Electric Current Density Distribution Research Articles

Nonparametric Statistics on Magnetic Properties at the Footpoints of Erupting Magnetic Flux Ropes

It is under debate whether the magnetic field in the solar atmosphere carries neutralized electric currents, in particular, whether a magnetic flux rope (MFR), which is considered the core structure of coronal mass ejections, carries neutralized electric currents. Recently Wang et al. (2023) studied magnetic flux and electric current measured at the footpoints of 28 eruptive MFRs from 2010 to 2015. Because of the small sample size, no rigorous statistical analysis has been done. Here, we include nine more events from 2016 to 2023 and perform a series of nonparametric statistical tests at a significance level of 5%. The tests confirm that there exist no significant differences in magnetic properties between conjugated footpoints of the same MFR, which justifies the method of identifying the MFR footpoints through coronal dimming. The tests demonstrate that there exist no significant differences between MFRs with preeruption dimming and those with only posteruption dimming. However, there is a medium level of association between MFRs carrying substantial net current and those producing preeruption dimming, which can be understood by the Lorentz self-force of the current channel. The tests also suggest that in estimating the magnetic twist of MFRs, it is necessary to take into account the spatially inhomogeneous distribution of electric current density and magnetic field.

Features of distribution of electric field strength and current density in the reactor during treatment of liquid media with high-voltage pulse discharges

Purpose. Development and use of a mathematical model of the stages of formation of high-voltage pulse discharges in gas bubbles in the discharge gap «rod-plane» to identify the features of the electric field intensity distribution in the reactor and determine the current density in the load during disinfection and purification of liquid media by high-voltage pulse discharges and find the most rational treatment. Methodology. To achieve this goal, we used computer modeling using the finite element method as a method of numerical analysis. An experimental reactor model was created that takes into account the dynamics of discharges in gas bubbles in water. The equations describing the system include the generalized Ampere equation, the Poisson equation and the electric displacement equation, taking into account the corresponding initial and boundary conditions, as well as the properties of materials. The dependence of the potential of a high-voltage electrode on time has the form of a damped sinusoid, and the specific electrical conductivity in a gas bubble is a function of time. Processes occurring at the front of the voltage pulse from 0 to 20 ns are considered. Results. It is shown that with an increase in conductivity and high-voltage potential to amplitude values in a gas bubble, the electric field strength in the water layer in the reactor reaches 70 kV/cm, and it is in the water layer that there is a strong electric field. The calculations show that already by 19th ns the density of conduction currents in water prevails over that of displacement currents. At the same time, additional inclusions in the water significantly affect the distribution of electric field strength and current density, creating a significant difference in their values at the boundaries of the interface between the bubble, conductive element and water. Originality. A simulation of the dynamics of transient discharge processes in a gas bubble and a layer of water with impurities was carried out, including an analysis of the distribution of the electric field strength and current density in a system with rod-plane electrodes in the phase transition section of a gas bubble-water. This approach allows us to reveal the features of processes in reactors and to investigate the influence of phase transitions on the distribution of electrophysical quantities. Practical value. Computer simulations confirm the prospect of using nanosecond discharges generated in gas bubbles within a volume of water for widespread industrial use and are of great interest for further experimental and theoretical research. References 25, figures 9.

A numerical study on effects of current density distribution, turbulence, and magnetohydrodynamics (MHD) on electrolytic gas flow with application to alkaline water electrolysis (AWE)

A three-phase Eulerian model is proposed to investigate the induced flow due to the generation of gas bubbles between two parallel plates without forced convection with application to alkaline water electrolysis (AWE). Earlier models, assuming a laminar regime, accurately predicted the multiphase flow near electrodes but struggled to calculate bulk liquid electrolyte flow away from them. Herein, we study the influences of electric current density distribution, turbulence effects, and the interaction between flow and the magnetic field known as magnetohydrodynamics (MHD). Based on our modeling results, the traditional method using an averaged uniform current density along electrodes (e.g. here 2000 A m−2) is feasible, as incorporating calculated non-uniform current distribution minimally affects the multiphase velocity field. The Lorentz force, originating from flow interaction with the (self-induced) magnetic field, is negligible compared to forces like drag or bubble dispersion. Consequently, MHD effects only become relevant upon introducing an external magnetic field. Including turbulence in the model, being minor in magnitude but non-negligible, significantly improves the predicted velocity profile. Modeling results are validated against an experiment.

Enhancing the circular dichroism of chiral dielectric nanostructure through the addition of a symmetric Au cylinder

Circular dichroism (CD) spectra play a crucial role in recognition, separation and detection of chiral molecules. Due to the inherent weak CD response of natural chiral molecules, researchers have endeavored to enhance CD signals through various artificial nanostructures. In this study, combining the advantages of both the dielectric and metal materials, we propose a hybrid dielectric-metal nanostructure consisting of a chiral Si nanorod dimer coupled with a symmetric Au cylinder to achieve robust CD responses. Owing to the plasmon resonance of the Au cylinder, the scattering-CD and absorption-CD of the hybrid system have been enhanced, which result in the enhanced extinction-CD response. Furthermore, the distributions of electric field, magnetic field and displacement current density of both the Si dimer and hybrid nanostructure have been meticulously crafted to elucidate the physical mechanisms underlying amplified CD signals. The synergistic coupling between the magnetic fields of dielectric materials and the electric fields of the Au cylinder leads to an increase in the electric field strength and the asymmetry of near-field distributions. Additionally, spatial overlaps between electric and magnetic fields occur. These factors contribute to the enhanced chiral response of the hybrid system. Meanwhile, the CD signal can be flexibly tuned by adjusting the size of the Au cylinder and Si nanorods. This design offers a versatile approach to enhancing the chiral response of dielectric nanostructures.

Rayleigh analysis and numerical simulations of metal-mesh/ transparent conducting oxide composite transparent electrode

Transparent conducting oxides (TCOs), especially indium tin oxides (ITOs), have played an important role in realizing optoelectronics devices. Composite electrodes fabricated by introducing different types of metal-meshes into TCO have exhibited improved electric properties as well as good transparency. This technology can also reduce the demand for ITO and provide the candidates of flexible electrodes for wearable devices. Analysis of the electric properties of this type of electrode, such as the variance of the sheet resistance of the composite electrodes with the embedded mesh structure parameters, can provide a theoretical basis for designing and fabricating this electrode. But detailed studies are still lacking. This work focuses on the electrical property analysis of the typical square hole and grid shaped metal mesh-TCO composite electrodes based on Rayleigh model and finite-element simulation, respectively. The electric potential distribution and current density distribution are obtained from the finite element calculations, revealing that the dramatic deformation of the metallic channels in the composite results in the failure of a conventional Rayleigh model for the moderate and high opening rates. Accordingly, we adopt a lattice correction to the Rayleigh model to reduce the channel deformation by increasing the symmetry of the exterior boundary of the lattice cell. A comparison of the results from the simulations with those from the second-order approximation of the lattice-adapted Rayleigh model shows that the new analytic form of the effective conductivity is applicable to a much larger opening-rate range for both the monolayer and the sandwich structures of metal-mesh TCO composite electrodes. The variances of the sheet resistance and the effective conductivity with different material and structure parameters of the composite electrodes are calculated and discussed based on the lattice-adapted Rayleigh approximation. The results are well consistent with experimental results. A comparison of our model with other theoretical models is also made, showing that this lattice-adapted Rayleigh approximation can be used as a simple and efficient theoretical tool to analyze and design the concerned transparent composite electrodes.

Using Magnetic Field Analysis for Localizing Defects of Fuel Cell & Electrolyzer Components

Production capacities of electrolysis and fuel cell technologies are expected to increase significantly in the upcoming years, reducing costs of stack components through numbering-up. To ensure reliability and durability and reduce costs along the manufacturing process, developing suitable in-line non-destructive diagnostic methods for quality control becomes essential for their industrialization.In both fuel cell and electrolyzer stacks, the main components' electrical resistance and current density distribution greatly influence stack efficiency and longevity. Here, the flowing electric current generates a magnetic field depending on its strength and direction. Potential defects caused by the manufacturing process, including cracks, defective welding spots, coating adhesion issues, delamination, and contamination, influence the components' electric conductivity and current density distribution and hence the magnetic field distribution.This work investigates non-destructive diagnostic methods using magnetic field analysis (MFA) to identify changes in the magnetic field distribution and, thus, local electrical resistance and current density distributions of fuel cell and electrolyzer components. The methods used are magnetic field imaging (MFI) and Eddy Current Testing (ECT). MFI analyzes the magnetic field distribution in all three spatial directions to trace electrical currents and identify electrical defects, creating a magnetic field signature that can potentially distinguish between functional and non-functional components along the manufacturing process. ECT measures variations in local conductivity by inducing eddy currents in the sample through an alternating magnetic field generated by a sender coil. These eddy currents create a detectable magnetic field in a receiver and are affected by defects and changes in electrical conductivity. Therefore, the method can characterize sheet resistance and material homogeneity through electrical anisotropy in electrically conductive components.In initial experiments, ECT measurements on coated and uncoated hollow embossed stainless steel bipolar half plates showed systematic differences depending on quality characteristics resulting in unique patterns and inhomogeneities which require further investigation. Furthermore, experiments with both methods on other stack components will be presented and discussed. In addition, their in-line capability will be assessed and evaluated. However, these first promising results imply that MFA is potentially useful as an in-line, non-destructive diagnostic method for quality control.

Multi-planar injection lap riveting

This paper is focused on multi-planar hybrid busbars made from copper and aluminum for electric energy distribution systems. The objective is to provide an overview of its assembly by injection lap riveting in multidirectional tools and to compare the electrical performance of its joints against that of conventional (in-plane) busbars.The injected lap riveted joints require a dovetail ring hole and a countersunk hole to be first machined in the overlapped copper and aluminum sheets and then to inject the semi-tubular rivets by compression through the lined-up holes in order to fix the sheets in position. In this work, the injection of the semi-tubular rivets was carried out in a laboratory multidirectional tool set that converts the vertical press stroke into two-orthogonal horizontal movements by means of cam slide units consisting of compression punch holders and sliding wedge actuators attached to the upper bolster.Experimental results obtained for a multi-planar, three-conductor, rake-shaped elbow of a hybrid busbar system allow concluding that while the required compression force is proportional to the number of injected lap riveted joints, the electrical performance is non-proportional due to changes in the distribution of electric current density. Numerical simulation with finite elements gives support to the discussion and allows readers to recognize the pitfalls of designing busbar joints exclusively based on mechanical requirements.

DISTRIBUTION OF ELECTRICAL CURRENT DENSITY INTO PLANAR MAGNETIC COMPONENTS ACCORDING TO FREQUENCY

This article presents a study on influence of frequency and magnetic material on electrical current density distribution and its intensity in a planar inductor.Studied structures are planar inductors without and with a magnetic material. These studies are performed in simulation using HFSS simulator and in experimental measurement using impedance-meter.

Optimization design of electrode structure of GaAs photoconductive semiconductor switch

Previous studies revealed that changing the electrode structures of a gallium arsenide photoconductive semiconductor switch (GaAs PCSS) can significantly affect the local electric field and current density at the electrodes. Knowing the optimization of the electrode structures of GaAs PCSS can improve the withstand voltage performance and current carrying capability. In this work, we optimize the surface contact electrode structure of GaAs PCSS, and numerical simulations are performed to systematically study the electric field and current density distribution in the bulk of the device. The result shows that the maximum transverse current density and maximum longitudinal current density of the embedded 172° isosceles trapezoid electrode structure are smaller than other kinds of electrode structures, which is the most favorable for improving the withstand voltage and current carrying capability of GaAs PCSS.

Multiple fields generated by two dissimilar conductive punches on thermoelectric material

Exposed to high load concentrations environments such as mechanical, thermal, and electrical, thermoelectric equipment may be damaged by the contact surface during operation, resulting in equipment failure. The effects of two dissimilar rigid punches on the thermoelectric material layer under mechanical force and thermoelectric loading are investigated in this article. Using the Fourier transform, the problem is turned into a system of three singular integral equations containing the thermoelectric effect, and the collocation methods are used to solve it numerically. The effects of thermoelectric load, thermoelectric material layer thickness, and the distance between two punches on the electric current density, energy flux, and surface normal stress distribution are thoroughly discussed. The results show that when the two punches are close to each other, below the two punches, the electric current density, energy flux, and contact stress values are larger near the distal end and lower at the inner edge. The stresses at the inner edge of the two indices show opposite characteristics with an increasing of total energy flow and total current, whereas they are consistent at the outer edge. The results aid in the measurement of the multifield coupling properties of finite-thickness thermoelectric material using indenter experiments.

Modeling and Comparative Performance Analysis of Perovskite Solar Cells with Planar or Nanorod SnO2 Electron-Transport Layers

Application of various electron-transport layers (ETLs) with desired morphology and dimensions is a key factor to be considered for the structural designs of perovskite solar cells (PSCs) in order to obtain enhanced optical and electrical properties. The metal-oxide ETLs composed of one-dimensional nanorod arrays are one of the most frequently used nanostructures for electron transporting in PSCs. In this work, computer-simulation methods are employed to investigate the optoelectrical properties of PSCs with planar and nanorod-based ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs. A two-dimensional optical model is used to determine the optical responses of devices and the standard drift-diffusion model is utilized to simulate their behavior and performance. The aspect ratio and the density of ${\mathrm{Sn}\mathrm{O}}_{2}$ nanorods are varied to examine their effect on the optical and the electrical properties of resulting devices and the findings are contrasted with those of planar devices. It is found that under optimum conditions, PSCs with thin planar ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs, which are referred to as reference planar devices, outperform PSCs with nanorod-based ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs even if the light-harvesting properties of the latter are improved with the implementation of structured ETLs. The underlying reasons for this phenomenon are analyzed and rationalized through a detailed analysis and comparison of electric field, current density, and carrier recombination distributions in PSCs. The findings of this work can be used as a theoretical guide for designing and fabrication of high-performance planar and structured PSCs using ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs.

Repetitive High-Power Microwave Pulses Induced Failure on a GaAs HBT LNA

This study aims at studying the damage effect of gallium arsenide (GaAs) heterojunction bipolar transistor (HBT) low noise amplifier (LNA) with repetitive high-power microwave (HPM) pulses. The theoretical function for the thermal accumulation effect is derived, which depends on the pulsewidth, the pulse repetition frequency (PRF), and the input power. A simulation model is established to investigate the thermal accumulation effect of repetitive HPM pulses on the HBT. The electric field, current density, and temperature distributions in the HBT with repetitive HPM pulses are discussed first. The influence of the repetitive HPM pulse parameters on the thermal accumulation effect is studied by theoretical analyses and simulations. Results show that the thermal recovery time increases with the pulsewidth or the input power increases. In addition, it is concluded that the frequency does not affect the thermal recovery time. The simulation results agree with the theoretical results. Finally, the damage effect of repetitive HPM pulses is experimentally verified.

Experimental and Numerical Investigations on Fabrication of Surface Microstructures Using Mask Electrolyte Jet Machining and Duckbill Nozzle

Abstract The consistency in the fabrication of microsurface structures on large workpieces remains a challenge for existing production techniques. Mask electrolyte jet machining (MEJM) is a hybrid mask-based electrochemical machining (ECM) process that combines the flexibility of Jet-ECM to flush the electrochemical by-products and the high throughput processing feature of through-mask electrochemical micromachining (TMEMM). In the present study, a duckbill-shaped nozzle is employed in the MEJM for the batch fabrication of microsurface structures which facilitates more uniform current density distribution over the entire machining area, resulting in better consistency. With a larger slit length, the duckbill nozzle will not only cover more processing area but also facilitates more uniform current density distribution over the entire machining area, resulting in a better consistency for batch fabrication. Thresholds of the ratio of slit length to the machining area were derived from a quantitative analysis, namely the efficient threshold and the performance threshold. The slit length of the duckbill nozzle should be at least twice as large as the machining area to wipe out any observable deviation on current density distribution in the machining area. An efficient and high-performance numerical simulation framework with a virtual gap concept is developed for the mask-based ECM processes to simulate microcavity profiles and associated current density distribution. The concept of a virtual gap is proposed to solve the simulation dilemma of elements being consumed in the mask-based ECM process. Quantitative analyses were carried out to study how the virtual gap influences the electric current density distribution in the interelectrode gap. A virtual gap smaller than 100 nm is recommended. Guidelines on how to ensure a smooth electric field transition across the coarse and fine-meshed zones are presented by conducting a quantitative analysis. As an example, this work has successfully fabricated several cavity arrays with different processing parameters. Both the experimental results and the numerical simulation frameworks are easy-to-implement and easy-to-extend for all the mask-based ECM processes.

Failure Mechanism of pHEMT in Navigation LNA under UWB EMP.

With the development of microelectronic technology, the integration of electronic systems is increasing continuously. Electronic systems are becoming more and more sensitive to external electromagnetic environments. Therefore, to improve the robustness of radio frequency (RF) microwave circuits, it is crucial to study the reliability of semiconductor devices. In this paper, the temporary failure mechanism of a gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) in a navigation low-noise amplifier (LNA) under the jamming of ultra-wideband (UWB) electromagnetic pulses (EMP) is investigated. The failure process and failure mechanism of pHEMT under UWB EMP are elaborated by analyzing the internal electric field, current density, and temperature distribution. In detail, as the amplitude of UWB EMP increases, the output current, carrier mobility, and transconductance of pHEMT decrease, eventually resulting in gain compression. The injection experiment on LNA, which effectively verified the failure mechanism, indicates that the gain of pHEMT is suppressed instantaneously under the jamming of UWB EMP and the navigation signal cannot be effectively amplified. When UWB EMP amplitude increases to nearly 10 V, the BeiDou Navigation Satellite System (BDS) carrier signal is suppressed by nearly 600 ns. Experimental results accord well with the simulation of our model. UWB EMP jamming is a new and efficient type of electromagnetic attack system based on the device saturation effect. The performance degradation and failure mechanism analysis contribute to RF reinforcement design.

Sacrificial Anode Cathodic Protection System Modelling Using Direct Boundary Element Method

Abstract Cathodic protection system is commonly employed approach for the protection of the metallic infrastructure placed in electrolyte against corrosion. Adequate design of the cathodic protection system requires the determination of electrical potential and current density distribution on the protected object surface that meets the defined criteria. In this paper, the application of the direct boundary element method in conjunction with Newton-Raphson method was considered for the calculation of the electric potential and current density distribution on the surface of the cathodically protected underground object. The considered method was applied on the sacrificial anode cathodic protection system of the underground pipeline. The non-linear boundary conditions of the electrode surfaces of the cathodic protection system are taken into account. The method was used to determine the current density and electric potential distribution on the external wall of the protected pipeline.

Experimental and numerical investigations of arc plasma expansion in an industrial vacuum arc remelting (VAR) process

In the present study, we investigate arc plasma expansion in an industrial vacuum arc remelting (VAR) process using experimental and numerical tools. Stainless steel is the alloy of interest for the electrode (cathode) and ingot (anode). During the operation of the VAR process, behaviors of cathode spots and plasma arc were captured using the high-speed camera (Phantom v2512). We found that spots prefer to onset and remain within the partially melted surface at the center of the electrode tip. Existing spots outside the melting zone accelerate toward the edge of the electrode to extinguish. We observed a fairly symmetrical and centric plasma column during the operation. For further investigation of the observed arc column in our experiment, we used the two-fluid magnetohydrodynamics (MHD) model of plasma proposed by Braginskii. Thus, we modeled the arc column as a mixture of two continuous interpenetrating compressible fluids involving ions and electrons. Through numerical simulations, we calculated plasma parameters such as number density of ions/electrons, electric current density, flow of ions/electrons, temperature of ions/electrons, and light intensity for the observed arc column in our experiment. The calculated light intensity of plasma was compared with images captured by the camera to verify the model. The distribution of electric current density along the surface of the anode, namely ingot, is a decisive parameter that impacts the quality of the final product (ingot) in VAR process. Herein, we confirm that the traditionally used Gaussian distribution of electric current density along the surface of the ingot is viable.

Numerical Simulation and Calculation of Resistance of Laminated Paper-Impregnated Insulation of Power Cables

Numerical simulation of polypropylene laminated paper insulation is a serious challenge, as it must take into account the layered structure and presence of longitudinal and radial gaps in the coils of the winded tape for cables with sector-shape conductive cores. Thus far, it has been performed only with serious simplifications. We propose a technique for numerical modeling of electric parameters in this type of insulation by reducing a complex 3D problem to a simplified 2D model that takes into account the main influencing factors. The results of modeling the distribution of electric field strength and current density in insulation are presented, and the influence of the location of gaps between the edges of winded tape on the conductivity of cable insulation is estimated. Analytical expressions are obtained for estimating the electrical resistance of insulation while taking into account the parameters of the butt gap between the insulating tapes. The results of calculations, numerical modeling, and experimentally measured values of electrical resistance are compared, showing that there is a good match. The main effects affecting the properties of polypropylene laminated paper insulation are described.

Multi-physics electrical contact analysis considering the electrical resistance and Joule heating

A multi-physics electrical contact model is developed to predict the contact pressure, temperature, and electric current density (ECD) distributions on the contact surface. The theoretical model takes the interfacial electrical resistance and its resultant Joule heating into account. The contact pressure and contact radius are calculated by solving the first kind of Cauchy singular integral equation. The temperature and ECD are obtained based on the obtained contact pressure. Then, a three-dimensional finite element model is established to simulate the mechanical, thermal, and electrical behaviors of electrical contact. The finite element model can consider both the interfacial electrical resistance and the constriction electrical resistance. The theoretical results of the electrical contact behaviors are compared with the numerical results. The influences of the electrical resistance, normal force, electric potential, and distribution form of the heat flux on the contact pressure, temperature, and ECD distributions are investigated. The results indicate that the proposed multi-physics contact model can provide an accurate prediction of electrical contact behaviors.

Function switchable broadband wave plate based on the Au-VO2 hybrid metasurface.

In recent years, the integration of active materials into a metasurface to achieve tunable devices has attracted much attention. Here, we design an Au-VO2 hybrid metasurface, which can switch between quarter-wave plate and half-wave plate due to the phase transition of VO2. At 298 K, the proposed structure acts as a quarter-wave plate in the 0.87-1.2 THz band, achieving the mutual conversion between linear polarization and circular polarization. Raising the temperature to 358 K, it works as a broadband half-wave plate in the range of 0.65-1.45 THz, with the reflective chirality preservation of circular polarization and the cross-polarization conversion of linear polarization. In the above cases, the response efficiencies are both above 90%. The switchable multifunction results from the tunable geometric phase of the metasurface, where the elaborately designed Au and VO2 blocks separately bring the phase of π/2. Furthermore, the electric field and current density distributions are employed to explain the physical mechanisms leading to the different functions. Such an active broadband metasurface is expected to find applications in tunable and multifunction devices manipulating the polarization and phase of terahertz waves.

Geometry optimization of an electrochemical reactor for bleaching kaolin

AbstractHigh-whiteness kaolinite mining reserves are scarce. In some locations, it is necessary to remove material to access them (adding to the cost). Therefore, processes have been developed to eliminate contaminants, such as iron, and provide alternatives to the used contaminated materials that, after being treated, meet quality criteria. In our previous research, we developed an electrochemical process for kaolin whitening at the laboratory level and bench scale, demonstrating the reaction mechanisms that occur during the removal of iron from kaolin. However, the geometry used at the laboratory level does not present the most suitable position for the electrodes. Therefore, in the present study, we focused on the geometry and the function of the electrodes. This is necessary during the escalation process to reach the pilot-scale level. The study was carried out using computer-aided engineering in the COMSOL Multiphysics computer program and by analysing the distribution of the electric potential and the electric current of the geometries considered while performing the scaling. The results indicated that the change in the anode position from perpendicular to parallel to the discs improved the distribution of electric current density on the cathode surface and so increased the elimination of iron through electrochemical deposition. Similarly, to reduce the amount of material used in the construction of the reactor, the anode-size effect was analysed, revealing that relatively small anodes improved the distribution of electric current density over the entire surface of the electrode and not only at the edges.