self-powered systems for smart tunnels.

Micromachines doi: 10.3390/mi17111283

Authors: Max Gonsalves Cruz Gonsalves Ziting Ma Lingping Kong

Micro-sized Li4Ti5O12 is attractive for fast-charging Li-ion batteries because its dense particles can improve electrode packing and reduce surface reactivity, but the long solid-state transport distance is expected to limit rapid Li+ storage. Here, we demonstrate that micro-sized Li4Ti5O12 retains two voltage-selective storage regimes with distinct kinetic signatures. Within the conventional 2.5–1.0 V window, the two-phase Li4Ti5O12/Li7Ti5O12 transition reaction exhibits a pronounced voltage plateau, peak current scaling close to the square root of the scan rate (v)1/2, and a dominant long-time impedance relaxation, consistent with diffusion- and phase-transformation-controlled storage. Extending the lower cutoff potential to 0.005 V activates a low-voltage pseudocapacitive process from Li7Ti5O12 to Li8Ti5O12, characterized by a linear dependence of peak current on the scan rate (v), power-law exponents of 0.83–0.85, and a substantially reduced slow-relaxation contribution during deep lithiation. When discharged to 0.005 V, micro-sized Li4Ti5O12 delivers reversible capacities of 233 mAh·g−1 at 20 mA·g−1 and 155 mAh·g−1 at 1000 mA·g−1. Post-cycling XRD, Raman spectroscopy, HRTEM, and Ti L2,3-edge EELS further show that the LTO framework remains preserved, with enhanced lithiation and Ti reduction near the particle surface. These results demonstrate that pseudocapacitive Li+ storage can persist in micro-Li4Ti5O12 and be accessed through voltage-window control.

Micromachines doi: 10.3390/mi17111282

Authors: Ju-Ho Lee Hangjoon Im Young-Ju Kim Chung-Hui Ma Hee-Chul Lee

Bulk chemical vapor-deposited silicon carbide (CVD-SiC) requires high mechanical strength and plasma etching resistance for semiconductor process components. This study investigated the effects of vacuum annealing at 1400, 1800, and 2000 °C for 1 h on its morphology, composition, crystallographic characteristics, mechanical properties, and CF4/O2 plasma etching behavior. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, flexural testing, and density measurements were performed. The 3C-SiC phase remained dominant under all investigated conditions. At 1800 °C, the mean projected image-area fraction of pit-like features and the (111) peak full width at half maximum reached their minimum values of 0.48% and 0.1137°, respectively. Flexural strength increased by 74.3%, from 427.4 to 744.8 MPa, while density varied little. The surface Si/C atomic ratio decreased from 1.007 to 0.547 with increasing temperature. Mean cumulative mass loss after plasma etching decreased by 19.9%, from 0.1051 g for untreated specimens to 0.0842 g at 1800 °C; the difference between 1800 and 2000 °C was not statistically significant. Annealing-induced changes in morphology, composition, and crystallographic state were associated with the observed property changes. Among the investigated conditions, annealing at 1800 °C provided the highest flexural strength and lowest mean plasma-etching mass loss.

Micromachines doi: 10.3390/mi17111281

Authors: Chao Tan Yingfei Ge Yifan Fei Li Tao Zhihao Song Junjie Chen

During the CO2 laser processing of fused silica optical components, rapid heating to localized high temperatures followed by fast cooling easily induces thermal accumulation effects and forms a heat-affected zone (HAZ). Material modifications occurring within the HAZ (e.g., material densification, changes in fictive temperature, and the generation of residual stress) enhance local absorption of the transmitted laser, thereby increasing the risk of re-damage to the components and compromising their service life. This paper systematically reviews the characterization methods and research progress regarding the HAZ generated during CO2 laser processing of fused silica optics. In terms of macroscopic characterization, the paper first reviews surface and subsurface morphologies and defects observed via optical and scanning electron microscopy (SEM). It then details measurements of absorption properties, molecular structural evolution, and fictive temperature spatial distributions using confocal Raman, photothermal, Fourier-transform infrared (FTIR), and X-ray diffraction (XRD) techniques. Finally, it addresses the evaluation and mitigation of residual stress fields in the HAZ based on fictive temperature and photoelasticity. In terms of microscopic characterization, it summarizes the progress of molecular dynamics (MD) simulations in revealing the atomic-scale evolution of the fused silica network under laser irradiation. It is concluded that reducing thermal accumulation and temperature gradients during laser processing, appropriately controlling the HAZ extent, and suppressing residual stress through methods such as annealing are key to improving the processing quality and operational reliability of fused silica optical components. Future work should further leverage molecular dynamics simulations to conduct precise calculations of microstructural changes as well as coupled calculations bridging microscopic and macroscopic scales, providing theoretical guidance for optimizing laser processing parameters, suppressing the HAZ, and eliminating residual stress.

Micromachines doi: 10.3390/mi17111279

Authors: Hongfeng Zhang Xudong Ren Jianqing Hong Yanqun Tong Long Zhang

This study systematically investigates the dynamic behavior of laser-induced cavitation bubbles and the micro-forming mechanism between parallel walls. The bubble is produced in the middle of the gap. Through integrated high-speed imaging, hydrophone detection, and numerical simulation, the dynamic behavior of cavitation bubbles under parallel-walls confinement is analyzed. The results reveal that bubble oscillation, collapse patterns, and jet formation are governed by the dimensionless parameter ρ (the ratio of bubble diameter to gap distance). Distinct regimes are identified: bubble splitting and dual-jet formation occur when ρ ≥ 0.6, while shock waves exhibit multiple peaks due to inter-wall reflections. Both the plasma shock wave and the first collapse shock wave generally increase with gap distance. Material deformation characteristics are evaluated under varied laser energies and gap distances. Specimens formed at 40 mJ with D ≤ 2 mm display clear fillet features. Surface roughness first decreases and then increases with gap distance, reaching a minimum of 1.82 μm at D = 2 mm. Forming depth increases with laser energy and decreases with gap distance, achieving a maximum of 88 μm at D = 1.2 mm. The most pronounced thinning occurs at the bottom area. These findings establish a theoretical foundation and provide a practical process window (ρ ≈ 0.79–1.03) for optimizing parallel-walls cavitation micro-forming of ultra-thin materials in confined spaces.

Micromachines doi: 10.3390/mi17111280

Authors: Ming Kang Yao Pan Yiming Luo Kaiyong Yang Yonglei Jia Hui Luo Jianhua Shi Shihao Zhu Xiaomeng Jia

During hemispherical resonator gyroscope (HRG) packaging, localized high temperatures cause nonuniform thermal distributions and degrade the stability of key dynamic parameters. To reduce these temperature effects, the HRG thermal field was analyzed using coupled simulations in COMSOL Multiphysics. First, the mechanisms for local high temperatures were analyzed. Second, thermal simulations of getter activation and hermetic welding were performed and optimization strategies were proposed. Third, the effects of housing materials and structural dimensions were investigated to further optimize the temperature effects. Finally, dynamic parameter stability experiments were conducted to evaluate the optimization effectiveness. Compared with the original packaging process, the optimization significantly reduced the disturbance effect of the high temperature on the key dynamic parameters. Throughout packaging, the maximum quality factor (Q factor) reached 1.775 × 107, the frequency split (Δf) remained below 1 mHz and the Q factor inhomogeneity (ΔQ) remained below 3.7%, indicating that the dynamic parameters of the gyroscope were well preserved. Meanwhile, the measured leak rates remained below 1 × 10−12 Pa·m3/s. These results demonstrate the optimization effectively mitigates packaging-induced thermal disturbances, improving dynamic parameter stability with excellent hermeticity. This provides a reliable dynamic parameter basis for the high-performance operation of the HRG.

Micromachines doi: 10.3390/mi17111274

Authors: Alexia Cash Hunter Fitzpatrick Gabriel Garibaldi Anjelyka Fasci Maria J. Londono R. Lyle Hood Michael B. Sano Gongchen Sun

Electroporation, a biophysical method that transiently permeabilizes cell membranes via externally applied electric pulses, has evolved from bulk, low-resolution approaches to highly controlled micro- and nano-electroporation (MEP/NEP) platforms. By inducing a transmembrane potential exceeding a critical threshold (≈0.5–1.5 V), nanoscale pores form, enabling delivery of nucleic acids, proteins, drugs, and probes without viral vectors or chemical carriers. Early work demonstrated efficient plasmid uptake in mouse lyoma cells using high-intensity, short-duration pulses, establishing the foundation for modern gene transfer applications. Contemporary MEP devices improve spatial and temporal field control, reducing voltage requirements and cellular damage, while NEP systems focus the electric field onto subcellular regions, magnifying the electrophoretic component of transport, which contributes to a lesser, cargo- and parameter-dependent degree in bulk and micro-electroporation as well, to achieve rapid, high-efficiency cargo delivery. Advances in device architecture, including microchannels, high aspect ratio nanostructures, nanochannel arrays, and nanofountain probes, have expanded capabilities across gene delivery, tissue engineering, drug screening, cell lysis, and cell fusion. Beyond cargo transport, the applied field is increasingly used as a biological stimulus, modulating extracellular vesicle secretion and cargo content for cell engineering and biomanufacturing. Nevertheless, challenges persist: achieving uniform pore geometry, preserving viability, scaling throughput, and translating in vitro designs to in vivo contexts. Ongoing innovations in electrode materials, fabrication techniques, and integrated microfluidic systems promise to overcome these barriers, positioning MEP/NEP as a versatile platform for accelerating biomedical research and therapeutic development.

Micromachines doi: 10.3390/mi17111273

Authors: Matteo Biscolli Mattia Borgarino

This paper studies the nonlinear behavior of a Gilbert cell multiplier. The investigation has been carried out by means of mathematical modeling and Cadence circuit simulations at room and cryogenic temperatures. The circuit has been implemented in the 130 nm SiGe BiCMOS SG13G2 technology by Innovations for High Performance (IHP) Microelectronics (Frankfurt am Oder, Germany). In addition, a similar investigation has been carried out for a Jones modulator. The comparison demonstrated that the Gilbert cell multiplier exhibits better spectral purity, especially at cryogenic temperatures. This suggests the Gilbert multiplier as a promising mixer for quantum computing control circuits, where spectral purity is critical for the quantum gate fidelity.

Micromachines doi: 10.3390/mi17111278

Authors: Shuyu Zhang Wenqi Guo Xueyang Li Bing Chen Ran Cheng

The interfacial layer (IL) in the gate stack of Hf0.5Zr0.5O2 (HZO) ferroelectric field-effect transistors (FeFETs) strongly affects device performance and reliability. In this work, high-κ IL engineering is investigated using calibrated TCAD simulations and experimental verification to study the role of dielectric constant, physical thickness, and interface traps on the performance enhancement of HZO FeFETs. Typical higher-κ materials, namely, Si3N4, Al2O3, and HfO2, are chosen as ILs. At a fixed physical IL thickness of 2 nm, increasing κ reduces the voltage drop across the IL and redistributes a larger fraction of the applied voltage to the HZO layer, thereby promoting more complete polarization switching. The simulated memory window (MW) consequently increases from 0.77 V for SiO2 to 2.20 V for HfO2. In contrast, at a fixed EOT of 1 nm, the memory performance of the FeFETs remains nearly unchanged among different IL materials, while higher-κ ILs substantially reduce the electric-field stress across the IL, suggesting a potential benefit for gate-stack reliability. Experimental measurements of the no-IL, SiO2-IL, and HfO2-IL devices are further used for model calibration and interface-trap analysis. By incorporating IL-associated interface traps into the calibrated model, the experimentally observed MW differences are discussed in terms of both interface-related effects and IL dielectric properties. These results clarify the condition-dependent benefits of high-κ IL engineering and provide design guidance for improving the memory performance and electric-field management of scaled HZO FeFETs.

Micromachines doi: 10.3390/mi17111275

Authors: Xinyi Wang Wei Li Xueping Li

A 60 GHz antenna array with enhanced radiation performance is investigated for indoor short-range communication applications. To improve array gain while maintaining a fixed number of equivalent elements, an optimized sparse-layout extension approach based on equivalent series-fed subarrays is proposed. An E-shaped microstrip patch and a 1 × 10 Chebyshev-tapered series-fed subarray are first designed, followed by the development of a 4 × 10 baseline planar array. Measurements demonstrate a −10 dB impedance bandwidth of 57.13–62.36 GHz, while the reconstructed radiation patterns indicate a peak realized gain of 17.23 dBi at 60 GHz. The 1 × 10 subarray is then treated as an equivalent element to establish 10-element compact uniform, equal-aperture uniform, and optimized sparse arrays. The equivalent-element positions are optimized using an ideal-array model implemented in MATLAB R2024a and subsequently mapped onto HFSS full-wave models for electromagnetic evaluation. Compared with the equal-aperture uniform array, the optimized sparse array increases the peak realized gain in the Φ = 90° plane from 22.57 to 23.94 dBi and reduces the maximum interport coupling from −12.31 to −26.33 dB while preserving a stable main-beam direction. The MATLAB–HFSS comparison shows similar beamwidths; analyses at 58, 60, and 62 GHz reveal frequency-dependent sidelobe and beam-pointing variations and assess excitation-error sensitivity.

Micromachines doi: 10.3390/mi17111276

Authors: Peng Liu Jiaqin Yang Tianfeng Zhou Aowei Xing Wenhan Yang Yichuan Zhang

Monocrystalline silicon is an ideal material for infrared optics microlens arrays, achieving excellent performance, but the processing is extremely difficult and poses a challenge to traditional processing processes. In this paper, a new process flow for processing monocrystalline silicon microlens arrays is proposed, combining femtosecond laser three-dimensional dynamic focusing processing technology with sandblasting and polishing finishing technology. Dynamic focusing technology is used to adjust the focus position in real time to adapt to the complex processing needs of three-dimensional structures, and the influence of different laser processing parameters on the processing size and morphology is studied. The mechanism of processing errors and surface defects is proposed to realize the compensation of three-dimensional processing errors. Through experiments and simulations, a 515 nm green light, 100 KHz repetition frequency, power of about 20 W—maintaining the same scanning speed of 3000 mm/s and isotropic filling scanning interval of 5 μm, with an on delay of 0.23 ms, an off delay of 0.12 ms, a corner delay of 0.13 ms, and a null walk delay of 0.24 ms, and a delamination height of 1 μm—were finally selected for the laser processing. The process parameters are feasible and the processing effect is good, providing a new solution for processing hard and brittle materials.

Micromachines doi: 10.3390/mi17111277

Authors: Sungmin Lim Juwon Kang Woochul Kang Doohyun Kim Jinwook Kim

High-intensity sonication systems operating at tens of kilohertz deliver acoustic energy from a Langevin transducer into a liquid medium, where the severe impedance mismatch between the metallic head mass and the liquid causes substantial reflection at the vessel wall and limits the pressure available for cavitation. Here, we present a two-step fabricated metastructured acoustic window that realizes continuous gradient acoustic-impedance matching for 40 kHz Langevin-coupled sonicators. The window is fabricated by printing a micro-pyramid array in glass-filled photopolymer, which features a high acoustic impedance of 6.3 MRayl, using a micro-precision stereolithography (SLA) printer, and casting low-viscosity epoxy (3.1 MRayl) into the interstices of the pyramid array, followed by room-temperature curing. Since the resin fill fraction decreases monotonically along the thickness direction, the effective acoustic impedance transitions continuously from the resin-rich base toward the liquid, thereby enhancing pressure transmission into the working medium near the targeted frequency (40 kHz). The performance of the gradient matching window was evaluated by k-Wave simulations, finite element analysis (FEA), and experiments with a 40 kHz Langevin sonicator. Numerical simulations indicated higher local pressure near 40 kHz, while relative receiver-voltage measurements provided preliminary support for the predicted output trend. The proposed two-step fabrication technique combining SLA printing and low-viscosity epoxy casting provides a simple and cost-effective strategy for gradient impedance matching and is expected to facilitate rapid prototyping and design of 40 kHz high-power sonicator components.

Micromachines doi: 10.3390/mi17111272

Authors: Jiaoyang Li Yuanyuan Li Tianyu Zhang Ziyue Zhao Yue Tang Jing Zhang Zhuolin Li Aiqin Luo Zikai Hao

Gut microbiota-associated molecules influence cardiovascular and neurovascular physiology through microbial production, intestinal transfer, host transformation, and systemic delivery. Organ-on-chip (OoC) and microphysiological systems (MPSa) provide experimental platforms for investigating these processes across human tissue interfaces. However, nominal molecular input does not necessarily represent exposure at the responding tissue. This difference complicates comparisons across experimental platforms. This review examines intestinal, inter-organ, cardiovascular, and neurovascular MPS along the pathway from microbial signal generation to tissue response. It examines how material interactions, fluidic conditions, and biological transport processes determine molecular delivery. Evidence across platforms shows that compound recovery and downstream concentration vary with molecular properties and device materials. Cardiovascular and neurovascular studies further relate defined molecular exposure conditions to endothelial, thrombotic, cardiac, and neurovascular responses. Comparisons of compound recovery, compartmental concentrations, mass balance, and functional responses clarify the factors influencing molecular delivery and biological effects across OoC/MPS platforms. This review highlights the importance of quantifying molecular delivery and tissue exposure when interpreting functional responses across OoC/MPS platforms.

Micromachines doi: 10.3390/mi17111270

Authors: Xiaoming Yang Tianqian Li Taiqiang Cao Xuan Lin Zhe Yang Zhongwu Cai

To improve the tradeoff between dynamic breakdown voltage (BVdyn) and specific on-resistance (Ron,sp) in SOI LDMOS devices, a double-step-doped SOI LDMOS with a P-type buried layer (DSD-PBL SOI LDMOS) is proposed. The device incorporates a double-step-doped (DSD) drift region and a uniformly doped P-type buried layer (PBL) beneath the buried oxide (BOX). The DSD drift region and the PBL jointly modulate the electric-field distribution, enabling a high drift-region doping concentration while preserving the breakdown capability. Simulation results show that the proposed device achieves a BVdyn of 678 V, which is comparable to the 680 V obtained by the step-doped SOI LDMOS (SD-SOI LDMOS) with the same DSD drift region and higher than the 605 V obtained by the conventional SOI LDMOS (C-SOI LDMOS). Meanwhile, the proposed device has a Ron,sp of 7.84 Ω⋅mm2, corresponding to reductions of 39.0% and 45.6% compared with the SD-SOI LDMOS and C-SOI LDMOS devices, respectively. Under identical switching and thermal-management conditions, the reduced Ron,sp results in lower conduction losses and improved thermal performance.

Micromachines doi: 10.3390/mi17111271

Authors: Liron Cohen Lidor Bazon Joseph B. Bernstein

Power-law exponents are widely used to describe time-dependent transistor degradation and to extrapolate accelerated measurements toward operating conditions. Their physical interpretation, however, depends on the baseline from which degradation is measured. This study examines baseline sensitivity using published gate-all-around (GAA) transistor degradation data and a zero-curvature baseline reconstruction rule. In a primary dataset of 24 degradation curves, each curve yields one admissible zero-curvature root, shifting the median nominal exponent n = 0.550 to a reconstructed value 1/m = 0.346. Within an established phenomenological framework, this shift changes the inferred correlation parameter from χ = −0.820 to χ = −1.899. The apparent decrease in the local exponent with accumulated degradation appears in 19 of the 24 nominal curves but remains in only 5 curves after baseline reconstruction and is not robust under cross-fitted analysis. Across 26 eligible external nanowire curves (≥5 time points, out of 32 total curves), 19 curves yield a single admissible zero-curvature root. These roots remain numerically stable under single-point deletion (median relative change in m of 2.97% across 15 eligible curves) without systematically improving the secondary log–log fit. Numerical root stability therefore does not establish physical baseline validity. Consequently, the empirical exponent remains a useful kinetic descriptor, but it does not by itself distinguish between HCI- and BTI-like behavior or establish a transition between them.

Micromachines doi: 10.3390/mi17111269

Authors: Melika Morsali Pranav Choori Ethan C. Ahn Mircea R. Stan

Filamentary metal–oxide RRAM conducts through a tunneling gap for which the current grows exponentially with bias, so its Read-range I–V characteristic follows a sinh(V/V0) law. This introduces a systematic, input-dependent multiply–accumulate (MAC) error when used in analog Compute-in-Memory (CiM) accelerators with inputs encoded as voltage amplitudes. Because the nonlinearity also varies with resistance state, a single correction factor cannot generally compensate for all programmed weights. We present a measurement-calibrated device-to-circuit study of this error and show how it can be mitigated by replacing voltage-amplitude inputs with fixed-bias time-domain inputs, as in Asynchronous Stream Computing (ASC), which uses constant-amplitude sigma–delta streams. RRAM samples from two independent processes, Pt/Ti/HfO2/Ta/Pt and Al/TiO2/Au/Ti, are characterized, and the Stanford compact model is calibrated to each process. Together with two published parameter sets, the fitted nonlinearity coefficient V0 spans 0.29–0.55 V across four stacks and varies with resistance state within individual devices. In 65 nm circuit simulations, voltage-amplitude encoding incurs up to 30% relative error in a single cell and approximately 8.5% full-scale-normalized error in single-bitline crossbars of 4 to 256 rows. At a 5 ms accumulation window, ASC reduces the array error to 0.4–0.8% with ideal-integrator readout and 0.8–2.3% with transistor-level AΣΔM readout. Under measured device variability, group-balanced Monte Carlo simulations yield 7.6–9.2% analog error versus 0.5–0.7% ASC error. Wire resistance reduces the fixed-bias advantage but does not eliminate it within the simulated conditions. First-order energy estimates identify accumulation time and cell read current as important costs, while practical implementation also requires wordline drivers and high-ratio current division.

Micromachines doi: 10.3390/mi17111266

Authors: Luming Chen Shenglin Ma Yingying Liu Ruochen Ding Xiaoqing He Yan Chen

Through-silicon via (TSV)-based 3D ICs continue to scale with advanced CMOS technology nodes. TSV interconnects therefore operate over a wide operating-temperature range, set jointly by the ambient temperature and by self-heating under rising power density. As a result, the temperature dependence of their electrical behavior can no longer be neglected. To address this, a temperature dependence equivalent circuit model for ground signal ground through silicon vias (GSG-TSVs) is proposed in this paper. The model simultaneously incorporates electrothermal coupling effects and the parasitic surface conduction (PSC) effect. The model is validated against HFSS simulations for three geometries (2.5/12.5, 3.5/25 and 5/50 μm) and against measurements of a fabricated 3.5/25 μm GSG-TSV from −40 °C to 100 °C and from DC to 50 GHz. Good agreement and scalability are achieved from −40 °C to 100 °C and from DC to 50 GHz. The influence of TSV size variations is further investigated. The results demonstrate that GSG-TSVs become increasingly susceptible to electrothermal effects as the diameter scales below 5 μm. This work provides a modeling methodology for analyzing the temperature-dependent behavior of TSV interconnects, including electrothermal coupling, over a wide temperature range.

Micromachines doi: 10.3390/mi17111267

Authors: Yihan Zhang Yiming Fan Mingrui Liu Zhongqian Niu Zuqiang Ou Jincai Qiao

Traditional planar interconnections in RF front ends limit multilayer integration, resulting in increased module size and high-frequency losses. To address these challenges, this work proposes an ultra-wideband vertical interconnect covering 10 kHz–100 GHz and develops a miniaturized local oscillator driver module for millimeter-wave spectrum analyzers. Measurements demonstrate that the proposed interconnect achieves a return loss better than 10 dB and an insertion loss below 3 dB across the entire frequency range. A K-band interdigital bandpass filter achieves an in-band insertion loss 2.7 dB and out-of-band suppression exceeding 60 dB. Furthermore, a multilayer cavity integrates frequency multipliers, amplifiers, and filters within a compact volume of 23 mm × 20 mm × 20 mm. The proposed approach enables low-loss, high-density integration and provides a practical solution for miniaturized millimeter-wave spectrum-analyzer front ends.

Micromachines doi: 10.3390/mi17111268

Authors: Guo Li Na Pang Fei Li Chunting Xu Yutian Shi

The residence time difference (RTD) fluxgate sensor exhibits high sensitivity and enables precise detection of weak magnetic fields, and has been widely applied in geophysical exploration and environmental monitoring. However, in practical measurements, the sensor is susceptible to environmental and intrinsic noise, resulting in degraded accuracy. To address this issue, a multi-stage denoising algorithm integrating wavelet thresholding, attention-based residual learning, and multi-scale adversarial optimization is proposed. First, high-frequency disturbances are suppressed via multi-scale wavelet soft-thresholding. Then, an attention residual autoencoder is introduced, where residual connections preserve signal characteristics, and the attention mechanism captures both local details and global temporal features, improving denoising performance and fidelity. Finally, a generative adversarial network (GAN) with multi-scale constraints is employed to further attenuate residual noise and enhance signal consistency. Experimental results show that, compared with wavelet transform, Channel Attention Transformer, and EMD methods, the VRI is improved by 0.86, 3.01, and 3.44, respectively, while the time-difference fluctuation is reduced by 12.9%, 61.4%, and 62.5%. The proposed method improves signal accuracy and stability, providing effective algorithmic support for high-precision RTD fluxgate measurements.

Micromachines doi: 10.3390/mi17111265

Authors: Junyang Zhao Han Yu Zhili Zhang Kefan Zhang Yuxuan Li Fan Zhang Qing Zhou

Event cameras and low-cost microelectromechanical systems (MEMS) inertial measurement units (IMUs) are widely used in event-based visual–inertial odometry (EVIO). However, the bias instability and noise of MEMS gyroscopes accelerate drift accumulation, making loop-closure detection essential for global consistency. Existing EVIO systems largely inherit loop-detection pipelines from conventional visual–inertial odometry, whose fixed score thresholds and raw inlier counts degrade when event-frame quality fluctuates during high-speed motion or under high-dynamic-range illumination. This paper proposes MEVFusion-LD, which fuses MEMS inertial and event-vision measurements using adaptive scoring and match-quality weighting. First, an adaptive scoring threshold (AST) mechanism updates the candidate-entry threshold online from the first- and second-order statistics of query scores, with bilateral clamping. Second, temporal-consistency voting accumulates retrieval votes within a sliding cache window to suppress sporadic false candidates. Third, match-quality-weighted verification (MQWV) replaces the raw inlier count with a quality-weighted inlier ratio for geometric confirmation, followed by 4-DoF pose-graph optimization for online drift correction. Experiments on the VECtor and MVSEC datasets, both collected using MEMS-grade inertial sensors, show that MEVFusion-LD reduces the mean absolute trajectory error by 29.8%, 41.1%, and 50.0% relative to ESVIO, ESIO, and PL-EVIO, respectively, achieves the best accuracy on 9 of 11 sequences, and reduces ATE by 52.8% on average through the loop module alone.

Micromachines doi: 10.3390/mi17111264

Authors: Abhijit Samant Ramanuj Kumar Ashok Kumar Sahoo Amlana Panda

Titanium-grade 9 (Ti-3Al-2.5V) is a lightweight alloy with high strength and corrosion resistance; however, its low thermal conductivity and chemical reactivity make machining challenging, resulting in high cutting temperature, high tool wear, poor surface quality, and high energy consumption. This study investigates the influence of laser-induced micro-textured carbide tools on the machinability of titanium-grade-9 alloy during CNC turning. Micro-textures were fabricated using a fiber laser machine on the rake and flank faces of the cutting tool. The experiments were designed using an L18 orthogonal array with four control factors, namely tool type (Tt), cutting speed (v), feed (f), and depth of cut (d). The tool type factor comprised three configurations: untextured tool (T1), grooved texture on both rake and flank face (T2), and dotted texture on the rake face combined with grooved texture on the flank face (T3). The machinability and texture tools performance were analyzed using results of surface roughness, cutting temperature, tool wear, and cutting-power consumption. T2 exhibited the best performance, while abrasion and adhesion were the most dominant forms of wear identified. CRITIC-MARCOS optimization identified tool type T2, a cutting speed of 80 m/min, a feed of 0.06 mm/rev, and a depth of cut of 0.2 mm as optimal parameters.

Micromachines doi: 10.3390/mi17111263

Authors: Xiao Su Duanling Li Fengkun Xu Jin Huang

Reconfigurable miniature modular robotic swarms realize flexible payload transportation by the serial assembly of micro vehicle modules. Strong dynamic coupling and unsynchronized motion among interconnected modules bring prominent challenges to the stable cooperative operation of micro-robotic transport systems. To tackle modeling and coordination control challenges of scalable micro modular robots with variable chassis structures, this paper develops a hierarchical nested constraint-following modeling and cooperative control framework based on UK analytical dynamics, with distinct mathematical and computational advances over conventional monolithic modeling approaches. Each miniature module is equipped with an integrated steering micro chassis and embedded controllers for real-time motion computation. First, an underactuated nonlinear dynamic model for each individual unit is built without redundant auxiliary variables. Based on this unit model, the proposed framework supports swarm system modeling for transportation swarms composed of an arbitrary number of modules. Second, inter-module geometric constraints are transformed into second-order acceleration equations. Moore–Penrose pseudoinverse analytically solves constraint forces, enabling recursive nested full-system modeling for n connected modules. From a computational perspective, the recursive nested architecture eliminates the need to reconstruct global mass and constraint matrices from scratch when the swarm configuration changes, which significantly reduces modeling complexity and enables scalable dynamic computation. Third, global trajectory tracking missions are recursively decomposed into independent constraint-following subtasks for each module, with a damping correction term embedded to eliminate initial tracking errors. Numerical simulations with four serially connected miniature modular robot units demonstrate that trajectory tracking errors converge to near zero within 0.5s. Compared with the LQR baseline controller, the proposed approach achieves a lower peak deviation and a substantially reduced cumulative tracking error. When subject to external torque disturbance, the system maintains satisfactory heading synchronization and rapidly recovers steady-state control outputs, verifying favorable disturbance-rejection performance. This work offers a unified modeling and coordination-control solution for reconfigurable micro robotic transport platforms, supporting micro-robotics haulage research.

Micromachines doi: 10.3390/mi17111262

Authors: Jiahua Zhong Haonan Li Xinyi Chen Hao Chen Dinghui Chen Guanchong Wu Lok Ting Chu Weijin Guo

Curved microwells have become increasingly important in three-dimensional (3D) cell culture because their concave geometry better represents the native cellular microenvironment, promotes spontaneous cell aggregation, and supports tissue-like organization compared to conventional flat substrates. However, traditional fabrication of such curved microwells often relies on complex, multistep processes that require cleanroom facilities, customized masks, or specialized equipment. Here, we present a simple, cost-effective, and single-step lithographic method using off-stoichiometry thiol-ene (OSTE) polymer to produce micropillar arrays with omega (Ω)-shaped tops, which serve as masters for replica-molding polydimethylsiloxane (PDMS) microwells. Our approach uses a porous, carbon-loaded PDMS membrane templated from processor pins as a combined mold and light-shielding layer. OSTE precursor is filled into the membrane pores and cured under a single diffused UV exposure through a glass diffuser, simultaneously forming both the pillars and their curved tops without the need for chrome masks or photolithographic tools. The resulting OSTE micropillar arrays exhibit tunable top diameters (666–1151 µm) controlled by UV exposure time, and show hydrophobic surface properties (contact angles up to ∼135°). PDMS replica casting faithfully reproduces the Ω-shaped geometry, yielding smooth, biocompatible microwells potentially suitable for 3D cell culture. This method significantly reduces fabrication complexity, time, and cost, offering a practical and scalable route to curved microstructures for tissue engineering and organoid applications.

Micromachines doi: 10.3390/mi17111261

Authors: Kaipeng Bi Di Li Yang He Dawei Mu Fei Liu Weijun Fu Pengchao Wang Shuwei Xiao

Congenital malformations, iatrogenic injuries, and acquired diseases of the ureter often lead to structural or functional defects, yet tissue engineering approaches for ureteral repair and reconstruction remain limited. In this study, a photo-crosslinkable bladder acellular matrix (BAMMA) was synthesized from porcine bladder acellular matrix (BAM) through enzymatic digestion and methacrylic anhydride modification. The mechanical and biological properties of GelMA, GelMA/BAMMA, and BAMMA hydrogels were comprehensively characterized, and 3D-bioprinted tubular scaffolds were fabricated using a GelMA/BAMMA hydrogel and adipose-derived mesenchymal stem cells (ADSCs) mixture as the bioink and subsequently embedded in the rat omentum. The GelMA/BAMMA hybrid hydrogel combined the favorable mechanical properties of GelMA with the biological activity of BAMMA, supporting the growth and proliferation of ADSCs. One week after omental embedding, histological and immunohistochemical analyses revealed enhanced tissue remodelling, neovascularization and mitigated local inflammatory response in the ADSC-seeded scaffolds compared with the unseeded controls. These findings demonstrate that ADSC-loaded GelMA/BAMMA bioprinted tubular scaffolds can undergo tissue remodeling and vascularization in a rat omental model, providing a feasible hydrogel bioink for ureteral tissue engineering and a foundation for future research on ureteral repair.

Micromachines doi: 10.3390/mi17111257

Authors: Yuan Sun Yue Zhang Linjing Liu Jie Wu Hang Xie Jinpeng Ma Yulin Yang Bin Yang

BaTiO3-based ceramics are regarded as one of the promising lead-free alternatives to PZT-based ceramics, and their property enhancement remains one of the most important research directions. This study presents Ba0.96Ca0.04Ti1−xHfxO3-5BT (x = 0.05, 0.07, 0.08, 0.09, 0.10) ceramics with enhanced piezoelectric properties using a crystallographic texture strategy. Highly textured Ba0.96Ca0.04Ti1−xHfxO3-5BT ceramics were successfully prepared by the templated grain growth method, and the effects of Hf content in matrix on the phase structure, morphology, and properties of the textured ceramics were investigated. The textured Ba0.96Ca0.04Ti0.93Hf0.07O3-5BT samples achieved a piezoelectric coefficient d33 of 580 pC/N, an electromechanical coupling factor kt of 0.62, and a high unipolar normalized strain Smax/Emax of 1390 pm/V (measured at 10 kV/cm), together with a strain hysteresis Hs as low as 3.7% under 30 kV/cm, demonstrating excellent piezoelectric properties and favorable strain hysteresis. The excellent comprehensive performance can be attributed to the high-quality preferred orientation and the orthorhombic and tetragonal phase coexistence. Moreover, the multilayer textured Ba0.96Ca0.04Ti0.93Hf0.07O3-5BT ceramics were fabricated by internal electrode co-firing method. The multilayer samples with 10 layers produced a displacement of 581 nm under a driving voltage of 250 V. This study demonstrates that textured BCTH-5BT ceramics can serve as promising eco-friendly lead-free candidates for potential piezoelectric actuation applications.

Micromachines doi: 10.3390/mi17111260

Authors: Yana Pigareva Arseniy Gladkov Vladimir Kolpakov Evgeny Isaev Ivan Tarasov Diana Yuzhakova Matvey Zaozerskiy Victor Kazantsev Irina Mukhina Konstantin Yashin Alexey Pimashkin

Gliomas are the most common primary malignant brain tumors and are frequently associated with severe neurological comorbidities, most notably tumor-associated epilepsy. Seizures affect 40% of all patients and up to 80% of patients with IDH-mutant low-grade gliomas, while more than half of these cases are refractory to standard antiseizure medications. Despite significant advances in molecular profiling, the mechanistic interplay between infiltrating glioma cells and peritumoral neuronal circuits remains poorly understood, largely due to the lack of adequate in vitro models that recapitulate both the cytoarchitecture and the electrophysiological complexity of the tumor microenvironment. In this Perspective, we discuss the use of microfluidic Glioma-on-a-Chip platforms as a transformative tool for studying glioma-neuron interactions. These compartmentalized devices, when integrated with multi-electrode arrays and patient-derived cells (including human iPSC-derived neurons), enable real-time monitoring of the interaction of neurons and cancer cells, tumor invasion, network hyperexcitability, and pharmacological responses. The integration of these advanced platforms offers the potential to generate more physiologically relevant disease models. Recent studies have demonstrated that glioma-on-a-chip platforms are valuable for unraveling fundamental mechanisms of network hyperexcitability and may facilitate personalized drug screening, improving clinical outcomes.

Micromachines doi: 10.3390/mi17111258

Authors: Han-Gyun Lim Minseo Son Min-Woo Ha Jongsung Park Dong-Won Kang

Monolithic perovskite/silicon tandem solar cells have reached certified efficiencies above 35% at small area, while large-area devices have reached the mid-30% range and full-area M10 tandems have exceeded 28%. Translating these gains to industrially standardized textured silicon wafers introduce a different class of manufacturing constraints. Although dry processing removes solvent-wetting and drying-front instabilities, it does not intrinsically guarantee conformal, compositionally uniform, or defect-free coverage on realistic silicon textures. The central problem is no longer simply whether a wide-bandgap perovskite can be deposited from the vapor phase, but whether a complete top-cell stack can be formed reproducibly over M6-, M10-, and ultimately G12-class wafers while preserving local texture coverage, composition, interface integrity, cycle time, and yield. This focused review examines dry-process engineering for wafer-scale perovskite/silicon tandems, with emphasis on the textured-surface problem, multi-source and sequential evaporation, close-space sublimation, dry carrier-selective contacts, transparent-electrode integration, source geometry, process monitoring, materials utilization, maintenance, and in-line metrology. We distinguish true conformal coating from valley filling or partial planarization and argue that dry deposition should be judged at the stack and wafer levels rather than by absorber uniformity alone. Finally, we propose manufacturing-oriented qualification metrics and a staged roadmap from texture-robust deposition to M10/G12 repeated-batch yield and reliability.

Micromachines doi: 10.3390/mi17111259

Authors: Yogesh Babu Margarita Chizh Sebastian Kisban Matthias Schmidt Gregor Feiertag Matthias Winter

This paper investigates radio-frequency (RF) interference mechanisms in micro-electro-mechanical systems (MEMS) microphones, identifying thermoacoustic (periodic heating of the ASIC resulting in pressure changes in the acoustic back volume of the microphone) coupling as the dominant mechanism responsible for generating audible artifacts. A TDK T5838 digital MEMS microphone was used as the test vehicle for this investigation. A simulation chain combining Ansys HFSS electromagnetic modeling, circuit simulation to identify ASIC power loss, and Ansys Icepak transient thermal simulation predicts back volume temperature oscillations and sound pressure via the ideal gas law. A conducted-immunity test bench was built following IEC 62132-4, i.e., direct power injection on I/O pins, sweeping the RF carrier from 500 MHz to 7 GHz with 80% amplitude-modulated (AM) interference. The interferer (hereafter referred to as noise) shows a trend toward higher amplitudes with increasing carrier frequency and lower amplitudes with increasing modulation frequency, consistent with thermoacoustic rather than electrical demodulation. Simulated and measured noise levels agree well across all four evaluated pins. Measurements under reduced pressure confirm the thermoacoustic origin: lowering the back volume air pressure reduces interference significantly and eliminates the modulation-frequency roll-off, exposing electrical demodulation close to baseline (without RF interferer) noise. As a mitigation strategy, we encapsulated bond wires, identified as heat exchangers into the back volume, with a thermally insulating silicone material, achieving 20 to 25 dB noise reduction. These results confirm thermoacoustic coupling as the primary RF interference path and point to practical strategies for improving RF robustness in next-generation MEMS microphone designs.

Micromachines doi: 10.3390/mi17111255

Authors: Tong Zhou Lanwei Lu Xiangting He Feng Zhang

Compact sensing systems can support the preparation and dilution of helium–air mixtures. This study presents a dual-electrode piezoelectric micromachined ultrasonic transducer (PMUT) for helium concentration calibration using its transient response. The inner electrode excites the membrane, and the outer ring electrode detects the response, enabling the amplitude-envelope area, fitted decay rate, and band-summed spectral index to be extracted from the same waveform. The PMUT comprises an aluminum nitride (AlN) piezoelectric layer and molybdenum electrodes on a silicon-on-insulator (SOI) substrate and was fabricated using a complementary metal–oxide–semiconductor (CMOS)-compatible process. Over 60–80 vol% helium, the fitted decay rate increased with an endpoint-based sensitivity of approximately 5.8 × 102 s−1 per vol%. For the measured concentrations within the 30–90 vol% interval, the spectral index exhibited a linear relationship with R2 = 0.9888 and an endpoint-based sensitivity of −0.21 V2 per vol%; the actual calibration points spanned 33.3–81.8 vol%. The envelope area decreased at higher helium fractions. These results establish concentration calibration in helium–air mixtures using a single PMUT and fixed-frequency excitation without frequency sweeps during measurement.

Micromachines doi: 10.3390/mi17111256

Authors: Ci Song Zheng Yu Xiaohong Chen Xiaojing Liu Wei Li Zao Ni Shuguang Yu Xinxin Li

Real-time monitoring of local muscle response during acupuncture could reveal mechanisms underlying acupuncture and provide objective feedback to support more precise needle control. However, the small dimensions of acupuncture needles impose stringent constraints on sensor miniaturization and packaging. This study presents an ultraminiature pressure sensor integrated into the tip of a 450-μm-diameter acupuncture needle. The sensor measures 200 × 1250 × 50 μm3 and incorporates an elongated pressure-sensitive diaphragm. Wafer-level AuSn solder deposition and thermocompression soldering connect the chip to an ultrafine wire ribbon routed through the 230-μm-diameter needle lumen. A 1.3-μm-thick Parylene C coating provides electrical insulation. After coating, the sensor exhibited a sensitivity of 40.3 μV/kPa at a 3.3 V excitation, retaining 78.4% of its uncoated sensitivity. Characterization over 90–150 kPa absolute and 25–45 °C yielded a maximum nonlinearity of approximately 0.73% of full scale (FS). The coated sensor exhibited a maximum hysteresis of 2.52% FS. In vivo experiments at the Zusanli acupoint in rats recorded pressure variations during thrusting–lifting manipulation. These results demonstrate the feasibility of monitoring local muscle response during acupuncture and their potential to provide quantitative feedback for needle manipulation.

Micromachines doi: 10.3390/mi17111254

Authors: Liming Qian Jiaqi Li Feng Guo

Soft magnetic tactile trajectory reconstruction depends on motion and deformation history. We investigated whether an empirical dynamic simulator could inform useful refinements of an existing real-trained reconstruction chain. Virtual exploration and real-record observations motivated a function-preserving multiscale causal-history expansion trained with real data only. In two source sessions, the selected joint-objective model reduced mean command-referenced planar error from 0.436 to 0.408 mm and from 0.452 to 0.424 mm, with approximately 45% lower residual step root-mean-square (RMS). Eighteen matched runs from one initialization showed that additional data and optimization alone did not reproduce the large stability gain; a representative residual gated-recurrent-unit (GRU) model did not reproduce it either. Eight sequences from a partial repeat execution of the test plan supported joint error and stability improvement. Measurements acquired after the original model freeze supplied a separate hemispherical-indenter check: in six of 12 sequences that met a fixed baseline-comparability criterion, the common-output planar error decreased from 0.474 to 0.453 mm and the residual step RMS from 0.259 to 0.169 mm. Eight-direction holds showed lower within-hold fluctuation but not consistently lower between-direction mean bias; the median paired command-response-proxy difference was zero. Command-derived references, limited assemblies and unmeasured physical uncertainty bound stronger accuracy and latency interpretations.

Micromachines doi: 10.3390/mi17111253

Authors: Joanna Smajdor-Baran

Recent advances in sensor science have significantly transformed modern healthcare, environmental monitoring, industrial diagnostics, telecommunications, transportation, and energy systems [...]

Micromachines doi: 10.3390/mi17111252

Authors: Dezhong Guo Gengxu He Xixi Mo Suodian Zhou Hongwei Li Maodan Yuan Xuanrong Ji Junjun Lei

Ultrasound-enhanced sedimentation offers a robust strategy for microparticle separation in microfluidics. Triangular cross-sectional channels have recently emerged as a promising architecture because the acoustic radiation force and acoustic streaming-induced drag act synergistically toward the channel base—a force-field configuration unattainable in conventional rectangular or circular channels. However, quantitative relationships between operational parameters and continuous-flow sedimentation remain unexplored. Here, we systematically investigate how five parameters—volumetric flow rate, number of active transducers, active transducer length, driving voltage, and particle diameter—affect sedimentation efficiency in a triangular glass capillary. The number of active transducers is the most influential: dual-transducer operation sustains an outlet sedimentation efficiency—defined as the fractional particle removal relative to the inlet concentration—of ~77% sedimentation at 30 μL/min versus <30% for a single transducer. Flow rate shows a threshold near 27 μL/min for the baseline configuration, and increasing transducer length from 10 to 40 mm raises the measured maximum allowable flow rate from 15 to ~50 μL/min. A minimum of 19 Vpp is required for ≥80% efficiency. Ultrasound provides the greatest benefit for 5 μm particles (from <40% by gravity to >90%), while 20 μm particles gain less. A normalized sensitivity analysis offers design guidance for acoustofluidic sedimentation platforms. These findings establish quantitative design rules and confirm the feasibility of triangular-channel architectures.

Micromachines doi: 10.3390/mi17111251

Authors: Stefania Petrosino Lucia Baldino Víctor Sebastián

Alginate nanogels are promising carriers for drug delivery owing to their biocompatibility, high water content, and mild ionic gelation process. However, conventional fabrication methods frequently rely on emulsion-based approaches involving surfactants and organic solvents, which may compromise their suitability for biomedical applications. In this work, a fully aqueous microfluidic strategy was developed to produce alginate nanogels through controlled ionic nanoaggregation of preformed polymer chains, avoiding the need for emulsion-based processing, surfactants, and organic solvents. The influence of hydrodynamic conditions, including total flow rate, flow rate ratio, and residence time, together with alginate and calcium chloride concentrations, was systematically investigated to elucidate the factors governing nanoaggregation, ionic crosslinking, and nanogel formation. The results demonstrate that nanogel properties depend on the interplay between mixing efficiency and crosslinking kinetics, defining an operating window in which small nanogels can be formed while minimizing uncontrolled aggregation. Under optimized conditions, nanogels with characteristic diameters below 60 nm were obtained by Cryo-SEM, although DLS measurements revealed the presence of larger aggregates in suspension. Comparison with conventional batch synthesis further demonstrated the advantages of the microfluidic approach in controlling nanogel formation and reducing aggregation. Finally, the optimized nanogels were used as confined reaction compartments for the in situ formation of palladium nanostructures through carbon monoxide-mediated reduction under mild conditions. Their characterization confirmed the formation of palladium nanosheets within the alginate matrix, demonstrating the potential of the platform for developing functional hybrid nanomaterials. This work establishes a microfluidic approach for controlling ionic nanoaggregation during nanogel formation and provides a versatile route towards functional alginate-based materials for biomedical applications.

Micromachines doi: 10.3390/mi17111249

Authors: Xinyi Chi Rui Gao

The rapid development of artificial intelligence, microelectromechanical systems, and wearable electronics, together with the diverse energy demands from the Internet of Things (IoT), drives the miniaturization of microelectronic systems. This has created an urgent need for compact, safe, and integrable energy storage technologies. Microbatteries are promising power sources for such microsystems, but they cannot be obtained by simply downsizing conventional lithium-ion batteries. At the microscale, size constraints and low active material loading, coupled with intertwined electrochemical transport, interfacial processes, fabrication, and system integration, lead to fundamental trade-offs among energy storage, power, reliability, and manufacturability. This review addresses microbattery development from the design-oriented and system-level perspectives. The root causes of the energy storage gap arising from microscale geometric and electrochemical scaling are firstly analyzed. Electrode materials, electrolytes, interface engineering, fabrication, packaging, and microsystem integration are considered in relation to these structural constraints. Particular attention is given to the translation of electrode-level performance into packaged-device performance. Improvements at the electrode level do not necessarily lead to corresponding gains at the device level, making consistent definitions of footprint, device volume, integration level, and operating duty cycle essential for meaningful comparisons. Practical microbattery development therefore requires the co-design of architecture, materials, fabrication, packaging, and load requirements.

Micromachines doi: 10.3390/mi17111250

Authors: Yi-Ren Wang Jong-Jang Lin Kuo-Kuang Jen Cheng-Hsun Li Jinyang Chen You-Jeng Hung Tzu-Hsuan Chang I-Chun Chiu Hung-Chih Ku Jung-Yi Weng

This study proposes an acoustic black hole (ABH) beam base for vibration suppression and piezoelectric energy harvesting in micro-to-small-scale multirotor unmanned aerial vehicles (UAVs). The long-term motivation is to reduce vibration transmitted to the battery module and supporting components mounted on the UAV base; however, the present study focuses on evaluating the vibration response of the UAV base structure itself. A conventional uniform beam base is replaced by a thickness-tapered ABH beam to guide and localize vibration energy toward the tapered region, where the energy can be dissipated or converted into electrical output through a piezoelectric patch. Theoretical modeling, ANSYS simulation, and experimental validation are conducted to compare the dynamic responses of the uniform beam base and the ABH beam base. The nonlinear uniform beam model, ABH beam model, and piezoelectric coupling equation are formulated and solved using numerical methods. ANSYS modal and forced-vibration simulations are further performed to verify the theoretical predictions. The simulation results show that the ABH beam base reduces the RMS displacement from 0.00908 m to 0.00625 m, corresponding to a reduction of 31.17%. Experimental shaker tests also confirm the vibration reduction trend, with the RMS displacement decreasing from 0.00801 m for the uniform beam base to 0.00601 m for the ABH beam base, corresponding to a reduction of 24.97%. In addition, the voltage generation performance of the ABH beam with an attached piezoelectric patch is evaluated, and the theoretical and simulated voltage outputs show reasonable agreement. These results demonstrate that the proposed ABH beam base can serve as a lightweight multifunctional structure for UAV base vibration mitigation and vibration-based energy harvesting.

Micromachines doi: 10.3390/mi17111248

Authors: Yangyang Xu Hongji Han Rui Yang

We report a fully metallic microwave array architecture that suppresses electromagnetic scattering through polarization-dependent phase cancellation and load dissipation. By arranging height-tailored metallic walls in a chessboard configuration, the reflection phase under x-polarized incidence is precisely manipulated, producing broadband destructive interference and suppressing backscattering without degrading the radiation characteristics. Under y-polarized incidence, the incident energy couples into the radiating units and is dissipated by the matched load. Experimental validation of an 8×8 prototype demonstrates a broad impedance bandwidth of 11.6–18.5 GHz and a peak realized gain of 26.5 dBi. The measured radar cross-section reduction exceeds 10 dB from 9.4 to 17.5 GHz (60.2%) for x-polarized normal incidence and 5 dB from 11.4 to 20 GHz (54.8%) for y-polarized normal incidence. This fully metallic architecture provides a practical approach for broadband radiation and scattering control.

Micromachines doi: 10.3390/mi17111247

Authors: Madina Alimova Aigerim Issimova Timur Namazbayev Elvira Kadylbekkyzy Tansaule Serikov Tolebi Tolebaiev Nurtay Albanbay Bekbolat Medetov

Electromagnetic vibration energy harvesters with magnetic levitation are of interest for powering autonomous low-power devices due to their high output power; however, their narrow operating region makes them sensitive to changes in the parameters of external vibration excitation. This study investigates the effects of excitation frequency and base acceleration amplitude on the harvester’s output characteristics and evaluates mean power retention under combined deviations in these parameters. Numerical simulations of steady-state regimes were performed. Within prescribed neighborhoods of operating points, the minimum mean power and local relative power variation were determined. For the configuration considered, increasing the deviation bounds from ±0.2 Hz and ±0.2 g to ±0.8 Hz and ±0.8 g reduces the highest retained fraction of the global maximum power in the investigated domain from 77.73% to 24.58%, while the local relative power variation at the corresponding operating points increases from 16.46% to 66.48%. These results highlight the risk of selecting a high-power operating point near a sharp power-drop boundary, where excitation deviations can leave the load underpowered. The proposed analysis addresses this risk by evaluating the minimum mean power across the prescribed deviation range and identifying operating regions that satisfy the load’s power requirement.

Micromachines doi: 10.3390/mi17111246

Authors: Costas Charitidis

Carbon-based materials have opened new routes in the development of advanced devices and systems [...]

Micromachines doi: 10.3390/mi17111244

Authors: Chengxuan Wang Siqiao Li Yuxing Luo Jinjin Wang Kai Jiang Shunda Zhan

Tungsten micro-rods are core components of micro-probes and micro-tool electrodes. Electrochemical etching, featuring no cutting force and hardness-independent machining, enables efficient fabrication of tungsten micro-rods. Nevertheless, the formation and removal mechanisms of surface black films during ECE are not fully understood. This work investigates bipolar pulse electrochemical etching of tungsten micro-rods, examining how pulse amplitude and temporal parameters affect etching and clarifying the evolution mechanism of the surface black film. Results show that positive pulse amplitude has a valid processing range. Excessively large positive pulses trigger black film formation, suppressing anodic dissolution and lowering machining efficiency. Negative pulse amplitude has a clear process window, and weak negative pulses cannot remove black films, whereas overly strong pulses cause violent reactions and uncontrolled micro-rod morphology. Furthermore, the positive pulse duty cycle strongly governs black film evolution. A high duty cycle shortens the negative pulse duration, weakens film removal, and impedes etching. Negative pulses boost interfacial mass transfer via cathodic hydrogen evolution and neutralize residual charges in the electric double layer. The black film consists of low-valence tungsten compounds from cathodic reduction. Bubble nucleation, growth, and detachment effectively strip this film and renew the electrode interface.

Micromachines doi: 10.3390/mi17111245

Authors: Deyi Kong Yu Fu Jiankui Chen

Air-floating transport provides a noncontact solution for handling large flexible sheets in precision manufacturing. However, variations in the spatial distribution of air-film support during transport can induce localized deformation, particularly when the sheet crosses gaps between adjacent support regions. This study investigates the deformation characteristics of thin flexible sheets during air-floating transport using a coupled model of the sheet and supporting air film. The evolution of sheet deformation is analyzed at representative transport positions. A relative displacement measure is introduced to quantify local edge sagging. The effects of guide gap, air supply conditions represented by the equivalent parameter Q, initial installation gap, and negative pressure are systematically examined. The results show that deformation is particularly pronounced near the sheet edges during transitions between support regions. Among the investigated parameters, guide gap has the strongest influence on edge sagging, while the effects of the equivalent supply parameter Q and negative pressure are relatively limited within the examined ranges. These findings provide guidance for configuring air-floating transport systems to reduce undesirable sheet deformation.

Micromachines doi: 10.3390/mi17111242

Authors: Jing Zheng Fan Yang Jinyong Wang Dongyang Li Yujing Ren Ge Cui Ming Xu Bo Wu Jian Ma

Ag-based electrochemical metallization (ECM) memristors offer low operating voltages and high ON/OFF ratios, but stochastic filament formation and rupture lead to severe switching variability. To address this, Ag/SiOx/TiOy/p++-Si memristors were systematically studied by separately varying the TiOy thickness, SiOx thickness, and compliance current (Icc). Moderate TiOy thickness and SiOx thickness yielded improved voltage uniformity and a larger switching window, whereas excessive SiOx thinning degraded the ON/OFF ratio. Moderate Icc was consistent with more complete filament dissolution and stable switching, while excessive Icc was consistent with filament overgrowth and residual channels after RESET, leading to a compressed resistance window. Conduction and XPS analyses suggest trap-related transport in the HRS and quasi-Ohmic conduction in the LRS, consistent with defect-assisted Ag+ migration mediated by oxygen vacancies and low-valence cations. Based on these results, a SiOx/TiOy bilayer thickness synergistic matching model is proposed: SiOx is proposed to mainly regulate Ag+ supply/injection, while TiOy is proposed to provide a defect-rich environment for Ag+ migration and nucleation and to determine the migration distance. Icc acts as an external control that governs the extent of filament growth without introducing an additional switching mechanism. The optimized device exhibited stable bipolar switching, preliminary endurance, retention, and preliminary device-to-device consistency under the optimized condition. This work provides a practical strategy for regulating filament dynamics through thickness-engineered bilayer design in Ag-based ECM memristors.

Micromachines doi: 10.3390/mi17111241

Authors: Heng Zhang Yang Liu Yongshuo Zhang Zhengdao Li Feiyong Chen

Improving chemiresistive CO2 sensing in real gas samples requires advances in both material response and signal calibration. Here, Au–Pt co-modified PrFeO3 (Au–Pt/PFO) was prepared by a citric-acid-assisted sol–gel method and evaluated against PFO, Au/PFO, and Pt/PFO to examine the effects of noble-metal modification on CO2 sensing. Au–Pt/PFO exhibited a specific surface area of 16.26 m2/g and an altered surface oxygen chemical environment. At 190 °C, its response (Rg/Ra) to 1000 ppm CO2 reached 9.68, corresponding to 2.61 times that of PFO, with response and recovery times of 22.38 and 16.37 s, respectively. During a 31-day test, it retained 99.38% of its initial response on Day 31. The sensing behavior was interpreted in terms of surface adsorption and interfacial charge modulation using characterization and electrical measurements. Seven features extracted from the response–recovery curves were subsequently used to construct a support vector regression (SVR)-assisted calibration model. Spectroscopic measurements served as references for evaluating CO2 concentration predictions in respiratory gas samples from imbibed rice seeds. Across separate groups comprising two gas-sample batches per method, the mean absolute relative errors were 97.55% for conventional response-based calibration and 33.07% for SVR-assisted calibration, corresponding to a relative reduction of 66.10%. These results demonstrate enhanced CO2 response through Au–Pt co-modification and improved concentration prediction in the investigated real gas samples through multiparameter-assisted calibration.

Micromachines doi: 10.3390/mi17111243

Authors: Subrat Bastola Shakila Peli Thanthri Scott Renkes Mingsen Pan Weidong Zhou George Alexandrakis

Cytochrome c oxidase (CCO) is widely regarded as the primary photoacceptor underlying photobiomodulation (PBM), in which light absorption stimulates mitochondrial respiration by promoting electron transfer through CCO. Single-molecule plasmonic nanopore measurements were used to examine cytochrome c (CC)–CCO interactions across three excitation wavelengths spanning the near-infrared range, which is preferred for PBM studies in vivo due to increased tissue penetration. Wavelength-dependent measurements of CC–CCO interactions were performed under normoxic, hypoxic, and allosterically inhibited conditions, revealing distinct interaction populations that are obscured in ensemble measurements. CC–CCO interactions were resolved into short-duration, long-duration, and heterogeneous populations for all wavelengths and oxygenation conditions. The short-duration population was selectively and substantially depleted by both hypoxia and ADDA5-mediated allosteric inhibition, supporting its assignment as a distinct, putative electron-transfer-associated interaction state. Allosteric inhibition strongly favored the long-duration population, whereas hypoxia predominantly increased heterogeneous duration interactions, consistent with non-specific binding. Under normoxia, 820 nm and 905 nm produced statistically comparable population fractions of the putative electron-transfer-active population, whereas the corresponding population fraction at 1064 nm was significantly lower but remained substantial. The short-duration binding population kinetics remained largely unchanged across wavelength and oxygenation states, indicating that these conditions primarily altered access to the CCO binding site rather than affecting its binding lifetime. These findings reveal the previously unresolved heterogeneity in CC–CCO interactions and provide a single-molecule framework for understanding how the excitation wavelength and oxygenation state may influence molecular interactions relevant to PBM efficiency.

Micromachines doi: 10.3390/mi17111240

Authors: Chen Liu Yuchen Zhang Jiyang Zhang Tao Chen Xin Wang Weimin Wang

MEMS constitutes a promising technological route toward micro-optical devices. This paper presents an innovative electrostatically actuated MEMS optical phased array with a concentric-ring structure, specifically designed for 3D optical scanning. Based on the ring-shaped MEMS optical phased array, a novel 3D optical scanning method utilizing the expansion of focused ring is proposed and studied. A detailed elucidation of the implementation mechanism and physical limits of the 3D scanning method is clarified through the mathematical modeling of the annular reflectivity function. The ring-shaped MEMS optical phased array is optimized using the angular spectrum diffraction method in conjunction with COMSOL finite-element simulations. The optimized device achieves focused spot lateral and axial dimensions of 1.282 and 1.664 times the diffraction limit, respectively, with an axial scanning range from 615.4 mm to infinity and a lateral scanning range of 0–6.5 mrad. The driving voltage of the array elements is below 21 V, and their response speed is on the order of microseconds. These findings suggest that the ring-shaped MEMS optical phased array is promising for 3D scanning.

Micromachines doi: 10.3390/mi17111239

Authors: Xiaojun Wei Shiyi Qin Kai Shi Fan Zhao Shiqiang Wu Xuecheng Sun Chong Lei

Orthogonal fluxgate sensors can measure static and low-frequency magnetic fields at room temperature and are valuable for geomagnetic exploration, navigation and positioning, and target recognition. In response to the sensitivity degradation and noise increase associated with device miniaturization, this paper presents a micro-orthogonal fluxgate sensor fabricated via MEMS technology, comprising a meander-shaped Cu/FeNi composite core and a three-dimensional solenoidal sensing coil. The performance of four sensors—Sensor A (4 core strips and 4.5 mm long, with a 40-turn sensing coil), Sensor B (4 core strips and 8.5 mm long, with an 80-turn sensing coil), Sensor C (10 core strips and 4.5 mm long, with a 40-turn sensing coil), and Sensor D (10 core strips and 8.5 mm long, with an 80-turn sensing coil)—was compared in fundamental mode. Under the optimized test conditions, Sensor D exhibited the best overall performance, with a sensitivity of 133.8 V/T and an equivalent magnetic-field noise spectral density of 0.67 nT/√Hz @ 1 Hz. During a 1 h test, its average zero offset was approximately 125 nT, with a maximum peak-to-peak variation of approximately 10 nT. Comparison of the four structures indicates that, within the tested designs, increasing the number of core strips and combining longer strips with more sensing-coil turns can help achieve high sensitivity and low noise in micro-orthogonal fluxgate sensors.

Micromachines doi: 10.3390/mi17111238

Authors: Dmitry Roshchupkin Luc Ortega Olga Plotitcyna

Features of the surface acoustic wave (SAW) and pseudo-surface acoustic waves (PSAW) propagation in a disordered piezoelectric crystal La3Ga5SiO14 (LGS, langasite) were studied using X-ray diffraction at the BESSY II synchrotron radiation source. The process of acoustic wave propagation in Z-cut of an LGS crystal was investigated. It has been shown that SAW and PSAW have different acoustic wave velocities, different amplitudes, and different power flow angles of acoustic energy propagation, which differ not only in value but also in sign.

Micromachines doi: 10.3390/mi17111237

Authors: Hung Hoang Frederic Zamkotsian Patrick Pittet Clémentine Symonds Lionel Simonot Celine Chevalier Alban Gassenq

This study demonstrates a single-step fabrication of blazed gratings on silicon substrates using direct laser greyscale lithography and aluminum coating. Three key parameters were studied for process optimization, i.e., the exposure dose of the photoresist, the focusing method, and the laser scan writing mode. We have shown that a bijective correspondence between dose and thickness ranging from 0 to 127 mJ/cm2, defined across 100 levels, enabled us to obtain a linear photoresist thickness profile. The stitching artifacts were then eliminated using fine optical autofocus with overlap writing mode. Finally, the optimized grating (3.3 µm period, 12° blaze angle, 0.52 µm depth) exhibits a well-defined saw tooth profile, confirmed by atomic force and scanning electron microscopies. Optical characterization using Fourier-plane imaging shows a dominant −1st diffraction order, confirming successful blaze behavior, especially for 700 nm wavelength. This work establishes direct laser greyscale lithography as a viable, cost-effective, and fast method for fabricating high-quality blazed gratings.

Micromachines doi: 10.3390/mi17111236

Authors: Hyerim Hong Alfi Rodiansyah Joonwon Lim

Charge-transport losses arising from carrier-specific trapping limit charge collection and the fill factor (FF) of formamidinium-rich perovskite solar cells. Carbon nanotubes (CNTs) are promising candidates for mitigating these losses owing to their outstanding carrier mobility. Unfortunately, the Fermi level of undoped CNTs is located below the conduction band of the TiO2 electron transport layer, which may hinder electron delivery from the nanotubes. Herein, we present nitrogen-doped CNTs (NCNTs) with a tailored Fermi level as electron-selective additives for (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cells. Nitrogen doping lowers the work function of CNTs from 4.6 to 4.2 eV, favorably aligning the Fermi level for electron transfer toward TiO2. Taking advantage of this alignment, NCNTs substantially enhance electron conduction and promote electron delivery to the electron transport layer, preserving hole transport. By contrast, undoped CNTs reduce the electron current, which is possibly attributed to electron trapping at their deep Fermi level. The selective enhancement of electron transport by NCNTs reduces the series resistance and improves the FF, raising the power conversion efficiency from 14.65% to 16.45%. Work function tailoring of conductive nanocarbon additives by heteroatom doping offers a promising materials strategy for efficient electron extraction in perovskite solar cells.

Micromachines doi: 10.3390/mi17111235

Authors: Qingqing Fan Qing Yu Junhong Li Yanfeng Huang

In order to simultaneously improve the imaging resolution and sensitivity of piezoelectric micromachined ultrasonic transducers (pMUTs), a pMUT with an I-shaped composite diaphragm was developed in this work. Compared with the conventional rectangular diaphragm structure, the I-shaped structure is formed by removing the piezoelectric layer along the edges of the two long sides while retaining the remaining portion. By this design, the residual stress of the piezoelectric film is effectively reduced, and both the sensitivity and the resonant frequency of the pMUT are improved. Moreover, unlike existing residual-stress-releasing structures such as hole- or groove-etched structures, where the diaphragm is no longer a continuous membrane and through-thickness holes or grooves are present, only the piezoelectric layer is etched in the proposed design. Consequently, no additional packaging requirements are imposed on the composite diaphragm, and the intricate sealing issue associated with through-hole structures is circumvented. A comprehensive comparison from multiple aspects was performed between ZnO-based and AlN-based pMUTs. It was shown by simulation results that the ZnO-based pMUT was superior to the AlN-based counterpart in terms of transmitting sensitivity, receiving sensitivity, and loop gain. On this basis, the ZnO-based pMUT with an I-shaped diaphragm was successfully fabricated and characterized. The performance of the PMUT was evaluated in electronic fluorinated fluid (FC-3283). The results show that the device exhibits a resonant frequency of 10 MHz, with a transmitting sensitivity level of 173.5 dB (re 1 μPa/V), a receiving sensitivity level of −242.1 dB (re 1 V/μPa), a loop gain of −68.6 dB, and a −6 dB bandwidth of 10.65%. These results indicate that high sensitivity was achieved at a high operating frequency, providing a technical reference for the design and application of high-frequency, high-sensitivity pMUT arrays, and demonstrating considerable potential for applications in underwater detection, ultrasonic imaging, and beyond.

Micromachines doi: 10.3390/mi17111234

Authors: Xinfu Deng Xuchen Wang Huazhou Kang Zicheng Qin Yixiao Yang

Different types of piezoelectric actuators and motors have attracted a great deal of modeling research in applications, with varying types and complexity. This paper specifically summarizes the modelings related to the inchworm piezoelectric motor to clarify the development achievements. It reviews the progress of dynamics models and characteristics models, classifying them by model features and abilities through development history. Finally, conclusions for existing research and possible future fields have been proposed.

Micromachines doi: 10.3390/mi17111233

Authors: Hae Jong Kim Sung Joo Hong

Periodic conductive metasurfaces provide a compact means of controlling frequency-selective electromagnetic transmission and shielding; however, their design is commonly performed using topology-specific parametric optimization, limiting the transferability of design knowledge across different unit-cell geometries. This study develops a topology-aware dimensionless scaling framework for square-loop and cross periodic conductive patterns supported by dielectric substrates. A spectral-domain surface-current method-of-moments solver was formulated using a zero-thickness sheet-admittance representation and validated through convergence tests and published full-wave benchmark cases, yielding a mean absolute resonance-frequency deviation of approximately 0.48%. A 162-case factorial dataset was then generated by independently varying normalized resonator size, conductor width, substrate thickness, and relative permittivity. An initial validation comparison showed that introducing a compact topology-dependent correction reduced the normalized-resonance RMSE from 0.05165 for the topology-blind model to 0.00504. Repeated paired nested cross-validation further demonstrated that the compact M2 model achieved a mean RMSE of 0.00518, while the fully topology-specific M3 model provided the lowest error of 0.00351. These findings quantify the trade-off between predictive accuracy and topology-dependent model complexity. Dense geometry and substrate validation sweeps further confirmed low prediction errors, with mean absolute errors below 0.52% across all evaluated cases. The results show that canonical conductive metasurfaces exhibit a common low-dimensional electromagnetic trend, while accurate cross-topology prediction requires only a limited topology-dependent correction. The proposed framework provides a compact and interpretable approach for topology-aware resonance-frequency prediction within the investigated conductive metasurface design space.

Micromachines doi: 10.3390/mi17111232

Authors: Ziyue Hu Wenwu Pan Kaijie Gu Shihao Wei Pengbo Guo Hailin Jing Ying Li Wengao Pan

SnO2 exhibits low cost, high electron mobility and good optical transparency, making it a promising candidate for the active layer of indium-free oxide thin-film transistors (TFTs). However, its film qualities are highly sensitive to deposition conditions. In this work, SnO2 thin films and TFTs were fabricated by radio-frequency magnetron sputtering under different substrate biases (0 V, −70 V and −110 V) to investigate the effects of substrate bias on film structure, defect state, interface quality and device performance. With increasing substrate bias magnitude, the film crystallinity improved, the relative area fraction of the defect-related O 1s component decreased from 31% to 19%, while the surface roughness increased, continuously. At a substrate bias of −70 V, the device exhibited relatively optimal overall performance, with a linear mobility (μlin) of 3.7 cm2/Vs, a subthreshold swing (SS) of 0.61 V/dec, and a threshold-voltage shift (ΔVth) of 6.0 V after 3600 s of positive bias stress. These results indicate that an appropriate substrate bias can achieve a balance between crystalline quality and interface condition, thereby improving the performance of SnO2 TFTs.

Micromachines doi: 10.3390/mi17111231

Authors: Zongxie Chen Zhijin Li Yasemin A. Geiger Benedikt K. Kaufmann Dilan Kılıç Valentina Leone Stefanie Sudhop Matthias E. Rebhan Shilpi Pandey Oliver Hayden Eckehard Steinbach

Established acoustofluidic lab-on-a-chip devices enable contactless, label-free trapping of cells, but do not provide a quantitative readout of a levitated sample’s orientation, restricting their analytical reach. We present a synthetic-to-real deep learning framework that addresses this gap by estimating the five-dimensional (5D) pose of a trident-shaped micro-calibrator co-trapped with the cells. Here, 5D pose denotes the two-dimensional (2D) bounding-box center in the image plane and the calibrator’s three-dimensional (3D) orientation. Printed by two-photon polymerization with 10, 15, and 20 μm arms, the calibrator provides the rigid, asymmetric geometry that a translucent, deformable spheroid lacks. The framework cascades detection, foreground segmentation, and rotation regression, with the normalized bounding-box center as a positional auxiliary input, and optionally applies temporal smoothing; it is trained on domain-randomized renderings, eliminating manual 3D pose annotation. On 15,000 synthetic test images, it reached a mean geodesic rotation error of 0.82°. The ablation study showed that the positional input substantially improves rotation estimation and background removal further lowers the error, and identified segmentation, not detection, as the dominant upstream error source. Pseudo-label adaptation raised the expert-assessed correctness rate from 34.71% to 83.62% on 5281 real microscopy frames from which the pseudo-labels were drawn (adaptation performance) and from 2.48% to 29.34% on 242 held-out fluorescence frames with adherent cells (generalization performance). This demonstrates the feasibility of a calibrator-based orientation readout on an established acoustofluidic platform without hardware change.

Micromachines doi: 10.3390/mi17111230

Authors: Xinghui Li Haijun Chen Jinjun Feng

Alkali atomic vapor cells are the key components of all kinds of atomic sensors, including atomic clocks, atomic gyroscopes, atomic magnetometers, Rydberg atom sensors, etc. With the miniaturization and integration trends of these atomic sensing devices, compact alkali vapor cells, particularly micromanufactured vapor cells with high performance, are urgently needed. The development history from glass vapor cells to MEMS vapor cells is reviewed. The bonding methods for macro-fabricated alkali atomic vapor cells, such as anodic bonding, metal film thermocompression bonding, glass–frit bonding, epoxy glue bonding and laser bonding, are analyzed and summarized. The alkali metal filling techniques for vapor cells are also discussed, including the physical methods of direct filling and wax package filling, and chemical methods of the reaction of alkali chloride with BaN6, ultraviolet (UV) light decomposition of RbN6 and CsN6, electrolysis of alkali-rich glass, and laser decomposition of alkali dispensers. Compared to traditional vapor cell dimensions, vapor cells with long laser paths are emphasized, and the corresponding design and realization processes are discussed. Finally, the vapor cells with inner anti-relaxation coatings and passivation coatings aimed at achieving long reaction times and long lifetimes are analyzed.

Micromachines doi: 10.3390/mi17111229

Authors: Chin-Chou Huang Cheng-Chih Hsu Ching-Liang Dai

This work presents a complementary metal oxide semiconductor (CMOS)-compatible photovoltaic energy harvester (PVEH) incorporating an S-shaped diffusion architecture for optical energy harvesting. The device is implemented using the CMOS process with an effective photovoltaic active area of 1 mm2. The structure employs an S-shaped p-type diffusion within the n-well together with closely spaced n-type diffusion regions to establish a compact photoactive region for photogenerated carrier collection. Three-dimensional TCAD simulations were performed to investigate the photovoltaic characteristics under irradiance levels ranging from 200 to 1000 W/m2. A post-CMOS process was subsequently employed to remove the dielectric layer above the photoactive region and provide optical access to the semiconductor surface. At 1000 W/m2, the fabricated PVEH exhibited an open-circuit voltage of 0.5 V, a short-circuit current of 405 μA, and a maximum output power of 137 μW, corresponding to an energy-conversion efficiency of 13.7%. These results demonstrate the feasibility of implementing the S-shaped diffusion architecture using standard CMOS technology and post-CMOS processing, providing a compact photovoltaic energy harvesting solution for low power sensors and self-powered microsystems.

Micromachines doi: 10.3390/mi17111228

Authors: Aodong Yi Yaowei Wei Qinghua Zhang Zhenfei Luo Qian Wu Fei Zhang Haibo Li Zhen Wang

Electron-beam evaporation (EBE) is a multi-energy conversion process in which electrons are accelerated by an electric field, transfer kinetic energy to the evaporation source, and generate localized thermal energy for material evaporation and film growth. Post-deposition annealing provides an additional thermal field that promotes structural relaxation and defect evolution. In this study, 1064 nm HfO2/SiO2 highly reflective coatings deposited by EBE were annealed at 200 °C for 1–8 h to clarify how the duration of the post-deposition thermal field affects microstructure and optical-loss evolution. Atomic force microscopy combined with power spectral density analysis, spatial photoluminescence mapping, cavity ring-down measurements, and thermal absorption testing were employed. The coating response was distinctly non-monotonic: moderate annealing suppressed multiscale surface fluctuations and defect-related luminescence, whereas prolonged treatment partially reversed these changes. The total optical loss decreased from 1191.05 ppm to 837.88 ppm after 2 h, a reduction of 29.7%. Loss separation showed that absorption remained nearly stable after its initial decrease, while scattering recovered markedly at longer durations and dominated the subsequent increase in total loss. Scattering correlated strongly with surface roughness (r = 0.92), whereas absorption showed a positive correlation with photoluminescence intensity (r = 0.85). These results are consistent with distinct morphology-related and defect-related contributions to scattering and absorption, respectively, in EBE HfO2/SiO2 coatings.

Micromachines doi: 10.3390/mi17111227

Authors: Muhammad S. Utomo Sacha J. Pidot David J. Collins

While droplet deformation analysis can shed light on droplet composition, the bulk of previous microchannel-based droplet deformation work has focused on unidirectional deformation, limiting the insights that can be gained. In contrast, sequential bidirectional droplet deformation in microchannels remains underexplored despite its potential to provide richer insights into droplet behavior and characterization. Understanding droplet deformation is particularly important for advancing label-free droplet analysis, which underpins applications in diagnostics, drug screening, and material synthesis. In this work, we report a novel application of a flow-focusing microchannel to investigate sequential bidirectional droplet deformation. Both experiments and computational modeling confirm the formation of localized high-strain regions driven by the interaction between the main and sheath flows. Using high-speed imaging, we capture the sequential bidirectional deformation as the droplets traverse these regions. Importantly, we establish a relationship between nondimensional parameters and droplet deformation, providing a framework for characterizing droplet rheology. This approach highlights the potential for developing high-throughput methods to estimate rheological properties on a single-droplet basis. Such capabilities have the potential to open new avenues for more efficient and precise droplet-based assays in biological and chemical research.

Micromachines doi: 10.3390/mi17111226

Authors: Minghan Hu Jiangnan Li Yiming Li Zheng Zhao Li Sun Jing Wang Jiantao Wu Han Zhang

To design an asymmetric supercapacitor device with high capacitance, high energy density, and excellent cycling stability, a NiCo2O4@NiWO4/MXene ternary composite cathode and a hydrophilic carbon nanotube (H-CNTs) anode were constructed and matched for device assembly. The NiCo2O4@NiWO4/MXene cathode with a “nanowire@nanosheet” core-shell hierarchical structure was prepared through a two-step hydrothermal method combined with high-temperature annealing, while hydrophilic carbon nanotubes were obtained by concentrated nitric acid modification. The microstructure, crystal structure, elemental valence states, and pore characteristics of the electrode materials were systematically characterized by SEM, TEM, XRD, XPS, and nitrogen adsorption–desorption measurements. The results showed that the introduction of Ti3C2Tx MXene formed an effective conductive network, while the core-shell hierarchical structure provided abundant electrochemically active sites and increased the specific surface area of the ternary composite to 156.4 m2/g. In a three-electrode system, the NiCo2O4@NiWO4/MXene electrode exhibited a specific capacitance of 1830 F/g at 1 A/g and retained 983 F/g at 15 A/g, while the H-CNTs anode delivered a specific capacitance of 774 F/g at 1 A/g. Based on the working potential windows, specific capacitances, and charge balance relationship of the positive and negative electrodes, the active material mass ratio was optimized to approximately 1:2.8. An asymmetric supercapacitor was subsequently designed using a “cathode–separator–anode” laminated configuration with NiCo2O4@NiWO4/MXene as the cathode, H-CNTs as the anode, glass fiber as the separator, and 6 M KOH as the electrolyte. The assembled NiCo2O4@NiWO4/MXene//H-CNTs device operated stably within a voltage window of 0–1.6 V and achieved a specific capacitance of 256 F/g at 1 A/g. The device delivered an energy density of 91.0 Wh/kg at a power density of 800 W/kg and maintained 97.3% of its initial capacitance after 12,000 charge–discharge cycles. These results demonstrate that the proposed electrode matching and laminated structural design can effectively improve the capacitive performance, energy storage capability, and cycling stability of the asymmetric supercapacitor, providing a useful basis for the design and performance optimization of high-performance supercapacitor devices.

Micromachines doi: 10.3390/mi17111225

Authors: Yuqing Dong Gang Nan Zhihui Xie Zhuoqun Lu Yanlin Ge

Ball grid array (BGA) is widely used in chip packaging, and the thermo-mechanical performance of its solder joints significantly affects the performance of packaged devices. To investigate and improve the thermo-mechanical performance of BGA solder joints under steady-state conditions, a thermo-mechanical coupling model of a BGA packaging chip under microchannel-forced liquid cooling is established based on a method combining constructal theory and multiphysics field coupled numerical calculation, and a composite evaluation indicator of maximum temperature and maximum deformation is proposed for optimizing the solder joint design. With the total number and total volume of solder joints as constraints, and the long/short half-axis ratio of solder joints and the layout of the ball grid array as design variables, the maximum temperature, the maximum deformation, and their composite function are selected as performance indicators. The effects of solder joint shape and layout evolution on the thermo-mechanical performance of the device are systematically investigated. The results indicate that among the array, rectangular-ambulatory, and staggered layout types, the rectangular-ambulatory type consistently yields the lowest maximum temperature and maximum deformation for all long/short half-axis ratios, whereas the array type and staggered type each have their own advantages and disadvantages under different ratios. In the studied cases, the difference between the maximum and minimum values of the maximum temperature is 7.8 K, and the difference between the maximum and minimum values of the maximum deformation is 5.88 × 10−3 mm, with a maximum reduction ratio of 74.5%. Under the three BGA layouts, the maximum temperature increases monotonically with the long/short half-axis ratio, while the maximum deformation decreases monotonically. The variation in the composite function with the long-to-short half-axis ratio changes with the weighting-factor ratio, but the optimal BGA layout remains unchanged and is always the rectangular-loop layout. When the weighting factor ratio is 7:3, there exists an optimal long/short half-axis ratio that minimizes the composite function. The methods and results presented in this study can provide a theoretical basis for the thermo-mechanical design of BGA packaging chips.

Micromachines doi: 10.3390/mi17111224

Authors: Petr Slobodian Jiří Matyáš Robert Olejník Berenika Hausnerová María Luz Rovatta Gustavo Monti Diego Fernando Acevedo César Alfredo Barbero Marek Jurča Martin Novák Markéta Sádecká

Triboelectric nanogenerators (TENGs) provide a simple approach for converting mechanical excitation into electrical signals through contact electrification and electrostatic induction. In this work, a triglyceride–sulfur copolymer (TGS), prepared by inverse vulcanization of elemental sulfur with soybean oil, was investigated with two waste-derived counter materials: recycled residual waste plastic (RRWP) and waste goatskin leather (WGL). The TGS–RRWP and TGS–WGL pairs exhibited opposite electrical polarities, with triboelectric charge densities of approximately +41.3 µC m−2 for TGS–RRWP and −56.0 µC m−2 for TGS–WGL, where the sign refers to the charge measured on the TGS electrode. Repeated contact–separation cycling showed an initial conditioning period followed by stabilization of the electrical response. Load-dependent measurements at 1 and 10 Hz revealed maximum output power at approximately 2–4 MΩ, reaching about 2.7 mW for TGS–RRWP and 1.8 mW for TGS–WGL at 10 Hz. Post-contact measurements further revealed reproducible voltage transients after circuit closure while the mechanically conditioned layers remained in static contact. Biexponential fitting showed that the faster decay time increased approximately linearly with effective load resistance, corresponding to apparent effective system capacitances of about 69 pF for TGS–RRWP and 44 pF for TGS–WGL, measured using a high-impedance differential probe to minimize measurement-induced loading, although residual parasitic contributions cannot be excluded. These results demonstrate opposite triboelectric polarity, load-dependent energy conversion, and a reproducible post-contact transient response with a substantial RC contribution.

Micromachines doi: 10.3390/mi17111223

Authors: Chuanjie Qin Anguo Ma Shuai Huang Likai Yang Le Hao Jiao Li Hong Xue Jianjun Wang Cun Li Yulong Zhao

SOI (silicon-on-insulator) piezoresistive pressure sensors are well suited for high-temperature applications because the buried oxide layer suppresses the p-n junction leakage current above 150 °C. Accurate simulation of the output voltage is essential for design. However, conventional approaches obtain the electrical output indirectly, first calculating the diaphragm stress with structural finite-element analysis and then converting it analytically into resistance or voltage changes. Although the output can be calculated directly by finite-element simulation incorporating the piezoresistive effect, the constant piezoresistive coefficients commonly used cannot reflect their dependence on temperature and doping concentration, limiting simulation accuracy. In this work, a coupled piezoresistive finite-element model with an empirical formula was developed to directly simulate the output voltage, in which the temperature- and doping-dependent coefficient π44 (T, N) is incorporated into the simulation. Using this method, a 0–20 MPa flat-diaphragm SOI pressure sensor was designed and simulated over 25–300 °C. The fabricated sensor delivers full-scale outputs of 104.91 and 73.39 mV with sensitivities of 1.0491 and 0.7339 mV/V/MPa at 25 °C and 300 °C, respectively; the simulated outputs deviate from the measurements by 7.26% and 10.28%, with an average deviation of 5.76%, improving the verifiability between design and experiment.

Micromachines doi: 10.3390/mi17111222

Authors: Jie Li Tao Hao Shitong Zhu Yu Li Lu Zheng

Microfluidic circuits use the pressure and flow characteristics of interconnected elements to regulate fluid transport and control operating sequences. Interconnection changes the operating conditions of individual elements, making their interactions important to the response of the assembled system. This paper presents a review of electronics-inspired microfluidic circuits, including their working principles, design methods and applications. The functional elements are classified according to their primary circuit functions, and their circuit representations are examined using the hydraulic–electrical analogy. Continuous flow regulation, logic and state storage, and oscillatory and sequential control are discussed in relation to the load and timing requirements. Modelling and design automation methods are considered together with fabrication and experimental verification to examine how the intended circuit response is obtained in a physical device. Applications in diagnostic assays, chemical processing, cell culture, wearable sensing and soft robotics are introduced. The advantages and limitations of different circuit arrangements are summarized, including their suitability for fixed sequences, reconfiguration and autonomous operation. The reviewed studies indicate that reliable integration requires the output pressure, available flow and switching time to be matched to the connected load. Performance evaluation should also account for the complete operating procedure, including the external equipment and user intervention required, to support the comparison and selection of circuits for different applications.

Micromachines doi: 10.3390/mi17111221

Authors: Tailong Shi Qi Li Hongfei Chen Shunyu Yao Liyi Li Hua Hong Li Zheng Shiwei Xia Zhongping Bao Andrew C. Chang

Glass substrates exhibit great potential in 2.5D/3D advanced packaging, but poor interfacial adhesion with metal layers remains a critical challenge. This work studies three different adhesion layer strategies, namely Parylene-C, photosensitive polyimide (PSPI), and atomic layer deposition (ALD) TiO2/TiN/Ru/Cu multilayer, to improve glass-Cu adhesion. A 30 µm Cu layer was electroplated over glass-Parylene-Ti/Cu, glass-PSPI-Ti/Cu, and glass-TiO2/TiN/Ru/Cu multilayer stacks. The 90° peel test results show that, at the layer thicknesses investigated here, all three strategies increase the glass-Cu peel resistance (approximately 6.5 to 10 times) compared with the conventional glass-PVD Ti/Cu control group (0.62 ± 0.06 N/cm). Parylene-C achieves the highest adhesion strength of 6.25 ± 0.03 N/cm, which is 31.9% higher than the ALD multilayer (4.74 ± 0.28 N/cm) and 55.5% higher than the PSPI (4.02 ± 0.10 N/cm). The adhesion enhancement mechanisms are analyzed, and the comprehensive performance of the three strategies is compared over multiple aspects. Overall, this work provides three practical solutions to improve the glass-Cu adhesion.

Micromachines doi: 10.3390/mi17111220

Authors: Kun Wang Jun Zhao Tao Long Jiahao Fu Xinqing Li Zheng Li

Silicon drift detectors (SDDs) and three-dimensional (3D) trench electrode silicon detectors have become core radiation-sensing devices for X-ray spectroscopy, pulsar navigation, high-energy-physics experiments and low-dose medical imaging. Conventional concentric-ring and first-order spiral SDDs suffer prominent drawbacks including distorted surface potential gradients, uneven drift electric fields, ill-defined electron drift channels and large Si/SiO2-interface leakage current. Traditional non-through 3D trench detectors have large substrate dead zones, leading to degraded charge-collection efficiency. Based on original structural designs and mathematical modeling from our research group and other researchers, this review sorts out the evolution route of silicon radiation detectors from planar two-dimensional spiral electrodes to 3D penetrating-electrode architectures. It elaborates the fundamental physics of SDDs and 3D trench electrode detectors and establishes a unified Sentaurus TCAD multi-physics simulation system with consistent substrate, thickness and bias boundary conditions. Four innovative two-dimensional spiral SDD architectures and two novel through-type 3D silicon detectors are summarized, together with their analytical models, optimization mechanisms and key performance features. Quantitative cross-comparison is implemented over multiple critical metrics to extract general structural-optimization rules. Industrial bottlenecks regarding fabrication yield, array uniformity, high-temperature stability and simulation-process matching are analyzed. Future trends of composite detectors, wafer-level manufacturing and coupled multi-physics simulation are forecasted with application-targeted design proposals. We hope this review can provide systematic theoretical reference and design guidance for developing next-generation high-performance silicon radiation detectors.

Micromachines doi: 10.3390/mi17111219

Authors: Liron Cohen Emmanuel Bender

Advanced FinFET technologies exhibit pronounced within-die process variations and localized aging phenomena that challenge the accuracy of conventional global reliability monitoring. Existing Ring Oscillator (RO)-based aging monitors typically provide a single degradation indicator for the entire die, potentially masking vulnerable regions that experience accelerated wear-out. This work presents a spatial reliability monitoring methodology implemented on a commercial 16 nm FinFET FPGA. An array of 240 distributed ROs was organized into twelve physically separated monitoring regions to enable localized degradation analysis. We performed five independent accelerated aging experiments. Each experiment lasted 220 h under elevated electrical and thermal stresses while RO frequencies were sampled once per minute. The measured frequency degradation was translated into localized Time-to-Failure distributions using Weibull statistical analysis. The experimental results reveal significant spatial variations in both the Weibull shape parameter and accelerated-stress Time-to-Failure, demonstrating a correlation between regional process variation and localized degradation behavior. These findings show that global degradation metrics can obscure the earliest failing regions within the die. By transforming distributed frequency measurements into a spatial reliability health map, the proposed methodology provides an experimental framework for identifying vulnerable logic regions and supports future reliability-aware resource management and predictive maintenance in advanced FPGA platforms.

Micromachines doi: 10.3390/mi17111218

Authors: Kexin Li Li Jin Yancheng Gong Chao Zhang Kunyang Xie Mengwei Li

This paper presents a dual-axis micro-displacement measurement system based on double-layer grating interference adopting a quasi-common-mode optical configuration. Utilizing the diffraction and interference effects of the grating pair, the system realizes decoupled high-precision dual-axis displacement measurement by detecting diffracted light intensity induced by out-of-plane and in-plane motions of the movable grating. The light-intensity response originating from grating-pair diffraction is theoretically derived to establish the quantitative relationship between displacement and optical intensity. An experimental setup is constructed to record intensity variation curves for out-of-plane and in-plane motions. Measurement accuracy along the two axes is systematically analyzed over a 1 mm working range. Experimental results yield a full-scale accuracy of 0.0039% and a resolution of 0.38 nm for out-of-plane displacement, while the in-plane displacement measurement achieves a full-scale accuracy of 0.08% with 19 nm resolution. Benefiting from its compact architecture, nanoscale resolution, and superior measurement precision, the proposed grating-pair scheme opens a new avenue for multi-dimensional micro-displacement sensing.

Micromachines doi: 10.3390/mi17111216

Authors: Eunsung Kim Sujith Lal Omkar A. Patil Chih-Ming Chen Baoyang Lu Sooman Lim Byungil Hwang

In this review, low-temperature Sn-Bi and Sn-Zn solders and the reliability of their Cu interfaces are summarized for advanced electronic packaging. Sn-58Bi can markedly reduce the soldering temperature because its eutectic temperature is approximately 139 °C; however, the brittle Bi-rich phase and the coarsening of the two-phase microstructure remain important problems. The addition of Zn or In has been used to reduce these problems. Bi addition to Sn-3.5Ag and Sn-9Zn also decreased the melting temperature and increased the joint strength under selected conditions. In addition, electrodeposited Sn/Bi bilayers and Sn-Sb/Sn-Bi mixed solders provide another route to form low-temperature joints during heating. The Cu interface was also considered because Cu6Sn5/Cu3Sn morphology, impurities in electroplated Cu, Cu grain size, and surface finish strongly affect IMC growth and void formation. The effects of thermomigration and electromigration are also discussed because they become important as the joint size decreases. This review will provide useful information for understanding low-temperature solder materials and for designing reliable Cu/solder interfaces for advanced electronic packaging.

Micromachines doi: 10.3390/mi17111217

Authors: Mustafa Konal

This paper presents a MOS-only current-mode full-wave rectifier with simultaneous non-inverting and inverting outputs. The core uses ten MOS transistors and no separate diodes or passive resistors. This count does not include the bias-generation circuit. Schematic-level simulations were performed in LTspice using TSMC 0.18 μm CMOS model parameters and ±0.9 V supplies. With a 100 μA sinusoidal input and 1 kΩ output load, the normalized RMS waveform error was 6.56% at 10 kHz and 10.10–10.28% at 100 MHz. Under the same input and load conditions, the proposed circuit gave lower waveform errors than the two-transistor rectifier used for comparison. The maximum absolute DC error over −120 to +120 μA was 10.06 μA, or 8.38% of full scale. Small-signal bandwidths ranged from 1.803 to 2.642 GHz at DC input currents of ±50 μA and do not define the usable large-signal rectification bandwidth. Supply power was 452.13 μW at zero input and 455.90 μW at 10 kHz with a 100 μA input. Further analyses examined noise and sensitivity to operating conditions. A 200-run Monte Carlo analysis with assumed independent Gaussian variations in transistor dimensions and threshold voltages gave a zero-input output-current offset standard deviation of 4.35 μA.

Micromachines doi: 10.3390/mi17111215

Authors: Ze Yan Ke Han Naibo Zhang Zhongliang Deng

A wideband pattern-reconfigurable antenna (PRA) integrating an asymmetric coplanar strip (ACS), coupled patches, and defected ground structure (DGS) loading is presented. The ACS provides the basic tilted-beam radiation, while the coupled patches and DGS provide complementary impedance-matching contributions in the upper and lower portions of the operating band, respectively. Their interaction with the original ACS response establishes three resonant responses that collectively broaden the matched band. The loading structures and two-PIN switching scheme are jointly designed to realize broadband radiation pattern reconfiguration, maintaining two selectable tilted-beam states across the wide operating band through a single feeding port. A prototype is fabricated and achieves a measured common −10 dB impedance bandwidth of 57.6%, covering 4.2–7.6 GHz. A radiation efficiency above 90% is obtained at the tested frequencies, and the measured radiation patterns generally maintain their overall tilted-beam shapes, with sidelobe levels more than 9 dB below the main beam. The proposed design provides a practical solution for broadband directional wireless applications requiring flexible coverage.

Micromachines doi: 10.3390/mi17111214

Authors: Tailong Shi Lihong Chen Qi Li Yubing Luo Shunyu Yao

Through-glass vias (TGVs), as key vertical interconnect structures in 2.5-D/3-D advanced packaging, offer low dielectric loss, low parasitic capacitance, and excellent high-frequency transmission performance. However, several challenges remain in TGV metallization, including (1) incontinuity of seed layers in high aspect ratio TGVs; (2) non-uniform distributions of copper-ion concentration and current density, leading to significant differences in copper deposition rates between the via interior and the via opening; (3) voids, seams, and double bridging caused by excessively rapid deposition at the via opening or poor control of the central bridging position; and (4) low filling rate and resulting high cost. This article reviews the research progress in TGV metallization to address the above issues. Several electroless plating studies were reported to improve the seed layer continuity and uniformity. Adjusting the concentrations of copper ions, chloride ions, accelerators, suppressors, and levelers in the plating bath are the keys to regulating the deposition rates at the via opening, via walls, and via center. Electroplating strategies, including pulsed electroplating and multistage electroplating, can optimize the electric-field distribution inside the vias. Ultrasonic agitation enhances forced convection within the vias and thereby improves mass-transport conditions. In summary, this paper reviews the research progress in TGV metallization, with emphasis on these key challenges and corresponding solutions, and discusses their prospects for high-density interconnects in advanced packaging.

Micromachines doi: 10.3390/mi17111213

Authors: Chi-Yuan Lee Lung-Jieh Yang Chia-Hung Chen Li-Hsing Fang Ching-Liang Dai Bo-Wei Wu Cheng-Kai Liao

A flexible eight-in-one microsensor was developed using micro-electro-mechanical systems (MEMS) technology for monitoring hydrogen/vanadium redox flow batteries (HVRFBs). The device integrates sensing functions for voltage, current, conductivity, temperature, pressure, humidity, flow rate, and hydrogen. During battery operation, the voltage measurements showed an approximately 200 mV difference between the upstream and downstream regions during charging, indicating spatial variation in the measured voltage. Conductivity, temperature, flow rate, and pressure measurements were also used to monitor operating conditions within the HVRFB. The hydrogen sensor was evaluated at one tested location under the hydrogen exposure condition used in this study; its resistance decreased and approached a steady response. Because measurements at multiple hydrogen concentrations were not conducted, concentration-dependent sensitivity, response and recovery times, and the limit of detection were not established. During a 200 h charge–discharge test at 25 °C, signals from the integrated sensing functions, including the SnO2/Pd hydrogen sensor, remained observable. However, quantitative pre- and post-test calibration data were not available to determine sensitivity retention, signal drift, or passivation. These results demonstrate the feasibility of integrating multiple sensing functions for monitoring HVRFB operation, but further testing is needed to quantify hydrogen-sensing performance and long-term stability.

Micromachines doi: 10.3390/mi17111212

Authors: Siyuan Ma Biao Yan Haijun Li Yanhui Hu Junjie Wang Chaowen Zheng Zhen Liu Xiulei Zhang Huilan Liu Lishuang Feng Dawei Li Aimin Wang Conghao Wang

The imaging performance of a Lissajous scanning two-photon microscopy system employing an ultra-compact electrostatic MEMS mirror depends critically on the stability of the scanning trajectory. However, asymmetry in driving circuit parameters and the response of the MEMS mirror introduce amplitude error and phase delay, resulting in trajectory distortion and degraded imaging performance. We establish an experimental characterization platform to evaluate the amplitude and phase responses of the driving circuit and the MEMS mirror. The frequency response of the MEMS mirror under sinusoidal excitation further reveals the phase delay between the driving signal and the mechanical motion. A two-photon microscopy imaging system is constructed to experimentally validate and correct image distortions induced by the driving circuit and response of the MEMS mirror. The research establishes a systematic framework for the realization of low-distortion Lissajous scanning in two-photon microscopy and miniaturized endoscopic imaging systems.

Micromachines doi: 10.3390/mi17101211

Authors: Qilin Jiang Jianfeng Wu Junming Hou Zhenxiang Yi

Micro-electro-mechanical system (MEMS) thermal flow sensors are attractive for compact gas-flow measurement because of their small size, rapid response and low power consumption. However, under non-clean operating conditions, particles carried by the gas can enter the sensing region and progressively deposit on the chip, altering the local flow field and heat-transfer boundary conditions and thereby causing output drift and cumulative measurement error. To improve long-term stability in particle-laden environments, a MEMS thermal flow sensor was designed and implemented, and contamination was controlled along the particle pathway from transport toward the sensing region to deposition on the chip surface. The finite element method (FEM) simulation showed effective thermal isolation between the heating and temperature-sensing regions at ΔT = 20 °C, while the heating power increased monotonically with flow velocity in agreement with heat-loss theory. Particle-laden experiments indicated that the average measurement error was reduced by approximately 22.5% using the curved bypass channel for the flow speed up to 70 SLPM, with a more pronounced improvement at medium and high flow rates. For particles that still reached the vicinity of the chip, the surface electric field was further adjusted through the operating voltage. The sensor was tested under particle-filled flow for 2 h, and the results demonstrate that the contaminated regions were 14.34%, 10.40%, and 3.84% at supply voltages of 7, 8, and 9 V, respectively, indicating that lower operating voltage mitigated particle deposition.

Micromachines doi: 10.3390/mi17101210

Authors: Chengyu Li Shuxing Xu Wenbo Li Dian Jin Yudong Zhao Chao Zhang Weishi Li Zhuoran Sun Siyu Zhou

Spinal musculoskeletal disorders demand continuous assessment of movement and loading, whereas routine clinical imaging provides important but episodic structural information. While wearable soft sensors offer a non-invasive approach to complement these assessments, translating laboratory-scale prototypes into robust clinical systems remains challenging because of electromechanical stability, signal fidelity, and data interpretation. This review critically examines the end-to-end development of soft wearable technologies for spinal monitoring, moving beyond a materials-focused survey to address these translational gaps. First, we evaluate advances in soft sensing mechanisms, highlighting the trade-offs between mechanical compliance and stable sensor performance. We then examine system-level integration, including soft or flexible sensing elements, conventional sensors on compliant substrates, rigid–soft interfaces, and multimodal systems for monitoring posture, motion, pressure, and muscle activity. Furthermore, we discuss signal-processing and artificial intelligence-assisted workflows for denoising and extracting meaningful physiological features. By comparing reported performance metrics and validation settings, we assess representative applications in scoliosis and chronic low back pain. Current evidence demonstrates technical feasibility in laboratory tests and small studies, but does not yet establish broad diagnostic benefit or routine clinical effectiveness. Finally, we identify key evidence gaps, including external validation, patient-based studies, standardized protocols, and long-term assessment, that must be addressed for clinical translation.

Micromachines doi: 10.3390/mi17101209

Authors: Jianfei Jiang Yangfan Liang Hong Zhang

Multiple SAW sensors working in separate frequency bands can encode multiple measurands in the frequency domain during a single interrogation. In such applications, software-defined radio is the most convenient platform to transceive wideband RF signals and process them in digital mode. This paper introduces a novel SDR platform that can interrogate a large number of resonant SAW sensors simultaneously. These sensors can be distributed in a frequency range from 70 MHz to 6 GHz, with an instantaneous bandwidth of 56 MHz. The 56 MHz wideband excitation signal is transmitted and received without frequency sweeping, so sensors operating at different resonant frequencies can be stimulated simultaneously, which is critical for accurate frequency-based measurement in multi-sensor applications. Five-sensor interrogation is described as an example, with an interrogation period of 15.12 μs. As the transceiver operates in time-division mode, the delay before reception and the listen-window width are designed to be parameter-adjustable to fit diverse applications, thereby improving system performance. The described SDR platform is based on USRP-B210 hardware and GNU Radio software. The USRP-B210 operates at its maximum sampling rate of 61.44 MHz with a bandwidth of 56 MHz. For decay-time-limited resonant sensors, the maximum sampling rate captures the most samples of the response signal, resulting in improved SNR performance.

Micromachines doi: 10.3390/mi17101208

Authors: Tun-Hui Yang Mu-Ju Wu Wen-Chieh Lee Ching-Ting Lee Chun-Hung Lin Hsin-Ying Lee

This study aimed to enhance the sensing performance of nitrogen dioxide (NO2) gas sensors fabricated using gallium oxide (Ga2O3) nanorod sensing membranes. The hydrothermal synthesis method was used to grow GaOOH nanorods on a roughened tin oxide (SnO2) seed layer with various periods fabricated using a nanoimprint system. Then, the GaOOH nanorods were converted to Ga2O3 nanorods by nitrogen annealing treatment. Under 10 ppm NO2 and operating temperature of 210 °C, the optimal response of the NO2 gas sensors using Ga2O3 nanorods grown on an 800 nm periodic seed layer was 56.2. To further improve the performance attributed to the spillover effect of noble metal, p-type gold-black nanoparticles (NPs) were deposited onto the n-type Ga2O3 nanorod surfaces using a vapor cooling condensation system to form p-n heterojunctions. When Ga2O3 nanorods were decorated with 1.02 at.% gold content, the optimal response was increased to 143.9 under 10 ppm NO2 at an operating temperature of 180 °C. To investigate the photo-activation effect on the NO2 gas sensors, 245 nm UV light was applied to the devices. Under the UV light intensity of 4.8 mW/cm2, the response of the resulting NO2 gas sensors without and with gold-black NPs was increased to 123.1 and 370.5, respectively.

Micromachines doi: 10.3390/mi17101207

Authors: Qian Li Tao Zhou Dan Qin Yongliang Wu Xiang Li Song Li Xiong Chen Zhipeng Wu

In this manuscript, a miniaturized ultrasonic Renal Denervation (RDN) catheter for removing sympathetic nerves around the renal artery is proposed. The RDN catheter consists of an ultrasonic transducer, a balloon catheter and a control system. Owing to the use of a piezoelectric ceramic tube as the ultrasonic transducer, the RDN catheter is designed to provide 360° circumferential acoustic exposure around the renal artery. The piezoelectric ceramic tube has an active length of 6 mm, an inner diameter of 1.1 mm, and an outer diameter of 1.6 mm and the material of piezoelectric ceramic tube is PZT8. The balloon catheter of the proposed RDN catheter is designed and optimized so that the diameter of the portion inserted into the vessel is ≤1.8 mm, with the aim of enabling access to the renal artery via Transradial Access (TRA). In addition, a liquid circulation system is integrated into the balloon catheter to cool the ultrasonic transducer, with the aim of limiting heating near the renal artery wall. The measured resonant and anti-resonant frequencies of the ultrasonic transducer are 8.72 MHz and 9.69 MHz, respectively. Under 70 W input electrical excitation at 9.69 MHz, the average acoustic pressure measured at 6–7 mm from the catheter surface is 2.11 MPa. In addition, the control system prototype is also developed. Finally, the thermal feasibility of the proposed catheter is evaluated through phantoms and ex vivo tissues. In the phantom, visible whitening appears by 0.5 s, and an annular whitened region is evident by 8 s; at 15 s, its image-estimated thickness is approximately 3.6 mm, with an adjacent transparent interval of approximately 1.2 mm. Ex vivo porcine liver also shows macroscopic discoloration consistent with thermal denaturation. These observations support the preliminary acoustic and thermal feasibility of the proposed RDN catheter.

Micromachines doi: 10.3390/mi17101206

Authors: Bin Yan Zhongyang Guo Yilong Chen Jiantao Zhao Yujun Yang Shugang Zhang Boyu Hao Huiliang Cao

High-overload micro-electro-mechanical system (MEMS) gyroscopes can retain an output after impact while exhibiting degraded sensing performance. This study examines a packaged four-mass gyroscope using a coupled mechanical model, transient finite element analysis and a single-device high-overload test. The transient model yields a peak stress of 181.412 MPa in the sensitive structure. The reported drive and sense frequencies change from 7734.0 and 7755.7 Hz to 7745.2 and 7751.3 Hz, respectively, reducing the frequency split from 21.7 to 6.1 Hz. Under a calibrated impact of 16,190 g, the zero-rate output changes from 0.00178 to 0.06733°/s and the reported bias instability from 3.52 to 143.8°/h. A smaller frequency split therefore does not establish improved post-impact performance. For unchanged effective modal mass, the reported frequencies imply equivalent stiffness changes of approximately +0.290% and −0.113%. These estimates do not establish silicon plasticity or uniquely identify a package mechanism. The results are interpreted as a mechanism-oriented case study, with residual stress redistribution and boundary condition changes considered possible explanations requiring further physical verification. Population reliability and repeatability are outside the evidence provided by this single-device, single-event dataset.

Micromachines doi: 10.3390/mi17101205

Authors: Lu Sun Peihong Wu Li Yang Jin Tian Zhenxiao Li Feifei He Yang Qiu

The E1 component of High-altitude Nuclear Electromagnetic Pulse (HEMP) is an electromagnetic wave with extremely high peak power and fast-rising transient fields that can cause irreversible damage to electronic devices in an extremely short period of time. Traditional irradiation tests used to assess its impact on communication interfaces have problems such as high costs and complex system setup. Moreover, HEMP injection test standards and the actual coupling waveforms of the interfaces have significant differences, which leads to inaccurate electromagnetic coupling effect test results and causes problems through unreasonable design of the protection circuit. This study, in combination with the field-line coupling simulation analysis of communication interface circuits, designs a coupling effect test method for irradiation-equivalent injection without the need for high-cost irradiation equipment. By setting up a test system to conduct equivalent injection tests, taking RS232 communication interfaces as a typical representative, the interference threshold of the interface circuits can be accurately obtained. This enables the implementation of targeted and accurate protective measures to ensure the safe use of electronic devices, and has significant engineering application value.

Micromachines doi: 10.3390/mi17101204

Authors: Jian Dong Jie Wu Wenbin Fu Xuxuan Ai Chengchao Pan

The equilibrium shape of a finite-volume axisymmetric sessile droplet is governed by surface tension, gravity and the energy associated with the three-phase contact line. A variational model is developed to predict the profiles and apparent contact angles of droplets on horizontal, macroscopically flat hydrophilic and hydrophobic surfaces. In the variational model, the free-surface variation yields the Bashforth–Adams equation for the profile, and the contact-line endpoint variation gives the transversality condition for the apparent contact angle. A numerical algorithm is developed to determine the equilibrium profiles and apparent contact angles. Experiments are conducted to calibrate and validate the model. The effective contact-line energy parameters, q, of water on the hydrophilic, SiO2, surface and the hydrophobic polytetrafluoroethylene, PTFE, surface are calibrated using measurements from droplets with volumes ranging from 10 to 100 μL. The calibrated, q, values are then used to predict the profiles and apparent contact angles of water droplets on the hydrophilic, SiO2, and hydrophobic, PTFE, surfaces with volumes of 25, 35, 55, and 75 μL, which are excluded from the calibration. Across all validation cases, the mean relative errors in the predicted apparent contact angles are 0.36% for SiO2 and 0.49% for PTFE, with an overall mean relative error of 0.43%. The predicted droplet profiles agree well with the experimentally extracted profiles.

Micromachines doi: 10.3390/mi17101203

Authors: Jiabao Tang Zifan Miao Yunjing Zhang Xingli He

Laterally excited bulk acoustic wave resonators (XBARs) on lithium tantalate (LiTaO3, LT) are promising for wideband radio-frequency filters, but spurious modes and costly full-wave optimization hinder development. Limited coupling-bandwidth flexibility in commercial LT cuts motivates exploring non-standard orientations. We present a numerical framework integrating the finite-element method (FEM), coupling-of-modes (COM) theory, and artificial bee colony (ABC) optimization, emphasizing non-commercial 120° YX-LT. Hierarchical FEM screens orientation and periodic-cell response and then resolves finite aperture, busbars, and membrane boundaries. Compared with rectangular boundaries, an irregular pentagonal membrane disrupts coherent edge reflections, suppressing in-band spurious glitches and slightly enhancing effective coupling. A thickness-dependent COM model calibrated across a broad SiO2 loading range reproduces FEM resonance and antiresonance frequencies within 1 MHz. The surrogate enables mixed-variable ABC optimization of finger-pair number, normalized aperture, and stage-specific wavelengths. Five-stage ladder filters are synthesized and verified by direct FEM reconstruction. Stage-dependent wavelengths improve simulated passband transmission and reduce ripple versus a common-wavelength baseline; COM–FEM stopband discrepancies indicate the need for full-wave verification. After calibration, ABC core search takes approximately 2.9 h without repeated full-wave solutions. This transferable framework provides a cost-effective pathway from full-wave physics to circuit-level filter synthesis on thin-film piezoelectric platforms.

Micromachines doi: 10.3390/mi17101202

Authors: Tengqing Liu Yaokang Zhang Yaoxun Feng Shuangfeng Wang Qianxi Zhang

This paper presents a circular ultra-thin vapor chamber (UTVC) with a thickness of 1.3 mm for LED lamp thermal management. Superhydrophilic patterned microstructure (SPMS) arrays are fabricated on the upper and bottom covers to replace the traditional wick structure. The heat transfer performance of the ultra-thin vapor chamber was experimentally investigated under different cooling water temperatures in the horizontal orientation. The cooling water temperatures range from 25 to 40 °C, and the input-heat loads range from 5 to 25 W. The results show that for the proposed UTVC with SPMS arrays, the temperatures rise rapidly with increasing input-heat load and then level off after a certain period, with the temperature rise being considerably smaller than that of the ceramic heater. The condenser temperature difference increases with both the input-heat load and the cooling water temperature, and it ranges from 1.2 to 7.3 °C. Both the heater-to-vapor-chamber thermal resistance and the system thermal resistance increase with a higher input-heat load and a lower cooling water temperature. The heater-to-vapor-chamber thermal resistance ranges from 0.80 to 1.34 K/W, and the system thermal resistance ranges from 3.10 to 4.13 K/W.

Micromachines doi: 10.3390/mi17101201

Authors: Stefano Rodinò Carmine Maletta

This paper presents the design and preliminary mechanical validation of a bistable switching module driven by shape memory alloy (SMA) springs for CubeSat reflector-panel applications. A pre-compressed curved compliant beam provides passive state retention, while two antagonistic SMA spring pairs trigger reversible switching. The module was sized for a 3U CubeSat reflector concept comprising nine panels and developed through finite-element analyses and staged prototyping. The numerical analyses supported preliminary geometry screening using the rise-to-thickness ratio and axial pre-compression. The actuator achieved a switching stroke slightly below 7 mm, and the integrated panel demonstrator reached an approximate edge displacement of 19 mm, compared with a simulated value of 21.3 mm, a difference of 10.8 percent. A ten-cycle sequence demonstrated short-term switching repeatability under the tested laboratory conditions. The results support actuator- and panel-level mechanical switching under laboratory conditions; they do not validate the surface accuracy or electromagnetic performance of a complete reflector.

Micromachines doi: 10.3390/mi17101200

Authors: Yoshiro Tajitsu Osamu Takeuchi Saki Shimada Takuto Nonomura

Piezoelectric braided cords composed of poly-L-lactic acid (PLLA) fibers can be integrated into textiles to detect mechanical signals without requiring sensors to be attached directly to the body. In this study, we investigated the potential of a bed-sheet-integrated piezoelectric braided cord sensor for unobtrusive physiological monitoring during sleep, using sleep apnea as an example of its possible applications. Finite element method (FEM) analysis was performed to qualitatively examine the directional characteristics of the piezoelectric response. Guided by these qualitative findings, a bed-sheet sensor with a multi-orientation stitching configuration was developed through iterative prototyping and experimental evaluation. Piezoelectric braided cord signals were recorded from 23 participants during their routine clinical polysomnography (PSG) examinations. The developed sensor enabled the detection of respiration- and pulse-related mechanical signals during sleep. During the initial analysis of data from a small number of these participants, we observed that a pulse-related periodic component remained detectable in the respiratory signal when respiratory motion decreased during apnea. Based on this observation, an apnea-related signal detection algorithm was developed and subsequently applied to the complete dataset of 23 participants. The sensor-based analysis was performed independently of the physicians’ PSG-based assessments. For the 18 participants with available physician-based apnea event assessments, the sensor-detected event counts were compared with PSG-based counts within 5-min intervals, without event-by-event temporal matching. These findings demonstrate the potential of the proposed sensing approach and provide a basis for future clinical investigations.

Micromachines doi: 10.3390/mi17101199

Authors: Enrique E. Zayas-Figueras Irene Buj-Corral Ot Godó-Estany

Polymeric gears are commonly employed in applications where low weight and noise, as well as corrosion resistance, are important, such as consumer products, automotive components, and medical devices. The use of additive manufacturing (AM) processes provides greater geometric freedom and lower production costs for short production runs than other manufacturing processes such as injection molding. This study presents an evaluation of the dimensional accuracy of helical gears manufactured using fused filament fabrication (FFF) technology. Three gear models with the same module and number of teeth—but with different helix angles of 15°, 25°, and 35°, respectively—were designed and 3D printed using PLA and PA66. Dimensional verification was performed using two approaches: (i) conventional methods, namely, the tip circle method for measuring tooth thickness, the sector span method, and the over-rollers method for measuring gear diameter; and (ii) a non-contact method, laser scanning, in which dimensional deviations between the theoretical and measured surfaces were determined. The results show that, as a general trend, PA66 gears have higher thickness and lower chordal distance than PLA gears. PA66 parts have a deficit of material at the tooth tip, while PLA gears obtained with β = 15° exhibit a slight deficit of material at the bottom part of the tooth space. This study confirms that the combination of conventional and digital measuring methods is appropriate for the dimensional evaluation of 3D-printed polymeric gears.

Micromachines doi: 10.3390/mi17101198

Authors: Amirhossein Azami Yupeng Wu Christopher K. Nguyen Justin R. Abbott Mark E. Orazem Kevin J. Otto Stuart F. Cogan Brian N. Kim

Microelectrode arrays are used for neural stimulation and recording; however, their performance is limited by the high impedance and low charge-injection capacity of conventional metallic interfaces. To overcome these challenges, a variety of coatings, including metal oxides, carbon nanotubes, and conductive polymers, are applied to improve the electrochemical performance of microelectrode arrays. Among these materials, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has gained significant attention due to its low impedance, high charge-injection capacity, and compatibility with microfabrication processes. Despite these advantages, the long-term electrochemical stability of PEDOT:PSS at high levels of stimulation charge injection remains insufficiently understood. In this study, we investigated the stability of PEDOT:PSS films electrodeposited on gold microelectrodes for prolonged electrical stimulation. Voltage transient (VT) analysis revealed that PEDOT:PSS degradation occurs when the maximum cathodic excursion (Emc) exceeds –0.6 V versus Ag|AgCl. The degradation is accompanied by the appearance of asymmetric access voltages and a voltage inversion in the anodal phase of the VT. Electrochemical impedance spectroscopy (EIS) revealed a sharp increase in PEDOT:PSS impedance at negative DC bias potentials, beginning at −0.5 V and increasing as the potential became more negative. These results identified –0.6 V as an electrochemical limit for PEDOT:PSS stability on gold and implicate the reduction and de-doping of PEDOT:PSS, and sequalae, in the observed PEDOT:PSS degradation. Nonetheless, PEDOT:PSS electrodes had stable charge-injection capacities of 3.6 mC/cm2 (200 µs pulse width) over the course of 200 million pulses.

Micromachines doi: 10.3390/mi17101197

Authors: Manlio Tassieri

Linear viscoelasticity provides a time-invariant mechanical fingerprint of materials and underpins predictive descriptions of their response to external deformation. The corresponding material functions reflect the hierarchy of inter- and intra-molecular interactions governing structure and dynamics across multiple scales, from atomistic motions to macromolecular and mesoscopic rearrangements. Access to linear viscoelastic properties over the widest possible frequency range therefore offers unique insight into the mechanisms controlling the behaviour of soft matter and complex fluids. However, obtaining reliable broadband viscoelastic spectra remains experimentally and analytically challenging owing to instrumental limitations, finite measurement windows, discrete data sampling, and the shortcomings of conventional transformation procedures. This Review/Perspective examines the evolution of the i-Rheo Framework, a model-free methodology for extracting broadband viscoelastic properties directly from finite experimental or simulated datasets without imposing predefined constitutive models. Originally developed to transform creep-compliance measurements into the complex shear modulus, the framework has subsequently been extended to bulk rheology, passive and active microrheology, optical tweezers, atomic force microscopy, macro-indentation, biomechanics, rheo-optical measurements, and molecular simulations. The recent development of i-Rheo-Tempo further establishes a reversible connection between time- and frequency-domain representations, providing a unified analytical framework for multiscale viscoelastic characterisation across soft-matter physics.

Micromachines doi: 10.3390/mi17101196

Authors: Tuğrul Uslu Erkin Gezgin

The field of medical microrobotics has emerged as a promising approach for delicate medical interventions in anatomical regions where conventional approaches lack efficiency. Due to the fact that constrained anatomical workspaces offer limited visibility, in order to fulfill desired tasks, the precise tracking of untethered microrobots becomes a vital necessity and a critical challenge. Although there are studies in the literature to overcome said challenge, drawbacks include but are not limited to prolonged exposure to high magnetic fields, limited tracking workspace, and robustness. In light of this, the current paper proposes a hybrid tracking system utilizing both optical and magnetic tools to provide real-time pose estimation of an untethered microrobot operated within a closed workspace. The proposed system utilizes a custom-made Hall-effect sensor array apparatus that is capable of single-degree-of-freedom actuation to execute a planar sweeping motion and three low-cost motion capture cameras to track the apparatus pose in real time. In combining precise optical tracking, magnetic sensing, and the proposed artificial neural network (ANN)-based estimation approach, the system overcomes visibility limitations of optical motion tracking systems and workspace limitations in magnetic sensing systems. Hardware verification studies of the constructed setup are carried out utilizing a KUKA KR6 R900 SIX serial robot manipulator to simulate untethered microrobot actuation. During verification procedures, the sensor apparatus motion, end effector of the manipulator, and microrobot are streamed into a 3D Slicer software virtual environment to enhance visual feedback with an efficient surgical navigation approach. The proposed approach shows efficient results and sub-millimeter accuracy in microrobot tracking.

Micromachines doi: 10.3390/mi17101195

Authors: Dominic Tung Manoj Sachdev Sanjit Jolly Naveen Chandrashekar

The demand for increased accessibility and effectiveness of automated external defibrillators (AEDs) exists due to the life-threatening nature of sudden cardiac arrest (SCA). Timely access to AEDs can significantly increase the chances of survival in individuals experiencing SCA. Traditional AEDs are bulky and difficult to transport, primarily because of the battery size required to overcome transthoracic impedance (TTI). This study assessed the feasibility of microneedle (MN) electrodes to reduce the TTI and hence improve AED portability. An electrode prototype was developed, consisting of eight arrays of microneedles attached to a 3D printed flexible base. A circuit measuring interelectrode resistance was created to mimic an operational AED while also providing a quantitative measurement of the electrode–skin interface resistance. Testing was conducted on human chest skin. The MN electrode demonstrated a 24% reduction in human transthoracic skin resistance compared to conventional AED pads, suggesting the potential for improved AED effectiveness and portability. These findings indicate the potential for reduced device size, although further research is needed to validate the broader implications.

Micromachines doi: 10.3390/mi17101194

Authors: Xiaoming Zhang Yan Gu Bin Fu Xuesong Wang Zisu Xu Yuan Xi Weidong Zhou Silin Liu

To address the issues of graphite flaking and interfacial microcrack propagation during conventional polishing of multiphase heterogeneous materials such as ductile cast iron, this study designed and validated a two-dimensional non-resonant flexible vibration-assisted polishing device (RVAPD) based on a series–parallel structure combined with a Scott Russell mechanism. The device decouples spatial motion from mechanical transmission through an irregular flexible hinge network. A theoretical model is established using the flexible matrix method and Lagrange equations, and static and dynamic simulations are conducted using ABAQUS finite element software. The simulation results show that the input and output stiffness values are 19,524 N/mm and 8197 N/mm, respectively. Experimental measurements revealed a natural frequency of 1120 Hz, a maximum output displacement of 12.58 μm, an output stiffness of 7200 N/mm, a static response delay of only 114 ms, and a positioning error below 2.76 μm, confirming the device’s high stiffness, wide bandwidth, and precise motion control capabilities. Polishing experiments indicate that 200 Hz provided the best surface-quality performance among the tested excitation frequencies, at which the surface roughness Sa decreased from 0.049 μm without vibration to 0.036 μm, while the maximum height Sz decreased from 1.927 μm to 0.983 μm. The polishing performance slightly deteriorated at 300 Hz, with Sa increasing to 0.043 μm. These results indicate that the tested excitation conditions can influence the surface-quality characteristics of the polished ductile cast iron. This research provides a basis for non-resonant vibration-assisted polishing of multiphase heterogeneous alloys.

Micromachines doi: 10.3390/mi17101193

Authors: Yunxing Lu Xiaohan Wang Qingchun Bai Qiang Shi Yiman Song Lin Zhou Zhenhua Wu Hongju Mao

Extracellular vesicles (EVs) carry key genetic biomarkers, such as somatic mutations, making them valuable targets for non-invasive cancer diagnostics. However, standard workflows that isolate EVs and detect low-abundance mutations typically require multi-step manual operations, leading to sample loss and potential cross-contamination. Here, we present an integrated microfluidic platform combined with a deep learning algorithm for the continuous processing and automated droplet analysis of EV-derived RNA mutations. The microfluidic chip integrates magnetic bead-based EV capture, online lysis, droplet generation, and arrayed RT-droplet digital PCR (RT-ddPCR) on a single device. To streamline signal readout, a deep learning framework based on Cellpose and K-means clustering was implemented to process individual fluorescence images, enabling droplet detection, background removal, gray-scale intensity extraction, and automatic positive/negative droplet classification. The system showed a linear response across a wide range of original-sample inputs (R2 = 0.9950). The platform was evaluated using EV samples derived from three cancer cell lines (NCI-H1975, SK-LU-1, and HepG2) and the detection of EGFR L858R and KRAS mutations were achieved. By coupling continuous sample processing with automated image interpretation, this platform offers a practical reference for integrated EV nucleic acid analysis for liquid-biopsy applications.