Spatial Distribution Of Electric Field Research Articles

Finite element simulation of hybrid microwave sintering based on power approach

Microwave (MW) sintering offers higher heating rate, rapid processing, reduced energy consumption, and reduced sintering temperature. However, the technique is not fully understood, difficult to control, and often relies on experience and trial-and-error approach. Consequently, hot spots, uneven heating, thermal runaway, and shape distortion develop in sintered compacts. Therefore, developing a model that can simulate the sintering process, enhance predictability, and determine the critical sintering conditions is essential. Multiphysics finite element (FE) modelling of hybrid MW sintering of a magnesium alloy AZ61 compact was undertaken in this study. The FE model coupled the electromagnetic, heat conduction, and densification equations. The model utilised parameters related to the furnace, compact, and susceptor to predict the spatial distribution of electric field, thermal response, and densification in the compact. A power-based sintering criterion was developed to predict the sintering of the compact and estimate its critical sintering energy. Modelling results showed that heating time, compact size, and thickness of the susceptor are critical to the sintering process. It was also shown that the susceptor not only mediated the sintering of the compact but also homogenised its temperature and densification. Thus, MW sintering of the compact was predicted to occur at 500 °C for 8 to 10 min with a predicted relative density of about 0.98. Experimental MW sintering data showed good concurrence with the developed model. These results are useful for controlling the MW sintering process, eliminating trial-and-error, and determining the critical sintering conditions.

Effects of the dynamic cathode sheath on electron transport at the initial period of HiPIMS pulse studied by Langmuir probe measurements and 2D PIC-MCC simulation

In high power impulse magnetron sputtering (HiPIMS) discharge, the cathode sheath is a particularly vital section which determines the spatial distribution of electric field and the energy and transport of charged particles. In this work, a single Langmuir probe is employed to explore the effects of dynamic cathode sheath on electron transport at the initial period of HiPIMS pulse. Measurements show that the electron temperature is as high as ~20 eV and the plasma density is much lower than ~1015–1016 m−3 at the beginning of HiPIMS pulse t < 3 μs; correspondingly, a feature of small low-energy amplitude and extended high-energy tail is found in the electron energy distribution function (EEDF). And the high-energy electrons can escape the magnetic trap and gradually diffuse to further axial positions, even to z = 140 mm with only several microseconds delay. The diffusion coefficient of electrons D⊥ is larger than the typical Bohm diffusion at z > 32 mm in our discharge case. The two-dimension Particle-in-cell Monte Carlo collision (2D PIC-MCC) simulation results are well in agreement with the experimental results. The net positive charge density ∆n near the target is lower than ~+9.2×1014 m−3 at t = 0.5 μs, and the charge separation is up to ~0.4. In this case, the cathode sheath has a large thickness and the axial electric field EZ outside the sheath is as strong as dozens of 10 kVm−1. The simulation results confirm, for the case of the expanding sheath, (i) the electrons can be accelerated and escape the magnetic trap with weak constraint; (ii) the electron group can maintain their kinetic energy when they diffuse from the ionization region (IR) to bulk plasma (BP). When the net charge density increases to ~+3×1016 m−3 at t = 2.5 μs, the sheath thickness is condensed to ~1 mm with ~600 V voltage drop.

Numerical Study of Negative Corona Discharge Characteristics at Different Electrode Gap Spacing

Atmospheric pressure needle-to-plane negative corona discharges have been studied considering the effect of photoionization in electrode gap spacing from 2.9 to 3.9 mm. Trichel pulses, spatial distributions of electron density and electric field, pulse duration time, and pulse frequency under different gap spacing were investigated in this work. It is found that peak value and duration time of the first Trichel pulse decrease with the increase of gap spacing. The movement of charged particles is faster in narrow gap spacing, which leads to higher pulse frequency. Moreover, the effect of photoionization on negative corona discharge under different gap spacing is also studied by numerical simulation. It is found that electric field, as well as electron density, is weakened due to the effect of photoionization. Besides, the magnitude of Trichel pulses, duration time of the first pulse, and pulse frequency are relatively small when taking the effect of photoionization into consideration. These results are of great importance to fully understand the mechanism of negative corona discharge under different conditions.

Modeling the dependence of the negative corona current density on applied voltage rise time

In this paper, a numerical simulation is used to investigate the influence of applied voltage rise time on negative corona current characteristics in SF6 at atmospheric pressure. There were 23 particle species and 67 kinds of reactions considered in plasma chemical reactions. The influence of different rise times of the applied voltage is investigated. The spatial distributions of the radial electric field and total density of electrons and positive and negative ions, at and after the inception time of the corona current pulse, are used to explain the role of the rise time of the applied voltage on the mechanism of corona current pulse formation. It is found that the corona inception time, inception voltage, peak value of current pulse, number of sub-current pulses, and the time between the sub-pulses are strongly affected by the movement of negative ion clouds produced by the attachment. The quantitative analysis of the negative ions shows that the light ions preceded the heavy ions in their motion far away from the cathode and that this motion is governed by the rise time of the applied voltage.

Innovative Stochastic Modeling of Residential Exposure to Radio Frequency Electromagnetic Field Sources

This study focused on the assessment of radio-frequency electromagnetic fields (RF-EMF) exposure in a realistic apartment due to the presence of a WiFi source deployed in uncertain position. In order to describe the 2D spatial distribution of electric field induced in the whole apartment for whatever position of the WiFi source, an innovative approach that combines Principal Component Analysis (PCA) and Gaussian process regression (Kriging method) was applied. The 2D surrogate model was used to investigate the exposure in three different usage scenarios of the WiFi sources, i.e. surfing to a new web site, using a Skype video call and watching a You Tube video at 1080p, evaluating the electric field E induced at each location of the apartment for 10,000 different positions of the source. Across all the examined conditions, we found E values distributions with median values in the range 2.2–96.1 mV/m and 90th percentiles in the range 4.9–209.3 mV/m. The 2D surrogate model allowed obtaining a complete statistical description of the exposure for any positions of the WiFi source in the apartment, with a computational effort equal to about 10% of the one needed by using only the WiCa Heuristic Indoor Propagation Prediction (WHIPP) network planner

In situ electric field driven assembly to construct adaptive graded permittivity BaTiO3/epoxy resin composites for improved insulation performance

The applications of dielectric functionally graded materials in high-voltage systems have emerged as a potential strategy to obtain superior insulation performance in recent years. However, the existing preparation methods mainly rely on simple lamination or centrifugal force intervention, and cannot adapt to the complex electric field spatial distribution. In this work, we developed low partial discharge (PD), high flashover voltage barium titanate/epoxy resin (BT/ER) insulation composites with graded permittivity, which were assembled by the in situ electric field. Our approach involves (a) the migration and deposition of BT in high electric field strength regions, driven by in situ electrophoretic forces in the BT/ER suspension (dispensable), (b) the alignment of BT in high electric field strength regions, driven by in situ dielectrophoretic forces in the BT/ER suspension, and (c) the “freezing” of the composite structure by curing. The insulation performance of the samples after this electric field structuring was assessed by PD measurements and flashover tests. The PD of the samples with 2.0 vol% BT and electric field treatment was significantly reduced, and the flashover voltage was increased by 31.8% compared with the pure ER sample. Optical microscope images, scanning electron microscope (SEM) images and finite element simulations also verify that this type of electric field structuring can effectively reduce the electric field non-uniform coefficient. We believe that the strategy of electric field assembly to prepare graded permittivity materials (GPMs) is promising candidate for high performance insulation applications.

Численный метод нахождения пространственных распределений водородного показателя и электрического поля в жидких электродах

Численный метод нахождения пространственных распределений водородного показателя и электрического поля в жидких электродах

Numerical simulation of multiple-current-pulse dielectric barrier discharge with ring electrodes in helium at atmospheric pressure

A two-dimensional fluid model was used to investigate the characteristics of a multiple-current-pulse dielectric barrier discharge (DBD) equipped with ring electrodes in helium at atmospheric pressure. The simulation results show that the discharge at peak moment follows the Townsend mode in the DBD with two current pulses in each half cycle. However, when there are three or four current pulses in each half cycle, the discharge mode at the first current peak transforms to the glow mode. Additionally, for the first and third current pulse, the breakdown first occurs in the radial center of the ring electrodes. But for the discharge in the second and fourth current pulse, it ignites from the periphery of the ring electrodes. Moreover, the discharge structure, i.e., the radial spatial distributions of current density, electron density, and electric field at peak moments, shows a feature of alternation between (1) higher current density, electron density, and electric field locating in the radial center of ring electrodes (center-advantage) and (2) higher current density, electron density, and electric field locating in the periphery of ring electrodes (periphery-advantage). This behavior is attributed to the fact that non-uniform surface charge accumulation during the previous discharge has different effects on the electric field in the gas gap in the subsequent discharge.

Edge-Termination Technique for High-Voltage Mesa-Structure 4H-SiC Devices: Negative Beveling

The prospects for the protection of high-voltage 4H-SiC-devices from edge breakdown via the formation of mesa structures with inclined walls (negative beveling) are considered. Numerical simulation of the spatial electric-field distribution in high-voltage (~1500V) reverse-biased mesa-epitaxial p+–p–n0–n+ 4H-SiC diodes is performed. It is shown that negative beveling with small angles of less than 10° from the plane of the p–n0 junction makes it possible to reduce severalfold the surface edge electric field as compared to that in the bulk. A combined protection method is suggested as the edge-termination technique for 4H-SiC diodes with a p+–n0–n+ structure, Schottky diodes with an n0 blocking base, and bipolar n+–p–n0 transistors via the implantation of boron along with negative beveling. The possibility of fabricating mesa structures with inclined walls via the photolithography and dry etching of silicon carbide is briefly discussed.

Interaction between spoof localized surface plasmon and terahertz vortex beam

We theoretically and experimentally investigate a method of exciting multipole plasmons, including terahertz dark spoof localized surface plasmon (Spoof-LSP) modes, by using normally incident terahertz vortex beam. The vortex beam with angular intensity profile and phase singularities, has well-defined angular momentum which can be decomposed into the polarization-state-related spin angular momentum (SAM) for characterizing the spin feature of photon, and the helical-wavefront-related orbital angular momentum (OAM) that is characterized by an integer &lt;inline-formula&gt;&lt;tex-math id="Z-20200915102424-1"&gt;\begin{document}$ (l) $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20200695_Z-20200915102424-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20200695_Z-20200915102424-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, called the topological charge. By illuminating terahertz vortex beam on the metallic disk with periodic subwavelength grooves normally, we find that the terahertz dark multipole plasmons can be excited by the terahertz vortex beam carrying different OAM and SAM. We analyze the correspondence between the spin and orbital angular momentum of vortex beam and the excited dark multipolar plasmon modes. In the experiment, a terahertz stepped spiral phase plate (SPP) with high transmission and low dispersion based on the Tsurupica olefin polymer is developed and the stepped SPP can generate a terahertz vortex beam having a topological charge of 1. Then, we further study the excitation of dark multipolar Spoof-LSPs by utilizing the stepped SPP in combination with the near-field scanning terahertz microscopy. The collimated terahertz wave, which is radiated from a 100 fs (&lt;i&gt;λ&lt;/i&gt; = 780 nm) laser pulse pumped photoconductive antenna emitter, is converted into terahertz circular polarized light (CPL) which can carry SAM by the combination of the quarter wave plate and the polarizer, and then terahertz CPL impinges on the stepped SPP, producing the terahertz vortex beam which can carry OAM. The spatial two-dimensional electric field distribution is collected in steps of 0.02 mm along the &lt;i&gt;x&lt;/i&gt;-direction and &lt;i&gt;y&lt;/i&gt;-direction by a commercial terahertz near-field probe which is located close (≈ 10 μm) to the one side of polyimide film by three-dimensional electric translation stage and a microscope (FORTUNE TECHPLOGY FT-FH1080). The experimental results are in good agreement with simulations. We believe that our method will open the way for detailed research on the terahertz physics, plasma and imaging fields.

О защите высоковольтных мезаструктурных 4H-SiC-приборов от поверхностного пробоя: прямая фаска

Abstract The prospects for the protection of high-voltage 4 H -SiC-devices from edge breakdown via the formation of mesa structures with inclined walls (negative beveling) are considered. Numerical simulation of the spatial electric-field distribution in high-voltage (~1500V) reverse-biased mesa-epitaxial p ^+– p – n _0– n ^+ 4 H -SiC diodes is performed. It is shown that negative beveling with small angles of less than 10° from the plane of the p – n _0 junction makes it possible to reduce severalfold the surface edge electric field as compared to that in the bulk. A combined protection method is suggested as the edge-termination technique for 4 H -SiC diodes with a p ^+– n _0– n ^+ structure, Schottky diodes with an n _0 blocking base, and bipolar n ^+– p – n _0 transistors via the implantation of boron along with negative beveling. The possibility of fabricating mesa structures with inclined walls via the photolithography and dry etching of silicon carbide is briefly discussed.

Designing Resonance Microwave Cavities to Optimize Plasma Generation

Methodology for designing the 2.45-GHz microwave (MW) coupling system to optimize the hydrogen plasma density in an electron cyclotron resonance (ECR) plasma reactor is presented. Two different plasma generator systems have been studied by experiments and 3-D simulations to find the criteria to reach an optimized design. The experimental work includes the detailed measurements and calculations of the electron energy distribution functions (EEDF) and ultrafast photography diagnostics to estimate the spatial distributions of plasma unbalanced charge density, potential, and electric field for both cases. It demonstrates that to simulate in 3-D, the distribution of the resonant stationary electric field along the entire MW driver system can be used to improve the design in order to reach higher plasma densities and temperatures.

Polarization Stark spectroscopy for spatially resolved measurements of electric fields in the sheaths of ICRF antenna.

A multichannel spectroscopic diagnostic based on the Stark effect on helium lines was developed and implemented in IShTAR (Ion Cyclotron Sheath Test ARrangement) to measure the spatial distribution of electric fields across the radio frequency sheaths of the ion cyclotron antenna. Direct measurements of the DC electric fields in the antenna sheaths are an important missing component in understanding the antenna-plasma edge interactions in magnetically confined fusion plasmas since they will be used to benchmark theoretical models against real antenna operation. Along with the high-resolution Czerny-Turner monochromator and a detector with an intensifier, the hardware relies on the 2 chained set of linear-to-linear fiber bundles that provide seven optical channels capable of resolving an 8.4 mm region in the vicinity of the antenna's box. The diagnostic is supported with local helium gas puff, enabling it to operate in nonhelium plasmas. Spatially resolved electric field was measured for two discharge configurations, one with and one without the ICRF antenna. The results show a clear difference in the shape of the DC electric field's spatial profile for the two cases studied, with the elevated values when the ICRF antenna was operating. This demonstrates the ability of the diagnostic to measure even small relative changes in the intensity of the electric field.

Tailoring the longitudinal electric fields of high-order laser beams and their direct verification in three dimensions

We demonstrate the tailoring of longitudinal electric fields that arise from tight focusing of spatially phase-shaped high-order laser beams, and verify their spatial distribution in three dimensions. To tailor the three-dimensional (3D) spatial distribution of longitudinal electric fields, we precisely control the relative phase delay between the two lobes of a HG10laser beam using a spatial light modulator (SLM) before tight focusing. To verify the longitudinal electric fields in the focal volume, we employ 3D microscopic mapping of second-harmonic generation (SHG) from a single semiconductor nanowire that is extremely sensitive to the orientation of the longitudinal electric field. The technique is direct, general and expected to be useful in harnessing and in probing longitudinal electric fields with arbitrary spatial intensity distributions in the 3D focal volume.

Mode transitions of a helium dielectric barrier discharge from Townsend, normal glow, to abnormal glow with varying voltage rising time

Transition from a Townsend mode to a normal glow mode has been reported in the literature for uniform dielectric barrier discharge (DBD) at atmospheric pressure. In this paper, through a one-dimensional fluid model, more modes of uniform DBD in helium and transitions between them are found with varying rising time of a saw-tooth voltage. The results indicate that a positive discharge initiates at the positive-slope voltage phase, whose pulse duration decreases, while the peak value increases with decreasing rising time. During this process, a negative discharge initiating at the negative-slope voltage phase keeps weakening to almost zero current. The predominant positive discharge is then investigated through analyzing spatial distributions of electron density, ion density, and electric field at the peak current moment. In combination with the voltage-current curve, discharge modes of DBD are revealed to transit from a Townsend, a normal glow, to an abnormal glow with decreasing voltage rising time. These mode transitions are qualitatively explained by analyzing the gap voltage and electron density averaged in the gap just before discharge initiation. The results also suggest that by reducing the rising time or increasing voltage amplitude, DBD is prone to operate in the abnormal glow mode. Moreover, DBD in the abnormal glow mode has an increasing peak current and a decreasing pulse duration with increasing voltage amplitude. Finally, the critical voltage amplitude is given as a function of voltage rising time for the mode transitions from the Townsend to the normal glow and the normal glow to the abnormal glow.

Influence of pollution on potential and electric field distribution of porcelain insulator in 110kV transmission line

The spatial potential and electric field distribution of clean insulator and insulator with different degrees of pollution in 110kV transmission lines are analyzed with Comsol Multiphysics software. The results show that: The curve connected by the voltage borne by the single piece insulator in the clean insulator string is saddle-shaped. The voltage borne by the high-voltage end and the low-voltage end is large, while the voltage borne by the middle part of the insulator string is small. With the increase of pollution degree, the overall trend of potential distribution remains unchanged, but the higher the pollution degree is, the greater the maximum voltage on the high-voltage side of the insulator will be, and the smaller the minimum voltage on the low-voltage side will be. With the increase of pollution degree, the general trend of electric field distribution around insulator string remains unchanged, but the maximum value of electric field increases.

Experimental study on the effect of spatial distribution and action order of electric field and magnetic field on oil-water separation

Electromagnetic synergistic promotion of emulsion separation is a new oil-water separation technology under the background of interdisciplinary and multi-field coupling. However, the lack of research on the influence of characteristic parameters on separation efficiency limits the development of this technology. In this paper, the effect of the spatial distribution and the action order of electric field and magnetic field on oil-water separation was investigated by using the electromagnetic synergistic oil-water separation experimental system. The experimental results show that the spatial position and action order of electric field and magnetic field have a significant influence on the separation performance, and the separation efficiency is the highest when they are vertically distributed and synchronously operated. The theory of ion enrichment based on electromagnetic synergism was proposed. It is considered that the polarization-electromagnetic force and ion enrichment effect are the main reasons for the higher separation efficiency of emulsion treated by the electromagnetic synergistic field with vertical distribution and synchronization. Among them, the polarization-electromagnetic force affects the dynamic behavior of droplets in the direction perpendicular to the electric field, while the ion enrichment effect affects the distribution of droplets in the electric field and the forces inside and outside the liquid bridge.

Engineering oxygen vacancies by one-step growth of distributed homojunctions to enhance charge separation for efficient photoelectrochemical water splitting

How to limit the recombination of photogenerated carriers is one of the grand challenges for exploring efficient photoelectrochemical (PEC) cells. In the present work, an engineering of oxygen vacancies within photoanodes by constructing distributed homojunctions for enhanced PEC performance is proposed. The distributed homojunctions are attributed to the formed hierarchical layers within the photoanodes, which were accomplished by one-step aqua-regia hydrothermal strategy. It is evidenced that the distributed homojunctions produced an improved spatial distribution of built-in electric field, thus significantly facilitating the charge separation for the PEC cells. As a proof of concept, the assembled WO3 photoanode exhibits a photocurrent density up to 1.81 mA cm−2 at 1.23 V vs. RHE in neutral electrolyte solution under AM 1.5G illumination without any cocatalysts and dopants, which is the state-of-the-art one ever reported.

Stochastic model of dispersive multi-step polarization switching in ferroelectrics due to spatial electric field distribution

A stochastic model for polarization switching in tetragonal ferroelectric ceramics is introduced, which includes sequential 90°- and parallel 180°-switching processes and accounts for the dispersion of characteristic switching times due to a nonuniform spatial distribution of the applied field. It presents merging of the recent multistep stochastic mechanism with the earlier nucleation limited switching and inhomogeneous field mechanism models. The model provides a much better description of simultaneous polarization and strain responses over a wide time window and a deeper insight into the microscopic switching mechanisms, as is exemplarily shown by comparison with measurements on lead zirconate titanate.

The Spatial Distribution of Electric Field as a Unifying Idea in Transmission Line Design

It is shown that the most important electrical design criteria for long (i.e., stability limited) high voltage overhead transmission lines operating at a given voltage are all related to the spatial electric field distribution between phase conductors. Hence, when designing a long transmission line, a change in one design parameter necessarily causes changes in the others. It is shown how an understanding of these relationships can lead to insight into the design and to the tradeoffs that must be made in designing these transmission lines. More specifically, a more spatially uniform electric field implies an increased power capacity for long transmission lines but also reduces the critical flashover voltage and increases the capacitance per unit length.