Search

Dielectric capacitors are widely used in aerospace, power systems, and other fields. Working environments with ever‐increasing temperatures pose a new challenge to energy storage performance. Polyetherimide (PEI) has gained extensive research for its good high‐temperature properties. In order to further improve its energy storage performance at high temperatures, many researchers have worked on PEI all‐organic composites doping with molecular semiconductors. Previous studies generally only considered the effect of introduced deep traps on macroscopic properties such as electrical conductivity, electrical breakdown, and energy storage performance. It has been shown that only qualitative analyses can be performed from the perspective of charge trapping, and it is difficult to obtain quantitative results. Therefore, this work proposes to study the macroscopic properties of polymer dielectrics by combining charge trapping with molecular displacement. A comprehensive conduction‐breakdown‐energy storage model was established to explain the influence mechanism of molecular semiconductors on the improved energy storage performance of PEI composites at high temperatures. The molecular semiconductor fillers increase the coefficient of friction between molecular chains, which restricts the movement of molecular chains and also limits charge hopping. Therefore, the dielectrics have higher breakdown strengths and smaller conduction losses, which synergistically enhance the energy storage performance. [ABSTRACT FROM AUTHOR]

High‐voltage electric pulse rock breaking has excellent potential for exploiting deep geothermal resources. Numerous researchers have conducted experimental studies on this topic, particularly in rock mechanics, where the breakdown occurs. However, there has been limited scholarly research on drilling fluid. Therefore, the study focuses on the drilling fluid suitable for electric pulse drilling, considering the characteristics of electric pulse rock breaking, which differ from traditional rock breaking. The study focused on the impact of various drilling fluid parameters on the effectiveness of electric impulse rock breaking using red sandstone as the experimental material. This was investigated using the finite element method, and indoor electric rock‐breaking tests were conducted in a drilling fluid environment. The results indicate that the plasma channel mainly grows in the permeable layer of the drilling fluid, resulting in shallow rock breaking depth in the drilling fluid environment. The pore permeated by drilling fluid guides the growth of the plasma channel. The higher the conductivity of the drilling fluid, the closer the ion channel of rock breaking by electric pulse is to the rock surface. This results in a smaller crushing volume and shallower damage depth, which is more detrimental to rock breaking by an electric pulse. The viscosity of drilling fluid can impede the breakdown to some extent. In this paper, the influence of drilling fluid parameters on electro‐pulse rock‐breaking technology is preliminarily studied, which has significant reference value for the selection of actual drilling fluid. [ABSTRACT FROM AUTHOR]

Advances in 5G and 6G communication technologies and their applications are in part limited by the capabilities of current electronic packaging materials, as expanded bandwidth is a pressing need for novel dielectric substrates capable of co-firing into packages and devices, characterized by low dielectric loss and enhanced thermal conductivity. This investigation provides further characterization in the dielectric, electrical and thermal conductivity properties over previously reported cold sintered composite of Sodium Molybdate Na 2 Mo 2 O 7 (NMO) with hexagonal Boron Nitride (hBN), such as relative permittivity (ε r) and dielectric loss (tan δ) values at high frequencies of 75–110 GHz, electrical resistivity (ρ) fitting to percolation theory, Weibull statistical analysis of electrical breakdown strength (E b) and its anisotropic thermal conductivity (κ) influenced by the filler's crystal structure. The cold sintered composites were systematically characterized with respect to filler volume fraction, temperature, and frequency. The findings in this analysis position engineered composites as a promising alternative for microwave substrate materials, with using a densification method that limits interactions and maximizes densification, hence the demonstration with cold sintering. [ABSTRACT FROM AUTHOR]

The high‐voltage electric pulse fracturing (HVEPF) technology represents a novel and highly promising approach in rock fracturing. The investigation of thermal damage inflicted upon rocks by high‐voltage electrical pulses under multi‐physical field coupling is of great significance in the development of deep geothermal energy. This study establishes a damage model for rocks under electric fragmentation conditions by integrating electric field, heat transfer field, and solid mechanics field. Based on the developed damage model, the insulating properties, temperature variations, and forms of damage of rocks during electric fracturing are explored. Subsequently, the influence of voltage on rock damage status is investigated. The findings reveal that damage to the rock does not occur immediately after electrical breakdown; rather, it increases with the growth of current and temperature within the breakdown channel. Initial damage occurs at the ends of the breakdown channel, followed closely by damage in the central region of the channel. The predominant form of damage in rocks is tensile failure, with shear failure playing a secondary role, and the volume of damage increases with voltage. These results elucidate the characteristics of rock damage during electric fracturing, providing valuable insights for the engineering application of electric fracturing techniques. [ABSTRACT FROM AUTHOR]

Ionization waves (IWs) of positive polarity are studied experimentally in several sealed discharge tubes containing neon at pressures of 0.6‒15 Torr and surrounded with a grounded metal screen. The IWs arise at the stage single-electrode breakdown development at moderate overvoltage conditions, and belong to "slow" ionization waves (velocity of 105‒108 cm/s). The wave propagation is accompanied by a monotonic loss of velocity and the electric potential magnitude at the IW front, indicating its significant spatial attenuation. The IWs are studied by recording x‒t diagrams supplemented with measurements of instantaneous velocities, front potentials, and attenuation coefficients at various pressures and applied voltages. An exponential nature of a decrease in the front potential and instantaneous velocity of the IWs with the distance traveled is established. It is found that the scales of the exponential decrease in both quantities do not coincide. The obtained results can be useful in planning experiments on breakdown in long tubes, ionization wave modeling, as well as their technological implementation [ABSTRACT FROM AUTHOR]

Epoxy/glass fibre composites possess excellent mechanical and electrical properties and are widely utilised in electrical and electronic power equipment. However, the composites exhibit relatively poor thermal conductivity, causing the temperature of the composites to increase during the operation of power equipment, resulting in a significant reduction in the electrical breakdown strength. Although the effects of thermal aging on polymeric materials have been widely studied, its influence on electrical strength mechanisms has not been investigated at the molecular level. In this study, epoxy/glass fibre composite specimens were subjected to accelerated thermal aging treatment for 360 h at 180 °C. Functional groups, molecular chain dynamics, and electrical breakdown are characterised using infrared spectroscopy, dielectric spectroscopy, and breakdown measurement. Subsequently, electrical breakdown mechanism and life prediction of the thermally aged composites are discussed. During thermal aging, the epoxy resin molecular chains undergo continuous oxidation and chain scission, which generate numerous polar functional groups and short chains and an increase in the free volume. This triggers an enhancement in the chain segmental dynamics, thereby significantly reducing the activation energy of the epoxy resin. After 360 h, activation energy decreased from 0.78 eV to 0.67 eV. The DC breakdown voltages of the specimens decreased from 168.28 kV/mm to 134.91 kV/mm. An insulation life prediction model for thermally aged epoxy/glass fibre composites is established based on the time-temperature equivalence theory. The prediction results indicate that the service life of the operational composites is approximately 11.2 years at 353 K, which is consistent with engineering experience.

A mathematical model has been developed for calculating the internal and external electric field of insulators based on the solution of the Laplace equation with respect to the phasor of the electric potential using the finite element method. The specified model has been used to calculate electric field intensity distributions in the surrounding air spaces of support-rod insulators С4-80-I, C4-80-II and also C4-80-IIСm (Chinese-made). It has been proposed to establish a relationship between the distribution of the electric field around the insulators and their test dry discharge voltage based on the average integral values of the modulus of the electric field intensity along the possible paths of the discharge, taking into account the sign of its tangential component. The average integral values of the electric field have been compared with the known experimental values of the air breakdown intensity between two rod electrodes, as well as in the electrode system of the rod and the grounded plane. It has been shown that the most probable path of development of the discharge for each of the considered insulators is the path closest to the minimum distance in the air between the cap and the flange, the discharge process is two-stage (firstly the section «cap-the rib nearest to the cap» is broken down), and the breakdown intensity of the air around the insulators corresponds to the breakdown intensity between two rod electrodes (the difference in values was 2,1...5,9%). [ABSTRACT FROM AUTHOR]

The development of nanoelectronics and nanotechnologies has been boosted significantly by the emergence of 2D materials because of their atomic thickness and peculiar properties, and developing a universal, precise patterning technology for single-layer 2D materials is critical for assembling nanodevices. Demonstrated here is a nanomachining technique using electrical breakdown by an AFM tip to fabricate nanopores, nanostrips, and other nanostructures on demand. This can be achieved by voltage scanning or applying a constant voltage while moving the tip. By measuring the electrical current, the formation process on single-layer materials was shown quantitatively. The present results provide evidence of successful pattern fabrication on single-layer MoS2, boron nitride, and graphene, although further confirmation is still needed. The proposed method holds promise as a general nanomachining technology for the future. ARTICLE HIGHLIGHTS: HIGHLIGHTS • Successful patterning of 2D materials by electrical breakdown. • A maskless, pollution-free method for patterning various 2D materials. • Nanopattern size is characterized by number of voltage scanning cycles. [ABSTRACT FROM AUTHOR]

This study is a numerical analysis of the transition process from the second to the third mode in transformer oil. In this study, it was determined how to change from the second to the third mode, which is thought to be a precursor to the process of electrical breakdown, which results in a significant loss of electrical energy and harm to electrical devices and equipment. The initiation time, length, rate of propagation velocity, and radius of the streamer discharge were determined. The transition from the second to the third mode during the electrical discharge process may lead to the occurrence of an electrical breakdown, which is one of the greatest challenges facing scientists and engineers who deal with the electrical power of transmission and generation devices. The model was designed by AutoCAD software, which included two electrodes: a needle, with a tip radius of (4μm), and a plate, with a gap of (1 mm) between them. The gap between the two electrodes was filled with transformer oil. The equations, which are Poisson's equation and the continuity equations for positive and negative ions and electrons, which are generated by applying an applied voltage (from 27 kV to within 278 kV), had been solved by a simulation process. All the schematics and drawings were extracted by the Comsol Multiphysics program. [ABSTRACT FROM AUTHOR]

Conductive graphitized grooves on the dielectric surface of diamond have been created by KrF excimer laser radiation. The advantages of such a circuit board in high-field applications is rather limited because the crystal surface has a relatively low electrical breakdown threshold. To increase the electrical strength, a method of encapsulating surface conductive graphitized structures by chemical vapor deposition of an epitaxial diamond layer has been proposed and realized. The quality of the growth diamond is proved by Raman spectroscopy. A comparative study of the electrical resistivity of graphitized wires and the breakdown fields between them before and after diamond growth was carried out. The proposed technique is crucial for diamond-based high-field electro-optical devices, such as THz photoconductive emitters. [ABSTRACT FROM AUTHOR]

In this article we present the results of time-of-flight mass spectrometry of volatile products formed during the electrical breakdown of polyethylene terephthalate and polypropylene polymer films in high vacuum. During the breakdown of films, all the substance emitted from the breakdown channel is a gas of low-molecular products of destruction of macromolecules. The breakdown mass spectra do not contain lines of carbon molecules, the presence of which could indicate carbonation of the channel. To explain the formation of charge carriers, the ionization mechanism of destruction of macromolecules in an electric field is used without the involvement of impact ionization. The final stage of electrical breakdown (the flow of a high-density conduction current) occurs when the critical concentration of traps and electrons ≈1024 m–3 is reached. [ABSTRACT FROM AUTHOR]

Electrical breakdown is an important physical phenomenon in power equipment and electronic devices. Recently, the mechanism of AC and DC breakdown has been preliminarily revealed as electrode–dielectric interface breakdown and bulk breakdown, respectively, based on space charge dynamics through numerical calculations. However, the AC breakdown mechanism still lacks enough direct experimental support, which restricts further understanding and the design and development of electrical structures. Here, in this study, LDPE films with various thicknesses ranging from 33 μm to 230 μm were surface modified with ozone for different durations to experimentally investigate DC and AC breakdown mechanism. The results indicate that carbonyl groups (C=O) were introduced onto the film surface, forming shallow surface traps and leading to a decreased average trap depth and an increased trap density. Such a surface oxidation modulated trap distribution led to enhanced space charge injection and bulk electrical field distortion, which decreased DC breakdown strength as the oxidation duration went longer, in all film thicknesses. However, such decreases in breakdown strength occurred only in films below 55 μm under AC stresses, as the enhanced electrical field distortion at the electrode–dielectric interface was more obvious and dominating in thin films. These experimental results further confirm the proposed electrode–dielectric interface breakdown of dielectric films and provide new understandings of space charge modulated electrical breakdown, which fulfills dielectric breakdown theory and benefits the miniaturization of power equipment and electronic devices. [ABSTRACT FROM AUTHOR]

The article presents the results of laboratory measurements of Ud breakdown voltages in a high-voltage vacuum insulating system for different pressures, contact gaps, type of electrode contacts and type of residual gas inside the discharge chamber. First of all, the electrical strength of the discharge chamber with a contact system terminated with contact pads made of W 70Cu 30 and Cu 75Cr 25 material was compared for selected values of contact gaps. It was found that below a pressure of p = 3.0 x 10 -1 Pa the electrical strength reaches an approximately constant value for each of the set contact gaps d. Analytical relationships were determined to calculate this value for each of the contact pads used. Above a pressure of p = 3.0 x 10 -1 Pa, the measured values of Ud breakdown voltages decrease sharply. The values of breakdown voltages in the discharge chamber with residual gases in the form of air, argon, neon and helium were also determined for selected values of contact gaps d. Depending on the residual gases used, significant differences were noted in the values of pressure p at which the loss of insulating properties in the discharge chamber occurred. These values were 3.3 x 10 -1 Pa for argon, 4.1 x 10 -1 Pa for air, 6.4 x 10 -1 Pa for neon, and 2.55 x 10 0 Pa for helium, respectively.

The sterilization operation in food production is a key process to ensure the safety of food products, and most existing technologies for food sterilization utilizes thermal and/or non-thermal effects. Conventional heat sterilization requires a heat transfer medium, which is completed in a certain period of time at a certain temperature. Electric field processing, a non-conventional food processing technology which utilizes both thermal and non-thermal effects, can reduce the effective temperature threshold and time of conventional heat sterilization, thereby better retaining the nutritional value of foods with less impact on the sensory quality, flavor and color. This paper reviews the principles of ohmic heating sterilization, high-voltage pulsed electric field sterilization and induced electric field sterilization as well as the frontiers and progress in these sterilization technologies in the food industry, discusses the characteristics and differences between the current electric field technologies, and presents an outlook on their future development.

A novel ethylene-anisylpropylene copolymer was tested as a candidate material for intrinsically self-healing electrical insulation layers. In addition to the thermal and mechanical properties, the dielectric properties were studied before and after induced mechanical and electrical damage to the specimens. The material was tested according to the standards for electrical insulating materials, which require a detailed characterization of the dielectric properties. Nonstandardized tests of self-healing were also included in the testing. The results revealed that the tested material exhibited excellent dielectric parameters and reasonable thermal and mechanical properties. The self-healing tests of the material revealed a 38 % efficiency for recovery of the mechanical properties after the first damage, and this remained almost unchanged after the second and third damage. The first initial results also indicated that the material recovered, to some extent, its electrical insulation properties even after electrical breakdown. By comparing the dielectric strength of the pristine and self-healed specimens, a promising self-healing efficiency of 63 % was determined.

The ultra-precision machine tool industry has been consistently improving to the point where machine tools with extreme thermal controls, vibration damping, and command resolutions of 0.1 nm are commercially available. As little research focus has been given to developing peripheral technologies, currently available work coordinate system setting methods are a bottleneck on the achievable accuracy of ultra-precision machine tools. One of the work coordinate system setting methods uses electrical breakdown. The electrical phenomenon occurs when a sufficiently large voltage difference is applied between two conductors. This phenomenon has been observed to have a linear relationship between the breakdown voltage and gap size at short gap sizes. Electrical breakdown is a capable work coordinate system setting with an accuracy of 100 s nm. However, this method is limited to electrically conductive cutting tools and workpiece materials. This study proposes a work coordinate system setting method for ultra-precision machining based on electrical breakdown for non-conductive materials. In this study, a conductive thin film coating is applied to polycrystalline diamond cutting tools to facilitate electrical breakdown work coordinate system setting. With similar motivation, a modification method was tested to enable electrical breakdown work coordinate system setting on non-conductive workpiece materials. The modification method used a 50-nm-thick platinum coating on the workpiece. This study also introduces a method for automatic work coordinate system setting using electrical breakdown and sensors built into the machine tool. [ABSTRACT FROM AUTHOR]

Spectral characteristics of ultrahigh-frequency radiation generated by a pulsed electric spark in a millimeter air gap are studied, together with its temporal correlation with the behavior of the discharge current and voltage in a nanosecond time scale. Systematic features of the UHF emission and general picture of possible phenomena in the spark gap are discussed. [ABSTRACT FROM AUTHOR]

The article describes the development of cell engineering technologies that use various electroporation modes and require knowledge of the electrical characteristics of living cells. Usually, cells are taken from laboratory animals of the same species, and the question of specific features of electrical characteristics of living cells remains open. Using the method of pulsed conductometry in an electric field of increasing strength, the electrical characteristics (conductivity, strength) were measured during electroporation and electrical breakdown of oocytes membranes of the following mammalian species: Mus musculus (mouse), Oryctolagus cuniculus (rabbit), Sus scrofa (pig), Bos taurus (cow), and Homo sapiens (human). Mathematical analysis of the experimental dependences of the conductivity of mammalian oocytes based on polynomial approximation was performed. The electrical characteristics of oocytes were obtained based on the analysis of approximating polynomials for the presence of maximum curvature (membrane electrical breakdown) and inflection points and local extrema (the degree of reversible electroporation). Significant species differences in the measured electrical characteristics of the studied oocytes were established. The measurement results showed a significant species specificity of electrical characteristics, reflecting the different resistance of oocytes to electrical breakdown and the degree of reversible electroporation of membranes, which is probably associated with the peculiarities of the lipid composition of oocyte membranes, the integrity of the cytoskeleton structure, and the resistance of cells as a whole to the impact of a pulsed field. The results obtained can be used to implement various modes of electromanipulation with a living cell, i.e., electrotransfection of deoxyribonucleic acid (DNA), genes, electrofusion, as well as for point lysis of cells with a lost apoptosis mechanism. [ABSTRACT FROM AUTHOR]

The article presents the results of laboratory measurements of Ud breakdown voltages in a high-voltage vacuum insulating system for different pressures, contact gaps, type of electrode contacts and type of residual gas inside the discharge chamber. First of all, the electrical strength of the discharge chamber with a contact system terminated with contact pads made of W70Cu30 and Cu75Cr25 material was compared for selected values of contact gaps. It was found that below a pressure of p = 3.0x10-1 Pa the electrical strength reaches an approximately constant value for each of the set contact gaps d. Analytical relationships were determined to calculate this value for each of the contact pads used. Above a pressure of p = 3.0 x 10-1 Pa, the measured values of Ud breakdown voltages decrease sharply. The values of breakdown voltages in the discharge chamber with residual gases in the form of air, argon, neon and helium were also determined for selected values of contact gaps d. Depending on the residual gases used, significant differences were noted in the values of pressure p at which the loss of insulating properties in the discharge chamber occurred. These values were 3.3 x 10-1 Pa for argon, 4.1 x 10-1 Pa for air, 6.4 x 10-1 Pa for neon, and 2.55 x 100 Pa for helium, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A partial discharge inception voltage modeling approach promoting design-for-reliability considerations in advanced power modules is presented. As power modules are being operated at higher voltages and become more compact to meet power density demands, there is an increased risk of partial discharge, the silent precursor to electrical breakdown that degrades insulation material. The trade-off between voltage class and module compaction must be quantified. This work presents a methodology to model the tradeoff for any substrate and encapsulant material. A surface charge density-based partial discharge inception voltage (PDIV) model was developed to overcome the challenges in electric field-based models. The model consists of a closed-form equation that accepts finite element simulation results as input and produces PDIV as output. The model was experimentally validated for various trace gaps in a 12/25/12 mil alumina DBC using Dow Corning 3-6635 dielectric gel. An expected trend of diminishing returns was observed between PDIV benefit and trace-gap. This approach quantifies this diminishing returns point. To design for reliability, the maximum operating voltage must be limited to the PDIV. For a material set and manufacturing process, this methodology can be used to determine the voltage class and trace gap design rules.

The spectroscopic analysis of low-current electrical discharges (approximately 0.1 mA) in liquid I-40A oil was carried out. The discharge spectrum is similar to that for photoluminescence and hydrodynamic luminescence and is determined mainly by the highlighting individual luminescent centers. There are components in the emission spectrum corresponding to the radiation of atoms of the electrode material, as well as a split Hα hydrogen line. From the analysis of the emission spectrum, the electric field strength was approximately 60 kV/cm and the concentration of electrons ∼1014 cm−3. There were no components corresponding to molecular radiation in the spectrum. It has been hypothesized that the discharge in a liquid occurs when the steam phase forms in the electric field. However, these results raise questions about the composition of this steam phase. Although similar emissions for I-40A oil were produced by electrical discharges and as photo- or hydroluminescence, ultrasonic sonoluminescence has never been observed for I-40A oil. Thus, there is no way to excite the environment with ultrasound, unlike for other forms of luminescence, such as by an electrical discharge. [ABSTRACT FROM AUTHOR]

Work coordinate setup in an ultra-precision machine tool is one of the important tasks to fabricate a structure at the desired position with high accuracy. Setting up the work coordinate is very challenging because it requires high precision, direct measurement, and non-contact preferred. This paper proposes a new method to measure the relative distance between tool-work materials using the electrical breakdown where current flows through electrical insulator when an applied voltage is higher than the breakdown voltage. The applied voltage is linearly proportional to the relative distance in nanoscale. Experiment with Al6061, SS316, AISI1018 steel, and OFHC Cu work materials, and WC and CBN tools showed a successful and easy application of this method in work coordinate setup with 70 nm uncertainty at low applied voltage. Surface damages by the electrical breakdown of Al6061, SS316, AISI1018 steel, and OFHC Cu were not found at less than or equal to 1, 2, and 3 V, respectively. An automated detection test was conducted and found approaching speed of 0.1 mm/min without surface damage. Standard uncertainty analysis validated the confidence of the proposed method. [ABSTRACT FROM AUTHOR]

The dependence of the electrical durability τ E (time from the application of constant voltage until breakdown) on the temperature T (in the range of 77–300 K) at different values of the electric field strength E of polymer compositions of polypropylene and low-density polyethylene (PP–LDPE) with different supramolecular structures (SMS) was measured. At elevated temperatures (∼ above 200 K), the dependence of lg τ E (T − 1) is linear, indicating a thermofluctuational mechanism of breakdown preparation; at low temperatures (∼ below 200 K) τ E does not depend on T , which will allow us to conclude about its tunneling mechanism. The transition temperature of the linear dependence of τ E on T lies in the ∼ 2 0 0 K range and depends on the value of the applied constant electric field. [ABSTRACT FROM AUTHOR]

The development of an electrical breakdown in water with a conductivity of 255 µS/cm under the effect of ultrasonic waves for the "tip–pin" geometry of electrodes with an interelectrode gap of 8 mm is experimentally studied. It is found that at the same voltage close to the minimum breakdown voltage the probability of the breakdown initiation and discharge closure of the gap increases by two times when exposed to ultrasound without cavitation, and the time of the pre-breakdown stage is reduced compared to the breakdown without ultrasound. [ABSTRACT FROM AUTHOR]

Conductive graphitized grooves on the dielectric surface of diamond have been created by KrF excimer laser radiation. The advantages of such a circuit board in high-field applications is rather limited because the crystal surface has a relatively low electrical breakdown threshold. To increase the electrical strength, a method of encapsulating surface conductive graphitized structures by chemical vapor deposition of an epitaxial diamond layer has been proposed and realized. The quality of the growth diamond is proved by Raman spectroscopy. A comparative study of the electrical resistivity of graphitized wires and the breakdown fields between them before and after diamond growth was carried out. The proposed technique is crucial for diamond-based high-field electro-optical devices, such as THz photoconductive emitters.

The electrical breakdown of a dielectric nanolayer between film electrodes under the combined action of direct current and capacitor discharge current makes it possible to form Josephson bridges with a reproducible resistance exceeding 1 Ω. A new feature of the formation of a bridge during the electrical breakdown, which is preceded by a series of preliminary breakdowns (auto breakdowns) of a dielectric nanolayer, has been discovered. The mechanism of the process and the role of the cathode film's thickness in forming the bridge are discussed. [ABSTRACT FROM AUTHOR]

Epoxy/glass fibre composites possess excellent mechanical and electrical properties and are widely utilised in electrical and electronic power equipment. However, the composites exhibit relatively poor thermal conductivity, causing the temperature of the composites to increase during the operation of power equipment, resulting in a significant reduction in the electrical breakdown strength. Although the effects of thermal aging on polymeric materials have been widely studied, its influence on electrical strength mechanisms has not been investigated at the molecular level. In this study, epoxy/glass fibre composite specimens were subjected to accelerated thermal aging treatment for 360 h at 180 °C. Functional groups, molecular chain dynamics, and electrical breakdown are characterised using infrared spectroscopy, dielectric spectroscopy, and breakdown measurement. Subsequently, electrical breakdown mechanism and life prediction of the thermally aged composites are discussed. During thermal aging, the epoxy resin molecular chains undergo continuous oxidation and chain scission, which generate numerous polar functional groups and short chains and an increase in the free volume. This triggers an enhancement in the chain segmental dynamics, thereby significantly reducing the activation energy of the epoxy resin. After 360 h, activation energy decreased from 0.78 eV to 0.67 eV. The DC breakdown voltages of the specimens decreased from 168.28 kV/mm to 134.91 kV/mm. An insulation life prediction model for thermally aged epoxy/glass fibre composites is established based on the time-temperature equivalence theory. The prediction results indicate that the service life of the operational composites is approximately 11.2 years at 353 K, which is consistent with engineering experience. [Display omitted] • Obtain chain dynamic parameters of thermal-aged composites by dielectric spectrum. • Clarify the effects of thermal aged chemical structure on chain dynamic characteristics. • Demonstrate the influence mechanisms of chain dynamics on electrical breakdown. • Establish a life prediction model based on chain dynamics and breakdown. [ABSTRACT FROM AUTHOR]

Electrical breakdown is an important physical phenomenon in power equipment and electronic devices. Recently, the mechanism of AC and DC breakdown has been preliminarily revealed as electrode–dielectric interface breakdown and bulk breakdown, respectively, based on space charge dynamics through numerical calculations. However, the AC breakdown mechanism still lacks enough direct experimental support, which restricts further understanding and the design and development of electrical structures. Here, in this study, LDPE films with various thicknesses ranging from 33 μm to 230 μm were surface modified with ozone for different durations to experimentally investigate DC and AC breakdown mechanism. The results indicate that carbonyl groups (C=O) were introduced onto the film surface, forming shallow surface traps and leading to a decreased average trap depth and an increased trap density. Such a surface oxidation modulated trap distribution led to enhanced space charge injection and bulk electrical field distortion, which decreased DC breakdown strength as the oxidation duration went longer, in all film thicknesses. However, such decreases in breakdown strength occurred only in films below 55 μm under AC stresses, as the enhanced electrical field distortion at the electrode–dielectric interface was more obvious and dominating in thin films. These experimental results further confirm the proposed electrode–dielectric interface breakdown of dielectric films and provide new understandings of space charge modulated electrical breakdown, which fulfills dielectric breakdown theory and benefits the miniaturization of power equipment and electronic devices.

Stabilization of soil for grounding purposes has been performed by adding different wt% of lime. Electrical breakdown measurements under lightning impulse voltage showed a reduction in breakdown voltage and the time to breakdown with increment in the lime content in the soil. These parameters also increased with curing period for all concentrations of lime of stabilized soil samples. The results show that pH and electrical conductivity of the expansive soil increase as the lime content increases, but decrease with increasing the curing period. Mineralogical and micro-structural analysis has been made by means of X-ray diffraction (XRD) studies and by scanning electron microscope (SEM) analysis. The axial strength obtained from unconfined compressive strength (UCS) analysis, the plasma temperature and the electron number density calculated from Laser Induced Breakdown Spectroscopy (LIBS) data tend to increase with increment in lime content as well as the curing period of the lime stabilized soil. Using univariate analysis, the normalized intensity ratio of Ca II peaks from LIBS spectral data are correlated with lime content in the soil samples at various curing periods. The partial least squares regression (PLSR) technique is successful in determining the soil parameters with the help of LIBS spectral data, at different curing periods with an R2 value greater than 0.95 and the percentage RMSE value smaller than 4%.

In this work, we have studied the impact of various stages of cryopreservation by vitrification in ethylene glycolsucrose medium on plasma membranes adhesive properties of 8-cell murine embryos and their specific electrical conductivity. Embryos were divided into the following experimental groups: the control, group I (incubation in vitrification medium) and group 2 (complete cycle of cryopreservation). The embryo exposure to vitrification medium did not affect their ability to cell-to-cell adhesion. After a complete cycle of cryopreservation, no embryo adhesion was observed. Electrical conductivity of embryo membranes was determined using the pulsed conductometry. After incubation in vitrification medium, their resistance to electric pulse was shown to decrease, that was manifested in the phenomenon of irreversible electric breakdown. The average values of electrical conductivity varied within the following ranges: ((12.1 ± 1.5)...(55.5 ± 2.6)), ((28.7 ± 5.7)...(44.± 8.9)), ((31.0 ± 9.3)...(87.9 ± 26.1)) μS/cm in the control, groups I and 2, respectively. These findings may be explained by appearance of first structural disorders in lipid bilayer of embryo membranes even at the stage of their incubation in vitrification medium. The lack of adhesive properties of blastomeres after vitrification-warming testified to a damage to the membrane adhesion proteins. [ABSTRACT FROM AUTHOR]

An extensive study has been conducted on a series of AlGaN/GaN high electron mobility transistor (HEMT) samples using metalorganic vapour phase epitaxy, to investigate the influence of growth modes for GaN buffer layers on device performance. The unintentional doping concentration and screw dislocation density are significantly lower in the samples grown with our special two-dimensional (2D) growth approach, compared to a widely-used two-step method combining the 2D and 3D growth. The GaN buffer layers grown by the 2D growth approach have achieved an unintentional doping density of 2 × 1014 cm−3, two orders lower than 1016 cm−3 of the GaN samples grown using a conventional two-step method. High-frequency capacitance measurements show that the samples with lower unintentional doping densities have lower buffer leakage and higher breakdown limits. This series of samples have attained sub-nA/mm leakages, a high breakdown limit of 2.5 MV/cm, and a saturation current density of about 1.1 A/mm. It indicates that our special 2D growth approach can effectively lessen the unintentional doping in GaN buffer layers, leading to low buffer leakage and high breakdown limits of GaN/AlGaN HEMTs. [ABSTRACT FROM AUTHOR]

Electrical breakdown of the dielectric nanolayer between film electrodes of niobium and an alloy of 50% indium and 50% tin forms a bridge of this alloy between the electrodes. The bridge resistance depends on the breakdown current. The length of the bridge is equal to the thickness of the dielectric (30 nm), and its diameter is 25 nm. The calculated coherence length of the alloy at 2 K is close to the length of the bridge. The calculated critical current of a bridge with a resistance of 1 Ω at a temperature of 0 K is 1 mA. It is concluded that such a bridge should have the properties of a Josephson contact at a temperature lower than the critical temperature of the alloy (6.5 K). [ABSTRACT FROM AUTHOR]

Infrared (IR) optical fibers based on crystals and ceramics of the AgBr–AgI system are transparent in the IR range from 3 to 26 μm, which is of interest for thermal imaging, laser technique, and spectroscopy. High photo- and radiation resistances make these materials especially attractive for solving the problems of optical radiation transfer in aggressive environment. To design optical equipment, it is necessary to have information on the electric properties of materials, which are most completely characterized by current–voltage characteristics (CVCs). In this work, we consider the dependences of the CVCs of optical materials of the AgBr–AgI system in the form of plates with thicknesses from 0.1 to 1.7 mm and AgI concentrations from 4 to 76 mol % on the composition and temperature in the range of 298–453 K. It is found that an increase in the AgI concentration in the AgBr–AgI crystals leads to a decrease in electric conductivity. The conductivity of AgBr–AgI ceramics is two–three orders of magnitude higher than that of the corresponding crystals at the same temperatures and applied voltages. The conductivity of ceramics is comparable with the conductivity of solid electrolytes. The β-AgI–α-AgI phase transition at a temperature of 463 K causes a jump in the conductivity of the AgBr–AgI ceramics. The IR transmission of the studied material was measured before and after electrical breakdown. It was found that electrical breakdown decreases the transmission by more than 20% in the entire spectral range. Information on the breakdown voltage for materials of the AgBr–AgI system with different compositions is important for ensuring reliability and safety of electrotechnical equipment using optical devices based on these materials. In this study, we observed deterioration of the optical properties of crystalline materials of the AgBr–AgI system with applying some voltage difference and determined the breakdown voltage. The breakdown voltage is determined by applying direct-current voltage, but it is the same in the case of alternating-current voltage. [ABSTRACT FROM AUTHOR]

Dry air is promising as an alternative insulation medium for SF6 gas in high-voltage equipment. Since its dielectric strength is about one-third of that of SF6 gas, one of the most effective ways to apply dry air to high-voltage gas-insulated switchgears (GISs) is to further increase gas pressure. In this article, impulse breakdown strength of dry air at high pressure under quasi-uniform electric field is measured. Furthermore, the probability distribution of breakdown voltage is predicted using the volume-time theory in consideration of initial electron generation probability in gas gap and field electron emission from an electrode. The predicted distribution of breakdown voltage by the volume-time theory is in line with the experimental results. [ABSTRACT FROM AUTHOR]

The high-voltage electrical pulses (HVEP) technology is the most potential method to improve the rate of penetration (ROP) in deep hard formations. A detailed understanding of the fragmentation mechanism by HVEP is essential to enhance ROP in rock-breaking and to optimize the electrical parameters. However, few pieces of researches are focused on the uneven dielectric properties of rock. This paper uses particle flow code software and Voronoi tessellation to generate granite models with different heterogeneity indexes; the granite models consider the differences in the micro-dielectric properties and particle size of various mineral components. The simulation of the plasma channel growth process, which considers the circuit equations of HVEP and the probabilistic development model, is analyzed. The results show that the concentration of the electric field in the feasible region makes the extreme value of the entire electric field smaller, which puts forward a higher energy demand for the initial breakdown of granite. The finer the grain size of granite, the smaller the broken ratio coefficient, and the better the crushing degree of HVEP. There is almost no difference in the energy efficiency of HVEP between granites with different heterogeneity indexes. The total length of the plasma channel is dominated by "directional self-direction" and "priority of tips", which is positively correlated with the energy efficiency of HVEP. The research results have definite guiding significance for engineering application of HVEP, bottom hole assembly design, and drilling tool design of HVEP. Highlights: This paper mainly established a simulation model of fragmenting granite by high-voltage electrical pulses to investigate the growth mechanism of plasma channels and to explore the difference in electrical breakdown caused by the heterogeneous dielectric properties of granite. The results show that the concentration of the electric field in the feasible region makes the extreme value of the entire electric field smaller, which puts forward a higher energy demand for the initial breakdown of granite; the finer the grain size of granite, the smaller the broken ratio coefficient, and the better the crushing degree of high-voltage electrical pulses; there is almost no difference in the energy efficiency of high-voltage electrical pulses between granites with different heterogeneity indexes. The total length of the plasma channel is dominated by "directional self-direction" and "priority of tips", which is positively correlated with the energy efficiency of high-voltage electrical pulses [ABSTRACT FROM AUTHOR]

In this work, we present an experimental study on electrical breakdown, also called dielectric failure on a material widely used as insulation in oil transformers and other equipment. This material is pressboard paper impregnated with insulating oil. The breakdown tests are carried out under three types of voltage and for several voltage rise speeds. Dielectric breakdown is a random phenomenon, many tests are carried out on a large number of samples and the results obtained have been subjected to statistical processing. The material is cut into square plates of 7.5 cm in length from a set of plates 2 m² in length and 500 µm in thickness. Prior to the tests, the samples were conditioned in a desiccator with silicone gel for at least 24 hours in order to eliminate any presence of moisture. Then they were impregnated with Borak22 insulating oil for at least one week. The tests consist of placing the sample concerned between two cylindrical bronze electrodes and applying a voltage ramp at constant speed until breakdown. After failure, the value of the breakdown voltage is taken. These tests are carried out in the laboratory at room temperature. However, we have tried to reproduce the same conditions for all the tests. These various tests relate to the effect of the form and the rate of rise of the applied voltage on the dielectric strength of the pressboard paper impregnated with Borak22 insulating oil. Two measuring devices were used, and the tests were carried out under three voltage forms: sinusoidal alternating current, continuous positive polarity, and continuous negative polarity, and at eight different voltage ramp speeds: 0,69; 1,07; 1,4; 1,89; 2,38; 2,94; 3,28 and 4, 17 kV/s. For each measurement point, 35 samples of pressboard paper are used and tested. A total of 840 results we re obtained and processed using the two-parameter Weibull statistical model. In order to validate this model, these results are subjected to a Kolmogorov-Smirnov adequacy test and are framed by 95% confidence bands. The maximum likelihood method is used for the estimation of the Weibull parameters and the smoothing of the experimental points. The results of the statistical tests on the breakdown voltage measurement points obtained confirm the use of the two-parameter Weibull model. The evolution of the nominal breakdown voltage as a function of the voltage ramp of the three forms of applied voltage gives three properties of the same form, which is akin to the letter 'S'. The breakdown voltage first increases linearly for low speeds, then increases and takes an exponential form for medium speeds, then tends towards a certain saturation for high speeds. The breakdown voltage under the DC voltage ramp is higher than the voltage obtained for the AC voltage ramp and are higher under negative polarity voltage than those under positive polarity voltage. [ABSTRACT FROM AUTHOR]

This paper investigated the influence of three aromatic voltage stabilizers (4‐n‐propylbenzoic acid, 2‐methoxyphenylboronic acid, and 3‐aminobenzoylmethylamide) on insulating properties of cross‐linked polyethylene (XLPE) at high temperatures for high voltage direct current (HVDC) applications. The XLPE blends containing 1 wt% voltage stabilizers were prepared through a solution‐blending method. The addition of voltage stabilizers suppressed the space charge inside the XLPE at high temperatures. The DC conductivity of XLPE and its blends increased with temperature. The DC conductivity of the XLPE blended with the 4‐n‐propylbenzoic acid was lowest at the different temperatures and electric fields. The DC breakdown strength of the tested materials continually decreased as the temperature increased. Notably, the DC breakdown strength of XLPE with the addition of 4‐n‐propylbenzoic acid and 3‐aminobenzoylmethylamide was higher than the reference XLPE at high temperatures. Moreover, the thermal stability of the XLPE remained unaffected after the voltage stabilizer's addition, whereas the thermal conductivity was improved. Quantum chemical calculations showed that the addition of voltage stabilizers with lower LUMO could effectively buffer the high‐energy electrons and improve the DC breakdown strength of the XLPE. A buffering mechanism of high‐energy electrons demonstrated the effect of the voltage stabilizers on the DC breakdown strength in the XLPE. [ABSTRACT FROM AUTHOR]

The electrostatic field in a nanocomposite represented by spherical nanoparticles (NPs) embedded into a dielectric between two parallel metallic electrodes is derived from first principles. The NPs are modeled by point dipoles which possess the polarizability of a sphere, and their image potential in the electrodes is found using a dyadic Green's function. The derived field is used to obtain the parameters which characterize the electrical breakdown in a nanocomposite capacitor. It is found, in particular, that for relatively low volume fractions of NPs, the breakdown voltage linearly decreases with the volume fraction, and the slope of this dependence is explicitly found in terms of the dielectric permittivities of the NPs and the dielectric host. The corresponding decrease in the maximum energy density accumulated in the capacitor is also determined. A comparison with the experimental data on the breakdown strength in polymer films doped with BaTiO 3 NPs available in the literature reveals a dominant role of the interface polarization at the NP-polymer interface and an existence of a nonferroelectric surface layer in NPs. This research provides a rigorous approach to the electrical breakdown phenomenon and can be used for a proper design of nanocomposite capacitors. [ABSTRACT FROM AUTHOR]

Delayed discharges due to electrical breakdown are observed in modulated pulsed pow er magnetron sputtering (MPPMS) plasma of titanium. The delayed discharge, which is remarkable with decreasing argon gas pressure, transforms the discharge current waveform from a standard modulated pulsed discharge current waveform to a comb-like discharge current waveform consisting of several pulses with high power. In addition, the delay times, consisting of statistical times and formative times in the delayed MPPMS discharges, are experimentally measured with the help of Laue plot analysis. The pressure dependence of delay times observed indicates that the delayed discharge behavior matches the breakdown characteristics well. In the present study, the delayed discharge dynamics of the comb-like discharge current waveform, which can be the origin of deep oscillation magnetron sputtering, are investigated based on measurement of the delay times and the characteristics of discharge current waveforms.

The plasma limiter (PL) is a suitable method to protect electronic devices from high-power electromagnetic pulses. The $S$ -band PL has target specifications of 100 kW of power handling capability, < 100 ns of response time, and < 0.5 dB of insertion loss. Carbon nanotube (CNT) can be used to reduce power losses and instrument corrosion under frequent electromagnetic attacks. This article used CNT-coated copper needles in a PL to increase the electric field for the rapid breakdown process. Furthermore, the impact of dimensional parameters (needle’s length, needle’s radius, and axial displacement of the needles) were investigated. The experiment was conducted at 1800 W of peak power and 25 ns of the $S$ -band (2.45 GHz) microwave duration. In this case, the height of 19 mm and diameter of 1 mm were found to be the optimal needle parameters, in which the fastest breakdown of the electric field is available. The finite-element method was used by CST software to verify the experiment results. The transmission losses were < 5% in the normal state. The breakdown electric field threshold was ~431 kV/m near the atmospheric pressures. There was an error of < 1.28 in the case with the lowest compatibility. [ABSTRACT FROM AUTHOR]

The unclear understanding of the mechanism of rock breaking and fracturing by high-voltage pulse discharge limits the development of electric pulse drilling technologies. The electrical breakdown of rock subjected to pulsed high voltage discharge is a prerequisite for electric fracturing. Based on the theory of breakdown in solid dielectrics, this paper treats field strength of a homogeneous rock subjected to electric pulses in a numerical simulation as the evaluation index and systematically studies the influence of discharge voltage, electrode spacing, rock thickness, rock minerals, insulating liquid and rock pores on electrical breakdown. The study shows that voltage level, electrode spacing and rock pores have a significant impact on electrical breakdown. The higher the voltage level, the better the electrical breakdown effect; smaller electrode spacing is not always better, but there is an optimal value to achieve the utmost electrical breakdown; field strength in rock pores is significantly enhanced, and microscopic pores as structure defects may be a controlling factor of electrical breakdown. The influence of rock thickness, insulating liquid medium and rock mineral composition on electrical breakdown is weak. The greater the thickness of rock, the worse the electrical breakdown effect. The lower the dielectric constant of insulating liquid, and the higher the dielectric constant of rock minerals, the better the electrical breakdown effect. A high-voltage electrical breakdown experiment was carried out, which clarifies the influence of physical properties of rock on the electrical breakdown and confirms the accuracy of the numerical simulation conclusions to a certain extent. [ABSTRACT FROM AUTHOR]

Transparent and flexible diodes could be useful for future transparent electronics. Here such diodes are discussed with electrical breakdown (EBR) comprises of W/ZnO/ITO structure on the polyethylene terephthalate substrates. The three‐layered structure shows rectifying characteristics with low breakdown voltage originated from the Schottky barrier at the W/ZnO (0.8 eV) and the ZnO/ITO (0.1 eV) interfaces. Mechanical endurance is retained after different bending strengths and the rectification ratio is showed stability for 104 cycles without any significant degradation. Steep slope transistors are designed by implementing such diodes in series with the conventional field effect transistors. Such diode plus transistor stack enables field effect transistors with steep subthreshold swing of < 5.2 mV dec−1 and an internal current amplification due to negative differential resistance induces across the Schottky diodes during the EBR. Also, one diode‐one resistor structure is successfully demonstrated by connecting the flexible diodes and resistive memory in series for applications in high density integrated non‐volatile memory applications. [ABSTRACT FROM AUTHOR]

Lightning puncture damage on the wind turbine blades can pose a severe threat to the safe operation of large-capacity wind turbines. We investigated its formation by performing long air gap discharge experiments under positive and negative downward leaders. Upward streamers were observed to emit from the sample blade before its electrical breakdown. To explain this phenomenon, a numerical model considering the streamer discharge in air, charge transport in GFRP laminate and surface charge accumulation on air-solid interfaces was established. It is found that streamer discharges can be triggered inside the blade hollow to generate space and surface charges, which strengthen the electric field on the outer blade surface and contribute to the upward streamer initiation. The upward streamer development leads to the accumulation of surface charges with opposite polarities on the two sides of GFRP laminate, which causes the electric field on the GFRP laminate to exceed its electrical breakdown threshold. The electrical breakdown, which occurs before the thermal effect of lightning current appears, is the initial stage of lightning puncture damage of blades. The electrical discharge inside the blade hollow and the surface charge accumulation on the GFRP blade should be suppressed to prevent the puncture damage of blades. [ABSTRACT FROM AUTHOR]

Purpose. To substantiate the breakdown mechanism of capacitor paper on the basis of numerical-field models with segmented cross-sections of cylindrical volumes of air and water, and also use the proposed models to determine the breakdown strength of air in micron-sized gaps under normal conditions. Methodology. The model bases on a finite element solution to an electrostatic problem in a volume of capacitor paper consisting of cellulose and pores with air and water. First, the possible scenarios for the growth of breakdown in capacitor paper are analyzed and to the conclusion is made, that complete breakdown developed from a partial breakdown in the air cavity. A brand of capacitor paper is chosen in such a way that when its thickness changed, the breakdown strength of the electric field changed over a wide range. Then, for the paper with the lowest average electric field intensity the possibility of explaining the complete breakdown by the breakdown of air segments on the basis of the Paschen dependence is checked. Further points of the obtained dependence by constructing models of papers of the same brand and a different thickness under the assumption of the similarity of electrostatic fields are determined. As such a criterion, the constancy of the equivalent effective permittivity are taken. Results. The dependence of the breakdown strength of the air in the range of 1.36...5.54 μm under normal conditions is determined. The obtained relationship is between the Peschot and Taev curves. Originality. For the first time, the possibility of indirectly estimation the breakdown strength of an insulating material using an electrostatic field model is indicated. Practical value. The proposed method for the numerical calculation of the breakdown voltage of air inclusions in the presence of water inclusions in the thickness of solid insulation can be applied to other types of solid thin-layer insulation.

Abstract Transparent and flexible diodes could be useful for future transparent electronics. Here such diodes are discussed with electrical breakdown (EBR) comprises of W/ZnO/ITO structure on the polyethylene terephthalate substrates. The three‐layered structure shows rectifying characteristics with low breakdown voltage originated from the Schottky barrier at the W/ZnO (0.8 eV) and the ZnO/ITO (0.1 eV) interfaces. Mechanical endurance is retained after different bending strengths and the rectification ratio is showed stability for 104 cycles without any significant degradation. Steep slope transistors are designed by implementing such diodes in series with the conventional field effect transistors. Such diode plus transistor stack enables field effect transistors with steep subthreshold swing of