Micromachines

16 pages, 4503 KiB

Open AccessArticle

A Single-Field Finite Difference Time-Domain Method Verified Using a Novel Antenna Design with an Artificial Magnetic Conductor Enhanced Structure

by Yongjun Qi, Weibo Liang, Yilan Hu, Liang Zhang, Cheng You, Yuxiang Zhang, Tianrun Yan and Hongxing Zheng

Micromachines 2025, 16(4), 489; https://doi.org/10.3390/mi16040489 - 21 Apr 2025

Abstract

The Finite Difference Time-Domain (FDTD) method is a powerful tool for electromagnetic field analysis. In this work, we develop a variation of the algorithm to accurately calculate antenna, microwave circuit, and target scattering problems. To improve efficiency, a single-field (SF) FDTD method is [...] Read more.

The Finite Difference Time-Domain (FDTD) method is a powerful tool for electromagnetic field analysis. In this work, we develop a variation of the algorithm to accurately calculate antenna, microwave circuit, and target scattering problems. To improve efficiency, a single-field (SF) FDTD method is proposed as a numerical solution to the time-domain Helmholtz equations. New formulas incorporating resistors and voltage sources are derived for the SF-FDTD algorithm, including hybrid implicit–explicit and weakly conditionally stable SF-FDTD methods. The correctness of these formulas is verified through numerical simulations of a newly designed dual-band wearable antenna with an artificial magnetic conductor (AMC) structure. A novel antenna fed by a coplanar waveguide with a compact size of 15.6 × 20 mm² has been obtained after being optimized through an artificial intelligent method. A double-layer, dual-frequency AMC structure is designed to improve the isolation between the antenna and the human body. The simulation and experiment results with different bending degrees show that the antenna with the AMC structure can cover two frequency bands, 2.4 GHz–2.48 GHz and 5.725 GHz–5.875 GHz. The gain at 2.45 GHz and 5.8 GHz reaches 5.3 dBi and 8.9 dBi, respectively. The specific absorption rate has been reduced to the international standard range. In particular, this proposed SF-FDTD method can be extended to analyze other electromagnetic problems with fine details in one or two directions. Full article

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13 pages, 5333 KiB

Open AccessPerspective

Interposer-Based ESD Protection: A Potential Solution for μ-Packaging Reliability of 3D Chips

by Xunyu Li, Zijin Pan, Weiquan Hao, Runyu Miao, Zijian Yue and Albert Wang

Micromachines 2025, 16(4), 488; https://doi.org/10.3390/mi16040488 - 21 Apr 2025

Abstract

The ending of Moore’s Law calls for innovations in integrated circuit (IC) technologies and chip designs. Heterogeneous integration (HI) emerges as a pathway towards smart future chips for more Moore time and for beyond-Moore time, featuring systems-on-integrated-chiplets (SoICs) and advanced micro-packaging (μ-packaging). Reliability, [...] Read more.

The ending of Moore’s Law calls for innovations in integrated circuit (IC) technologies and chip designs. Heterogeneous integration (HI) emerges as a pathway towards smart future chips for more Moore time and for beyond-Moore time, featuring systems-on-integrated-chiplets (SoICs) and advanced micro-packaging (μ-packaging). Reliability, particularly with regard to electrostatic charge (ESD) failure, is a major challenge for 3D SoIC chips in μ-packaging, which is an emerging design-for-reliability challenge for future chips. This perspective article articulates that interposer-based ESD protection will be an important potential solution for 3D SoIC chips in μ-packaging against the devastating ESD failure problem. Full article

(This article belongs to the Special Issue Microelectronics Assembly and Packaging: Materials and Technologies, 2nd Edition)

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18 pages, 20007 KiB

Open AccessArticle

Design and Driving Characteristics of a Bidirectional Micro-Device Based on Multi-Electrothermal Co-Actuation

by Yujuan Tang, Zihao Guo, Yujiao Ding and Xinjie Wang

Micromachines 2025, 16(4), 487; https://doi.org/10.3390/mi16040487 - 21 Apr 2025

Abstract

In this paper, a bidirectional micro-device based on multi-electrothermal co-actuation is proposed for a fuze safety system, combining the advantages of the simple structure, small size, low input voltage, large output, and absence of electromagnetic interference in electrothermal actuators. Based on the working [...] Read more.

In this paper, a bidirectional micro-device based on multi-electrothermal co-actuation is proposed for a fuze safety system, combining the advantages of the simple structure, small size, low input voltage, large output, and absence of electromagnetic interference in electrothermal actuators. Based on the working principle of the multi-electrothermal co-actuation device and the mathematical model of the single V-shaped electrothermal actuator established in this paper, the temperature distribution of the V-shaped electrothermal actuator is simulated. In addition, the dynamic response and the effect of geometric factors on the output performance of the multi-electrothermal co-actuation device are analyzed in detail. Furthermore, driving characteristics tests of the electrothermal micro-device are carried out. The experimental findings indicate that a displacement of approximately 258.95 μm with a response time of about 156.51 ms can be achieved by the V-shaped electrothermal actuator when the applied voltage is 1.2 V. In a single cycle, a total displacement of 340 μm is obtained by the co-actuation device in around 1.28 s. Full article

(This article belongs to the Special Issue MEMS Actuators and Their Applications)

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16 pages, 37103 KiB

Open AccessArticle

Mechano-Filtering Encapsulation: A Stitching-Based Packaging Strategy Implementing Active Noise Suppression in Piezoresistive Pressure Sensors

by Yi Yu, Yingying Zhao, Tao Xue, Xinyi Wang and Qiang Zou

Micromachines 2025, 16(4), 486; https://doi.org/10.3390/mi16040486 - 20 Apr 2025

Abstract

Flexible pressure sensors face the dual challenges of weak signal extraction and environmental noise suppression in wearable electronics and human-machine interfaces. This research proposes an intelligent pressure sensor utilizing chitosan/carbon nanotube/melamine sponge (CS/CNT/MS) composites, achieving high-performance sensing through a dual-stage noise reduction architecture [...] Read more.

Flexible pressure sensors face the dual challenges of weak signal extraction and environmental noise suppression in wearable electronics and human-machine interfaces. This research proposes an intelligent pressure sensor utilizing chitosan/carbon nanotube/melamine sponge (CS/CNT/MS) composites, achieving high-performance sensing through a dual-stage noise reduction architecture that combines mechanical pre-filtration and electrical synergistic regulation. An innovative compressed-stitching encapsulation technique creates pressure sensors with equivalent mechanical low-pass filtering characteristics, actively eliminating interference signals below 3 kPa while maintaining linear response within the 3–20 kPa effective loading range (sensitivity: 0.053 kPa⁻¹). The synergistic effects of CS molecular cross-linking and CNTs’ three-dimensional conductive network endow the device with a 72 ms response time, 24 ms recovery speed, and over 3500-cycle compression stability. Successful applications in smart sport monitoring and tactile interactive interfaces demonstrate a material-structure-circuit co-design paradigm for mechanical perception in complex environments. Full article

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21 pages, 16024 KiB

Open AccessArticle

Posture Detection of Dual-Hemisphere Capsule Robot Based on Magnetic Tracking Effects and ORB-AEKF Algorithm

by Xu Liu, Yongshun Zhang and Qiancheng Wang

Micromachines 2025, 16(4), 485; https://doi.org/10.3390/mi16040485 - 20 Apr 2025

Abstract

Posture detection is essential for capsule robots to be manipulated in a relatively closed gastrointestinal (GI) tract and to fulfill some medical operations. In this paper, a posture detection technique for a magnetic-actuated dual-hemisphere capsule robot (DHCR) is proposed. In this method, the [...] Read more.

Posture detection is essential for capsule robots to be manipulated in a relatively closed gastrointestinal (GI) tract and to fulfill some medical operations. In this paper, a posture detection technique for a magnetic-actuated dual-hemisphere capsule robot (DHCR) is proposed. In this method, the DHCR realizes fixed-point posture adjustment based on tracking effects, and feature points are recognized and matched with the help of the ORB algorithm on the GI image acquired by a vision sensor. The system model is derived from the dynamic model and feature point information. Then, the posture is optimized by using the adaptive extended Kalman filter (AEKF) algorithm. As a result, the posture detection method based on the tracking effects and the ORB-AEKF algorithm is formed. The effectiveness and superiority of the proposed method are verified through experiments, which provide a good foundation for the subsequent, accurate closed-loop control of the DHCR. Full article

(This article belongs to the Special Issue Advanced Applications in Microrobots)

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19 pages, 14110 KiB

Open AccessArticle

A 3D DC Electric Field Meter Based on Sensor Chips Packaged Using a Highly Sensitive Scheme

by Pengfei Yang, Xiaolong Wen, Xiaonan Li, Zhaozhi Chu, Chunrong Peng and Shuang Wu

Micromachines 2025, 16(4), 484; https://doi.org/10.3390/mi16040484 - 20 Apr 2025

Abstract

This study presents a 3D DC electric field meter (EFM) that uses three identical 1D MEMS chips. The shielding electrodes and sensing electrodes of the MEMS chips employ a combination of rigid frames and short strip-type beams to improve vibrational stability. To enhance [...] Read more.

This study presents a 3D DC electric field meter (EFM) that uses three identical 1D MEMS chips. The shielding electrodes and sensing electrodes of the MEMS chips employ a combination of rigid frames and short strip-type beams to improve vibrational stability. To enhance sensitivity, our MEMS chips feature inner convex packaging covers. Moreover, the integrated design and wireless transmission efficiently eradicate the impact of ground potential on detection results. Detailed simulations have been conducted to analyze the electric field distribution within the chip package and the electric field distribution on the EFM’s surface. A prototype was then developed, calibrated, and validated. The test results indicate that the sensitivity of our proposed 3D EFM is at least 4.64 times higher than the highest sensitivity observed in previously reported MEMS 3D EFMs. The maximum relative deviation is a mere 2.2% for any rotation attitude. Remarkably, even in high humidity conditions, the EFM’s linearity remains within 1%. Additionally, the resolution of any single axis is less than 10 V/m. Full article

(This article belongs to the Special Issue MEMS/NEMS Devices and Applications, 3rd Edition)

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17 pages, 20569 KiB

Open AccessArticle

A Slanted-Finger Interdigitated Transducer Microfluidic Device for Particles Sorting

by Baoguo Liu, Xiang Ren, Tao Xue and Qiang Zou

Micromachines 2025, 16(4), 483; https://doi.org/10.3390/mi16040483 - 20 Apr 2025

Abstract

Sorting particles or cells of specific sizes in complex systems has long been a focus of many researchers. Acoustic surface waves, which generate acoustic radiation forces on particles or cells and, thus, influence their motion, are commonly used for the non-destructive separation of [...] Read more.

Sorting particles or cells of specific sizes in complex systems has long been a focus of many researchers. Acoustic surface waves, which generate acoustic radiation forces on particles or cells and, thus, influence their motion, are commonly used for the non-destructive separation of particles or cells of specific sizes. In previous studies, the frequency of acoustic surface wave generation has been limited by the interdigitated transducer (IDT). To extend the effective operating frequency range of the IDT, a slanted-finger interdigitated transducer (SFIT) with a wide acoustic path and multiple operating frequencies was designed. Compared with traditional acoustic sorting devices, which suffer from a limited frequency range and narrow acoustic paths, this new design greatly expands both the operating frequency range and acoustic path width, and enables adjustable operating frequencies, providing a solution for sorting particles or cells with uneven sizes in complex environments. The optimal resonance frequency is distributed within the 32–42 MHz range, and the operating frequencies within this range can generate a standing wave acoustic path of approximately 200

μ

m, thus enhancing the effectiveness of the operating frequencies. The microfluidic sorting device based on SFIT can efficiently and accurately sort polystyrene (PS) with particle sizes of 20

μ

m, 30

μ

m, and 50

μ

m from mixed PS microspheres (5, 10, 20

μ

m), (5, 10, 30

μ

m), and (5, 10, 50

μ

m), with a sorting efficiency and purity exceeding 96%. Additionally, the device is capable of sorting other types of mixed microspheres (5, 10, 20, 30, 50

μ

m). This new wide-acoustic-path, multi-frequency sorting device demonstrates the ability to sort particlesin a high-purity, label-free manner, offering a more alternative to traditional sorting methods. Full article

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44 pages, 9568 KiB

Open AccessReview

MEMS Varifocal Optical Elements for Focus Control

by Chen Liu, Tong Wang, Xin Wang, Manpeng Chang, Yu Jian and Weimin Wang

Micromachines 2025, 16(4), 482; https://doi.org/10.3390/mi16040482 - 19 Apr 2025

Viewed by 72

Abstract

As microelectronic devices become more prevalent daily, miniaturization is emerging as a key trend, particularly in optical systems. Optical systems with volume scanning and imaging capabilities heavily rely on focus control. The traditional focus tuning method restricts the miniaturization of optical systems due [...] Read more.

As microelectronic devices become more prevalent daily, miniaturization is emerging as a key trend, particularly in optical systems. Optical systems with volume scanning and imaging capabilities heavily rely on focus control. The traditional focus tuning method restricts the miniaturization of optical systems due to its complex structure and large volume. The recent rapid development of MEMS varifocal optical elements has provided sufficient opportunities for miniaturized optical systems. Here, we review the literature on MEMS varifocal optical elements over the past two decades. Based on light control mechanisms, MEMS varifocal optical elements are divided into three categories: reflective varifocal mirrors, varifocal microlenses, and phased varifocal mirrors. A novel indicator is introduced to evaluate and compare the performance of MEMS varifocal optical elements. A wide range of applications is also discussed. This review can serve as a reference for relevant researchers and engineers. Full article

(This article belongs to the Section A1: Optical MEMS and Photonic Microsystems)

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17 pages, 6680 KiB

Open AccessArticle

Research on Machining Parameter Optimization and an Electrode Wear Compensation Method of Microgroove Micro-EDM

by Xiaodong Zhang, Wentong Zhang, Peng Yu and Yiquan Li

Micromachines 2025, 16(4), 481; https://doi.org/10.3390/mi16040481 - 18 Apr 2025

Viewed by 103

Abstract

In the process of micro-EDM, tool electrode wear is inevitable, especially for complex three-dimensional cavities or microgroove structures. Tool electrode wear accumulates during machining, which will finally affect machining accuracy and machining quality. It is necessary to reduce electrode wear and compensate it [...] Read more.

In the process of micro-EDM, tool electrode wear is inevitable, especially for complex three-dimensional cavities or microgroove structures. Tool electrode wear accumulates during machining, which will finally affect machining accuracy and machining quality. It is necessary to reduce electrode wear and compensate it through micro-EDM. Therefore, based on an established L27 orthogonal experiment, this paper uses the grey relational analysis (GRA) method to realize multi-objective optimization of machining time and electrode wear, so as to achieve the shortest machining time and the minimum electrode wear during machining under the optimal machining parameter combination. Then, the orthogonal experiment results are used as dataset of artificial neural networks (ANNs), and an ANN prediction model is established. Combined with image processing technology, the bottom profile of the machined microgroove is extracted and then an electrode axial wear compensation equation is fitted, and a fixed-length nonlinear compensation method for electrode axial wear is proposed. Finally, the GRA optimal experiment shows that machining time, electrode axial wear and radial wear are reduced by 13.89%, 3.31%, and 10.80%, respectively, compared with the H17 orthogonal experiment with the largest grey relational grade. For the study of electrode axial wear compensation methods, the consistency of the depth and width of the machined microgroove structure with compensation is significantly better than that of the microgroove structure without compensation. This result shows that the proposed fixed-length nonlinear compensation method can effectively compensate electrode axial wear in micro-EDM and improve machining quality to a certain extent. Full article

(This article belongs to the Special Issue Emerging Micro Manufacturing Technologies and Applications, 3rd Edition)

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18 pages, 6869 KiB

Open AccessArticle

A Trimming Strategy for Mass Defects in Hemispherical Resonators Based on Multi-Harmonic Analysis

by Yimo Chen, Fanrui Kong, Kai Zeng, Xiang Xi, Yan Shi, Dingbang Xiao and Xuezhong Wu

Micromachines 2025, 16(4), 480; https://doi.org/10.3390/mi16040480 - 18 Apr 2025

Viewed by 78

Abstract

This study investigates the impact of etching trimming parameters on the multiple harmonics of the mass distribution in hemispherical resonators and proposes a novel 1st harmonic trimming scheme. As mass balancing technology advances, the extension of identification and trimming from frequency split to [...] Read more.

This study investigates the impact of etching trimming parameters on the multiple harmonics of the mass distribution in hemispherical resonators and proposes a novel 1st harmonic trimming scheme. As mass balancing technology advances, the extension of identification and trimming from frequency split to multiple harmonics remains a challenge. Initially, a multi-harmonic identification scheme based on spurious mode detection was established, considering the influence of the first three harmonics of the mass distribution on the dynamic characteristics of hemispherical resonators. Finite element method modeling and analysis revealed that common structural geometric errors significantly introduce the 1st harmonic. By integrating a rectangular pulse function into the mass distribution function to simulate etching grooves, spectral analysis revealed that groove depth and width determine the amplitude and gradient of introduced harmonics. This research introduces an innovative discrete trimming scheme aimed at addressing the frequency split and mode mismatch issues associated with traditional single-point trimming of the 1st harmonic. By decomposing the trimming task into primary and auxiliary etching grooves, the 4th harmonic introduced by the primary etching is compensated by the secondary 4th harmonic introduced by the auxiliary etching, achieving decoupling of the 1st harmonic from frequency split during the trimming process. The scheme was verified through finite element simulations and experimental testing. Results demonstrate that, for a similar reduction in the 1st harmonic, the variation in frequency split during the discrete trimming process is only 11% of that observed in single-point trimming, facilitating efficient and low-damage trimming of the 1st harmonic. Full article

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14 pages, 2091 KiB

Open AccessArticle

Influence of Oil Viscosity on Hysteresis Effect in Electrowetting Displays Based on Simulation

by Wei Li, Linwei Liu, Taiyuan Zhang, Lixia Tian, Li Wang, Cheng Xu, Jianwen Lu, Zichuan Yi and Guofu Zhou

Micromachines 2025, 16(4), 479; https://doi.org/10.3390/mi16040479 - 18 Apr 2025

Viewed by 65

Abstract

As the most promising new reflective display technology, electrowetting displays (EWDs) have the advantages of a simple structure, fast response, high contrast, and rich colors. However, due to the hysteresis effect, the grayscales of EWDs cannot be accurately controlled, which seriously restricts the [...] Read more.

As the most promising new reflective display technology, electrowetting displays (EWDs) have the advantages of a simple structure, fast response, high contrast, and rich colors. However, due to the hysteresis effect, the grayscales of EWDs cannot be accurately controlled, which seriously restricts the industrialization process of this technology. In this paper, the oil movement process in an EWD pixel cell was simulated, and the influence of oil viscosity on the hysteresis effect was studied based on the proposed simulation model. Firstly, the cause of the hysteresis effect was analyzed through the hysteresis curve of an EWD. Then, based on the COMSOL Multiphysics simulation environment, the oil movement process in an EWD pixel cell was simulated by coupling the phase field of laminar two-phase flow and electrostatic field. Finally, based on the simulation model, the influence of oil viscosity on the hysteresis effect in an EWD pixel cell was studied. We observed that the maximum hysteresis difference in the hysteresis effect increased with the increase in oil viscosity and decreased with the decrease in oil viscosity. The oil viscosity had little effect on the maximum aperture ratio of EWD. The pixel-on response time and pixel-off response time increased with the increase in oil viscosity. Full article

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30 pages, 9650 KiB

Open AccessArticle

Kinetostatic Modeling and Workspace Analysis of Redundant Actuated n-4R Compliant Parallel Pointing Mechanism

by Jun Ren, Yikang Shu and Youwei Lin

Micromachines 2025, 16(4), 478; https://doi.org/10.3390/mi16040478 - 18 Apr 2025

Viewed by 91

Abstract

The workspace of the compliant parallel mechanism (CPM) is generally limited due to the small deformation range of flexible hinges, which are usually at the micro/nano scale. This paper takes the 2-DOFs n-4R compliant parallel pointing mechanism (n-4R CPPM) as [...] Read more.

The workspace of the compliant parallel mechanism (CPM) is generally limited due to the small deformation range of flexible hinges, which are usually at the micro/nano scale. This paper takes the 2-DOFs n-4R compliant parallel pointing mechanism (n-4R CPPM) as the object and optimizes the workspace performance of the mechanism through redundant actuation, aiming to maximize the workspace. First, the kinetostatic model and the flexible hinge displacement model of the redundant actuated n-4R CPPM are established, successively. The former model reveals the relationships between the output displacements and the input forces/displacements, while the latter relates the flexible hinge deformation and the input forces/displacements. Second, a space pointing trajectory is chosen to validate the accuracy of the kinetostatic model of the redundant actuated 3-4R CPPM through finite element (FE) simulation. The results show that the relative error between the analytical and the FE results does not exceed 2.1%, and the high consistency indicates the accuracy of the kinetostatic model. Finally, the workspace performance of the 3-4R and 4-4R CPPMs is successively optimized through redundant actuation. The results indicate that, compared with the non-redundant actuation case, the workspace can be effectively enlarged and become more symmetric by means of the redundant actuation. The maximum achievable pitch angle ψ_a and the y-direction motion range of the mobile platform both increase by 100%. Moreover, it is shown that the workspace in the non-redundant actuated case is a subset of the workspace in the redundant actuated case, and the position-workspace shape changes from planar to 3-D. Full article

(This article belongs to the Special Issue Advanced Applications in Microrobots)

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14 pages, 19446 KiB

Open AccessArticle

Wide-Range, Washable Piezoresistive Pressure Sensor Based on MCNT-PDMS Dip-Coated PDMS Sponge

by Kun Luo, Xinyi Wang, Tao Xue, Yingying Zhao and Qiang Zou

Micromachines 2025, 16(4), 477; https://doi.org/10.3390/mi16040477 - 17 Apr 2025

Viewed by 147

Abstract

Flexible pressure sensors have great potential for wearable applications such as human health monitoring and human–computer interaction, which require different trade-offs between the sensitivity and operating range. However, preparing washable and wide-range piezoresistive pressure sensors remains a great challenge. Here, we developed a [...] Read more.

Flexible pressure sensors have great potential for wearable applications such as human health monitoring and human–computer interaction, which require different trade-offs between the sensitivity and operating range. However, preparing washable and wide-range piezoresistive pressure sensors remains a great challenge. Here, we developed a porous flexible elastomer sponge based on a carbon nanotube composite network coating for pressure sensors with extremely high stability and washability over a wide range. Specifically, a sugar template was used to fabricate a homogeneous macroporous PDMS sponge as a substrate, and a dip-coated MCNT-PDMS composite was used as a conductive layer. The high degree of adhesion formed between the substrate and the conductive layer resulted in a sponge with greatly enhanced mechanical properties and stability, while improving the operating range. The pressure sensors exhibited a broad operating range of 0–650 kPa, demonstrating excellent sensitivity (0.0049 kPa⁻¹ in the range of 0–74 kPa, 0.0010 kPa⁻¹ in the range of 74–310 kPa, and 0.0004 kPa⁻¹ in the range of 310–650 kPa), as well as a fast response time of 143 ms and recovery time of 73 ms, long-term cycling stability of over 10,000 cycles, and excellent washable stability. Finally, we demonstrate that the sensors can be applied to gesture monitoring, human motion gait monitoring, and cycling pressure monitoring. Full article

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17 pages, 9262 KiB

Open AccessArticle

Infrared Absorption of Laser Patterned Sapphire Al₂O₃ for Radiative Cooling

by Nan Zheng, Daniel Smith, Soon Hock Ng, Hsin-Hui Huang, Dominyka Stonytė, Dominique Appadoo, Jitraporn Vongsvivut, Tomas Katkus, Nguyen Hoai An Le, Haoran Mu, Yoshiaki Nishijima, Lina Grineviciute and Saulius Juodkazis

Micromachines 2025, 16(4), 476; https://doi.org/10.3390/mi16040476 - 16 Apr 2025

Viewed by 175

Abstract

The reflectance (R) of linear and circular micro-gratings on c-plane sapphire Al₂O₃ ablated by a femtosecond (fs) laser were spectrally characterised for thermal emission

\propto (1 - R)

in the mid-to-far infrared (IR) spectral range. An [...] Read more.

The reflectance (R) of linear and circular micro-gratings on c-plane sapphire Al₂O₃ ablated by a femtosecond (fs) laser were spectrally characterised for thermal emission

\propto (1 - R)

in the mid-to-far infrared (IR) spectral range. An IR camera was used to determine the blackbody radiation temperature from laser-patterned regions, which showed (3–6)% larger emissivity dependent on the grating pattern. The azimuthal emission curve closely followed the Lambertian angular profile

\propto cos θ_{a}

at the 7.5–13 μm emission band. The back-side ablation method on transparent substrates was employed to prevent debris formation during energy deposition as it applies a forward pressure of >0.3 GPa to the debris and molten skin layer. The back-side ablation maximises energy deposition at the exit interface where the transition occurs from the high-to-low refractive index. Phononic absorption in the Reststrahlen region 20–30 μm can be tailored with the fs laser inscription of sensor structures/gratings. Full article

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17 pages, 12485 KiB

Open AccessArticle

Research and Experimentation on Acoustic Monitoring Technology for Laser Drilling Penetration

by Bowen Lian, Kewen Pan, Liqun Wang, Liwu Shi, Jianhua Yao and Wei Guo

Micromachines 2025, 16(4), 475; https://doi.org/10.3390/mi16040475 - 16 Apr 2025

Viewed by 167

Abstract

To prevent back wall damage in cavity workpieces during laser drilling, it is crucial to monitor hole penetration status in real time. This study proposes a laser drilling penetration monitoring method based on acoustic principles. First, the acoustic module parameters of the system [...] Read more.

To prevent back wall damage in cavity workpieces during laser drilling, it is crucial to monitor hole penetration status in real time. This study proposes a laser drilling penetration monitoring method based on acoustic principles. First, the acoustic module parameters of the system were simulated and calibrated using COMSOL Multiphysics (version 6.1) software, resulting in an optimal sound source frequency of 35 kHz and an incident angle of 30° for the acoustic waves. Next, a nickel-based alloy laser drilling acoustic monitoring platform was designed and constructed, and the system’s upper computer control software was developed. Subsequent drilling trials were performed on the validated platform. During the experiments, the threshold for hole penetration signals under the specified experimental parameters was determined, enabling the acquisition of acoustic signals and the identification of hole penetration status. Furthermore, a correlation between the intensity of the acoustic signals and the exit aperture of the drilled holes was established. The results demonstrate the feasibility of using acoustic principles to monitor hole penetration status and measure machining aperture, providing both theoretical and experimental foundations for active laser drilling to prevent back wall damage. Full article

(This article belongs to the Special Issue Optical and Laser Material Processing, 2nd Edition)

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27 pages, 16472 KiB

Open AccessReview

Recent Research on Structural Design, Performance Optimization, and Applications of Piezoelectric Pumps

by Qiufeng Yan, Zhiling Liu, Le Wang, Wanting Sun and Mengyao Jiang

Micromachines 2025, 16(4), 474; https://doi.org/10.3390/mi16040474 - 16 Apr 2025

Viewed by 219

Abstract

With the advantages of simple structure, low power consumption, no electromagnetic interference, and fast response, piezoelectric pumps (PPs) have been widely used in the fields of chip cooling, biomedical applications, chemical applications, and fuel supply applications. In recent decades, scholars have proposed various [...] Read more.

With the advantages of simple structure, low power consumption, no electromagnetic interference, and fast response, piezoelectric pumps (PPs) have been widely used in the fields of chip cooling, biomedical applications, chemical applications, and fuel supply applications. In recent decades, scholars have proposed various PPs, and this article reviews the recent research results. In this review, according to the “valve” structure, PPs are divided into valve-less piezoelectric pumps (VLPPs), valve-based piezoelectric pumps (VBPPs), and piezoelectric pumps with valve and valve-less state transitions (PPVVSTs). Firstly, the design methods of typical structures were discussed, and comparisons were made in terms of driving frequency, driving voltage, output pressure, flow rate, structure materials, and pump size. The advantages and disadvantages of VLPPs, VBPPs, and PPVVSTs were analyzed. Then, we compared the driving parameters, output performance, structure materials, and pump size of single-chamber piezoelectric pumps (SCPs) and multi-chamber piezoelectric pumps (MCPs) and analyzed the advantages and disadvantages of SCPs and MCPs. Optimization methods proposed in recent years have been summarized to address the issues of the cavitation phenomenon, the liquid back-flow problem, and low output performance in PPs. Subsequently, the application research of PPs and the distribution of academic achievements were discussed. Finally, this review was summarized, and future research hot spots for PPs were proposed. The main contribution of this review is to provide piezoelectric pump (PP) researchers with a certain understanding of the structural design, optimization methods, practical applications, and research distribution of PPs, which can provide theoretical guidance for future research. Full article

(This article belongs to the Section E：Engineering and Technology)

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12 pages, 6694 KiB

Open AccessArticle

Normally Off AlGaN/GaN MIS-HEMTs with Self-Aligned p-GaN Gate and Non-Annealed Ohmic Contacts via Gate-First Fabrication

by Yinmiao Yin, Qian Fan, Xianfeng Ni, Chao Guo and Xing Gu

Micromachines 2025, 16(4), 473; https://doi.org/10.3390/mi16040473 - 16 Apr 2025

Viewed by 169

Abstract

This study introduces an enhancement-mode AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) featuring a self-aligned p-GaN gate structure, fabricated using a gate-first process. The key innovation of this work lies in simplifying the fabrication process by utilizing gate metallization for both electrical contact and etching [...] Read more.

This study introduces an enhancement-mode AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) featuring a self-aligned p-GaN gate structure, fabricated using a gate-first process. The key innovation of this work lies in simplifying the fabrication process by utilizing gate metallization for both electrical contact and etching mask functions, enabling precise self-alignment. A highly selective Cl₂/N₂/O₂ inductively coupled plasma (ICP) etching process was optimized to etch the p-GaN layer in the access regions, with a selectivity ratio of 33:1 and minimal damage to the AlGaN barrier. Additionally, a novel, non-annealed ohmic contact formation technique was developed, leveraging ICP etching to create nitrogen vacancies that facilitate contact formation without requiring thermal annealing. This technique streamlines the process by combining ohmic contact formation and mesa isolation into a single lithographic step. Incorporating a SiNx gate dielectric layer led to a 4.5 V threshold voltage shift in the fabricated devices. The resulting devices exhibited improved electrical performance, including a wide gate voltage swing (>10 V), a high on/off current ratio (~10⁷), and clear pinch-off characteristics. These results demonstrate the effectiveness of the proposed fabrication approach, offering significant improvements in process efficiency and manufacturability. Full article

(This article belongs to the Special Issue GaN Heterostructure Devices: From Materials to Application, 2nd Edition)

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41 pages, 7054 KiB

Open AccessReview

Seeking Solutions for Inclusively Economic, Rapid, and Safe Molecular Detection of Respiratory Infectious Diseases: Comprehensive Review from Polymerase Chain Reaction Techniques to Amplification-Free Biosensing

by Yaping Xie, Zisheng Zong, Qin Jiang, Xingxing Ke and Zhigang Wu

Micromachines 2025, 16(4), 472; https://doi.org/10.3390/mi16040472 - 15 Apr 2025

Viewed by 141

Abstract

Frequent outbreaks of respiratory infectious diseases, driven by diverse pathogens, have long posed significant threats to public health, economic productivity, and societal stability. Respiratory infectious diseases are highly contagious, characterized by short incubation periods, diverse symptoms, multiple transmission routes, susceptibility to mutations, and [...] Read more.

Frequent outbreaks of respiratory infectious diseases, driven by diverse pathogens, have long posed significant threats to public health, economic productivity, and societal stability. Respiratory infectious diseases are highly contagious, characterized by short incubation periods, diverse symptoms, multiple transmission routes, susceptibility to mutations, and distinct seasonality, contributing to their propensity for outbreaks. The absence of effective antiviral treatments and the heightened vulnerability of individuals with weakened immune systems make them more susceptible to infection, with severe cases potentially leading to complications or death. This situation becomes particularly concerning during peak seasons, such as influenza outbreaks. Therefore, early detection, diagnosis, and treatment are critical, alongside the prevention of cross-infection, ensuring patient safety, and controlling healthcare costs. To address these challenges, this review aims to identify a comprehensive, rapid, safe, and cost-effective diagnostic approach for respiratory infectious diseases. This approach is framed within the existing hierarchical healthcare system, focusing on establishing diagnostic capabilities at hospitals, community, and home levels to effectively tackle the above issues. In addition to PCR and isothermal amplification, the review also explores emerging molecular diagnostic strategies that may better address the evolving needs of respiratory disease diagnostics. A key focus is the transition from amplification technologies to amplification-free biosensing approaches, with particular attention given to their potential for home-based testing. This shift seeks to overcome the limitations of conventional amplification methods, particularly in decentralized and home diagnostics, offering a promising solution to enhance diagnostic speed and safety during outbreaks. In the future, with the integration of AI technologies into molecular amplification technologies, biosensors, and various application levels, the inclusively economic, rapid, and safe respiratory disease diagnosis solutions will be further optimized, and their accessibility will become more widespread. Full article

(This article belongs to the Special Issue Recent Progress of Lab-on-a-Chip Assays)

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12 pages, 3517 KiB

Open AccessArticle

High-Efficiency Wireless Power Transfer System Based on Low-Frequency AlScN Piezoelectric Micromechanical Ultrasonic Transducers for Implantable Medical Devices

by Wanyun Cui, Jianwei Zong, Junxiang Li, Qiang Ping, Lei Qiu and Liang Lou

Micromachines 2025, 16(4), 471; https://doi.org/10.3390/mi16040471 - 15 Apr 2025

Viewed by 167

Abstract

In recent years, implantable medical devices (IMDs) have introduced groundbreaking solutions for managing various health conditions. However, traditional implanted batteries necessitate periodic surgical replacement and tend to be relatively bulky, posing significant inconvenience to patients. To overcome these limitations, researchers have investigated various [...] Read more.

In recent years, implantable medical devices (IMDs) have introduced groundbreaking solutions for managing various health conditions. However, traditional implanted batteries necessitate periodic surgical replacement and tend to be relatively bulky, posing significant inconvenience to patients. To overcome these limitations, researchers have investigated various wireless power transfer (WPT) techniques, among which the ultrasonic wireless power transmission (UWPT) technique has distinct advantages. However, limited research has been conducted on ultrasonic power transfer at lower operating frequencies. Therefore, this study explores wireless power transfer using scandium-doped aluminum nitride (AlScN) piezoelectric micro-electromechanical transducers (PMUTs) in deionized (DI) water. Experimental results indicate that at an operating frequency of 14.075 kHz, the power transfer efficiency (PTE) can reach up to 2.68% under optimal load resistance conditions. Furthermore, a low-frequency UWPT system based on a AlScN PMUT has been developed, delivering a stable 3.3 V output for implantable medical devices and contributing to the advancement of a full-spectrum UWPT framework. Full article

(This article belongs to the Section A：Physics)

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16 pages, 5056 KiB

Open AccessArticle

Prognostic Value of the Number of Circulating Tumor Cells in Patients with Metastatic Non-Small Cell Lung Cancer

by Arthur B. Volovetsky, Victoria A. Novikova, Anastasia Boloban, Aleksej S. Rzhevskiy, Alina Kapitannikova, Elena G. Ovchinnikova, Tatjana P. Klejmentjeva, Vladislav A. Grishin, Yana Pigareva, Andrei V. Zvyagin, Majid Ebrahimi Warkiani and Anna V. Maslennikova

Micromachines 2025, 16(4), 470; https://doi.org/10.3390/mi16040470 - 15 Apr 2025

Viewed by 193

Abstract

Investigating the molecular and genetic characteristics of circulating tumor cells (CTCs) presents a promising approach for personalizing treatment in patients with malignant neoplasms, given the limitations of traditional biopsy and histopathology. This study aimed to isolate, characterize, and analyze CTC dynamics in the [...] Read more.

Investigating the molecular and genetic characteristics of circulating tumor cells (CTCs) presents a promising approach for personalizing treatment in patients with malignant neoplasms, given the limitations of traditional biopsy and histopathology. This study aimed to isolate, characterize, and analyze CTC dynamics in the peripheral blood of 30 patients with metastatic lung cancer to develop criteria for treatment response and prognosis. We detected CTCs before the start of the treatment and monitored changes during treatment, correlating these with responses evaluated by standard imaging methods. A decrease in the CTCs in the course of the therapy was linked to a favorable tumor response, while the stable CTC counts indicated a lack of response and poor survival prognosis. The OS of patients was analyzed and compared with the initial number of CTCs in peripheral blood samples. The significant reductions in median OS were evident in patients with >3 total CTCs at baseline compared to those with ≤3 total CTCs (median survival 26 months, n = 10, vs. median survival 8 months, n = 19, respectively with HR = 2.6, 95% CI 1.07 to 6.4). Full article

(This article belongs to the Special Issue Micro-/Nanofluidic and Lab-on-a-Chip Devices for Biomedical Applications, 3rd Edition)

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16 pages, 3089 KiB

Open AccessArticle

Backstepping Controller for Nanopositioning in Piezoelectric Actuators with ANN Hysteresis Compensation

by Asier del Rio, Oscar Barambones, Eneko Artetxe, Jokin Uralde and Isidro Calvo

Micromachines 2025, 16(4), 469; https://doi.org/10.3390/mi16040469 - 15 Apr 2025

Viewed by 174

Abstract

Piezoelectric actuators (PEAs) are widely used in high-precision applications but suffer from nonlinear hysteresis effects that degrade positioning accuracy. To address this challenge, this study presents a backstepping controller with an Artificial Neural Network (ANN)-based feedforward compensation scheme to enhance trajectory tracking performance. [...] Read more.

Piezoelectric actuators (PEAs) are widely used in high-precision applications but suffer from nonlinear hysteresis effects that degrade positioning accuracy. To address this challenge, this study presents a backstepping controller with an Artificial Neural Network (ANN)-based feedforward compensation scheme to enhance trajectory tracking performance. The ANN compensates for the hysteresis effects, while the backstepping strategy ensures robust reference tracking. The proposed controller is validated through real-time experiments using a piezoelectric actuator system. Comparative analysis with a conventional PID controller demonstrates the superiority of the backstepping approach, achieving significantly lower tracking errors across different reference signals and frequencies. Error metrics have been employed to confirm the improved accuracy and robustness of the proposed method. These findings highlight the effectiveness of the proposed ANN-enhanced backstepping control in overcoming hysteresis-related challenges in precision positioning applications. Full article

(This article belongs to the Special Issue Design and Real Time Implementation of Intelligent Control Schemes for Actuators)

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12 pages, 8262 KiB

Open AccessArticle

High-Sensitivity and Wide-Range Flexible Pressure Sensor Based on Gradient-Wrinkle Structures and AgNW-Coated PDMS

by Xiaoran Liu, Xinyi Wang, Tao Xue, Yingying Zhao and Qiang Zou

Micromachines 2025, 16(4), 468; https://doi.org/10.3390/mi16040468 - 15 Apr 2025

Viewed by 180

Abstract

Flexible pressure sensors have garnered significant attention due to their wide range of applications in human motion monitoring and smart wearable devices. However, the fabrication of pressure sensors that offer both high sensitivity and a wide detection range remains a challenging task. In [...] Read more.

Flexible pressure sensors have garnered significant attention due to their wide range of applications in human motion monitoring and smart wearable devices. However, the fabrication of pressure sensors that offer both high sensitivity and a wide detection range remains a challenging task. In this paper, we propose an AgNW-coated PDMS flexible piezoresistive sensor based on a gradient-wrinkle structure. By modifying the microstructure of PDMS, the sensor demonstrates varying sensitivities and pressure responses across different pressure ranges. The wrinkle microstructure contributes to high sensitivity (0.947 kPa⁻¹) at low pressures, while the PDMS film with a gradient contact height ensures a continuous change in the contact area through the gradual activation of the contact wrinkles, resulting in a wide detection range (10–50 kPa). This paper also investigates the contact state of gradient-wrinkle films under different pressures to further elaborate on the sensor’s sensing mechanism. The sensor’s excellent performance in real-time response to touch behavior, joint motion, swallowing behavior recognition, and grasping behavior detection highlights its broad application prospects in human–computer interaction, human motion monitoring, and intelligent robotics. Full article

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12 pages, 1776 KiB

Open AccessArticle

A Progressive Search Method for Roundness Evaluation Based on Minimum Zone Criterion

by Jian Mei, Binbin Li, Guohua Hu, Chuanzhi Fang, Sheng Zhang, Juan Zheng, Qian Zhang, Lei Hong and Qiangxian Huang

Micromachines 2025, 16(4), 467; https://doi.org/10.3390/mi16040467 - 15 Apr 2025

Viewed by 174

Abstract

With the rapid development of micro-machining technology, the feature size of object parts becomes smaller whilst the roundness tolerance must be critically verified at sub-micrometers or nanometers. Therefore, establishing a method is critically important for evaluating roundness errors to guarantee the machining quality. [...] Read more.

With the rapid development of micro-machining technology, the feature size of object parts becomes smaller whilst the roundness tolerance must be critically verified at sub-micrometers or nanometers. Therefore, establishing a method is critically important for evaluating roundness errors to guarantee the machining quality. A progressive search method is proposed based on the minimum zone criterion in the Cartesian coordinate system in this paper. The least-square center of the measured points is used as the initial reference center by establishing a search circle model for progressively approaching the minimum zone circle center. To testify to the feasibility and performance of the proposed method, comparison and simulation experiments are implemented. The results demonstrated that the progressive search method is effective, reliable, and can evaluate roundness error accurately and quickly with not more than 0.1 s and 10 times. Full article

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45 pages, 10822 KiB

Open AccessReview

Progress in CO₂ Gas Sensing Technologies: Insights into Metal Oxide Nanostructures and Resistance-Based Methods

by Yash Ughade, Shubham Mehta, Gautam Patel, Roopa Gowda, Nirav Joshi and Rohan Patel

Micromachines 2025, 16(4), 466; https://doi.org/10.3390/mi16040466 - 14 Apr 2025

Viewed by 161

Abstract

The demand for reliable and cost-effective CO₂ gas sensors is escalating due to their extensive applications in various sectors such as food packaging, indoor air quality assessment, and real-time monitoring of anthropogenic CO₂ emissions to mitigate global warming. Nanostructured materials exhibit [...] Read more.

The demand for reliable and cost-effective CO₂ gas sensors is escalating due to their extensive applications in various sectors such as food packaging, indoor air quality assessment, and real-time monitoring of anthropogenic CO₂ emissions to mitigate global warming. Nanostructured materials exhibit exceptional properties, including small grain size, controlled morphology, and heterojunction effects, rendering them promising candidates for chemiresistive CO₂ gas sensors. This review article provides an overview of recent advancements in chemiresistive CO₂ gas sensors based on nanostructured semiconducting materials. Specifically, it discusses single oxide structures, metal-decorated oxide nanostructures, and heterostructures, elucidating the correlations between these nanostructures and their CO₂ sensing properties. Additionally, it addresses the challenges and future prospects of chemiresistive CO₂ gas sensors, aiming to provide insights into the ongoing developments in this field. Full article

(This article belongs to the Special Issue Gas Sensors: From Fundamental Research to Applications)

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23 pages, 6425 KiB

Open AccessArticle

The Feasibility and Performance of Thin-Film Thermocouples in Measuring Insulated Gate Bipolar Transistor Temperatures in New Energy Electric Drives

by Bole Xiang, Guoqiang Li and Zhihui Liu

Micromachines 2025, 16(4), 465; https://doi.org/10.3390/mi16040465 - 14 Apr 2025

Viewed by 130

Abstract

In the new energy electric drive system, the thermal stability of IGBT, a core power device, significantly impacts the system’s overall performance. Accurate IGBT temperature measurement is crucial, but traditional methods face limitations in IGBT’s compact working space. Thin-film thermocouples, with their thin [...] Read more.

In the new energy electric drive system, the thermal stability of IGBT, a core power device, significantly impacts the system’s overall performance. Accurate IGBT temperature measurement is crucial, but traditional methods face limitations in IGBT’s compact working space. Thin-film thermocouples, with their thin and light features, offer a new solution. In this study, Ni 90% Cr 10% and Ni 97% Si 3% thin-film thermocouples were prepared on polyimide substrates via magnetron sputtering. After calibration, the Seebeck coefficient of the thin-film thermocouple temperature sensors reached 40.23 μV/°C, and the repeatability error stabilized at about 0.3% as the temperature rose, showing good stability. Researchers studied factors affecting IGBT temperature. Thin-film thermocouples can accurately monitor IGBT module surface temperature under different conditions. Compared to K-type wire thermocouples, they measure slightly higher temperatures. As the control signal’s switching frequency increases, IGBT temperature first rises then falls; as the duty cycle increases, the temperature keeps rising. This is consistent with RAC’s junction temperature prediction theory, validating the feasibility of thin-film thermocouples for IGBT chip temperature measurement. Thin-film thermocouples have great application potential in power device temperature measurement and may be a key research direction, supporting the optimization and upgrading of new energy electric drive systems. Full article

(This article belongs to the Special Issue Micro/Nanostructures in Sensors and Actuators, 2nd Edition)

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19 pages, 6895 KiB

Open AccessArticle

A Hybrid GRA-TOPSIS-RFR Optimization Approach for Minimizing Burrs in Micro-Milling of Ti-6Al-4V Alloys

by Rongkai Tan, Abhilash Puthanveettil Madathil, Qi Liu, Jian Cheng and Fengtao Lin

Micromachines 2025, 16(4), 464; https://doi.org/10.3390/mi16040464 - 14 Apr 2025

Viewed by 215

Abstract

Micro-milling is increasingly recognized as a crucial technique for machining intricate and miniature 3D aerospace components, particularly those fabricated from difficult-to-cut Ti-6Al-4V alloys. However, its practical applications are hindered by significant challenges, particularly the unavoidable generation of burrs, which complicate subsequent finishing processes [...] Read more.

Micro-milling is increasingly recognized as a crucial technique for machining intricate and miniature 3D aerospace components, particularly those fabricated from difficult-to-cut Ti-6Al-4V alloys. However, its practical applications are hindered by significant challenges, particularly the unavoidable generation of burrs, which complicate subsequent finishing processes and adversely affect overall part quality. To optimize the burr formation in the micro-milling of Ti-6Al-4V alloys, this study proposes a novel hybrid-ranking optimization algorithm that integrates Grey Relational Analysis (GRA) with the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). This approach innovatively combines GRA and TOPSIS with a random forest regression (RFR) model, facilitating the exploration of nonlinear and complex relationships between input parameters and machining outcomes. Specifically, the effects of spindle speed, depth of cut, and feed rate per tooth on surface roughness and burr width generated during both down-milling and up-milling processes were systematically investigated using the proposed methodology. The results reveal that the depth of cut is the most influential factor affecting surface roughness, while feed rate per tooth plays a critical role in controlling burr formation. Moreover, the GRA-TOPSIS-RFR method significantly outperforms existing optimization and prediction models, with the integration of the RFR model enhancing prediction accuracy by 42.6% compared to traditional linear regression approaches. The validation experimental results agree well with the GRA-TOPSIS-RFR-optimized outcomes. This research provides valuable insights into optimizing the micro-milling process of titanium components, ultimately contributing to improved quality, performance, and service life across various aerospace applications. Full article

(This article belongs to the Special Issue Advances in Digital Manufacturing and Nano Fabrication)

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17 pages, 9524 KiB

Open AccessArticle

Design of an Electronic Nose System with Automatic End-Tidal Breath Gas Collection for Enhanced Breath Detection Performance

by Dongfu Xu, Pu Liu, Xiangming Meng, Yizhou Chen, Lei Du, Yan Zhang, Lixin Qiao, Wei Zhang, Jiale Kuang and Jingjing Liu

Micromachines 2025, 16(4), 463; https://doi.org/10.3390/mi16040463 - 14 Apr 2025

Viewed by 228

Abstract

End-tidal breath gases originate deep within the lungs, and their composition is an especially accurate reflection of the body’s metabolism and health status. Therefore, accurate collection of end-tidal breath gases is crucial to enhance electronic noses’ performance in breath detection. Regarding this issue, [...] Read more.

End-tidal breath gases originate deep within the lungs, and their composition is an especially accurate reflection of the body’s metabolism and health status. Therefore, accurate collection of end-tidal breath gases is crucial to enhance electronic noses’ performance in breath detection. Regarding this issue, this study proposes a novel electronic nose system and employs a threshold control method based on exhaled gas flow characteristics to design a gas collection module. The module monitors real-time gas flow with a flow meter and integrates solenoid valves to regulate the gas path, enabling automatic collection of end-tidal breath gas. In this way, the design reduces dead space gas contamination and the impact of individual breathing pattern differences. The sensor array is designed to detect the collected gas, and the response chamber is optimized to improve the detection stability. At the same time, the control module realizes automation of the experiment process, including control of the gas path state, signal transmission, and data storage. Finally, the system is used for breath detection. We employ classical machine learning algorithms to classify breath samples from different health conditions with a classification accuracy of more than 90%, which is better than the accuracy achieved in other studies of this type. This is due to the improved quality of the gas we extracted, demonstrating the superiority of our proposed electronic nose system. Full article

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28 pages, 16516 KiB

Open AccessReview

Recent Advances in Microfluidics-Based Monitoring of Waterborne Pathogens: From Isolation to Detection

by Guohao Xu, Gaozhe Cai, Lijuan Liang, Jianxin Cheng, Lujie Song, Rui Sun, Feng Shen, Bo Liu, Shilun Feng and Jin Zhang

Micromachines 2025, 16(4), 462; https://doi.org/10.3390/mi16040462 - 14 Apr 2025

Viewed by 283

Abstract

Waterborne pathogens seriously threaten human life and can cause diarrhea, gastrointestinal disorders, and more serious systemic infections. These pathogens are usually caused by contaminated water sources that contain disease-causing microorganisms, such as bacteria, viruses, and parasites, which cause infection and disease when they [...] Read more.

Waterborne pathogens seriously threaten human life and can cause diarrhea, gastrointestinal disorders, and more serious systemic infections. These pathogens are usually caused by contaminated water sources that contain disease-causing microorganisms, such as bacteria, viruses, and parasites, which cause infection and disease when they enter the human body through drinking water or other means. Due to the wide range of transmission routes and the high potential risk of waterborne pathogens, there is an urgent need for an ultrasensitive, rapid, and specific pathogenic microorganism monitoring platform to meet the critical monitoring needs of some water bodies’ collection points daily monitoring needs. Microfluidics-based pathogen surveillance methods are an important stage towards automated detection through real-time and multi-targeted monitoring, thus enabling a comprehensive assessment of the risk of exposure to waterborne pathogens and even emerging microbial contaminants, and thus better protection of public health. Therefore, this paper reviews the latest research results on the isolation and detection of waterborne pathogens based on microfluidic methods. First, we introduce the traditional methods for isolation and detection of pathogens. Then, we compare some existing microfluidic pathogen isolation and detection methods and finally look forward to some future research directions and applications of microfluidic technology in waterborne pathogens monitoring. Full article

(This article belongs to the Special Issue Integrated Optical, Electrochemical, and Electrical Biomicrofluidics)

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15 pages, 28317 KiB

Open AccessArticle

Flexible Pressure Sensor with Tunable Sensitivity and a Wide Sensing Range, Featuring a Bilayer Porous Structure

by Yunjiang Yin, Yingying Zhao, Tao Xue, Xinyi Wang and Qiang Zou

Micromachines 2025, 16(4), 461; https://doi.org/10.3390/mi16040461 - 13 Apr 2025

Viewed by 258

Abstract

Flexible piezoresistive pressure sensors have great potential in wearable electronics due to their simple structure, low cost, and ease of fabrication. Porous polymer materials, with their highly deformable internal pores, effectively expand the sensing range. However, a single-sized pore structure struggles to achieve [...] Read more.

Flexible piezoresistive pressure sensors have great potential in wearable electronics due to their simple structure, low cost, and ease of fabrication. Porous polymer materials, with their highly deformable internal pores, effectively expand the sensing range. However, a single-sized pore structure struggles to achieve both high sensitivity and a broad sensing range simultaneously. In this study, a PDMS-based flexible pressure sensor with a bilayer porous structure (BLPS) was successfully fabricated using clamping compression and a sacrificial template method with spherical sucrose cores. The resulting sensor exhibits highly uniform pore sizes, thereby improving performance consistency. Furthermore, since different pore sizes and thicknesses correspond to varying Young’s moduli, this study achieves tunable sensitivity across a wide pressure range by adjusting the bilayer thickness ratio (maximum sensitivity of

0.063 {kPa}^{- 1}

in the 0–23.6 kPa range, with a pressure response range of 0–654 kPa). The sensor also demonstrates a fast response time (128 ms) and excellent fatigue stability (>10,000 cycles). Additionally, this sensor holds great application potential for facial expression monitoring, joint motion detection, pressure distribution matrices, and Morse code communication. Full article

(This article belongs to the Section E：Engineering and Technology)

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21 pages, 12826 KiB

Open AccessArticle

HeSARIC: A Heterogeneous Cyber–Physical Robotic Swarm Framework for Structural Health Monitoring with Augmented Reality Representation

by Alireza Fath, Christoph Sauter, Yi Liu, Brandon Gamble, Dylan Burns, Evan Trombley, Sai Krishna Reddy Sathi, Tian Xia and Dryver Huston

Micromachines 2025, 16(4), 460; https://doi.org/10.3390/mi16040460 - 13 Apr 2025

Viewed by 295

Abstract

This study proposes a cyber–physical framework for the integration of a heterogeneous swarm of robots, sensors, microrobots, and AR for structural health monitoring and confined space inspection based on the application’s unique challenges. The structural issues investigated are cracks in the walls, deformation [...] Read more.

This study proposes a cyber–physical framework for the integration of a heterogeneous swarm of robots, sensors, microrobots, and AR for structural health monitoring and confined space inspection based on the application’s unique challenges. The structural issues investigated are cracks in the walls, deformation of the structures, and damage to the culverts and devices commonly used in buildings. The PC and augmented reality interfaces are incorporated for human–robot collaboration to provide the necessary information to the human user while teleoperating the robots. The proposed interfaces use edge computing and machine learning to enhance operator interactions and to improve damage detection in confined spaces and challenging environments. The proposed swarm inspection framework is called HeSARIC. Full article

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Micromachines, Volume 16, Issue 4 (April 2025) – 133 articles

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