Steady-state Electric Field Research Articles

A fast numerical method for calculating SPND space charge effect at steady state

To address the issue of low efficiency and long computation times in calculating the space charge effect in Self-Powered Neutron Detectors (SPNDs), we developed a fast and efficient numerical method to calculate the steady-state electric fields in SPND insulators. Previous calculations have shown that even when the electric field in the SPND insulator reaches 1 GV/m, its effect on electron transport is negligible. Therefore, we assume that the electric field has a negligible effect on electron transport. Based on this assumption, we developed a one-step numerical method for calculating the steady-state electric field in the insulator. This fast method is based on the charge conservation equation in equilibrium, thus requiring only a single charge deposition result without an electric field to obtain the distribution of the electric field under steady-state conditions. We validated our method by comparing it with precise iterative calculation results and experiments. The computational results indicate that, for three typical experimental scenarios, the fast method only takes up to one percent, or even less, of the time required by the iterative method. At the same time, the Mean Relative Error (MRE) in the electric field distribution between the fast method and iterative calculations are 1.48%, 0.31%, and 5.12%, respectively; whereas the relative errors in sensitivity calculations based on the electric field compared to iterative calculations are all less than 2%. Therefore, the fast method can significantly reduce computation time and ensure sufficient accuracy of steady state electric field distribution when the electric field is less than 1 GV/m. The introduction of this method has made it possible to conduct space charge effect assessments and precise sensitivity calculations for the placement of detectors throughout the entire reactor core.

Controlling the thermal and electric fields in isotropic and anisotropic media

In this study, we theoretically propose cloaking and concentration devices allowing simultaneous control of electric and thermal fields in spherically inhomogeneous layered medium with isotropic and anisotropic layers. The above combination of layers (isotropic and anisotropic ones) is obtained by the transformation coordinate approach applied to a spherically inhomogeneous layered medium which contains isotropic and anisotropic layers. It is shown that in steady-state conditions, both thermal and electric fields can pass smoothly around the targeted area while preventing any disturbance in the surrounding medium. The constitutive parameters of both fields have been determined analytically. In this work, we have combined two different methodologies to achieve cloaking in ideal state and in homogenized structure for cylindrical and spherical cases. Numerical validation of the obtained solutions using COMSOL software is performed in this study.

Particle-in-cell modelling of comet 67P/Churyumov-Gerasimenko

Context.Sufficiently far from the Sun, all comets go through a phase of low activity. Rosetta observations at large heliocentric distances of approximately 3 au showed that the plasma at a low-activity comet is affected by both steady state electric fields and low-frequency waves.Aims.Our goal is to provide a model for the electric fields in the inner coma at a low-activity comet and to simulate waves and field structures farther away from the nucleus.Methods.We compare analytical models for the convective, ambipolar, and polarisation electric fields to the results of an electrostatic particle-in-cell simulation of a scaled-down low-activity comet.Results.We find good agreement between the steady state field model and the simulation results close to the nucleus. At larger cometocentric distances, waves dominate the electric field. These waves are interpreted as the scaled-down electrostatic limit of the previously observed singing comet waves. The comet ion density is not spherically symmetric.Conclusions.Low-activity comets can be modelled using electrostatic particle-in-cell simulations of a scaled-down system. Outside the innermost part of the coma (r≳ 40 km), the plasma is not spherically symmetric and the electric field is dominated by waves.

Structural optimization and simulation of piezoelectric- piezoresistive coupled MEMS steady-state electric field sensor

Abstract: In view of the problems of large volume, high energy consumption and difficult maintenance of electric field measurement sensors in existing power systems, non-contact miniature electric field sensors have become a hot topic in current research. In this paper, a MEMS miniature electric field measurement sensor model based on the principle of piezoelectric-piezoresistive coupling is constructed, and the sensor structure is optimized by analyzing the steady-state characteristics of the piezoelectric material and semiconductor membrane of the sensor. The input and output characteristics of the sensor were tested. The test results show that the sensor has excellent mechanical strain capacity, and the output voltage of the sensor has a linear relationship with the electric field strength, thus verifying the feasibility of the sensor measurement in the electric field. The research results will provide some reference for the development of contactless coupled sensors.

Effect of high- and low-side blocking on short-circuit characteristics of SiC MOSFET

Silicon carbide (SiC) metal oxide semiconductor field-effect transistors (MOSFETs) are susceptible to unexpected short-circuit (SC) impacts in high-voltage inverters operating in complex applications. This paper presents a research on the effect of high-side blocking and classical low-side blocking on short circuit characteristics. Simulation of the steady-state electric field, which equivalent to the states after LSB and HSB, was performed. The obvious electric field concentration appears in the source-drain pn junction of the DUT after the LSB, and is much larger in value than that appearing in the DUT after the HSB. DUTs, which failed, were decapsulated from the side of the drain to allow for an emission microscope (EMMI) investigation. In response to the results of the EMMI investigation, it was discussed that the occurrence of source leakage was caused by electric field concentration after the DUT is blocked. The hazards of this failure and the expected further research are mentioned simply.

Conductivity Characterization of Insulation and Its Effects on the Calculation of the Electric Field Distribution in HVDC Cables

The calculation of an electric field distribution provides the basis for the structural design of the insulation, and an accurate characterization of conductivity as a function of temperature and electric field forms an important basis for the simulation of the electric field distribution in HVDC (high-voltage direct current) cables. However, the conductivity functions that describe the insulating materials used for HVDC cables in different studies are different, and very little has been reported regarding how to choose the most accurate function. In this work, the conductivity of insulating materials used for HVDC cables is characterized, and the effects of the conductivity characterization on the simulation of the electric field in HVDC cables are studied. First, eight common conductivity functions are compared qualitatively. Then, the conductivities of XLPE for different temperatures and electric fields are measured, and a data fitting technique is used to analyze the coincidence degree between different functions and the test results. Finally, the steady-state electric field distributions of HVDC cables for different temperature gradients are simulated in COMSOL Multiphysics. The results show that the sum of the square of the relative errors of the fitting when using the original functions is larger than that achieved when using the logarithmic form of the functions. The deviations in the electric field caused by taking the logarithm of different functions are smaller.

Proximity-induced electrodeformation and membrane capacitance coupling between cells

Membrane capacitance and transmembrane potential are sensitive to the proximity of neighboring biological cells which eventually induces anisotropic perturbation of the local electric field distribution in a cell assembly and/or a tissue. The development of robust and reliable multiphysics approaches is essential to solve the challenge of analyzing proximity-induced capacitance coupling (CC) between cells. In this study, we ask to what extent this CC is a minor perturbation on the individual cells or whether it can fundamentally affect bio-electromechanical cues. A key component of our continuum electromechanical analysis is the consideration of elastic models of cells under steady state electric field excitation to characterize electrodeformation (ED). Analyzing the difference between the ED force for a pair of cells and its counterpart for a single reference cell allows us to determine a separation distance-orientation angle diagram providing evidence of a separation distance beyond which the electrostatic interactions between a pair of biological cells become inconsequential for the ED. An attenuation-amplification transition of ED force in this diagram suggests that anisotropy induced by the orientation angle of the cell pair relative to the applied electric field direction has a significant influence on ED and CC. We furthermore observe that the shape of this diagram changes when extracellular conductivity is varied. The results obtained are then contrasted with the corresponding diagrams of similar cell configurations under an oscillating electric field excitation below and above the α-dispersion frequency. This investigation may provide new opportunities for further assessment of electromechanical properties of engineered tissues.

Distortionless Pulse Transmission in Valley Photonic Crystal Slab Waveguide

A valley photonic crystal is one type of photonic topological insulator, the realization of which needs only P-symmetry breaking. The domain wall between two valley-contrasting photonic crystals supports robust edge states, which can wrap around sharp corners without backscattering. Using the robust edge states, one can achieve pulse transmission. Here, using time-domain measurements in the microwave regime, we show distortionless pulse transmission in a sharply bended waveguide. An \ensuremath{\Omega}-shaped waveguide with four 120\ifmmode^\circ\else\textdegree\fi{} bends is constructed with the domain wall between two valley photonic crystal slabs. Experimental results show the progress of Gaussian pulse transmission without distortion, and the full width at half maximum of the output signal changes slightly in the \ensuremath{\Omega}-shaped waveguide. By measuring the steady-state electric field distribution, we also confirm the confined edge states without out-of-plane radiation, which benefits from dispersion below the light line. Our work provides a way for high-fidelity optical pulse signal transmission and the development of high-performance optical elements, such as photonic circuits or optical delay lines.

Electro-chemo-mechanical model to investigate multi-pulse electric-field-driven integrin clustering

The effect of pulsed electric fields (PEFs) on transmembrane proteins is not fully understood; how do chemo-mechanical cues in the microenvironment mediate the electric field sensing by these proteins? To answer this key gap in knowledge, we have developed a kinetic Monte Carlo statistical model of the integrin proteins that integrates three components of the morphogenetic field (i.e., chemical, mechanical, and electrical cues). Specifically, the model incorporates the mechanical stiffness of the cell membrane, the ligand density of the extracellular environment, the glycocalyx stiffness, thermal Brownian motion, and electric field induced diffusion. The effects of both steady-state electric fields and transient PEF pulse trains on integrin clustering are studied. Our results reveal that electric-field-driven integrin clustering is mediated by membrane stiffness and ligand density. In addition, we explore the effects of PEF pulse-train parameters (amplitude, polarity, and pulse-width) on integrin clustering. In summary, we demonstrate a computational methodology to incorporate experimental data and simulate integrin clustering when exposed to PEFs for time-scales comparable to experiments (seconds-minutes). Thus, we propose a blueprint for understanding PEF/electric field effects on protein induced signaling and highlight key impediments to incorporating experimental values into computational models such as the kinetic Monte Carlo method.

Dynamics of surface charge and electric field distributions on basin‐type insulator in GIS/GIL due to voltage polarity reversal

In this study, a simulation model of surface charge accumulation has been established. The model considers three accumulation ways, i.e. electrical conduction within the gas, through insulator volume and along the insulator surface. The generation, diffusion, drift and recombination of charge carriers are also taken into account. Based on it, the influence of polarity reversal, reversal time on surface charge and electric field distribution on a basin-type insulator are studied. The polarity of the surface charges and the direction of the electric field change after the voltage polarity reversal. When the preload voltage is equal to reversal voltage, the surface charge and the electric field distributions at steady state before and after voltage polarity reversal are all the same with opposite sign, and not affected by the reversal time. However, the time to reach the steady state varies with different reversal time. The steady-state surface charge and electric field increased with the rise of reversal voltage. The transient normal and tangential electric field would not exceed the value of the steady state, which means voltage polarity reversal has no additional influence on insulation performance. This research can provide guidance to the design and manufacture of DC GIS/GIL.

Electric field distribution based on radial nonuniform conductivity in HVDC XLPE cable insulation

The steady-state electric field distribution in a polymeric insulated HVDC cable is determined by the electrical conductivity, which is dependent upon the temperature and electric field in homogeneous cable insulation. In practice, the radial inhomogeneity of the morphological structure and crosslinking byproducts in XLPE insulation will lead to a radial nonuniformity of the conductivity, which may further result in the change of electric field distribution in the insulation. In this paper, the conductivity distribution characteristics in XLPE insulation of HVDC cable are investigated at various temperatures and electric stresses. It is found that the difference of conductivity across the insulation is from several times to two orders in magnitude at given temperature and electric stress. Besides, the standard deviation of conductivity indicates that the difference in magnitude is generally larger at lower temperature. Then, the electric field distribution is analyzed at operating and at test voltages with or without load based on above results. A nonuniformity coefficient C E is introduced to characterize the degree of deviation of the actual electric field distribution from the mean electric stress; a distortion rate δ E characterizes the difference of the field distribution based on the radial nonuniform conductivity from the uniform conductivity. It shows that C E and δ E are larger at no load than at full load. Under zero load at 1.85 U 0 , C E and δ E can reach 2.26 and 92.25 %, respectively. The results show that the radial nonuniform conductivity has a significant impact on the electric field distribution in the application of HVDC XLPE cable especially with thick insulation. The effect of conductivity with radial nonuniformity on the modification of field distribution should be considered in the development and the qualification tests for HVDC cables.

Electric field measurements under DC corona discharges in ambient air by electric field induced second harmonic generation

Electric field distribution is critically important for quantitative insights into the physics of nonequilibrium plasma like corona. To analyze the electric field as well as the ion flow (space charge) distribution under DC corona discharges, the ion flow model has been widely adopted; Kaptzov's assumption, which states that the steady state electric field at the conductor surface remains at the corona onset value, serves as a boundary condition. In this Letter, we investigate the electric field distribution under DC corona discharges between coaxial cylindrical electrodes in ambient air by electric field induced second harmonic generation with nanosecond pulse laser beams. The electric field distribution (with or without the corona discharge) is obtained. By comparing the measurements with the results predicted by the ion flow model for the negative corona discharge, it is found that the electric field at the conductor surface is proportional to the current density of the corona discharge with a negative constant of proportionality. Therefore, for negative corona discharges, Kaptzov's assumption is valid only when the discharge current approaches zero or is small.

A Novel Amorphous Selenium Avalanche Detector Structure for Low Dose Medical X-Ray Imaging

A novel amorphous selenium (a-Se) avalanche detector structure for low dose direct-conversion flat-panel X-ray detector is proposed. The proposed structure contains blocking layers to reduce carrier injection from metal electrodes and hole trapping layer to separate X-ray absorption layer from avalanche gain region. The feasibility of the structure for avalanche gain with negligible avalanche noise is studied by using the semiconductor module of COMSOL multiphysics together with a cascaded linear system. The model considers carrier injection from electrodes and charge carrier transport through various layers of multilayer a-Se structure in order to analyze the transient and steady-state electric field distribution across the detector. A cascaded linear system model that includes reabsorption of ${K}$ -fluorescent X-rays, carrier trapping in bulk and trapping layer, and avalanche multiplication of charge carrier is used to calculate the frequency-dependent detective quantum efficiency [DQE( ${f}$ )] and modulation transfer function (MTF) of the proposed structure. The avalanche gain enhances the signal strength and improves the DQE( ${f}$ ) by overcoming the effect of electronic noise at low X-ray doses. The structure is applied for breast tomosynthesis and observed that the proposed structure offers the required avalanche gain to ensure quantum noise limited operation at reduced exposures.

NUMERICAL CALCULATIONS OF THE ELECTRON ENERGY DISTRIBUTION FUNCTION IN (50% SF6 - 50 % Xe) MIXTURE WITH CORRESPONDING TRANSPORT PARAMETERS

We used EEDF software package program to solve Boltzmann equation to calculate the electron energy distribution function in (50% SF6 – 50% Xe) mixture. The calculations are achieved under a steady state electric field using the classical two - term approximation. The electron energy distribution function (EEDF) and the corresponding transport coefficients (mean electron energy, characteristic energy, mobility of electron, diffusion coefficient, and drift velocity) for constant and various electron concentrations are calculated and graphically represented. It is found that variations of electron concentration have a significant effect on transport coefficients of the mixture. The work is in a well agreement with previously experimental and computational researches.

Field measurement and verification of the UHF calibration platform based on the GTEM cell

The measurable electric field of the partial discharge ultra-high-frequency (PD UHF) detection system calibrated by a gigahertz transverse electromagnetic cell (GTEM) has been used as a key indicator to evaluate the performance of the detection system and regarded as the electric power standard. In this study, the sweep frequency and pulse signal were injected to the GTEM cell, and then the waveform and amplitude of the calibrated field strength were calculated by using the transfer function and voltage response of the monopole antennas. In the case of sweep frequency, comparing the measured result of the Narda field strength metre and the calculated result of monopole antennas, the error was found to be <8%, which verifies the correctness of the calibration of the monopole antennas to the steady-state electric field in the GTEM. In the case of pulse injection, comparing the simulation result of computer simulation technology and the calculated result of monopole antennas, the error of the peak of the field strength was found to be 1.7%, which verifies the correctness of the calibration of the monopole antennas to the pulse electric field in the GTEM.

Regularity analysis of the temperature distribution of epoxy impregnated paper converter transformer bushings

The converter transformer epoxy impregnated paper bushing is a multi-media electrical equipment, and the main materials include the internal conductor, the external conductor, transformer oil, SF6 gas, the air inside internal conductor, the main insulation material epoxy impregnated paper, sheath, and fittings. In actual operating, the converter transformer bushing is undertaken by the harmonic current with large number of high harmonics and the temperature distribution of the epoxy impregnated paper converter transformer bushings under actual current waveform needs to be researched. What's more, the temperature distribution of the epoxy impregnated paper converter transformer bushings is affected by several factors and to provide basis for the optimization of bushings it's necessary to research about the impact of these factors on the temperature distribution of the epoxy impregnated paper converter transformer bushings. In this paper, on the basis of our previous paper [8], the 3-D temperature distribution of the 400 kV epoxy impregnated paper converter transformer bushing under actual current waveform with large number of harmonics has been simulated by using the computational fluid dynamics (CFD) and finite element method (FEM) analysis. The temperature distribution regularity of the 400 kV converter transformer bushing under different influencing factors has been computed and analyzed. The dissipation structure of the bushing has been optimized and the DC steady-state electric field distribution of the 400 kV converter transformer bushing has been obtained considering the temperature gradient in epoxy impregnated paper.

Study of virtual cathodes formation during beam-wave interaction in the reltron oscillator

In the present work, a high power microwave oscillator—reltron has been analyzed to investigate the virtual cathode formation mechanism during the beam-wave interaction. In reltron, a side coupled modulation cavity is used as its RF interaction structure containing three metal grids along the longitudinal direction. The space charge current responsible for the virtual cathode and its steady state electric field distribution has been analyzed. Space charge and beam impedance conditions for efficient device operation have been demonstrated. It has been shown that during the beam-wave interaction in the device, first a virtual cathode forms in the post-acceleration gap, and then the second virtual cathode develops between the first and second grids of the modulation cavity. These two virtual cathodes co-exist and cause the formation of a third virtual cathode between the second and third grids. At this instant, only the third virtual cathode remains, and for sustained device oscillation, this process repeats periodically in the device. The present study would be useful in understanding the beam-wave interaction mechanism as well as the design and development of efficient reltron devices.

Comparison of activation energies for the electrical conductivity of silicate glasses obtained by dc and ac techniques

The electrical conductivity of glasses with composition (mol%) 22Na2O·8CaO·65SiO2·5MO2 (M=Si, Ti, Ge, Zr, Sn, Ce) was evaluated by two different experimental methods: low-voltage ac impedance and high-voltage dc resistivity. The ac measurements were carried out by the traditional impedance spectroscopy between 90 and 415°C. In the dc method, a steady-state electric field of about 1MV/m was applied during 5s at temperatures between 100 and 210°C, and the onset current, Io, was measured. Activation energies between 0.71 and 0.81eV were obtained. The differences between the values obtained by the dc and the ac methods are within experimental errors. The high electric field does not influence the concentration nor the mobility of the charge carriers for these experimental conditions and glass compositions. The dc method applied showed to be a suitable alternative to determine the temperature dependence of the electric conductivity of glasses to further calculation of the activation energy.

Enhanced infrared transmission through gold nanoslit arrays via surface plasmons in continuous graphene.

Graphene is a monolayer plasmonic material that has been widely studied in the area of plasmonics and nanophotonics. Combining graphene with traditional plasmonic structures provides new opportunities and challenges. One particular application for nanostructured metals is enhanced optical transmission. However, extraordinary transmission (EOT) is known to have a frequency-selective performance due to size and periodicity of the nanohole arrays. Here, we propose to use a continuous graphene layer to enhance transmission through gold nanoslit arrays at mid-infrared (mid-IR) wavelengths. Although graphene absorbs 2.3% of light, by exciting surface plasmon polaritons (SPPs) at the graphene/gold nanoslit arrays interface, we have theoretically demonstrated enhanced infrared transmission over broad range of wavelengths in the mid-IR region. Our analyses of the effects of various structure parameters on the transmittance spectra shows that surface plasmon polaritons excited at the graphene/metal interface is responsible for enhanced transmission behavior. Moreover, calculated steady-state electric field distribution supports our predictions. Our work opens new directions to study 2D plasmonics using a continuous graphene film without the need of structuring it and also employs the broadband optical response of graphene to enable broadband extraordinary transmission enhancement.

Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.