Root-mean-square measure of nonlinear effects to the transient response of thin wires

A root-mean-square (rms) measure of effect of nonlinear loading on the transient response of thin wires is proposed. The transient behavior of nonlinearly loaded wires is analyzed directly in the time domain. The problem is formulated via the space-time Hallen integral equation. The equation is solved by the space-time Galerkin Bubnov boundary element procedure. Numerical results for the transient response of a thin wire computed by a time domain code based on this method are compared with results obtained from a frequency domain code. Some illustrative numerical results for the spatial distribution of the rms values of time varying currents are also presented.     

Time-domain modeling of electromagnetic field coupling to finite-length wires embedded in a dielectric half-space

The transient behavior of a single straight line embedded in a dielectric half-space and illuminated by the electromagnetic pulse (EMP) is analyzed directly in the time domain using the wire antenna approach. The formulation is based on the corresponding space-time Hallen integral equation. The effects of a two-media configuration are taken into account via the Fresnel reflection and transmission coefficient, respectively. The space-time Hallen integral equation is handled by the time-domain version of the indirect Galerkin-Bubnov boundary element method. The transient response obtained using the direct time-domain approach is compared with the results obtained via an indirect frequency-domain analysis method. Some illustrative numerical results are presented in the paper. Numerical results obtained via the different approaches agree satisfactorily, i.e., the maximum deviation between the results is around 6%.     

Time-Domain Analysis of a Large EMP Simulator

The purpose of this paper is to determine numerically the transient electric-field distribution in an EMP simulator. The simulator is composed of three flat-plate transmission-line sections which are approximated by thin wire structures. The problem is treated in the space-time domain using an integral equation which is solved by numerical techniques. The transient electric field is determined in the conical and working regions. The nonuniformity of the field amplitude, the presence of transversal components with noticeable amplitude, and the rise-time variations are analyzed. The influence of some parameters, e.g., the number of wires, is also studied.     

电磁场积分方程时间步进解法稳定性的研究

本文对用三角片状单元剖分及做相应的矢量基函数展开,采用空间域的Galerkin矩量法,时间域采用步进递推方法解电磁场时空积分方程并进行了程序实现.研究了这种方法的优缺点,分析了计算中出现的振荡发散现象,与细线栅网结构剖分方法进行了比较,从中得到关于时空积分方程时间步进解法稳定性的一些结论.     

Transient response of a thin wire to a moving charged particle

The transient current on a thin wire induced by a charged particle moving parallel to the wire axis is studied. An explicit analytical solution for the induced current is obtained by utilizing the natural-mode method in conjunction with the method of asymptotic expansion. It is found that the solution can be split into two parts: one part consists of damped sinusoidal oscillations and the other exhibits quasistatic-like behavior. Numerical results are presented and compared with some selected results obtained directly by numerically solving a spacetime domain integral equation for the induced wire current.     

A stable solution of time domain electric field Integral equation for thin-wire antennas using the Laguerre polynomials

In this paper, a numerical method to obtain an unconditionally stable solution of the time domain electric field integral equation for arbitrary conducting thin wires is presented. The time-domain electric field integral equation (TD-EFIE) technique has been employed to analyze electromagnetic scattering and radiation problems from thin wire structures. However, the most popular method to solve the TD-EFIE is typically the marching-on in time (MOT) method, which sometimes may suffer from its late-time instability. Instead, we solve the time-domain integral equation by expressing the transient behaviors in terms of weighted Laguerre polynomials. By using these orthonormal basis functions for the temporal variation, the time derivatives can be handled analytically and stable results can be obtained even for late-time. Furthermore, the excitation source in most scattering and radiation analysis of electromagnetic systems is typically done using a Gaussian shaped pulse. In this paper, both a Gaussian pulse and other waveshapes like a rectangular pulse or a ramp like function have been used as excitations for the scattering and radiation of thin-wire antennas with and without junctions. The time-domain results are compared with the inverse discrete Fourier transform (IDFT) of a frequency domain analysis.     

细线结构时域电场积分方程的有限差分求解

提出一种求解基于细线结构的时域电场积分方程 ( TDEFIE)的方法 -有限差分方法。与传统求解时域电场积分方程的时域矩量法相比 ,该方法易于数值实现。文中还利用该方法研究了电磁辐射、散射的三个经典问题 ,并将结果与时域矩量法的结果进行了比对 ,研究表明 ,该方法求解细线结构的 TDEFIE非常有效。     

Aperture Excitation of a Wire in a Rectangular Cavity

The problem of determining the currents excited on a wire enclosed within a rectangular cavity is considered. The wire and cavity interior are excited by electromagnetic sources exterior to the cavity which couple to the cavity interior through a small aperture in the cavity wall. It is assumed that the wire is thin, straight, and oriented perpendicular to one of the cavity walls. An integral equation is formulated for the problem in the frequency domain using equivalent dipole moments to approximate the effects of the aperture. This integral equation is then solved numerically by the method of moments. The dyadic Green's function for this problem are difficult to compute numerically; consequently, extensive numerical analysis is necessary to render the solution tractable. SampIe numerical results are presented for representative configurations of cavity, wire, and aperture.     

The space-time domain magnetic vector potential integral equations

The space-frequency domain magnetic vector potential integral equations for the current distribution on wire antennas (Hallen's integral equation and Mei's generalization) are used to derive their counterparts in the space-time domain. Equations for both straight and curved wires are readily derived using a Fourier transform.     

Electromagnetic transmission through mesh covered apertures and arrays of apertures in a conducting screen

The problem of electromagnetic transmission through wire mesh covered arbitrarily shaped aperture or arrays of apertures (possibly covered by a thin lossy dielectric sheet) in a perfectly conducting ground plane is considered. The equivalence principle and image theory are used to derive an integral equation for the equivalent magnetic currents. The method of moments is utilized to solve the integral equation, with the aperture modeled by triangular patches. Numerical results are presented for transmission coefficients and transmission cross-section patterns for electrically small apertures.     

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     

Scattering by thin wire loaded with a ferrite ring

A coupled integral equation formulation and a method of moments (MoM) solution are presented for the problem of scattering by a thin conducting wire of circular cross section with ferrite loading. It is proved that ferrite loading can be used to reduce the radar cross section of long thin objects at their resonant frequency     

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。     

Application of on-surface MEI method on wire antennas

The formulas of the on-surface measured equation of invariance (OSMEI) for wire antennas are derived. The unknowns of each node on the antenna surface are expressed by the vector potential function and surface current density. The unknowns in the vicinity of each node are coupled in a linear equation and the coefficients of the linear equation are determined by the measured equation of invariance (MEI) method. The final impedance matrix obtained by the OSMEI is a highly sparse matrix. It demonstrates that the currents on thin wire antennas may also be solved by a differential equation-based formulation in addition to the conventional integral equations     

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     

积分方程的多重网格解法及其在天线分析中的应用

本文将多重网格方法应用于积分方程，建立了Ｆｒｅｄｈｏｌｍ积分方程的多重网格解法，并将其应用于线天线的分析研究，对不同长度的线天线进行了数值分析，得到了较好的结果。数值实验表明，多重网格方法是一种十分有效的快速迭代方法，为分析大阵问题提供了一种新的数值方法     

On the integral equations of thin wire antennas

The feasibility of direct numerical calculations of antenna integral equations is investigated. It is shown that integral equation of Hallen's type is the most adequate for such applications. The extension of Hallen's integral equation to describe thin wire antennas of arbitrary geometry is accomplished, and results are presented for dipole, circular loops, and equiangular spiral antennas.     

A unified theory of thin material wires [EM scattering]

The author presents an integral equation and method of moments (MM) solution to the problem of scattering by a thin material wire of circular cross section. In general the material wire has permittivity and permeability different from those of free space. The wire of radius a must be sufficiently thin so that k₀a ≪1, where k₀ is the free space wavenumber. However, there is no restriction on |k|a, where k is the wavenumber in the material wire. The method is referred to as unified in that it applies to thin material wires of arbitrary complex permittivity and permeability. Thus, a single or unified formulation applies to a low-density dielectric/ferrite wire or to a highly conducting metallic wire     

Transient excitation of a straight thin-wire segment: a new look atan old problem

The transient excitation of a straight thin-wire segment is analyzed with the aid of a one-dimensional integral equation for the current along the wire. An almost exact derivation of that equation, in which only the radial current on the end faces is approximated, is given. The integral equation obtained turns out to be identical to the reduced version of Pocklington's equation. On the basis of this derivation, existing and new numerical solution techniques are critically reviewed. Pocklington's equation and Hallen's equivalent form are solved directly by marching on in time as well as indirectly via a transformation to the frequency domain. For Pocklington's equation, a conventional moment-method discretization leads to a Toeplitz matrix that is inverted with Levinson's algorithm. For Hallen's equation, the Toeplitz structure is disturbed, and the frequency-domain constituents are determined with the aid of the conjugate-gradient-FFT method. Illustrative numerical results are presented and discussed