Search Results (3,225)

To investigate the multi-factor aging mechanisms of silicone rubber used in the outer sheath of composite bushings, this study focused on HTV silicone rubber employed in the sheath layer of 1100 kV high-voltage bushings. The samples were subjected to temperature–humidity–corona coupled aging in a multi-factor aging platform. The aged samples were characterized by scanning electron microscopy, energy-dispersive spectroscopy, Fourier-transform infrared spectroscopy, hydrophobicity measurements, hardness tests, and dielectric constant measurements. The results indicate that different aging factors affect the material differently. Corona aging primarily affects the sample surface, leading to substantial methyl group detachment, surface oxidation, and a decrease in hydrophobicity, with the local static contact angle decreasing by up to 70%. In contrast, wet heat aging affects the bulk material; under high-temperature and high-humidity conditions, the internal small-molecule chains accelerate silicon-oxide crosslinking, leading to a marked increase in hardness and a relative dielectric constant that initially decreases and then increases. Considering the complex field environment, surface performance measurements are easily influenced by external factors. Therefore, hardness and relative dielectric constant are proposed as key indicators for evaluating the aging degree of silicone rubber sheaths in service. The findings provide a valuable reference for the service-life evaluation of composite bushings. Full article

The present study proposes a fractal-inspired multiscale framework to interpret the structural, thermal, mechanical and dielectric properties of polylactic acid (PLA). Experimental investigations were performed using tensile testing, TG-DTA thermal analysis, X-ray diffraction (XRD) and dielectric spectroscopy. The structural organization was analyzed using XRD data, where a scaling tendency compatible with power-law behavior was identified over a limited $\mathrm{q}$-range. The thermal degradation exhibited a sharp transition, while the mechanical and dielectric responses reflected the heterogenous behavior typical of semicrystalline polymers. Rather than claiming a fully validated fractal model, the present work introduces a conceptual multiscale interpretation, supported by experimental observations, and proposes a fractal integrity index (FII) as an exploratory descriptor integrating structural, thermal and mechanical information. The results suggest that fractal-based descriptors may provide a useful complementary framework for interpreting complex polymer behavior, although further validation across multiple materials and experimental conditions is required. Full article

Cordierite-based ceramics (Mg₂Al₄Si₅O₁₈) were successfully synthesized and comprehensively characterized to evaluate their structural and dielectric behavior for high-temperature electronic applications. Morphological, microstructural and vibrational analyses confirm the high phase purity and structural integrity of the synthesized material. Dielectric measurements reveal high real permittivity (ε′) values at low frequencies and elevated temperatures, mainly attributed to interfacial polarization arising from Schottky-type barriers at grain–grain and surface–volume interfaces, underscoring the crucial influence of heterogeneous interfaces on the dielectric response. The electrical conductivity follows a thermally activated hopping mechanism involving both intra-grain and grain-boundary charge transport. Analysis of the electric modulus formalism provides further insight into relaxation dynamics: the real (M′) and imaginary (M″) components highlight pronounced space-charge effects, with M″ exhibiting a distinct relaxation peak (M″) associated with grain contributions. The systematic shift of this peak toward higher frequencies with increasing temperature indicates enhanced charge-carrier mobility and a strongly thermally activated relaxation process. The frequency-dependent conductivity displays two regimes: a low-frequency plateau corresponding to dc conductivity and a high-frequency dispersive region following a power-law behavior characteristic of hopping conduction, with power-law exponents (α₁ and α₂) markedly lower than unity, confirming the non-Debye character of the relaxation processes. The hopping frequency (ω) increases with temperature, further supporting the thermally activated nature of charge transport. Activation energies extracted from Arrhenius plots of dc conductivity are 0.88 eV for grain boundaries and 0.83 eV for grains, demonstrating that both microstructural regions significantly contribute to the overall conduction process. Full article

HfO₂ films have become a critical component for advanced electronics and a wide range of applications. However, their implementation requires control of their microstructure and defects, which often act as charge carrier traps, leading to leakage current in devices and hindering their dielectric properties. Here, we deposit HfO₂ thin films by atomic layer deposition (ALD) on sapphire, Ga₂O₃, and InGaO₃ substrates at low temperature and investigate the dependence of their crystal structure on substrate type, annealing, and thickness. X-ray diffraction measurements showed that alloying Ga₂O₃ with a modest amount of Indium transferred HfO₂ films from amorphous to polycrystalline, an important finding that may be applicable to the deposition of other material systems. The study also presents an interesting approach to measuring shallow and deep traps formed in the films and shows how to control their levels and distributions in the band gap. The measurements reveal that the difference in band gap between the substrate and film, as well as the presence of impurities, strongly influences trap densities and depths. Electron paramagnetic resonance (EPR) measurements were performed to probe the electronic structure of specific point defects detectable by EPR and to correlate these results with trap measurements. Full article

This study presents a comparative evaluation of four drying methods for carrot, red beet, and pumpkin pomace to produce natural functional food ingredients. The work addresses the valorization of 35–45% vegetable processing waste—a rich source of bioactive compounds—aligning with circular bioeconomy principles and Kazakhstan’s goals for deep processing of agricultural raw materials. The compared methods were convective drying (CD), ultrasound pretreatment + convective drying (US + CD), vacuum-microwave drying (VMD), and ultrasound pretreatment + vacuum-microwave drying (US + VMD). Drying kinetics, water activity, physicochemical and functional properties of powders, retention of bioactive compounds, color characteristics, thermal stability, and sensory attributes were assessed. Kinetics were fitted using Midilli et al., Page, and Weibull models. US + VMD provided the highest drying acceleration (6–11 times faster than CD), reaching final moisture of 5.1–5.9%, water activity a_w 0.27–0.31 in 80–170 min, and bioactive compound retention of 90–95% (carotenoids 92–95%, betalains 90–94%). It also delivered superior flowability (Carr’s index 22.5–30.4%), dispersibility (80–88% in 30 s), and thermal stability (75–85% at 200 °C). Acceleration varied by raw material: maximum for beet (up to 11×) due to soluble sugars and nitrates, minimum for pumpkin (5.5–8×) due to dietary fibers and pectins, and intermediate for carrot (6–9×) influenced by carotenoids’ dielectric properties. The results highlight US + VMD’s strong potential for producing functional powders to replace synthetic additives in food systems. Effective method selection and parameter optimization require consideration of raw material type and rheological characteristics. Full article

Millimeter-wave and sub-millimeter-wave techniques are widely used in non-destructive testing of multilayered materials due to their ability to penetrate non-conductive media and resolve dielectric stratifications. However, conventional thickness estimation methods suffer from an inherent resolution limit dictated by the available frequency bandwidth. In this paper, a MUSIC-based approach is proposed to achieve super-resolution localization of echoes in the reflective response of the structure under test. The method exploits the sparsity of the reflective response, similarly to compressive sensing approaches, while providing improved reconstruction accuracy. Moreover, the proposed strategy enables the retrieval of dielectric permittivities and layer thicknesses without resorting to complex nonlinear fitting procedures. Finally, the method operates on magnitude-only data, with phase information recovered through an interferometric holographic technique, making the proposed framework well-suited for cost-effective industrial applications. Full article

Dielectric elastomer actuators (DEAs) are attracting much attention as candidates for next-generation flexible actuation. Among various DE matrices, polyacrylate rubber (AR) is especially promising owing to their intrinsically high dielectric constant (ε_r) and good mechanical performance. In particular, its mechanical behavior is close to that of porcine bladder tissue, making it a potentially good material for soft biomedical actuators for artificial bladder constructs. To achieve high actuated strain, which requires high ε_r, high breakdown strength, and low elastic modulus, an AR DE composite filled with silane-functionalized TiO₂ was fabricated, exhibiting good electromechanical performance enabled by strengthened interfacial polarization. To improve compatibility between TiO₂ and AR matrix, TiO₂ was preferentially modified with a silane coupling agent (CA) that features a double bond as its functional group, which can be introduced on TiO₂ surface and participate in vulcanization with AR, thereby forming co-crosslinking bridges that strengthen interfacial bonding, improve filler dispersion, and increase interfacial polarizability within the matrix. As a result, at relatively low filler loadings, the composite exhibits a significantly increased ε_r, while maintaining low modulus, low dielectric loss and high elasticity. The 10 CA@TiO₂/AR composite exhibits a maximal actuated strain of 7.9% at 31.9 kV/mm without pre-stretch, which is 1.48 times that of pure AR and 1.32 times that of the 10 TiO₂/AR composite. Full article

Alumina is a commonly used ceramic material known for high permittivity, low dielectric loss, good thermal conductivity, and low cost. In the development of electronic devices, the size effect of powdery materials is crucial, particularly in applications involving composite materials. This study introduces the field-enhancement method (FEM) to measure the resonant frequency ($f_0$) and the quality factor (Q) of alumina powders packed in a Teflon container and placed on top of the central rod in the proposed cavity. The measured resonant condition ($f_0$ and Q) is mapped to a contour plot and simulated using a high-frequency structure simulator (HFSS). The contour mapping technique allows the researchers to obtain the effective complex permittivity of alumina–air composites. The complex permittivity of the alumina powder is retrieved using a hybrid model and the effective medium theories (EMTs), respectively. The Landau–Lifshitz–Looyenga (LLL) model is compared with the results using the hybrid model for its applicability. The dielectric constant and the loss tangent of the alumina powder are found to increase as the powder size reduces. A power relation is found to fit the obtained permittivity, covering sizes ranging from nanometers to micrometers, and a surface-charge scaling argument is proposed to explain the observed trend. This finding opens a new avenue for manipulation of permittivity in composite materials and has potential applications in stealth/absorber technology and as a self-limiter for grain growth during sintering. Full article

A cost-effective and practical method for characterizing the dielectric properties of liquids at 1 MHz is presented in this article. A cylindrical parallel-plate capacitive sensor was developed, in which the circular end plates function as electrodes and the sidewall is formed by a thin polyvinyl chloride ring cut from a standard water pipe to enclose the liquid sample. Dielectric constant values of air, distilled water, ethanol, and methanol were determined through analytical calculations, electromagnetic simulations, and experimental measurements at 1 megahertz. Consistent results were obtained across all methods, and the extracted values were found to agree well with theoretical values, yielding extraction errors of 0.06% for methanol and 1.85% for ethanol with respect to theoretical values from the literature. A calibration technique was applied in which air and water were used as reference materials with known dielectric constants, effectively mitigating uncertainties associated with sensor geometry, spacer material, and fringing fields. Through this work, a practical and effective technique for dielectric characterization at low frequency has been demonstrated, with core validation of four reference materials (air, deionized water, ethanol, and methanol) at 1 MHz and an additional application example in which cow’s milk is characterized over 10–30 MHz. The 10–30 MHz measurement demonstrates the applicability of the proposed method in the low megahertz region, while the primary validation is conducted at 1 MHz. The technique is applicable to a wide range of applications in materials science, chemical, and biomedical engineering. Full article

PVDF has expanded the application of ferroelectric materials in flexible and wearable electronics due to its flexibility, corrosion resistance, ease of processing, and low cost. However, the polarization of ferroelectric polymers is low, with a bottleneck value of 10 µC cm⁻². In this study, flexible ferroelectric composite films comprising Ca₂Nb₃O₁₀ (CNO) nanosheets and PVDF were fabricated via direct ink writing (DIW). By modulating the nozzle-to-substrate height in conjunction with flow-induced shear within the syringe and the application of additional shear force at the nozzle, effective alignment of low-content (2 wt.%) CNO nanosheets dispersed in a highly fluid ink was achieved. The enhanced orientation degree of the CNO nanosheets increased the breakdown strength of the PVDF–CNO composite films to 524 MV/m. Furthermore, the remanent polarization (P_r) was significantly increased by 207% compared to pure PVDF films, reaching a value of 11.6 µC cm⁻². This study provides a simple and efficient DIW-based strategy for improving filler orientation in composites and demonstrates the substantial enhancement in dielectric and ferroelectric properties achievable through such filler alignment. Full article

Piezoelectric actuators are essential for sub-millimeter robots and reconfigurable microstructures owing to their advantages, including the ability to operate in air and high-speed response. However, the substantial performance degradation observed in piezoelectric actuators with sub-micrometer thickness poses a critical challenge for the design of low-voltage microactuators capable of achieving large bending curvature. Here we develop a coupled analytical–numerical framework for designing multilayer lead zirconate titanate (PZT) nanofilm microactuators under a low voltage constraint (≤5 V). An analytical multilayer beam model is extended to incorporate thickness-dependent material properties and an interfacial dead layer that reduces the effective electric field at small thicknesses. This enables rapid exploration of curvature and the neutral-axis position as functions of the thicknesses of PZT, electrodes, and the dielectric layer. Two- and three-dimensional finite-element simulations provide complementary predictions of neutral-axis location, voltage-dependent curvature response, and eigenmode shapes. The resulting design maps reveal a non-monotonic optimum for PZT thickness in the few-hundred-nanometer range to maximize the curvature change at low voltages and identify ultrathin top electrodes as a key design lever that enhances bending by reducing parasitic stiffness while shifting the neutral axis favorably. These findings offer quantitative guidelines for designing low-voltage, high-curvature piezoelectric microactuators for microrobotic systems. Full article

Photonic jets (PJs) generated from mesoscale dielectric particles can achieve sub-diffraction-scale light field constraints and significant near-field intensity enhancement, which have important application value in the fields of nanoimaging, optical sensing, and laser processing. Recent studies show that the axial-extension and transverse-focus characteristics of PJs can be effectively regulated through interface engineering methods, such as using double-layer structures and truncated geometries. Such structures can be referred to as Janus microstructures separated by surface refracted interfaces. However, systematic research on the effect of incident light polarization on the formation and regulation of PJs on the surface interfaces of Janus systems is lacking. In this study, the PJ characteristics under polarization regulation in curved-interface Janus microcylinders are systematically investigated by performing full-wave numerical simulations. The results show that polarization modulation introduces a new degree of freedom for regulating the energy flow distribution and morphology of PJs. An appropriate polarization state can be selected to effectively regulate key characteristic parameters, such as the length, peak intensity, and full width at half maximum of the nanojet, without changing the particle geometry or material composition. This study reveals the synergy between the surface-interface Janus structures and polarization engineering, providing a new physical method for the flexible regulation of PJs in near-field optics. Full article

The increasing demand for sustainable materials in electrical engineering has encouraged the substitution of conventional fillers in epoxy insulation with recycled industrial by-products. This study investigates the potential use of waste tire rubber particles and zinc oxide recovered from electric arc furnace dust as eco-friendly fillers for epoxy resins in high-voltage insulation applications. Four material variants were fabricated: pure epoxy, epoxy with 10 wt% ZnO (0.7 mm thickness), epoxy with 10 wt% tire rubber (0.9 mm thickness), and epoxy with 20 wt% tire rubber (0.9 mm thickness). The breakdown voltage of each composite was measured under AC voltage. Results indicate that filler type and concentration influence breakdown behavior within each thickness group. The 10 wt% ZnO-filled epoxy exhibited a moderate enhancement in breakdown voltage compared with pure epoxy of the same thickness, consistent with interfacial modifications commonly observed in oxide-filled epoxy systems. Conversely, tire rubber fillers led to reduced breakdown performance, likely due to increased dielectric heterogeneity introduced by the elastomeric phase. No direct comparison between ZnO- and rubber-filled systems was performed due to differences in manufacturable sample thickness. The findings contribute to the evaluation of recycled fillers in dielectric composite systems within a circular-economy framework. Full article

Biomaterials are engineered to interact with biological systems for therapeutic or diagnostic purposes. Among them, natural biomaterials offer important advantages over many synthetic polymers, including intrinsic biocompatibility, non-toxicity and biodegradability. Silk fibroin, a fibrous protein derived mainly from Bombyx mori cocoons, has re-emerged as a particularly versatile platform because it combines favourable mechanical, thermal, electrical and optical properties with aqueous processing and tuneable degradation. In this review, we first summarise the key structural, physicochemical and functional properties of regenerated silk fibroin, including its mechanical behaviour, thermal stability, dielectric and piezoelectric response, optical transparency and low autofluorescence. We then describe how extraction and regeneration protocols are used to produce defined material formats—fibres and nanofibrous mats, porous 3D scaffolds and hydrogels, sub-micron particles, thin films and microstructured devices—and outline major functionalisation strategies, ranging from physical blending and encapsulation to covalent chemistry, genetic engineering of recombinant silk variants, and enzyme-mediated conjugation approaches. Building on this foundation, we critically examine biomedical applications of silk fibroin with a particular emphasis on (i) hybrid silk–fluorophore systems for bioimaging and biosensing (nanodiamonds, quantum dots and organic dyes), (ii) optical fibre, wearable and edible sensors for health and food monitoring, (iii) wound dressings and wound-sensing platforms, and (iv) tissue engineering scaffolds and drug-delivery depots. Finally, we discuss current limitations, including process variability, the trade-offs introduced by blending and cross-linking, and the challenges posed by non-degradable inorganic fillers and clinical translation. Together, these perspectives highlight silk fibroin’s potential and constraints as a multifunctional biomaterial for next-generation biomedical devices and theranostic systems. Full article

With the rapid development of smart devices for body area networks and smart packaging, there is a significant demand for low-waste and low-impact electronic systems in industries such as healthcare and transportation. We demonstrate that the dielectric material from capacitors in resistor-inductor-capacitor (RLC) wireless, chipless, resonant temperature sensors can be successfully recovered from flexible PCBs, with pristine sensors re-introduced to the tag’s sensor loading. First, we demonstrate that replacing the dielectric in a parallel plate capacitor with a pristine component, with recycled electrodes and sub-miniature-A (SMA) adaptor, results in only a 3% change in broadband capacitance. An identical substitution of the sensing element in an RLC circuit tuned to resonate at 21.0 MHz, with recycled parallel plates, a resistor, and an inductive PCB coil, results in a change of only 7.6% in the resonant frequency of the tag to 19.4 MHz. This work demonstrates the recyclability of chipless tags for temperature sensing for the first time, offering sustainability gains in smart packaging applications, with the potential to be expanded to other sensing tags for pH, humidity, and chemical analytes, towards chipless product passports. Full article