Search Results (201)

The escalating consumption of fossil fuels and the rapid development of portable electronics have increased interest in alternative energy solutions that can sustainably self-power wearable devices. Triboelectric nanogenerators (TENGs), which convert mechanical energy into electricity through contact electrification and electrostatic induction, have emerged as a promising technology due to their high voltage output, lightweight design, and simple fabrication. However, the performance of TENGs is often limited by a low surface charge density, inadequate dielectric properties, and poor charge retention of triboelectric materials. To address these challenges, recent research has focused on the use of polymer composites that incorporate various functional fillers. The filler materials play roles in improving dielectric performance and enhancing mechanical durability, thereby boosting triboelectric output even in harsh environments, while also diminishing charge loss. This review comprehensively examines the role of polymer composite design in TENG performance, with particular emphasis on materials categorized by their triboelectric polarity. Tribo-negative polymers, such as PDMS and PVDF, benefit from filler incorporation and phase engineering to enhance surface charge density and charge retention. By contrast, tribo-positive materials like nylon and cellulose have demonstrated notable improvements in mechanical robustness and environmental stability through composite strategies. The interplay between material selection, surface engineering, and filler design is highlighted as a critical path toward developing high-performance, self-powered TENG systems. Finally, this review discusses the current challenges and future opportunities for advancing TENG technology toward practical and scalable applications. Full article

The paper describes the simulation of energy absorption in polymer micro-composites that include dielectric inserts (commercial Al₂O₃ and TiO₂ particles, with three particle sizes of 1, 5 and 25 µm, respectively). The investigated frequency spectrum, mainly from 0.001 to 100 GHz, is designed for various uses as substrates in electronic technologies. The electromagnetic simulation software chosen was CST Studio Suite, which evaluates the power loss at different frequencies, playing a crucial role in creating the ideal structure of these substrates. The effective limits of the electromagnetic simulation are specified. It is shown that a considerable increase in absorption occurs, by a factor of 12 to 120, depending on the dielectric material used for the inserts and the mass ratio applied in the insertion technique. Dielectrics with high permittivity provide higher absorption, but also create a nonuniform field distribution within the material, resulting in a high peak-to-average absorption ratio. In scenarios where this behavior is intolerable, the technology must be carefully tuned to improve the consistency of the insertions in the substrate material. The final outcomes of the simulations indicated that for creating new substrates for flexible electronics, polyethylene composites with TiO₂ insertions are suggested, particularly at lower concentrations of up to 7% and with a larger radius, such as 25 μm, which could offer significant economic advantages considering that the current concept advises the use of costly particles ranging from nanoscale particles to those 1 μm in size and a composition exceeding 10%. Full article

Power transformer insulation systems, composed of liquid and solid insulators, are continuously exposed to thermal and electrical stresses that degrade their performance over time and may lead to premature failure. Since these stresses are unavoidable during operation, selecting effective insulating materials is critical for long-term reliability. In this study, Kraft insulation paper was used as the solid insulator and impregnated with three different liquids: mineral oil and two natural esters (NE1204 and NE1215), to evaluate their stability under simultaneous thermal and electrical stress. The degradation behavior of the oil-impregnated papers was assessed using frequency-domain dielectric spectroscopy (FDS) and Fourier-transform infrared spectroscopy (FTIR), enabling early fault detection. Comparative analyses were conducted to evaluate the withstand capability of each liquid type during operation. Results revealed strong correlations between FTIR indicators (e.g., oxidation and hydroxyl group loss) and dielectric parameters (permittivity and loss factor), confirming the effectiveness of this combined diagnostic approach. Post-aging breakdown analysis showed that natural esters, particularly NE1215, offered superior preservation of insulation integrity compared to mineral oil. Differences between the two esters also highlight the role of chemical composition in insulation performance. This study reinforces the potential of natural esters as viable, eco-friendly alternatives in thermally and electrically stressed applications. Full article

This paper presents the development and analysis of a planar microfluidic microwave sensor featuring three circular complementary split-ring resonators (CSRRs) fabricated on an RO3035 substrate. The sensor demonstrates enhanced sensitivity in characterizing liquids contained in a fine glass capillary tube by leveraging a novel configuration: a central 5-split-ring CSRR with a drilled hole to suspend the capillary, flanked by two 2-split-ring CSRRs to improve the band-stop filtering effect. The sensor’s performance is benchmarked against another CSRR-based microwave sensor with a similar configuration. High linearity is observed (R² > 0.99), confirming its capability for precise ethanol concentration prediction. Compared to the replicated square CSRR design from the literature, the proposed sensor achieves a 35.22% improvement in sensitivity, with a frequency shift sensitivity of 567.41 kHz/% ethanol concentration versus 419.62 kHz/% for the reference sensor. The enhanced sensitivity is attributed to several key design strategies: increasing the intrinsic capacitance by enlarging the effective area and radial slot width to amplify edge capacitive effects, adding more split rings to intensify the resonance dip, placing additional CSRRs to improve energy extraction at resonance, and adopting circular CSRRs for superior electric field confinement. Additionally, the proposed design operates at a lower resonant frequency (2.234 GHz), which not only reduces dielectric and radiation losses but also enables the use of more cost-effective and power-efficient RF components. This advantage makes the sensor highly suitable for integration into portable and standalone sensing platforms. Full article

In view of the limitations of traditional offline detection and external excitation online detection of 10 kV cables, this paper proposes a method to evaluate the insulation aging condition of power cables by online measuring of the phase angle of the cable’s ground current, and explores the impact of load fluctuations on cable insulation. By setting the relative permittivity of the cable to characterize the phase variation of the ground current under different aging degrees, and analyzing the phase variation of the cable’s ground current under different load changes at the same aging degree, a load correction-based dynamic dielectric loss evaluation method for cables is proposed. Through the construction of cable simulation models and the processing of field data, the following conclusions have been reached: Under a 1 MW load, the phase angle of the sheath grounding current in the aged phase increases as the dielectric constant of the insulation increases. At the same aging degree, with an increase in load, the phase differences of the aging phase sheath ground current and the steel armor ground current both show a decreasing trend. To eliminate the impact of load, a dynamic dielectric loss load correction method is proposed, and combined with field data analysis, the dynamic dielectric loss of cables under different loads is corrected to a 1 MW load. Specifically: Under 0.3 MW, the correction coefficients k for the sheath and steel armor are 0.609 and 0.778, respectively. Under 3.5 MW, the correction coefficients k for the sheath and steel armor are 1.435 and 1.089, respectively. This study provides a theoretical basis and experimental verification for online cable monitoring methods. Full article

This paper presents the first demonstration and comparison of two identical oscillator circuits employing piezoelectric zinc oxide (ZnO) microelectromechanical systems (MEMS) resonators, implemented on conventional printed-circuit-board (PCB) and three-dimensional (3D)-printed acrylonitrile butadiene styrene (ABS) substrates. Both oscillators operate simultaneously at dual frequencies (260 MHz and 437 MHz) without the need for additional circuitry. The MEMS resonators, fabricated on silicon-on-insulator (SOI) wafers, exhibit high-quality factors (Q), ensuring superior phase noise performance. Experimental results indicate that the oscillator packaged using 3D-printed chip-carrier assembly achieves a 2–3 dB improvement in phase noise compared to the PCB-based oscillator, attributed to the ABS substrate’s lower dielectric loss and reduced parasitic effects at radio frequency (RF). Specifically, phase noise values between −84 and −77 dBc/Hz at 1 kHz offset and a noise floor of −163 dBc/Hz at far-from-carrier offset were achieved. Additionally, the 3D-printed ABS-based oscillator delivers notably higher output power (4.575 dBm at 260 MHz and 0.147 dBm at 437 MHz). To facilitate modular characterization, advanced packaging techniques leveraging precise 3D-printed encapsulation with sub-100 μm lateral interconnects were employed. These ensured robust packaging integrity without compromising oscillator performance. Furthermore, a comparison between two transistor technologies—a silicon germanium (SiGe) heterojunction bipolar transistor (HBT) and an enhancement-mode pseudomorphic high-electron-mobility transistor (E-pHEMT)—demonstrated that SiGe HBT transistors provide superior phase noise characteristics at close-to-carrier offset frequencies, with a significant 11 dB improvement observed at 1 kHz offset. These results highlight the promising potential of 3D-printed chip-carrier packaging techniques in high-performance MEMS oscillator applications. Full article

Polytetrafluoroethylene (PTFE) has been widely used as a high-frequency dielectric substrate due to its excellent dielectric properties and thermal stability. However, with its low intrinsic thermal conductivity, PTFE falls short in meeting the escalating heat dissipation demands of high-power density, high-frequency communication systems. Although the thermal conductivity of PTFE composites can be effectively improved by the high thermal conductivity fillers, it is always accompanied by a decline in dielectric properties. Molecular chain ordering is regarded as an effective strategy to improve the intrinsic thermal conductivity of polymers while maintaining dielectric properties. Unfortunately, the conventional preparation methods for ordered molecular chains, such as electrostatic spinning and uniaxial stretching, are not applicable to the preparation of PTFE substrates. In this work, fluorinated graphite (FGi) is employed to induce the in-plane orientation of PTFE molecular chains. As a result, the PTFE composite with 0.5 wt% FGi loading exhibits an in-plane thermal conductivity of 1.21 W·m⁻¹·K⁻¹, six times higher than the in-plane thermal conductivity of pure PTFE. In addition, this composite exhibits a superior dielectric constant of 2.06 and dielectric loss of 0.0021 at 40 GHz. This work introduces a facile method to achieve improved thermal conductivity of PTFE while maintaining its excellent dielectric properties. Full article

Cross-linked polyethylene (XLPE) cables will gradually experience aging under various stresses during long-term operation, which may lead to faults and seriously affect the safe and stable operation of the power system. This article prepares aged cable samples by accelerating the thermal aging of XLPE cables, and combines frequency-domain dielectric spectroscopy (FDS) and the polarization–depolarization current method (PDC) for detection and analysis. By measuring the dielectric loss of aged cables using frequency-domain dielectric spectroscopy, it was found that the dielectric loss value in the low-frequency region significantly increases with aging time, indicating that aging leads to an increase in polarity groups and polarization loss. The high-frequency dielectric loss also significantly increases with the strengthening of dipole polarization. At the same time, using the polarization–depolarization current method to measure the polarization current and depolarization current of cables, it was found that the stable value of polarization current increases with aging time, further verifying the changes in the conductivity and polarization characteristics of insulation materials. Combining the broadband dielectric response characteristics of FDS (0.001 Hz–1 kHz) with the time-domain charge transfer analysis of PDC, the molecular structure degradation (dipole polarization enhancement) and interface defect accumulation (space charge effect) of cable aging are revealed from both frequency- and time-domain perspectives. The experimental results show that the integral value of the low-frequency region of the frequency-domain dielectric spectrum and the stable value of the polarization depolarization current are positively correlated with the aging time, and can make use of effective indicators to evaluate the aging state of XLPE cables. Full article

In this research work, two distinct types of three-dimensional (3D) capacitors were successfully fabricated, each with its own unique features and advantages. The first type of capacitor is centered around a 3D nanoporous structure. This structure is formed on a nickel substrate through anodic oxidation. After undergoing high-temperature thermal oxidation, a monolithic Ni-NiO-Pt metal–insulator–metal (MIM) capacitor with a nanoporous dielectric architecture is achieved. Structurally, this innovative design brings about several remarkable benefits. Due to the nanoporous structure, it has a significantly increased surface area, which can effectively store more charges. As a result, it exhibits an equivalent capacitance density of 69.95 nF/cm², which is approximately 18 times higher than that of its planar, non-porous counterpart. This high capacitance density enables it to store more electrical energy in a given volume, making it highly suitable for applications where miniaturization and high energy storage in a small space is crucial. The second type of capacitor makes use of Through-Glass Via (TGV) technology. This technology is employed to create an interdigitated blind-via array within a glass substrate, attaining an impressively high aspect ratio of 22.5:1 (with a via diameter of 20 μm and a depth of 450 μm). By integrating atomic layer deposition (ALD), a conformal interdigital electrode structure is realized. Glass, as a key material in this capacitor, has outstanding insulating properties. This characteristic endows the capacitor with a high breakdown field strength exceeding 8.2 MV/cm, corresponding to a withstand voltage of 5000 V. High breakdown field strength and withstand voltage mean that the capacitor can handle high-voltage applications without breaking down easily, which is essential for power-intensive systems like high-voltage power supplies and some high-power pulse-generating equipment. Moreover, due to the low-loss property of glass, the capacitor can achieve an energy conversion efficiency of up to 95%. Such a high energy conversion efficiency ensures that less energy is wasted during the charge–discharge process, which is highly beneficial for energy-saving applications and systems that require high-efficiency energy utilization. Full article

This paper proposes a compact 2 × 2 on-chip microstrip antenna array operating for W-band applications. The design utilizes a low-loss glass substrate to mitigate dielectric losses and integrates an embedded feeding structure with wideband T-junction power dividers, addressing bandwidth limitations and feed network losses in conventional approaches. Experimental results demonstrate a relative bandwidth of 10.1% (76.11–83.87 GHz) with gain exceeding 10 dBi across the bandwidth, closely aligning with simulated predictions. This work provides a cost-effective solution for millimeter-wave and terahertz antenna systems, balancing high-performance requirements with fabrication simplicity for automotive radar and 5G/6G communication applications. Full article

The ongoing electrification process also requires improvements in the efficiency of power transmission devices, such as transformers, the main part of which is the magnetic core. Despite great progress in the development of core material, losses and audible noise during their operation is still a critical issue to be solved. Currently, a magnetic material used to produce the transformer core is amorphous steel, which is gaining popularity. Compared to traditionally used grain-oriented silicon electrical steel, a significantly larger number of very thin amorphous ribbons is needed to produce the core, which is due to the fact that they are about an order of magnitude thinner, making mechanical stability a challenge. The presented article describes the preparation of a hybrid binder for amorphous steel based on the two types of silanes, tetraethyl orthosilicate and 1,2-bis(triethoxysilyl)ethane, for which their anticorrosive character and good dielectric properties were confirmed. Using the obtained binders, model toroidal cores were produced and their magnetic and acoustic properties were tested. The obtained results indicate that the applied silane-based hybrid binders improved important functional properties by reducing the magnetic no-load losses and audible noise. Full article

Cables are critical to the safe and reliable operation of nuclear power plants (NPPs) since they are widely used as a connection medium for various safety-critical equipment. According to research data and operational experience (OPEX), cable materials can degrade with time, resulting in reduced dielectric strength and higher leakage current. Cables may degrade gradually over time under normal service conditions and fail unexpectedly as a result of sudden exposure to harsher environments, such as Secondary Steam Line Breaks (SSLBs), or when required to operate under the severe conditions of a design basis event, such as a Loss-of-Coolant Accident (LOCA). To assess the condition of medium- and low-voltage cables in Canadian nuclear power plants, numerous inspection methods and electrical testing techniques are employed. These techniques include dielectric spectroscopy, polarization/depolarization current analysis, reflectometry, dielectric standby tests, AC partial discharge, and very-low-frequency (VLF) Tan Delta assessments for medium-voltage (MV) cables. While these methods provide precise diagnostic insights, they require cables to be disconnected at both ends and de-energized, posing operational constraints. Consequently, on-line plant cable monitoring has garnered significant interest, particularly for new reactor developments and large-scale NPP refurbishments. This paper provides a comprehensive benchmarking of existing technologies and a state-of-the-art review of modern cable assessment methodologies. It examines commercially available solutions and ongoing research in power testing for low-voltage (LV) and MV cables, with a particular focus on their applicability in nuclear power settings. Full article

High-temperature-resistant epoxy composites play a crucial role in enhancing the operational reliability and service life of devices such as DC bushings, which is of great significance for the long-term stable operation of ultra-high voltage and flexible power transmission and distribution systems. In this study, the epoxy composite was prepared, and long-term thermal aging tests were conducted at 250 °C and 270 °C. The changes in physical properties, electrical characteristics, and bending strength of epoxy composite were systematically investigated, and the thermal aging mechanism of these materials was elucidated. The experimental results revealed that with the progression of thermal aging, the epoxy composites exhibited volume shrinkage due to the breaking of chemical bonds. After 10 thermal aging cycles at 270 °C, the mass loss rate of the epoxy composite reached 20.52%. At 250 °C, the breakdown strength decreased by 9.9% compared to the unaged state. After aging at 250 °C and 270 °C, the volume resistivity decreased by a maximum of 53.75% and 76.94%, respectively, while the dielectric constant decreased by a maximum of 50.34% and 41.94%, respectively. After 10 aging cycles at 250 °C and 270 °C, the bending strength of the cured epoxy composite decreased by 39.79% and 53.91%, respectively. These findings provide valuable insights into the thermal aging characteristics of epoxy composites used in DC bushings and other electrical devices, offering a scientific basis for material selection and reliability assessment in high-voltage insulation applications. Full article

The performance of enameled wires has an important impact on new energy vehicle motors. The mainstream practice of existing technology is to improve partial discharge inception voltage (PDIV) by doping powder to inhibit corona and increase varnish thickness, the limitations of which are also obvious. Powder doping has the problem of dispersion stability, and increasing the varnish thickness affects the size and power density of the motor. In this paper, a novel insulation structure design was given. The electronic field stress was controlled by using different dielectric constant materials, and the dielectric constants can be controlled by adjusting the free volume of the polymer. Finally, we specifically create a preparation scheme to increase the corona voltage and the PDIV, without a loss of the breakdown margin of the enameled wire, and the simulation results show that the outermost electric field strength of the enameled wire model decreases by 22.11% and the enameled wire breakdown margin increases by 26.85%. Full article

The corrugation of the interfaces of the cross-section of hollow core fibers based on the inhibited coupling waveguiding mechanism is modeled and the impact on propagation loss analyzed. The proposed model is based on a combined use of coupled-mode theory and Azimuthal Fourier Decomposition. It shows that such transverse roughness causes coupling between the core modes and the dielectric modes of the cladding and consequently an increase of the fiber loss. The model is validated by comparing theoretical and numerical results obtained by applying both deterministic and stochastic corrugations to tubular lattice and nested fibers. Scaling laws and impact of the fibers’ parameters are discussed. The model shows that the loss increase is not directly correlated to the root mean square of the stochastic roughness but only to the value of the power spectral density in specific spatial frequency ranges. In particular, the spectral components characterized by a periodicity lower than ${10}^{-1}$ of the tube circumference must have a power spectral density value lower than 0.2 nm² to ensure a negligible effect of the transverse roughness on fibers with losses lower than 0.1 dB/Km. Full article