Transient current distribution in a sphere by feeding a current on the surface from a loop of arbitrary shape

Contents  The complete electromagnetic field of an arbitrary transient current distribution in a sphere can be represented by a superposition of a transverse electric and a transverse magnetic field. In this paper, the transient current distribution in a permeable and conducting hollow sphere is calculated for an exciting current of arbitrary time dependence which is fed into the sphere via the surface from an open loop of arbitrary shape. The original configuration is separated into two characteristic configurations whose current distributions are derived from a transverse electric and a transverse magnetic second order potential. The transverse magnetic field is determined by the position of the feeding points on the surface of the sphere. The transverse electric field is influenced only by the contour of the exciting loop in the nonconducting space. If the exciting loop is closed outside the hollow sphere, the transverse magnetic field vanishes and the solution for the transverse electric field can be used to describe the shielding of the transient electromagnetic field by a spherical screen. The general transient solution is proved for the special case of a sinusoidal time dependence and compared with the direct solution of the differential equation for the complex amplitudes of field quantities. An energy balance is introduced which describes the energy flow during the transient process. Received: 18 October 2000     

Calculation of radiated electromagnetic fields from electronic systems

The electromagnetic radiation from electronic systems is formulated in terms of an integral equation for the electric and the equivalent magnetic current density, which is numerically solved by the method of moments. The electromagnetic coupling to conducting thin wires, thin plates, and aperture fitted cabinets is taken into account by appropriate operator equations. In order to solve the integral equation of electrically large conducting structures, suitable basis functions are needed to minimize the computation time. B-spline functions of the second and third degree are used as a basis in the moment method, which lead to a decrease of the computation time. A second way to decrease the computation time is given by the possibility of determining which parts of the structure of a printed circuit board (PCB) have to be considered and which parts can be neglected. Examples show that the influence of near source conducting areas to the radiated emissions is strong. It will be shown that this influence depends on the geometrical symmetry, the shape, and the distance of the scattering body.     

Enhanced Second Harmonic Generation From Noncentrosymmetric Nanohole Arrays in a Gold Film

A subwavelength aperture array in a gold film is fabricated for the purpose of second harmonic generation (SHG). The sunglass aperture shape is chosen to have an apex to increase the local field; however, unlike past research on double-hole structures, the inversion symmetry of the structure is intentionally broken to enhance the SHG. A systematic study of the influence of array periodicity and aperture shape is provided. The conditions for maximum SHG are discussed in terms of local field enhancement, excitation of the localized surface plasmon resonances, and the influence of array periodicity. Fully vectorial finite-difference electromagnetic calculations provide the effective index of the aperture modes, as well as the surface electric field to quantify the discussion. Both the sunglass and double-hole structures are promising for future implementation with less-expensive optical lithography since it is mainly composed of two holes; yet they produce sharp apexes for enhanced local field and thereby enhanced nonlinear light–matter interaction.      

导电材料磁导率和电导率测量

分析研究船舶、飞机等独立供电系统中地阻抗引起的传导干扰问题，需要准确测量作为公共地平面的金属导电材料在不同频率下的磁导率和电导率。该文通过分析二维细长圆柱导体和三维圆环导体内部的电磁场分布，推导并给出由规则导体内部阻抗求取导电材料磁导率和电导率的计算公式；提出用阻抗分析仪测量规则导体内部阻抗的实用方法；基于上述计算公式和测量方法，测量计算不锈钢材料在不同频率下的磁导率和电导率，结果与实际值相符。     

Numerical modelling of anisotropy and eddy current effects in ferromagnetic laminations using a co‐energy formulation

The paper deals with a numerical model for the evaluation of electromagnetic fields in one steel lamination under the influence of a rotating magnetic flux, taking into account anisotropy effects. For this purpose a detailed material model, described by a differential permeability tensor, is included in the macroscopic electromagnetic field calculations in one lamination. Here, by geometrical and physical considerations, the governing Maxwell equations are reduced to a system of parabolic PDEs for the components of the magnetic field vector, under appropriate boundary and initial conditions. We present a suitable numerical approximation based upon a finite element–finite difference method, which properly takes into account the material characteristics. The study leads to a more realistic numerical modelling of the electromagnetic phenomena inside electric and magnetic conducting laminations due to anisotropy effects. Numerical results are compared with those from simplified analytical formulae. Copyright © 2001 John Wiley & Sons, Ltd.     

球和线圈共轴的涡流问题解析解

导电导磁球和轴对称线圈的共轴电磁系统可用于球的涡流无损检测。文章利用磁矢量位和洛化兹规范,建立了均匀导电导磁珠和圆环线圈共轴电磁系统的时谐场边值问题,用分离变量法解得到了球的散射场解析解。在此基础上,导出了球和空芯圆柱线圈共轴电磁系统的电磁场解析解上,导出了球和空芯圆柱线圈共轴电磁系统的电磁场解析解和线圈的阻抗增量解析式。为便于计算,给出了复宗量的球贝塞尔函数的计算方法。实验表明,阻抗增量的理论计     

The modelling of EM leakage into advanced composite enclosures using the TLM technique

The TLM technique has been enhanced to allow the accurate modelling of EM diffusion through advanced composite material shells. This is a significant development owing to the rapidly increasing use of conducting composite materials in aerospace vehicle design. The accurate EM modelling of this class of materials is important for correct design of vehicles with regard to electromagnetic compatibility (EMC). Existing 3-D time-domain TLM models a non-perfectly conducting shell using a resistive sheet (or sheets) to simulate the surface. The results from this model are shown to be slightly inaccurate and require lengthy computer solution times. A separate 1-D, frequency-domain transmission-line model has been developed elsewhere to better analyse the diffusion properties of composite materials. The incorporation of the results from this frequency domain code into the 3-D time-domain TLM algorithm is outlined.     

ESD辐射场与带孔缝金属腔体耦合的数值研究

采用FDTD法研究了ESD电流注入细导线所产生的辐射场在其近场区域与带孔缝金属腔体的耦合问题 ,建立了耦合数值模型。计算分析表明 ,在金属腔体内的孔缝周围区域存在较强的耦合场 ,腔体内被激励起以TE10 1模、TE2 0 1模和TE112 模为主的谐振场 ;对面积相等的方孔、矩形孔和孔阵 ,通过长边与导线垂直的矩形孔和方孔的耦合场比较强 ,而通过长边与导线平行的矩形孔和孔阵的耦合场比较弱     

Teaching electrodynamic levitation theory

A theoretical approach to teaching the principles of electrodynamic levitation is described. Two theories are used to obtain analytical solutions to predict the performance of a simple MAGLEY arrangement. The first theory, based on Maxwell's equations and vector force relationships, is for a simplified model allowing for a finite-thickness track conductor. The second theory is for a thin plate track and is a straightforward calculation of the lift and drag forces for a particular electromagnetic repulsion geometry, involving solution by one-dimensional integral equations. The magnetic flux source travels at a constant velocity and is derived from a sinusoidally distributed current sheet which in practice can be derived from windings or permanent magnets. Edge and end effects are neglected in both cases, which is equivalent to assuming infinite iron above the excitation surface and below the conducting plate. The simplified theory is illustrated quantitatively by a laboratory experiment in which a tray of permanent magnets is suspended over a rotating conducting plane. Gap magnetic field and drag force are measured as functions of velocity. The theoretical approach allows the following aspects to be investigated: the magnetomotive force and physical dimensions to produce suitable field magnitudes and measurable forces; the effect of harmonics by practical measurement of field profiles; and the effect of skin depth and conducting plate dimensions     

海面与上方目标复合电磁散射的矩量法研究

采用Monte Carlo方法模拟了一维PM谱海面.运用矩量法研究了一维PM谱海面及其上方二维矩形截面导体柱的复合电磁散射特性,并将计算结果与FDTD结果进行了比对,验证了该算法的正确性。数值计算得到了复合散射系数随散射角的变化曲线,讨论了海面风速、矩形截面柱尺寸和倾角、矩形截面柱中心距离粗糙面的高度对复合散射系数的影响。结果表明,矩形截面柱参数对非镜向复合散射散射系数影响显著,而对镜向散射系数较小。     

Frequency characteristics of electromagnetic wave radiated from GISapertures

Partial discharge (PD) measurement using electromagnetic wave by antennas is a promising technique to diagnose the insulation performance of SF₆ GIS. In order to establish high sensitive diagnosis technique of GIS insulation, frequency characteristics of electromagnetic wave, which are determined by GIS apertures such as insulating spacers and bushings, should be clarified. In this paper, we measured the electromagnetic wave radiated from different GIS apertures and also analyzed it using transient analysis program “PSpice.” Comparing the measurements with the theoretical analyzes, we investigated the relationship between the GIS aperture configuration and the radiated electromagnetic wave spectrum from the aperture. We also discussed how the aperture condition contributed to the radiation characteristics of electromagnetic wave. Finally, we concluded that the electromagnetic wave radiated from GIS aperture was based on different radiation mechanism in frequency     

导电聚合物电磁屏蔽材料及其应用

丰富的电磁波资源在信息行业得到广泛应用的同时,产生的电磁干扰也会带来许多危害。导电聚合物作为一种新型材料在屏蔽电磁波方面展现出了良好的应用前景。介绍了导电聚合物的屏蔽原理,综述了聚合物电磁屏蔽材料的主要制备方法和屏蔽织物性能的评价方法,探讨了聚合物电磁屏蔽材料的应用领域。     

Analysis of Protective Hoods Near High-Voltage Power Lines With Installed Communication Antennas

This paper studies the effect of the conducting hoods used to protect workers from the exposure to high-voltage power frequency and high-frequency communication electromagnetic fields. The finite-difference time-domain technique is employed to solve for the electric-field strength inside a human head model filled with biological material representing the human brain. By evaluating the field at several points and comparing the results with and without the hood, it is shown that at some spots in the head, the field is higher by a significant factor when the hood is present. It is also shown that with the presence of a see-through screen, the field intensity inside the head can be drastically reduced by eliminating the resonance effects. Following our analysis, a general safety guideline can be prescribed and used by the workers when exposed to a broad frequency range spanning from extremely low frequencies to the radio frequencies. The method also enables investigations on how to design a hood that is most suitable for a given frequency spectrum.      

Diffraction and scattering of electromagnetic waves by spheres with elliptic slit apertures and interior loading

Contents An analytical method is presented for solving the problem of diffraction of electromagnetic waves by a perfectly conducting sphere with an elliptic slit aperture. The interior of the sphere is filled with two different media which are radially stratified. The treatment of this canonical shielding problem may provide a better insight into the coupling mechanism of electromagnetic waves through slit apertures in realistic shielding structures. The solution of this three-dimensional diffraction problem is based on the spherical multipole expansion of the electromagnetic field.

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Beugung und Streuung elektromagnetischer Wellen an einer Kugel mit einer elliptischen Schlitzapertur und radial geschichteten Medien im Inneren

Übersicht Es wird ein analytisches Lösungsverfahren für die Beugung und Streuung elektromagnetischer Wellen an einer ideal leitenden Hohlkugel mit einer elliptischen Schlitzapertur vorgestellt. Das Innere der Hohlkugel kann zusätzlich mit zwei radial geschichteten Materialien gefüllt sein. Die Behandlung dieses kanonischen Abschirmungsproblems dient der Untersuchung des Einkoppelverhaltens elektromagnetischer Wellen in reale Abschirmungs-strukturen mit schlitzförmigen Aperturen (Türrand-Problem). Die Lösungstechnik beruht auf der sphärischen Multipolentwicklung des elektromagnetischen Feldes.

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This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG).     

电气设备电磁参数的灵敏度分析与自动设计

提出了电气设备电磁参数的灵敏度计算公式。在一次有限元网格剖分的基础上,通过 场有限元计算,同时获得电磁参数和它对设备尺寸的灵敏度,克服了基于差商计算灵敏度导致多次有限元网格生成和有限元计算的缺点,极大地降低了计算量。将该公式应用于电磁参数的自动设计,以便计算目标函数对设备尺寸的梯度。应用该公式对光纤电压互感器的分析比和壳式电力变压器的阻抗压进行灵敏度分析和自动设计,取得了满意结果。     

Revolving magnet wheels with permanent magnets

A new type of actuator with both magnetic levitation and linear drive is proposed. The actuator, called magnet wheel, has a rotating magnetic field obtained by revolving permanent magnets with high coercivity mechanically. The induction repulsive-type magnetic lift force with self-stabilization can be obtained by linking the rotating flux to a conducting plate. The induced simultaneous drag torque, which causes power loss, is used to obtain thrust in two proposed ways. These are called “tilt type” and “partial overlap type,” respectively. In the tilt type, the magnet wheel is tilted against the surface of a conducting plate. In the partial overlap type, the magnet wheel operates near the edge of a conducting plate. In this paper, the fundamentals of the structure of proposed magnet wheels are described. The basic characteristics at parallel to the conductor are shown by using a numerical three-dimensional electromagnetic analysis and measured results. The generation of both lift force and thrust in tilt type and partial overlap type magnet wheel are proved by experiments, respectively.     

三相逆变器共模传导电磁干扰的建模与分析

为了预测进而抑制三相逆变器的共模传导电磁干扰(EMI),需要研究其建模和分析方法。本文首先通过对三相逆变器各个开关管的开关状态的分析,得到了三相逆变器共模传导EMI干扰源的简便表示方法,进而提出一种由共模传导EMI干扰源和传播通道模型构成的等效电路模型。通过实验测量和电磁场数值计算,获得等效电路中的各个高频参数。对其共模传导EMI进行仿真和实测1,50kHz～30MHz频段的仿真与实测频谱基本吻合,说明采用本文方法建立的共模等效电路模型是可行的。该方法可作为计算评估三相逆变器共模传导EMI的一种可行方案。     

On the surface field integral equations

Surface field integral equations are the basic tools for electromagnetic waves scattering calculations. They are of particular importance for the evaluation of the ocean or soil surface contributions to backscattering and emissivity in remote sensing applications based on the use of radars or microwave radiometers. The proofs of these fundamental integral equations are disseminated in the scientific literature, and the original references are old. This paper proposes a comprehensive derivation of these relationships for both perfectly conducting and dielectric bodies, starting from Maxwell equations, through Kottler's formulas. Several basic properties for discontinuities in vector surface integrals are required, and the derivations are included. Some original proofs are also provided.     

Electromagnetic Fields Generated by Overhead and Buried Short Conductors Part 1 - Single Conductor

The fundamental concepts and analytical development related to the low frequency electromagnetic fields generated by a single current-carrying conductor immersed in a medium of infinite extent and in a conducting half-space are described and discussed. It is shown that vertical conductors buried in earth are not detectable by above earth surface measurements of magnetic fields. Examples and numerical results involvinq energization of typical intact and broken single conductors are then described and commented on. It is shown that earth surface potentials and above earth magnetic fields are significantly distorted by a break in horizontal and oblique conductors. Finally, experimental measurements on a model with considerable heterogeneities confirm the significant influence of conductor discontinuities on the potential and magnetic field profiles.     

Sleeve monopole on a circular ground‐plane

This paper presents a modal‐expansion analysis of a sleeve monopole antenna on a finite ground‐plane. Two perfectly conducting plates (one above the monopole and the other under the ground‐plane) are introduced to confine the modeling region and to facilitate the modal‐expansion analysis. The resulting guided‐wave structure is then divided into a number of regions and the electromagnetic field components in each region are expanded into the summation of its modal functions. The surface current distribution on the monopole and the antenna's input impedance and radiation pattern are obtained by finding the expansion coefficients through matching the tangential field components across the regional interfaces. Calculated results by the modal‐expansion method agree well with measured results for the return loss of a sleeve monopole fed through a circular ground‐plane by a coaxial probe. Numerical results for the surface current distribution, input impedance, and radiation pattern of a sleeve monopole on a circular ground plane are presented and discussed. Copyright © 2003 John Wiley & Sons, Ltd.