Current Skin Effect Research Articles

3D Analysis on Distribution of Pulsed Current in Electromagnetic Launcher Considering Contact State and Movement

In electromagnetic launcher, the pulsed current is concentrated by contact state, current skin effect (CSE) and velocity skin effect (VSE), and heat the material locally. It will lead to melt or degradation, reducing stability and service life of the launcher. In order to study the current distribution with all these various influences, a 3D transient current analysis model with dynamic conductivity assignment and contact layer is proposed in this paper. It is found that the short contact length in armature moving direction can make two peaks overlap caused by CSE and VSE, and VSE can disturb the current distribution in horizontal direction. When designing armatures, it is recommended that the contact length in the moving direction should be long enough during the entire launch process, so to isolate the two peaks, and that the central length of the armature tail should be longer than the lateral length, so to prevent the current from concentrating more at the lateral edge. These conclusions help the optimization of the launcher structure to reduce local damage caused by current concentration and extend service life. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Performance gradient distribution of (Ti,W)C cermet by skin effects of high‐frequency spark plasma sintering

AbstractA (Ti,W)C cermet with graded properties was prepared using high‐frequency spark plasma sintering (HF‐SPS). The effects of the sintering process on the microstructure and mechanical properties of the prepared cermet material were studied, and the densification behavior of the material was analyzed using scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Owing to the skin effect and pulse current discharge in HF‐SPS, the experimental results showed different sintering effects, as indicated by the current density difference between the surface layer and bulk. On one hand, the surface‐layer grains were larger, the metal phase was concentrated, and the hardness was high; however, the bulk grains were smaller, the metal phase was uniformly distributed, and the strength and toughness were high, causing the material to account for the higher hardness of the surface layer and the bulk strength and toughness. The skin effect of pulse direct current was key for the performance gradient distribution, whereas increases in the current density and sintering temperature decreased the skin effect. In general, the Joule heat effect was more significant, leading to abnormal grain growth.

Method of Calculating Inductance Gradient for Complex Electromagnetic Rail Launcher

Electromagnetic rail launch technology has made impressive progress; however, the analytical method of calculating the inductance gradient for a complex electromagnetic launcher is still insufficient. By fully considering the characteristics of electromagnetics and current distribution in a device, this paper describes a model of the current skin effect by simplifying the line current distribution in the device. Based on Biot–Savart Law, an analytical method of calculating inductance gradient for an electromagnetic rail launcher with complex structure is proposed. This method has the advantages of fast calculation speed and accurate calculation results. Because of error analysis, the calculated value relatively corresponds to the simulation result of the eddy current field. To reflect the transient electromagnetic emission process, the effects of different configurations, current frequency, and armature position on the inductance gradient are further summarized. The results show that the error rate of this method in calculating the inductance gradient is about 4%, which meets the requirement for calculation accuracy. The inductance gradient of the enhanced four-rail electromagnetic launcher is about 2.22 times that of the nonenhanced one due to the equal conditions; the inductance gradient decreases with the increase in current frequency and decreases as the armature approaches the muzzle.

Research on the Influence of the Arm Edge Effect on the Rotational Stability of the Spinning Projectile for the Railgun

For the stability of the spinning projectile launched by a railgun, calculation is carried out to analyze the influence of the arm edge effect (AEE). The AEE refers to that when the edge of an arm is in contact with the edge of a rail, it may produce an asymmetric electromagnetic to create an extra rotation torque. Since the current skin effect may change the magnetic field distribution when some current flow through the arm’s edge. A finite element model is established to simulate the AEE. Results show that for the projectile with separated arms, the AEE may cause the rotation torque to reverse, and the rotation torque may vary alternately between positive and negative value. When increasing the number of arms, the variation amplitude of torque is decreasing and closer to the average value. However, increasing the number of arms will also weaken its strength, so this is not a good method. Therefore, this article proposes an improved projectile, which is connecting the rear arms by a ring. This allows the current to enter the ring first and then into the arms, what may keep the rotation torque constant, and increase the strength. This article may have important guiding significance for the research of launching spinning projectile by a railgun.

High-Radiation Efficiency in Array Antennas Using Cu/Co Metaconductors

High radiation-efficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4 $ </tex-math></inline-formula> array antennas consisting of multiple nanolayered nonmagnetic copper (Cu) and ferromagnetic cobalt (Co), termed as Cu/Co metaconductor, are reported for 5G and millimeter-wave applications. The performance of a ten paired Cu/Co metaconductor-based array antenna, where the thickness of each metal layer is 150 and 25 nm, respectively, is compared with that of two reference antennas. The first reference antenna has the same total thickness but is made of sputtered solid copper and the second one made of five times thicker electroplated solid copper. Because of eddy current cancellation and skin effect reduction in metaconductor, the Cu/Co-based antenna shows lower RF resistance in both feeding lines and antenna patches than reference antennas in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K_{a}$ </tex-math></inline-formula> -band. Nearly 6 dB enhancement in the received signal power and the bandwidth (BW) improvement of 0.18 GHz is obtained for the Cu/Co-based antenna compared to the reference ones. Also shown is the possibility of more than 80% conductor weight reduction without losing antenna performance. Analysis for the enhancement in the antenna gain and BW is provided. Simulations performed in a high-frequency structural simulator are compared with the measured results. The total area of a fabricated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$ </tex-math></inline-formula> array antenna is 5.6 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Electromagnetic design method of linear induction motor considering lateral end effect

Due to the complex end effect, it is difficult for the linear induction motor to design and analyze with the "road" calculation and two-dimensional field calculation. Considering the end effect, skin effect and secondary leakage reactance of the eddy current of the secondary induction plate, a linear induction motor electromagnetic design and calculation program was programmed via VB language. A two-dimensional finite element analysis method was proposed to approximate the lateral end effect on linear induction motor performance by multiplying the two lateral end effect coefficients into secondary induction plate resistivity and air-gap relative permeability. The accuracy for both calculation of end effect coefficients by "road" calculated program and considering lateral end effect in two-dimensional finite element analysis was validated by using the experiment and three-dimensional full model finite element, respectively. This work proposes the calculation method of the lateral end effect, which is faster and more accurate for the electromagnetic design as well as the finite element simulation of linear induction motor.

Analysis of electromagnetic characteristics of a new electromagnetic ejection device

Electromagnetic ejection technology is a new launching technology which uses electromagnetic force to accelerate the projectile to ultra-high sound speed. This technology can break through the speed limit of traditional gunpowder launching, and realize the accurate control of exit speed by controlling the excitation pulse current.Four track electromagnetic launcher is a special enhanced electromagnetic launcher, which has many advantages that dual track electromagnetic launcher does not have. Its development greatly promotes the application of electromagnetic launch technology in aerospace field. In this paper, according to the practical needs of electromagnetic space launch technology, a simple four orbit electromagnetic launch device is designed and established; the finite element analysis of the model is carried out, and the electromagnetic and current characteristics are simulated, and the skin effect and proximity effect of current are obviously observed; the theoretical analysis and formula derivation of inductance gradient are carried out, and finally two kinds of inductance gradient are proposed based on the finite element theory simulation A simple example is given.

Research on Heat Dissipation Optimization of a Novel Liquid-Cooling Eddy Current Brake

As an auxiliary brake element, the eddy current brake is widely used to ensure safe driving in heavy vehicles due to its noncontact braking characteristics. It is important to increase the power density of the eddy current brake and suppress the thermal derating of its braking performance. According to the principle of the eddy current braking and current skin effect, a decline in temperature can greatly increase the eddy current density of the low-frequency electromagnetic device. In this paper, a new heat dissipation method is proposed to cool the heating surface of the eddy current brake directly. The electromagnetic field model and the flow-heat coupling model are established to predict and analyze the steady-state temperature distribution and braking torque. A new type of internal liquid cooling eddy current brake prototype was manufactured for a bench test. The experimental data prove that the computational model is effective. The calculation results show that the new internal liquid cooling eddy current brake has improved heat dissipation advantages.

A new eddy current probe with deep penetrating field trajectories for the inspection of deep cracks in metal materials

The detectability of deep cracks in metal materials is an important performance index of eddy current probes. However, because of the limitations of the skin effect of eddy currents, it is difficult to obtain deep crack information in materials using an ordinary probe. This paper proposes a new probe with deep penetrating field trajectories for the inspection of deep cracks. To optimise its performance, contributions of the coil radius, the pick-up position and the excitation frequency to penetration depth of eddy currents are studied. The results show that the capability of the new probe in the inspection of deep cracks is greatly improved when compared to traditional pancake probes.

Resistance Variations in High-Frequency Inductors Considering Induced Fields Among Conductors

In the high-frequency alternating current (ac) fields, both skin effect and proximity effect account for the significant part of losses in an inductor. In particular, serious losses between multiple wires occur due to the proximity effect. A stranded wire has two or more strands with twisted structure so that the analysis of stranded wire-wound inductors requires lots of computational time for detailed discretization in finite element analysis (FEA). The analytical method can be alternatively used to help achieve fast (real-time) estimation by reducing the complexity of the original model. However, the proximity effect cannot be accurately predicted due to induced fields by eddy current from adjacent conductors (strands and wires). In this article, induced fields among adjacent conductors are discussed for the accurate analytical calculation. The concepts of a complex permeability and homogenization can help improve the estimation of frequency-dependent resistance in an inductor. The proposed estimation is verified and compared with the computed value by FEA and measurement data with a spiral inductor.

Theoretical and numerical simulation study on jet formation and penetration of different liner structures driven by electromagnetic pressure

The use of a shaped liner driven by electromagnetic force is a new means of forming jets. To study the mechanism of jet formation driven by electromagnetic force, we considered the current skin effect and the characteristics of electromagnetic loading and established a coupling model of “Electric–Magnetic–Force” and the theoretical model of jet formation under electromagnetic force. The jet formation and penetration of conical and trumpet liners have been calculated. Then, a numerical simulation of liner collapse under electromagnetic force, jet generation, and the stretching motion were performed using an ANSYS multiphysics processor. The calculated jet velocity, jet shape, and depth of penetration were consistent with the experimental results, with a relative error of less than 10%. In addition, we calculated the jet formation of different curvature trumpet liners driven by the same loading condition and obtained the influence rule of the curvature of the liner on jet formation. Results show that the theoretical model and the ANSYS multiphysics numerical method can effectively calculate the jet formation of liners driven by electromagnetic force, and in a certain range, the greater the curvature of the liner is, the greater the jet velocity is.

Join Al–steel dissimilar metal by novel high frequency electric cooperated arc welding

ABSTRACTA novel high frequency electric cooperated arc welding method (HFAW) was developed to join aluminium and steel of 3.0 mm thickness without groove. Owing to the skin effect and proximity effect of high frequency current, a part of welding heat was directly distributed all over weld side wall. Consequently, sound double-sided weld formation was achieved under a low MIG heat input and high welding speed. The average thickness of interfacial layer was limited to 2.3 µm. Benefitted from the balanced heat input and thin interfacial layer, the failure mode of the HFAW joint was necking at Al base metal. For traditional MIG joint, however, poor back weld formation and thick interfacial layer resulted in spontaneous fracture at interface.

A novel high efficiency low heat input welding method: High frequency electric cooperated arc welding

High efficiency and low heat input are the pursuit of modern welding. In this paper, an innovative high frequency electric cooperated arc welding (HFAW) was developed. The process and joint characteristics of the HFAW were compared with that of traditional arc welding (TAW). In the HFAW, a part of welding heat is generated all over the surface of weld side wall (WSW) directly and rapidly due to the skin effect and proximity effect of high frequency current. The limitation of heat conduction on the TAW was broken through. Benefited from the ultra-speed welding thermal process, the HFAW reaches 3–4 times the welding speed of the TAW, while the heat input needed in the HFAW was only about 60% that in the TAW. Meanwhile, the HFAW joint presented sound weld formation, complete penetration and finer microstructure, which made the joint possess an equal tensile strength with the base metal.

Transient skin effect in power electronic applications

This study describes transient electromagnetic phenomena in electrical conductors that are connected to modern power electronic circuits and therefore subjected to current controlled pulses with fast rise times and high peak current ratings. Electromagnetic field diffusion is discussed and a brief review of alternating current skin effect phenomena is presented before it is generalised to transient regimes of operation. It is shown that the magnetic field diffuses into the conductor from the outside on the initiation of a current pulse and therefore the axial current density distribution inside the conductor changes with time under a transient current due to the well-known electromagnetic relations – the current begins at the conductor surface and diffuses inwards. The implications of such behaviour are briefly discussed in the context of modern power electronics and its applications.

3D Multi-field Coupling Analysis of Three-Phase GIS Bus Bar

The temperature in gas insulated bus bars are outcomes of coupled multiphysics field, such as thermal field, fluid field and eddy current field in which skin effect of current plays a considerable role. In this paper, the 3D model of GIS bus bar is established, and the skin effect of current is considered by further fine grids in the calculation to reach accurate loss value. Finite element method and fluid analysis are used to predict the distribution of temperature field of three-phase GIS bus bar.

Operation of an induction motor supplied by voltage with interharmonics

The paper discusses the effects of interharmonics, i.e. frequencies higher than the fundamental frequency, not being its total multiplicity, in the voltage supplying the induction motor. The emergence of interharmonics in a three-phase grid is mainly the result of the swinging of peak mains voltages. In induction machines, this results in the occurrence of currents with interharmonic and subharmonic frequencies, the generation of alternating moments, the swinging of the rotor speed and the change in the RMS value of the current of the fundamental frequency. The paper explores these phenomena simulation, taking into account the skin effect of currents in the rotor cage. The research was carried out both for interharmonics with a positive sequence of phases as well as for the negative sequence. The paper is a continuation of work [1].

Research on Thermal Stress by Current Skin Effect in a Railgun

In this paper, a research on the damages of material caused by thermal stress in electromagnetic launch is presented. 3-D finite-element program is established to calculate the transient electromagnetic fields and temperature fields including a moving armature. The focus is mainly on the high temperature and large thermal stress damages to the rail. Thermal stress is produced by the current density concentration and defined as the skin effect. There are two main reasons for the current skin effect. One is due to the rapid changes of the current wave. The other is due to the moving conductors known as the velocity skin effect. The simulation results illustrate that with the influence of the current skin effect, the thermal stress will concentrate at a small area. This area may cause the grooving damage at startup, besides, the gouging damage at high velocity. Finally, the results are in agreement with the experiments.

Influences of Electric Parameters of Pulsed Power Supply on Electromagnetic Railgun System

To analyze the electric parameters of a pulsed power supply (PPS) system and their influence on muzzle velocity, a stable and reliable 200-kJ compact PPS system used for electromagnetic railgun system has been developed. The PPS system consists of ten modules, and each module is comprised of a high energy density capacitor (3270 $\mu $ F/3.5 kV), 4-in thyristor, a pulse shaping inductor (1.5 $\mu $ H), and a crowbar diode. At the same time, a railgun circuit model for simulation was established. In this model, velocity skin effect, current skin effect, and friction were taken into consideration. Some electromagnetic launching experiments were carried out to verify the correctness of the railgun circuit model. Influence of different electric parameters of PPS on muzzle velocity was analyzed by the computer aided circuit design program PSPICE based on this model. The parameters include capacitance, equivalent series resistance (ESR) of the capacitor, inductance, and jitter time of the thyristor. The simulation results show that the ESR is the most critical influencing factor (the deviation of velocity is −4.286% when the ESR is 5 m $\Omega $ ). The following is the change of the capacitance (the deviation of velocity is −3.827% when the capacitance decreases to 95%C0). In the meantime, the changes of the resistance of inductor do have an influence on muzzle velocity (the deviation of velocity is −0.908% when the resistance of inductor is 1 m $\Omega $ ). However, the changes of inductance and the jitter time of the thyristor impose no significant effect on muzzle velocity. The conclusions provide reference to the overall optimization of PPS design and quality control of the manufacturing process.

Modeling of Electromagnetic Rail Launcher System Based on Multifactor Effects

In this paper, circuit simulation was chosen as the main methodology to analyze the characteristics of an electromagnetic (EM) rail launcher (or EM railgun) system, and a complex simulation model was proposed, which was not merely built on the static electrical parameters. Moreover, practical physical processes contributed to the system have also been taken into consideration and expressed as electrical parameters. Thus, the description of a relatively complex system could be realized by a comparatively simple manner, and the simulation result is more accurate and reliable compared with the traditional circuit simulation ones with the static electrical parameters. A circuit simulation model of an EM launch system based on PSpice software was built, in consideration of multifactor effects, such as current skin effect, contact pressure, and contact resistance on the contact surface of the armature and the barrel, velocity skin effect, friction drag, and temperature coefficient of electrical resistivity. Simulations were made based on the proposed model as well as the traditional one. Last but not the least, a comparison between the simulation results and the experimental ones was made to verify the accuracy and effectivity of the improved model.

Skin Effect Analysis for Pulse Current in the PEA Based on Frequency Domain Method

To study some of the mechanisms in passive electromagnetic armor (PEA), the pulse current skin effect and the action of the current along the length of a shaped charge jet as it passes through PEA are researched. Considering the different characteristic of the pulse current from the alternating current, a frequency domain analysis method of skin effect is introduced. With the background of PEA, time and frequency characteristics of the pulse current are analyzed based on the equivalent circuit model, and calculation method of the pulse current density distribution in shaped charge jet is obtained. Consequently, the skin depth during the discharge is researched. The validity of the method is approved by contrasting it with the Finite Element Method analysis results. Finally, a distribution of the specific action in the shaped charge jet elements is obtained based on the action time model. The results indicate that pulse current has a broadband, and its skin effect phenomenon is different from that of an alternating current. It shows that current density increases with the decrease in depth not all the time, but declines on the surface of the conductor at the trailing edge of the pulse current. And the specific action is concentrated on the tail of the jet whose velocity is less than 4 km/s. While the action in the radial direction becomes larger, the element gets closer to the surface.