The escalating demands of high-frequency applications demands the development of dielectric materials with low relative permittivity (dielectric constant) for efficient signal propagation. In light of the prevailing challenges and barriers, this article delves into the intricate mechanisms underlying the dielectric constants of low-k polymer composites while highlighting the challenges associated with their utilization. This study discusses the importance of consistent performance across various frequencies, processing conditions, and filler-matrix compatibility in dielectric properties. It also discusses the impact of thermal conductivity on dielectric behavior, the challenges of controlling porosity, moisture reduction implications, and the significance of haze in low-k and loss dielectric materials for high-frequency applications. The review also explores the impact of scattering and light transmission on material performance. Finally, this study outlines the utilization of various low-k polymer composites, including Polytetrafluoroethylene (PTFE), Polyimide (PI), Polyphenylene oxide (PPO), Polyethylene (PE), Polypropylene (PP), Polyvinylidene difluoride (PVDF), Cyclic Olefin Copolymer (COC), Perfluoroalkoxy’s (PFA), & Poly(benzoxazoles) (PBO) to highlight their potential applications in high-frequency scenarios. By comprehensively investigating the dielectric constant and related challenges in low-k polymer composites, this study article aims to contribute to understanding and advancing materials for high-frequency applications. The insights provided herein offer valuable guidance for researchers, engineers, and manufacturers in the ongoing pursuit of efficient and reliable dielectric materials for the modern high-frequency electronic packaging industries. 

Polymer-based low dielectric constant and loss materials for high-speed communication network: Dielectric constants and challenges

The construction of the future energy structure of China under the 2050 carbon-neutral vision requires compact direct current (DC) gas-insulation equipment as important nodes and solutions to support electric power transmission and distribution of long-distance and large-capacity. This paper reviews China's 10-year progress in DC gas-insulated equipment. Important progresses in basic research and industry perspective are presented, with related scientific issues and technical bottlenecks being discussed. The progress in DC gas-insulated equipment worldwide (Europe, Japan, America) is also reported briefly. 

/pdf/china-s-10-year-progress-in-dc-gas-insulated-equipment-from-1n0pl0qg.pdf

China's 10-year progress in DC gas-insulated equipment: From basic research to industry perspective

A denoising method combined with singular value decomposition (SVD) and Variational mode decomposition (VMD) is proposed to eliminate noise in on-site partial discharge (PD) signals from high-voltage electrical equipment. In the Fourier transform power spectrum, periodic narrowband interference was eliminated after SVD was offered to determine the number of singular values of periodic narrowband interference. Then, the PD signal was decomposed into K intrinsic mode function components by VMD. The empirical mode decomposition method was used to determine the K value of white noise’s intrinsic mode function components. An improved 3σ criterion threshold method was proposed to eliminate the residual noise in the PD signal. The denoising method was compared with the other two methods to analyze the denoising effect on the simulation and experimental PD signal. This paper’s denoising method can eliminate periodic narrowband interference and white noise in different PD signals of cavity discharge, corona discharge, and those from the motors’ coil. The denoised PD pulse waveform has a higher signal-to-noise ratio and normalized correlation coefficient and a lower mean square error, indicating that the waveform’s original characteristic remains. 

A denoising method of partial discharge signal based on improved SVD-VMD

Metamaterials have received widespread attention for their unique properties and broad application prospects. With inspiration from bamboo, metamaterials can be rationally designed to achieve anisotropic functionality. Using a combination of 3-D printing and subsequent hot pressing of dual-curing composites, we describe a simple method for creating well-aligned silicon carbide (SiC) whisker (SiC <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {w}}{)}$ </tex-math></inline-formula> composites that mimic bamboo and have achievable anisotropic thermal conductivity (TC), dielectric properties (DP), and flashover performances (FPs). The anisotropic structure is proved by scanning electron microscope (SEM) and X-ray diffraction (XRD) observations. At the low loading of 8 vol% SiCw, the axial TC of the structured composites can reach 0.655 W <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}\,\,\text{K}^{-{1}}$ </tex-math></inline-formula> , whereas the radial TC is only 0.281 W <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}\,\,\text{K}^{-{1}}$ </tex-math></inline-formula> , with a high anisotropic TC ratio of 2.33. Strong anisotropy in the dielectric constant was also observed with the permittivity of 134 along the axial direction versus that of 65 along the radial direction at 1 kHz, with a high anisotropic DP ratio of 2.06. Notably, metamaterials exhibit significant anisotropy in both their surface conductivity and flashover voltage (FV), with a high conductivity ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 10000. The FV in the diametrical direction is six times that in the axial direction and 60% higher than that of the neat resin. This study shows that this approach is anticipated to offer a new path for the creation of high-performance functionally anisotropic materials to meet the diversified requirements of modern electronics. 

Design of Bioinspired Highly Aligned Bamboo-Mimetic Metamaterials With Structural and Functional Anisotropy

Compared to the traditional aircraft, electrification of power system in aircraft has potential to revolutionise the aviation industry. Typically, more ‐ electric aircraft (MEA), even all ‐ electric aircraft has been developed and delivered to decrease the greenhouse gas emission and increase the energy efficiency. The next generation of MEA will operate at high voltage to facilitate the transfer of significant levels of electrical power in an electrified aircraft. However, the higher voltage inevitably leads to an increased risk to the insulation of the electrical components and power system. This study aims to provide a critical overview of the insulation challenges from the perspective of electrified aircraft, typically MEA application. The development of MEA and the special working conditions are explained at the beginning. Then the insulation challenges of power modules, electric machines, aeronautical cables etc. are discussed in detail. Finally, the existing technical barriers and future prospects of insulation for electrified aircraft are summarised. It provides a reference for the future design and test in power system of next generation MEA and related electrified air transportations.

A review on insulation challenges towards electrification of aircraft

The 2050 carbon-neutral vision spawns a novel energy structure revolution, and the construction of the future energy structure is based on equipment innovation. Insulating material, as the core of electrical power equipment and electrified transportation asset, faces unprecedented challenges and opportunities. The goal of carbon neutral and the urgent need for innovation in electric power equipment and electrification assets are first discussed. The engineering challenges constrained by the insulation system in future electric power equipment/devices and electrified transportation assets are investigated. Insulating materials, including intelligent insulating material, high thermal conductivity insulating material, high energy storage density insulating material, extreme environment resistant insulating material, and environmental-friendly insulating material, are categorised with their scientific issues, opportunities and challenges under the goal of carbon neutrality being discussed. In the context of carbon neutrality, not only improves the understanding of the insulation problems from a macro level, that is, electrical power equipment and electrified transportation asset, but also offers opportunities, remaining issues and challenges from the insulating material level. It is hoped that this paper envisions the challenges regarding design and reliability of insulations in electrical equipment and electric vehicles in the context of policies towards carbon neutrality rules. The authors also hope that this paper can be helpful in future development and research of novel insulating materials, which promote the realisation of the carbon-neutral vision. 

/pdf/insulating-materials-for-realising-carbon-neutrality-2ym29t1u.pdf

Insulating materials for realising carbon neutrality: Opportunities, remaining issues and challenges

In this work, electrical tree inception and ageing experiments were conducted to investigate the initiation, growth characteristics and structural characteristics of electrical trees of nano-SiO2 doped epoxy resin at different temperatures. Electrical tree inception and ageing experiments were conducted using power frequency voltage of 15 kV at 20, 40, 60, 80 and 100°C. Electrical breakdown properties of epoxy resin were investigated by applying AC and DC voltages at 20, 40, 80 and 120°C. There are two major observations based on the experimental results. With the increase of temperature, the morphological structure of the electrical trees changes from dendritic to plexiform, the tree inception voltage decreases and the growth rate of the electrical trees increases obviously. Either under DC or AC voltage, the breakdown strength of the nano-SiO2 doped epoxy resin decreases as the temperature increases. Finally, based on the space charge and the trap level measurement, the mechanism of the electrical tree propagation and breakdown in nano-SiO2 doped epoxy resin was analysed. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1049/hve2.12321

Mitigation of electrical treeing at high temperature in nano‐SiO
 2
 doped epoxy resin

This article investigates the surface electrical properties of polyether-ether-ketone (PEEK) and cross-linked polyethylene (XLPE) before and after the fluorination modification. The samples are tested for surface conductivity, surface morphology, and surface antiaging characteristics. The samples are also tested for flashover voltage with ramping voltage under 100, 20, and 10 kPa. The results showed that the surfaces of PEEK and XLPE become slightly smoother with the increase in the fluorination time and the conductivity increased with the increase in the fluorination time. After fluorination, the surface of PEEK shows significant hydrophilicity, while the surface hydrophobicity of XLPE is slightly reduced, and there is a trend of recovery with the extension of the fluorination time. After fluorination, the surface antiaging performance is significantly improved. Compared with the untreated samples, the fluorinated PEEK has a higher flashover voltage at 100 kPa, and the flashover voltage is slightly increased at 10 and 20 kPa, while the flashover voltage of XLPE after fluorination shows a downward trend, especially under low pressures. This study provides a reference for fluorinated polymers as promising candidates for the insulation systems for all-electric aircraft.

/pdf/fluorinated-peek-and-xlpe-as-promising-insulation-candidates-23wrgyum.pdf

Fluorinated PEEK and XLPE as Promising Insulation Candidates for the Propulsion System of All-Electric Aircraft

By establishing a finite element simulation model in COMSOL, the electric field distribution of a 15kV power module is analyzed, and the local maximum electric field is reduced by using nonlinear conductivity materials. The characteristics and coating length $L$ of nonlinear conductivity materials are analyzed in detail. The simulation results show that with the increase of the $L$, the electric field decreases, and the leakage current increases. When the trench is completely coated, the peak electric field can be decreased by 84% and the leakage current will be increased by 20%. Considering the difficulty in controlling the length of coating in practice, coating the entire trench is suggested. It is identified that the efficient peak electric field mitigation of the non-linear conductivity coating requires engineering the coating parameters to both geometry and operating conditions. In the configuration studied in this paper, optimum nonlinear coating parameters are identified to be a switching field of 7.5kV/mm and a low-field conductivity of 10−11 S/m to achieve low electric field, low leakage current, and simple operation.

Analysis of Nonlinear Conductivity Coating used to Improve Electric Field Distribution in Medium Voltage Power Module

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Papers

Insulating materials for realising carbon neutrality: Opportunities, remaining issues and challenges

Mitigation of electrical treeing at high temperature in nano‐SiO 2 doped epoxy resin

Fluorinated PEEK and XLPE as Promising Insulation Candidates for the Propulsion System of All-Electric Aircraft

Analysis of Nonlinear Conductivity Coating used to Improve Electric Field Distribution in Medium Voltage Power Module