Non-uniform Electric Field Research Articles

Thin Luminous Tracks of Particles Released from Electrodes with A Small Radius of Curvature in Pulsed Nanosecond Discharges in Air and Argon

Features of the nanosecond discharge development in a non-uniform electric field are studied experimentally. High spatial resolution imaging showed that thin luminous tracks of great length with a cross-section of a few microns are observed against the background of discharge glow in air and argon. It has been established that the detected tracks are adjacent to brightly luminous white spots on the electrodes or in the vicinity of these spots, and are associated with the flight of small particles. It is shown that the tracks have various shapes and change from pulse to pulse. The particle tracks may look like curvy or straight lines. In some photos, they can change their direction of movement to the opposite. It was found that the particle’s track abruptly breaks and a bright flash is visible at the break point. The color of the tracks differs from that of the spark leaders, while the bands of the second positive nitrogen system dominate in the plasma emission spectra during the existence of a diffuse discharge. Areas of blue light are visible near the electrodes as well. The development of glow and thin luminous tracks in the gap during its breakdown is revealed using an ICCD camera. Physical reasons for the observed phenomena are discussed.

Bridging Characteristics of Cellulosic Particles in Flowing Transformer Oil

The flow of contaminated transformer oil has a significant influence on the formation of bridges composed of impurity particles and in turn affects its breakdown progress, but the relevant phenomenon may be not well interpreted by the classical suspended solid particle mechanism. In this paper, an oil circulation device was built, and the development of cellulosic bridges in slightly non-uniform electric field at different flow velocities was recorded by a high-speed camera. The results show that, when DC voltage was applied, the time required to form cellulosic bridges across the oil gap (named complete bridge) firstly decreased and then increased with the rise of flow velocity. It indicates that the low-speed oil flow could accelerate the formation of complete bridge in the DC field while the high-speed oil flow delays or prevents it. When AC voltage was applied, the length of the longest partial bridge (it did not bridge two electrodes) and the number of cellulose particles accumulated in the gap both increased first and then decreased with the rise of flow velocity. Finally, the results were analyzed according to the force conditions of particles. This paper contributes to understanding the effect of oil flow on bridging characteristics of cellulose particles and lays the foundation for the subsequent studies of breakdown mechanism about flowing contaminated liquid dielectrics.

Space Charge Characteristics of Electrothermally Aged Oil-Paper Insulation Under Slightly Nonuniform Electric Field

To study the change characteristics of space charge in oil paper insulation under a slightly non-uniform electric field and a uniform electric field, the existing space charge measuring device was improved, and sphere–plate and column–plate electrode models were prepared. Oil paper insulation samples at different aging stages were obtained via electrothermal aging. The real-time waveforms of the space charge distribution in the samples at different aging stages were measured in the process of polarization with a direct-current (DC) voltage and depolarization with a DC voltage, and the effects of different electric-field types on the charge distribution and motion characteristics of oil paper insulation samples at different aging stages were examined. The results indicated that the existence of a slightly non-uniform electric field accelerated the change in the charge-density peak at the interface and increased the fluctuation range of the charge-density curve in the process of applying a DC voltage. With the aggravation of electrothermal aging, the amount of charge injected into the sample increased, and the slightly non-uniform electric field intensified this process, affecting the accumulation and dissipation of space charge in the sample. Electrothermal aging increased the trap distribution density and energy-level depth. However, for an oil paper insulation sample at the same aging stage, compared with the uniform electric field, the slightly non-uniform electric field had no obvious effect on the trap energy-level depth, but it increased the amount of trapped charge and changed the trap density distribution in the sample. The results of this study provide a theoretical basis for examining the influence of slightly non-uniform electric fields on the space charge distribution characteristics of oil paper insulation subjected to AC/DC combined electrothermal aging.

Modeling of radio frequency heating of packed fluid foods moving on a conveyor belt: A case study for tomato puree

Computer simulation models were used to study radiofrequency heating of liquid foods moving on a conveyor belt between staggered-through field electrodes of non-uniform electric field distribution. Voltage across the electrodes was estimated using a finite-element model and a one-dimensional model, and these were utilized to simulate heating of tomato puree mixtures of varying dielectric and thermal properties, at various nominal voltages and electrode gaps. The experimental results for volume average temperatures showed good agreement with the outcome of both simulation models. Although the temperature profiles indicate a concentration of heat at the bottom and edges of the bottle, natural convection and the shape of the container helped mitigate heat localization. It was determined that, while simple models could provide accurate volume average temperatures, incorporating convectively enhanced conductivity was necessary to accurately predict temperature distribution. The heating rate was found to decrease with an increase in salt concentration. Industrial relevanceIn-package tunnel pasteurization is preferred over continuous-flow pasteurization for certain commercial products such as carbonated beverages or semi-solid foods of high viscosity. Dielectric heating can be applied in these cases with much lower requirements of floor space, water, and energy, while reducing heat losses and localized overheating. However, the radiofrequency heating of liquid foods has not been extensively studied, especially for in-package thermal treatments. A better understanding of the effect of various processing parameters on temperature distribution and heating rates could support a wider adoption of this technology in industrial processes.

High‐Energy‐Heavy‐Ion Engineering Low‐Tortuosity and High‐Porosity 3D Metallic Electrodes for Long‐Life Lithium Anodes

AbstractLithium metal anodes are the most hopeful candidate for new‐generation energy storage batteries because of their high energy‐density and low electrochemical redox potential. However, the sluggish ion diffusion and nonuniform electric field in lithium anodes hinder their high rate properties and long‐life performance with deep capacities. Here, a highly interconnected 3D metallic Cu&CuAux matrix with both low‐tortuosity (1.3) and ultrahigh porosity (81.5%) is fabricated by using a high energy heavy ion‐tracking method. As a consequence, the 3D metallic Cu&CuAux matrix can highly accelerate the transfer of Li+ and reduce the Li nucleation barrier during the Li deposition process due to its low‐tortuosity and ultrahigh porosity. Furthermore, finite element simulation reveals that the unique 3D Cu&CuAux structure can highly homogenize the electric field and Li‐ion flux as well as decrease the lithium‐ion concentration gradient in Li anodes. As a result, the composite 3D Cu&CuAux‐Li anodes exhibit ultrahigh cycle life more than 2000 h and high rate capabilities. Full cells consisting of the 3D Cu&CuAux‐Li anodes and LiFePO4 cathodes also demonstrate a good capability and stable cycle life up to 200 cycles.

Particle motion and drift in non-uniform electric fields

This paper analyzes the two-dimensional motion of a charged particle in constant mutually perpendicular electric and magnetic fields. The magnetic field is assumed to be uniform, and the electric field components are assumed to be linear functions of the Cartesian coordinates. Under these assumptions, the equations of particle motion can be solved analytically. This solution is used to study the stability of particle motion and to assess the accuracy of the guiding center approximation in the presence of electric field gradients. It is well known that if the gradient of a one-dimensional electric field is sufficiently large, the motion of the charged particles becomes unstable and the particles are effectively energized by the electric field. This paper, however, demonstrates that the instability threshold depends on the spatial derivatives of both electric field components and is, under certain conditions, very sensitive to both. The analytical solution is averaged over the gyroperiod to derive simple expressions for the drift speed and the position of the gyrocenter, which explicitly account for the electric field gradient. The results of this averaging are used to develop equations for tracing the particle gyrocenter location, which incorporate the effects of non-uniformity of the electric field. These equations are shown to be noticeably more accurate than those based on the standard E × B drift velocity, which is exact only for uniform electric and magnetic fields. Simple expressions for the local errors in the E × B drift velocity are also derived, which arise from the electric field gradients.

Monte Carlo simulation of ion kinetics in nitrogen and oxygen plasmas under non-uniform electric field conditions

The kinetics of N4+ and O− ions was numerically studied in nitrogen and oxygen plasmas in a highly non-uniform electric field. Mean ion energy and reaction rate coefficients in a background gas at pressures from 1 to 10 Torr were calculated through a Monte Carlo simulation. The ion characteristics followed the local reduced electric field at high pressures, whereas nonhydrodynamic effects leading to a nonlocal dependence of the mean ion energy and rate coefficients on the field were obtained at low pressures. As a result, the rates of N4+ ion dissociation, electron detachment from O− ions, and charge exchange in collisions between O− and O2 lagged the local field value. The non-local effect on the ion rate coefficients was more profound when the field decreased in space. We suggested a simplified method of describing ion rates in spatially varying electric fields on the basis of the Monte Carlo simulation of these rates for uniform electric field conditions and mean ion energy calculations in non-uniform fields. This method is similar to the local-mean-energy approximation utilized for describing electron swarm parameters in varying electric fields. The results of the simplified method were compared with the results of the direct Monte Carlo simulation.

Three-dimensional lab-on-a-foil device for dielectrophoretic separation of cancer cells.

A simple, low-cost, three-dimensional (3D) lab-on-a-foil microfluidic device for dielectrophoretic separation of circulating tumor cells (CTCs) is designed and constructed. Disposable thin films are cut by xurography and microelectrode array are made with rapid inkjet printing. The multilayer device design allows the studying of spatial movements of CTCs and red blood cells (RBCs) under dielectrophoresis (DEP). A numerical simulation was performed to find the optimum driving frequency of RBCs and the crossover frequency for CTCs. At the optimum frequency, RBCs were lifted 120µm in z-axis direction by DEP force, and CTCs were not affected due to negligible DEP force. By utilizing the displacement difference, the separation of CTCs (modeled with A549 lung carcinoma cells) from RBCs in z-axis direction was achieved. With the nonuniform electric field at optimized driving frequency, the RBCs were trapped in the cavities above the microchannel, whereas the A549 cells were separated with a high capture rate of 86.3%±0.2%. The device opens not only the possibility for 3D high-throughput cell separation but also for future developments in 3D cell manipulation through rapid and low-cost fabrication.

Cable Coupling Characteristics of Wireless Network Convergence Nodes by Transient Electromagnetic Fields in Intelligent Substations

Switching operations in intelligent substations generate a wide range of extremely strong and asymmetric transient spatial electromagnetic fields, and this complex transient electromagnetic field can have a coupling effect with the wireless network sink node equipment cables. We conducted a study on the networking method of wireless network equipment in smart substations and analyzed the types of sink node cables used. In the GIS room of the 110 kV GIS smart substation, the transient spatial electromagnetic field generated by switching operation and the transient induced current of the sink node cable under different operating conditions were tested and obtained, and the time domain and frequency domain comparative analysis was performed. A near-field coupling model of the asymmetric and non-uniform cable transient spatial electric field at the sink node is established, and the validity of the model is verified by comparing and analyzing the measurement and simulation results. The results of the study can provide a reference for transient electromagnetic disturbances in 110 kV GIS intelligent substations and contribute to improving the reliability of wireless network equipment operation.

EHD augmented heat transfer during upward bubbly flow boiling for low to medium frequency AC electric fields

The effect of a non-uniform AC electric field on the flow regime and heat transfer performance of upward flow boiling has been investigated experimentally using HFE-7000 as the working fluid in a tubular transparent heat exchanger. The non-uniform electric field was established by a concentric electrode connected to a high-voltage power supply and an Indium Tin Oxide (ITO) film on the tube outer wall. High-speed videography was employed to visualize the flow regimes. The experiments were performed for the initially bubbly flow regime and inlet pressure of 1.2 bars, subcooling of 2 K, and mass flux of 100 kg/m2s. Of key interest is the influence of low to medium AC frequency, which was varied between 1 Hz ≤ f ≤ 100 Hz for a square waveform of 10 kV peak-to-peak amplitude. One very striking observation was the strong electrophoretic interaction with the phases. At lower frequencies, the electrophoretic force interaction was clear from bubbles being attracted to the electrode, opposite to the direction of the dielectrophoretic force. For heat fluxes up to 10 kW/m2, the initially bubbly flow heat transfer coefficient was enhanced up to 3.5-fold and optimal frequency of f = 10 Hz. This research underpins enhancement and potential solid-state control of vertical two-phase heat exchangers, as well as two-phase heat exchangers in microgravity conditions, where similar flow regimes exist.

Giant flexoelectric effect with liquid crystal dimer CB7CB between concentric cylinders

ABSTRACT Liquid crystal dimer CB7CB (1″,7″-bis(4-cyanobiphenyl-4′-yl)heptane) is confined between two concentric cylinders with the liquid crystal director initially aligned axially along the concentric cylinder. When a non-uniform radial electric field perpendicular to the concentric cylinder axis is applied, the director is gradually changed as the applied voltage increases. We obtain a threshold voltage analytical formula for the angular deformation of the director between two concentric cylinders. In addition, the effect of different flexoelectric coefficients on the deformation of the director between two concentric cylinders under the radial electric field was also investigated. The results show that the flexoelectric coefficients will determine how the director will be deformed. It provides a more accurate theoretical analysis for predicting the coupling effects of dielectric effect and giant flexoelectric effect on the director orientation distribution between two concentric cylinders under a non-uniform radial electric field.

Effects of light size and intensity on photoconductive effect-based optically-induced dielectrophoresis for three-dimensional manipulation

This study aims to study the effect of light size and intensity on photoconductive effect-based optically-induced dielectrophoresis (ODEP) for three-dimensional manipulation of cells. HL-7702 cells and SMMC-7721 cells in sucrose solution were manipulated three-dimensionally by ODEP. We found that the ODEP force generated by the three-dimensional non-uniform electric field will form a three-dimensional space, and the positive ODEP force will attract the cells near the space into it. When the number of cells is large, the three-dimensional stacking phenomenon will occur, that is, the three-dimensional assembly of cells. When the size of the light spot is similar to that of the cell, the projector with weak light intensity can only manipulate a single cell, while the laser with higher light intensity can carry out cell three-dimensional assembly. When the light intensity is similar, the larger size of light can produce larger a three-dimensional assembly space. So the cell three-dimensional manipulation by ODEP is achieved only when the photoconductive effect induced by the light pattern reaches the required intensity. The three-dimensional manipulation of cells by ODEP is from plane to stereo, and its realization is related to the light size and the photoconductive layer resistance determined by light intensity. And the three-dimensional space of assembling cells is related to the light size and intensity, and the larger and stronger the light, the larger the space.

Continuous Flow Separation of Red Blood Cells and Platelets in a Y-Microfluidic Channel Device with Saw-Tooth Profile Electrodes via Low Voltage Dielectrophoresis

Cell counting and sorting is a vital step in the purification process within the area of biomedical research. It has been widely reported and accepted that the use of hydrodynamic focusing in conjunction with the application of a dielectrophoretic (DEP) force allows efficient separation of biological entities such as platelets from red blood cell (RBC) samples due to their size difference. This paper presents computational results of a multiphysics simulation modelling study on evaluating continuous separation of RBCs and platelets in a microfluidic device design with saw-tooth profile electrodes via DEP. The theoretical cell particle trajectory, particle cell counting, and particle separation distance study results reported in this work were predicted using COMSOL v6.0 Multiphysics simulation software. To validate the numerical model used in this work for the reported device design, we first developed a simple y-channel microfluidic device with square "in fluid" electrodes similar to the design reported previously in other works. We then compared the obtained simulation results for the simple y-channel device with the square in fluid electrodes to the reported experimental work done on this simple design which resulted in 98% agreement. The design reported in this work is an improvement over existing designs in that it can perform rapid separation of RBCs (estimated 99% purification) and platelets in a total time of 6-7 s at a minimum voltage setting of 1 V and at a minimum frequency of 1 Hz. The threshold for efficient separation of cells ends at 1000 kHz for a 1 V setting. The saw-tooth electrode profile appears to be an improvement over existing designs in that the sharp corners reduced the required horizontal distance needed for separation to occur and contributed to a non-uniform DEP electric field. The results of this simulation study further suggest that this DEP separation technique may potentially be applied to improve the efficiency of separation processes of biological sample scenarios and simultaneously increase the accuracy of diagnostic processes via cell counting and sorting.

Investigation of droplet pairs’ movement under the electric field generated by matrix electrodes

Electric dehydration technology has gained lots of attention as an oil-water separation technology that has only been around for a short time. Many research scholars have studied the laws of droplet motion in electric fields. However, previous research on the droplet motion law in a non-uniform electric field has only focused on the single droplet, ignoring the dipole-dipole interaction between droplets, which plays an important role in the droplet coalescence process. In this paper, the motion of droplet pairs in a non-uniform matrix electric field is studied by means of theoretical analysis and numerical simulation. A mathematical model of the migration velocity and coalescence time of droplet pairs was established. The results show that the migration velocity of droplet pairs under dielectrophoresis and dipole-dipole interactions is significantly greater than that of single droplets and that the droplet velocity is related to the electric field strength, continuous phase viscosity, droplet diameter, and droplet pair center distance. This study increases our understanding of droplet electrocoalescence kinetics, enriches the electrocoalescence mechanism of droplets under non-uniform electric fields, and provides a basis for the design of subsequent electrodehydration equipment.

Insulation Characteristics of HFO-1336mzz(E) and Its Mixtures as Eco-Friendly Alternatives to SF6 for Medium-Voltage Switchgears

HFO-1336mzz(E) is considered a potential eco-friendly insulating gas, with a low global warming potential and high dielectric strength. This study investigates the insulation properties of HFO-1336mzz(E) and its mixtures with CO2 or dry air to evaluate their feasibility as eco-friendly alternatives to sulfur hexafluoride (SF6) for medium-voltage switchgears. The physicochemical properties of HFO-1336mzz(E) were first introduced and its saturated vapor pressure characteristics were analyzed to determine the optimal mixing ratio to meet the minimum operating temperature requirement for applications. Then, direct current (dc) and lightning impulse (LI) breakdown tests were conducted under uniform and nonuniform electrical fields. Under uniform fields, the dielectric strength of pure HFO-1336mzz(E) is approximately 1.6–1.8 times higher than that of SF6. For HFO-1336mzz(E)/CO2 and HFO-1336mzz(E)/air mixtures, equivalent dielectric strength of SF6 can be reached when the volume fraction of HFO-1336mzz(E) is around 40%. The synergy in HFO-1336mzz(E)/air is better than that in HFO-1336mzz(E)/CO2. Based on the breakdown results under nonuniform fields, the HFO-1336mzz(E) and its mixtures are more sensitive to the field inhomogeneity than SF6. This is also verified by the partial discharge (PD) experiment, which shows that HFO-1336mzz(E) mixtures exhibit lower PD inception voltage (PDIV) and more PD activities under the same condition.

New Insight Into Total-Ionizing-Dose Effect-Induced Breakdown Voltage Degradation for SOI LDMOS: Irradiation Charge Field Modulation

In this article, the concept of irradiation charge field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> ) is proposed to provide a new insight into total-ionizing-dose (TID) effect-induced breakdown voltage (BV) degradation for high-voltage silicon-on-insulator (SOI) lateral double-diffused metal–oxide-silicon (LDMOS). A unified explanation on TID-induced BV degradation is given that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> exerts modulation on net electric field, changing the relationship between lateral BV (BVL) and vertical BV (BVV). <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> would weaken electric field at silicon side of silicon/buried oxide interface and enhance that at oxide side, resulting in BVV increasing monotonously. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> would also weaken surface electric field at drain side and enhance that at source side, resulting in BVL changing with two potential trends: monotonic descent and nonmonotonic descent, corresponding to different initial surface breakdown points. Eventual BV degradation is determined by the combined result of BVV and BVL changing. Based on the new insight, a radiation hardening design strategy is proposed. Nonuniform initial surface electric field distribution with single drain peak is pursued, breaking the conventional optimization principle. Nonmonotonic descent of BV is achieved to enhance TID tolerance and verified by the developed 80-V SOI LDMOS with the proposed radiation hardening strategy.

Formation of plasma density cavities caused by nonuniform stochastic electric fields

The effect of depletion of the density of ions and electrons and the formation of a spatial cavity in a plasma-like medium due to inhomogeneous stochastic electric fields is considered. This effect is caused by collisions of charged plasma particles with random fluctuations of inhomogeneous electrostatic turbulence, as a result of which the particles are pushed out of the region with an increased level of fluctuations. To determine the final stationary distribution of the plasma density, the Fokker–Planck equation is used, the coefficients of which are determined from the equation of motion of particles in a stochastic electric field.

Uniform Action of Plasma of a Nanosecond Pulsed High-Voltage Discharge on the Surface of a Flat Anode

The results of an experimental study of the effect of a plasma of a nanosecond pulsed high-voltage discharge in air at atmospheric pressure, excited in a sharply nonuniform electric field, on the surface of a flat-grounded electrode are presented. It is shown that at relatively large interelectrode distances between the pointed cathode and the flat anode, a diffuse discharge is implemented, which ensures a uniform action of the discharge plasma on the anode surface.

Experimental Study on Response of Non- and Externally-Gapped Metal-Oxide Arresters Excited by Nanosecond-Level Transient Electromagnetic Disturbances

Metal-oxide arresters (MOA), including the non-gapped MOAs (NG-MOA) and externally-gapped MOAs (EG-MOA), are the main equipment applied to protect the power system against conducted transient electromagnetic disturbances (TED). However, MOAs exhibit quite different electrical characteristics under microsecond-level and nanosecond-level transients. In order to figure out the response of MOAs under nanosecond-level TED, experimental platforms are built which contain a pulse generator with the amplitude of pulse current adjustable from 0 kA to 5 kA and the rise time of 20 ns. Then the dynamic hysteresis loops, the static V-I characteristics, the response time delay and the full response process of five types of 10-kV MOAs are investigated. From the dynamic hysteresis loops of NG-MOAs, the impedance conversion process can be seen clearly and can be explained by the grain-boundary theory. But EG-MOAs has not this conversion process due to the air-gap. And the experimental results demonstrate that there is no noticeable nanosecond-level conduction delay on NG-MOAs whereas the electric field non-uniformity of the air-gap has a significant influence on the time delay of the EG-MOAs. The response time delay of EG-MOAs changes ranging from tens of nanoseconds to hundreds of nanoseconds. This feature makes EG-MOAs more likely to raise insulation risks under nanosecond-level TED compared with NG-MOAs.

Corona Discharge Behaviors with Presence of Floating Electrode in Air Insulation using Numerical Model Analysis

This paper deals with numerical analysis method for analyzing the partial discharge behaviors in terms of corona discharge in the presence of a floating electrode under lightning impulse voltage. To analyze the corona discharge behaviors at 0.5 mm short electrode gap system as basic research work between main conductor and floating electrode, we considered fully coupled numerical model based on the charge continuity equations for positively charged ion, negatively charged ion and free electrons. Poisson’s equation is coupled with hydro-dynamic drift-diffusion equations derived from the three kinds of charge continuity equation. Fowler-Nordheim field emission is assumed that the electron emission by electric field is used as boundary conditions for main conductor and floating electrode. As a results, it is found that the floating electrode creates a non-uniform electric field distribution with a large field enhancement, causing ionization to initiate corona discharge. In other words, floating electrode is early corona discharge inception by collecting the induced charge developed by high voltage electrode. This result is expected to be applicable to various corona discharge generating systems as well as insulation design of power apparatus with presence defects such as a floating metal particle under lightning impulse voltage.