Courant induit par une onde incidente sur un conducteur rectiligne et filiforme situé au voisinage du sol

An analytical result for the current induced by an incident wave on a thin straight wire located in the vicinity of the ground and parallel to the interface is presented. Two methods are presented to solve this problem in the frequency domain. The first one uses the current on an infinite wire; the current induced on a finite wire is obtained adding to the preceding solution the reflected currents of different orders. The second uses the reflection coefficient of the transmission line theory. The results are compared with those obtained from another method in which Sommerfeld integrals are numerically evaluated.     

The excitation of current on an infinite horizontal wire above earth by a vertical electric dipole

The formal solution to the problem of finding the current induced on a horizontal wire above earth by a vertical electric dipole is given. A simple solution for the case where the dipole is electrically distant from the wire is developed. The interpretation and restrictions of this solution are discussed.     

Wire antennas in the presence of a dielectric/ferrite inhomogeneity

A moment method solution for treating thin-wire antennas in the presence of an arbitrary dielectric and/or ferrite inhomogeneity is presented. The wire is modeled by an equivalent surface current density, and the dielectric/ferrite inhomogeneity is modeled by equivalent volume polarization currents. The conduction currents on the wire and the polarization currents in the dielectric/ferrite inhomogeneity are treated as independent unknowns and determined in the moment method solution. The method is applied to the problem of a loop antenna loaded with dielectric or ferrite. Numerical results are presented, and are in good agreement with measurements and previous calculations.     

Current on a long, thin wire in a chiral medium

The propagation of current on a thin, straight wire in an infinite chiral medium is examined by solution of the integral equation for an infinite wire and also from the moment-method solution for a long wire of finite length. The current on the infinite wire is shown to consist of three components: a discrete mode that decays exponentially and two continuous-spectrum components from branch cuts from the two chiral wavenumbers. The integral equation for a finite wire in the chiral medium is solved by the method of moments using a modified version of the numerical electromagnetics code (NEC). The moment-method solution is shown to be in close agreement with the modal solution for the infinite wire, providing validation for the numerical treatment     

Analysis of a monopole mounted near or at the edge of a half-plane

The problem of a monopole antenna mounted near or at the edge of a half-plane is solved using a hybrid moment method solution with an integral expression for the exact half-plane Green's function. Results are presented for input impedance of alambda/4monopole versus distance from the half-plane edge and versus angle for an edge-mounted antenna, Simple expressions for the surface current density induced on the half-plane are derived, and an attachment mode is constructed for use with the author's previously developed surface patch moment method solution when a wire is attached at or near an edge of a finite plate. Results obtained from the MM/GTD method are also presented for comparison.     

Transmission Line Mode Response of a Multiconductor Cable in a Transient Electromagnetic Field

This paper describes a technique for obtaining the induced worst case currents on individual wires of a multiconductor cable as a result of a transient electromagnetic radiation field. The technique involved a development of the expression for the induced current in matrix form where the mutual coupling terms and the other cable currents are the pertinent parameters. A worst case solution results from the assumption of maximum coupling orientation of the individual wires. A short example and some test results are presented. The test results show wave shapes for inductive and capacitive coupling. The solution for the individual wire current due to a transient electromagnetic field is important, since it will greatly reduce the required number of cable measurements and will allow the development of improved shielding techniques.     

Analysis of Radiation from a Traveling-Wave Current and Comparison with the Standing-Wave Sinusoidal Current Filament

The traveling-wave current (TWC) has served as one kind of "canonical" current distribution for simulating the behavior of a wire antenna, as has the standing-wave, sinusoidal current filament (SCF). Besides yielding closed-form solutions for their far-field patterns and radiated powers, the sinusoidal current filament and traveling-wave current can approximate the current on a wire antenna that is appropriately excited. The traveling-wave current's power distributions, as obtained using the induced EMF method and the FARS (far-field analysis of radiation sources) method, together with similar results for the sinusoidal current filament, are discussed in this brief note     

Courant induit par une onde incidente sur un conducteur rectiligne et filiforme situé au voisinage du sol

An analytical result for the current induced by a plane incident wave on a thin straight insulated wire buried in the ground and parallel to the interface is presented. Two methods are presented to solve this problem in the frequency domain; the first one uses the current on an infinite wire; the current induced on a finite wire is obtained adding to the preceding result the reflected currents of different orders. The second uses the reflection coefficients of the transmission line theory. The results are compared with those obtained from another method in which the Sommerfeld integrals are numerically evaluated.     

线天线和散射体时域分析的半解析法

针对细线结构电磁辐射和散射问题,构造了一种求解导体上瞬态电流的半解析法。以频域内近似解为初值,结合积分方程,通过迭代得到频域内的改进解,并通过傅里叶逆变换得到时域内的相应迭代方法。与数值方法相比,该方法易于数值实现。辐射和散射实例的数值分析结果与Feko仿真结果相吻合,表明该方法对于细线结构时域分析是有效的。     

Transient current on a wire penetrating a cavity-backed circular aperture in an infinite screen

The problem of a wire penetrating a circular aperture in an infinite conducting screen and entering a circular cylindrical cavity is considered. Results for the transient current propagating along the wire both inside and outside the cavity are presented. The current in both regions is evaluated in the frequency domain by the method of moments (MOM). An approximate method for evaluating the exterior current at an observation point far from the aperture is discussed. To obtain the transient response, a numerical inverse Fourier transform is used. The current response is examined as a function of cavity and aperture dimensions. Results obtained with the approximate method are compared with the MOM solution. It appears that information concerning the interior cavity dimensions is present in these exterior observations.<>     

The analysis of the RF response of a solid wire excited by a focused laser beam

The solution is presented for the current excited on a solid cylindrical wire with a flat endcap which is excited by a short current filament oriented parallel to the wire axis and located on or near the endcap surface. This wire/source geometry has become of interest as a result of experimental findings in which transient source filaments have been excited on metal targets due to the incidence of a high-power short-pulse laser beam. Steady-state solutions are developed which show the basic characteristics of the responses and their dependence on critical wire and source parameters. Transient responses also are presented and shown to exhibit excellent agreement with measured results.     

Scattering by a perfectly conducting and a coated thin wire using aphysical basis model

A traveling-wave model is used in conjunction with a Galerkin's solution of the exact integral equation to solve for the scattering by a thin perfectly conducting and a thin dielectrically coated wire. The proposed current model consists of three weighted traveling-wave components; one is associated with the current on the infinite wire whereas the other two describe the reflected traveling waves from the wire terminations. Several current distribution and scattering patterns are presented which serve to validate the accuracy of the model and the derived analytical formulas     

Coil bobbin composed of high-strength polyethylene fiber reinforced plastics for a stable high-field superconducting magnet

High-field superconducting solenoid magnets sometimes quench by wire motion induced by electromagnetic force. Fiber reinforced plastic [Dyneema fiber reinforced plastic (DFRP)] pipes composed of high-strength polyethylene fiber by filament winding method could be constructed so as to expand in the circumferential direction when cooled to low temperature with an appropriate selection of winding angle and shape of the pipes. In the case of a superconducting coil fabricated with a DFRP bobbin, it is expected that wire motions in high field are decreased by expansion of the coil bobbin. In this paper, tap voltage between both ends of the coils fabricated with DFRP bobbin and stainless steel (SUS) bobbin were measured with increasing current. The coil using SUS bobbin showed many sharp peaks in tap voltage induced by quick wire motions. In contrast, those using DFRP bobbin showed only a few small peaks. These results suggest that wire motions were constrained by DFRP bobbin. The training effects were observed in both cases.     

On bounding the excitation of a terminated wire behind an aperture in a shield

A formulation is developed for determining the voltage and current induced on an impedance-terminated wire behind an aperture in a shield. Loading effects on the aperture are included by using receiving antenna theory. Upper bounds for the current and voltage are obtained and numerical results are presented for a thin slot antenna.     

应用矩量法对任意线天线辐射特性的分析

采用矩量法对线形导体上的辐射特性进行了分析，该方法是基于伽略金法，以三角矢量函数作为空间的基函数和检验函数对任意形状的线结构的电场积分方程进行求解，并以此求解天线上的电流分布和天线的功率辐射方向图。给出了篇例，结果表明，该方法是有效的，为超宽带天线的分析奠定了基础。     

Multipolarizability tensors of thin-wire scatterers: a directcalculation approach

A new and efficient method for the computation of multipolarizability tensors is developed. The discussion is restricted to thin-wire scatterers. On the basis of a numerical solution for the current on the wire a fully analytical series expansion is deduced. This series representations allows one to identify the different multipolarizability terms. As shown, two constraints on the implementation of the numerical method have to be introduced to ensure reciprocity. The calculated results are cross-checked on the basis of mixing theories with published theoretical and measured chiral constitutive parameters. Finally, direct measurements performed on a single scatterer are compared to the theoretical results     

Scattering by a thin wire parallel to a ground plane using the singularity expansion method

A thin wire parallel to a ground plane is analyzed using moment methods to find the complex natural resonant frequencies and modal current distributions. The resonant frequencies are found as functions of the wire radius and distance above the ground. The complex frequencies appear to be divisible into two classes: 1) those associated with the resonant length of the dipole and 2) those associated with interactions of the dipole and its image. For large dipole radii, the two classes interact and some anomalies, which appear, are investigated. The time domain response to a step-function plane wave is computed using the singularity expansion method and the results compare favorably with the Fourier transform solution.     

Electromagnetic field coupling to a line of finite length: theoryand fast iterative solutions in frequency and time domains

A system of integral-differential equations for evaluating currents and voltages induced by external electromagnetic fields on a finite-length horizontal wire above a perfectly conducting ground is derived under the thin wire approximation. Based on perturbation theory, an iterative procedure is proposed to solve the derived coupling equations, where the zeroth iteration term is determined by using the transmission line (TL) approximation. The method can be applied both in the frequency and in the time domains. The proposed iterative procedure converges rapidly to the exact analytical solution for the case of an infinite line, and to the NEC solution for a line of finite length. Moreover, with only one iteration, an excellent approximation to the exact solution can be obtained. The method is applied to assess the validity of the TL approximation for plane wave coupling to an overhead line of finite length. It is shown that the resulting errors for the early-time response are generally higher than those corresponding to infinite lines     

On the use of spatio-temporal wavelet expansions for transient analysis of wire antennas and scatterers

To analyze a wire antenna excited by a time varying voltage source or a wire scatterer excitated by transient electromagnetic incident wave, the problem is formulated in terms of a time-domain integral equation for the induced current. To solve the integral equation, we reduce it to matrix equation via the method of moments using the known-to-be-stable implicit scheme. However, rather than directly constructing and solving the relatively large matrix equation, we propose an iterative procedure which allows us to gradually obtain a solution of refined accuracy both everywhere and simultaneously at any time instance. To render this procedure rapidly converging, we use a basis of spatio-temporal wavelet functions. This basis facilitates a good approximation of the induced current using far less basis functions than would be needed if other expansions, such as standard-pulse or Fourier basis functions were chosen. The use of this basis further enables the iterative procedure to increase the temporal and spatial resolutions where required without unnecessarily affecting their levels elsewhere.     

Electromagnetic Subsurace Radar Using the Transient Field Radiated by a Wire Antenna

A radar based on the propagation of a short pulse of current along a wire parallel to the ground surface is described. The wire acts both as a traveling-wave transmitting antenna and as a receiving antenna. For applications to civil engineering, the depth of exploration may be less than 1 m, the purpose being, for example, to detect discontinuities situated near the ground surface, to measure the thickness of a thin layer (10-50 cm), or to characterize a change in its reflection coefficient. Therefore, the width of the pulse of current is about 1 ns. The theoretical approach shows that the wire must be situated at about 10 cm above ground and that there is an optimum position for the current probe that detects the induced current due to a reflecting layer. Several experiments will also be described showing the feasibility of the method.