An alternative solution of the scattering from an anisotropic cylindrical dielectric shell

A method based on the approximate wave functions for anisotropic media and the mode-matching approach is developed to solve the problem of the electromagnetic scattering from an anisotropic cylindrical dielectric shell. The cylindrical shell is assumed to be infinite in length, and it is illuminated by a plane wave or a cylindrical wave from a line source. The problem is two-dimensional and the solutions to both types of polarization (TE and TM) are presented. The validity of this solution is verified by comparing the numerical results with those in literatures and the previous calculations based on the exact wave functions for anisotropic media. Numerical results show the higher computational efficiency of the present method for bounded anisotropic media.     

用FD－MEI计算横各向异性媒质柱的电磁散射特性

本文推导了二维横各向异性媒质中电磁散射的差分方程，得到了９点的差分格式，并将不变性测试方程与该差分方程结合计算了具有任意横截面、非均匀、有耗和一般张量形式的二维横各向异性媒质柱的电磁散射。文中给出一些典型数值算例。数值结果表明，该方法在分析计算此类问题时是有效的且具有一定的优势。     

Finite element solution for a class of unbounded geometrics [EMscattering]

An efficient and systematic procedure is described for the finite-element solution of a class of electromagnetic radiation and scattering problems involving unbounded geometries. The numerical procedure is well suited for analyzing infinite metallic structures with cavity regions filled with inhomogeneous and anisotropic media. The formulation is based upon an approach that combines the finite-element method (FEM) with the surface integral equation to truncate the mesh region. The efficiency of the proposed technique arises from the use of the Green's function of the first kind in the surface integral. Illustrative numerical representations that demonstrate the validity, versatility, and efficiency of the method are included     

厄米-高斯波束对各向异性圆柱的散射特性研究

为了研究厄米-高斯波束在各向异性媒质中的散射特性，采用了将各向异性圆柱的散射场和内部场用圆柱矢量波函数展开，应用电磁场边界条件和投影法，提出了一种分析单轴各向异性圆柱对厄米-高斯波束散射特性研究的精确半解析方法; 获得了厄米-高斯波束通过单轴各向异性圆柱的内场以及近场的归一化强度分布图; 对两种不同的厄米高斯波束入射情形做出了分析和对比。结果表明，两种波束在通过圆柱后都有入射波和反射波叠加而成的驻波现象，而TEM₁₀(x′)模式厄米-高斯波束入射后近场强度增强，且有明显的折射现象。该研究结果对厄米-高斯波束的应用具有一定的参考价值。     

Scattering from an anisotropic cylindrical dielectric shell

The electromagnetic scattering from an anisotropic cylindrical dielectric shell is formulated by using the wave functions for anisotropic media and the boundary-value method. The cylindrical shell is assumed to be infinite in length, and it is illuminated by a plane wave or a cylindrical wave from a line source. The problem is two-dimensional and the solutions to both types of polarization (TE and TM) are presented. Numerical results for the effects of various geometrical and electrical parameters on the bistatic radar cross section are presented.     

平面分层媒质空域Green函数快速计算(Ⅰ)

格林函数法是电磁场数值分析中的一种基本方法,平面分层媒质的空域格林函数通常表达成Sommer-feld积分形式。文中针对该问题快速求解的几种基本方法进行了系统分析,对各种分析方法进行了分类,根据研究进展情况,概述了传统离散复镜像法(DCIM)、二阶DCIM、增强型DCIM(EDCIM)、柱面波逼近和支割线积分以及其他方法,阐明了各种方法的优缺点;对计算得到的闭式Green函数在具体电磁散射与辐射计算中产生的误差控制、定阶、维数、媒质有耗问题进行了分析,给出了一种简便的有耗媒质DICM方法,数值计算结果显示文中方法的正确性。     

On the scattering of electromagnetic waves by bodies buried in a half-space with locally rough interface

A method for the scattering of electromagnetic waves from cylindrical bodies of arbitrary materials and cross sections buried beneath a rough interface is presented. The problem is first reduced to the solution of a Fredholm integral equation of the second kind through the Green's function of the background medium. The integral equation is treated here by an application of the method of moments (MoM). The Green's function of the two-part space with rough interface is obtained by a novel approach which is based on the assumption that the perturbations of the rough surface from a planar one are objects located at both sides of the planar boundary. Such an approach allows one to formulate the problem as a scattering of cylindrical waves from buried cylindrical bodies which is solved by means of MoM. The method is effective for surfaces having a localized and arbitrary roughness. Numerical simulations are carried out to validate the results and to show the effects of some parameters on the total field. The present formulation permits one to get the near and far field expression of the scattered wave.     

导体球涂覆各向异性铁氧体介质电磁散射的解析解

该文用球矢量波函数对各向异性铁氧体介质涂覆导体球的电磁散射解析解开展研究。各向异性铁氧体介质中电磁场的球矢量波函数解可表示成第一、二、三、四类球矢量波函数之和。根据球Bessel函数的性质,可以得出导体球涂覆各向异性铁氧体介质的球矢量波函数解析解。应用铁氧体与自由空间分界面上电磁场切向连续和在导体球面上切向电场等于零的边界条件以及球矢量波函数切向正交性质,可分别得出铁氧体介质中电磁场和散射场的展开系数。给出了平面波入射情况下的数值计算结果。该文的结果可应用于有关微波器件、天线以及目标特征的分析和计算。     

平面分层媒质空域Green 函数快速计算

格林函数法是电磁场数值分析中的一种基本方法,平面分层媒质的空域格林函数通常表达成Sommer-feld积分形式。文中针对该问题快速求解的几种基本方法进行了系统分析,对各种分析方法进行了分类,根据研究进展情况,概述了传统离散复镜像法(DCIM)、二阶DCIM、增强型DCIM(EDCIM)、柱面波逼近和支割线积分以及其他方法,阐明了各种方法的优缺点;对计算得到的闭式Green函数在具体电磁散射与辐射计算中产生的误差控制、定阶、维数、媒质有耗问题进行了分析,给出了一种简便的有耗媒质DCIM方法,数值计算结果显示文中方法的正确性。     

曲面共形阵列结构快速数值分析方法

针对曲面共形阵列结构电磁散射特性的高效、精确仿真分析需求,提出了一种并行综合函数矩量法处理方案.该方法是传统电磁经典数值算法——矩量法的一种改进形式,通过几何区域分解处理和综合基函数的方式极大降低了算法的内存消耗,使得单机分析电大尺寸问题和大规模阵列问题成为可能.更为重要的是,针对周期阵列结构,该方法具备综合函数复用特性和多区域并行处理特性,能够大大提高算法的综合处理效率.一个6×11的柱面共形贴片阵列被用于验证所提方法的性能,仿真结果表明,对于周期阵列结构,该方法的计算精度与多层快速多极子算法相当,虽然计算效率略低于多层快速多极子方法,但内存消耗比多层快速多极子方法低一个数量级.     

基于MoM-PO的各向异性阻抗面电磁散射研究

该文基于阻抗边界条件(IBC),采用矩量法-物理光学(MoM-PO)混合算法,研究了3维各向异性阻抗面的电磁散射特性。根据表面等效原理,将空间散射场等效为MoM区和PO区电磁流的辐射场,感应电磁流以3维RWG (Rao-Wilton-Glisson)矢量基函数展开。以表面阻抗并矢表征电磁参数,给出典型各向异性阻抗面目标的电磁仿真算例,结果与Mie级数等精确解吻合良好,显示了该方法的有效性。     

A comparison of anisotropic PML to Berenger's PML and itsapplication to the finite-element method for EM scattering

The use of an anisotropic material for the boundary truncation of the finite-element method is considered. The anisotropic material properties can be chosen such that a plane-wave incident from free space into the anisotropic halfspace has no reflection. Because there is no reflection, the material is referred to as a perfectly matched layer (PML). The relationship between the anisotropic PML and the original PML proposed by Berenger (see J. Comp. Phys., vol.114, p.185-200, October 1994) is considered. The anisotropic PML is applied to the finite-element solution of electromagnetic (EM) scattering from three-dimensional (3-D) objects. Numerical results are presented to demonstrate the accuracy of the PML     

Closed-form solutions for one-dimensional inhomogeneous anisotropicmedium in a special case. II. Inverse scattering problem

For pt. I see ibid., vol.45, no.5, p.936, 1997. An analytical method is presented for the inverse scattering problem of a one-dimensional (1-D) inhomogeneous anisotropic medium in a special case. Using the closed-form formulations for the reflection coefficients derived in the first part of this paper, reconstruction formulas are obtained for the wave impedance profiles, permittivity profiles or permeability profiles of the anisotropic medium, all of which are given in closed form. In the meantime, a partial inverse scattering method for the electric parameters at the interface of the medium with free space is also investigated by using a Wedtzel-Kramers-Brillouin (WKB) approximation. Numerical examples show the validity of the methods     

A moment method solution for TMz and TEzwaves illuminating two-dimensional objects above a lossy half space

A moment method (MM) solution for analyzing the electromagnetic shielding and scattering properties of two-dimensional (2-D) objects over a lossy half space is presented. The materials of the objects can be metal, dielectric, or magnetic. Also, the lossy half space is included to simulate the effects of the earth ground or any flat homogeneous lossy surface. An MM based on a volume formulation and a special Green's function in the spectral domain is developed. Both TM _z and TE_z waves incident upon 2-D metal or lossy material structures are demonstrated for the shielding effects of those bodies in the presence of the lossy ground. Besides, the echo widths of a composite object either in free space or above the lossy half space are determined by using the MM. Some of the results are compared with those by other methods, and good agreements are obtained. The MM solution can be used to study the shielding and scattering problems for cylindrical structures located over a lossy ground     

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere of multilayers

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere is formulated and obtained, where the inhomogeneous plasma anisotropic sphere is divided into (s-1) homogeneous anisotropic spherical layers. The electromagnetic fields in the inner spherical multilayers and outer free space of the inhomogeneous plasma anisotropic spherical structure can be expanded in terms of the spherical vector wave functions in plasma anisotropic medium and in isotropic medium, respectively. By applying the continuous boundary conditions of electromagnetic fields on the spherical interfaces of the (s-1)-layered homogeneous anisotropic plasma medium, the unknown expansion coefficients of fields in the multilayered plasma spherical structure are obtained, and then the electromagnetic field distributions are calculated. Numerical results for the very general inhomogeneous plasma dielectric material sphere are given and the data in a special case are obtained using the present method and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach and compared to each other to verify the correctness and applicability of the present analysis.     

Electromagnetic scattering from nonlinear anisotropic cylinders. I.Fundamental frequency

The solution of the problem of electromagnetic scattering of obliquely incident plane waves by homogeneous, nonlinear anisotropic cylindrical structures is obtained. The medium of the scatterer is characterized by Volterra-type integrals for the electric and magnetic flux density vectors D and B, respectively. The nonlinear problem is solved using the perturbation method. The effects of nonlinearities on the field properties both inside and outside the scatterer, together with the effect on the radar cross section, are investigated for the fundamental frequency components. To demonstrate the validity of the approach, the results obtained by the perturbation method are compared with those obtained using the plane wave representation method of D. Censor (1983), where the iteration method is used to solve the resulting dispersion equation. The results are in very good agreement in both amplitude and phase of the fields for the case of very weak nonlinearity. When the relative magnitude of the nonlinear component of the permittivity is increased, the iteration method shows a faster divergence of the phase from the linear phase     

Closed-form solutions for one-dimensional inhomogeneous anisotropicmedium in a special case. I. Direct scattering problem

An analytical formulation is presented for the direct scattering problem of one-dimensional (1-D) inhomogeneous anisotropic medium in a special case. This method gives nonlinear differential equations for the reflection coefficients of the anisotropic medium. Applying the discontinuity condition of the dielectric parameters at the interface of the medium with free space, approximate closed-form solutions for the reflection coefficients are obtained. Numerical examples show the validity of the method     

Oblique Plane-Wave Scattering From a General Bi-Isotropic Cylindrical Shell With an Interior Advanced Composite-Material Backing

This paper presents a rigorous and efficient theoretical model for analyzing the oblique plane-wave scattering properties of a multilayered bi-isotropic cylindrical shell backed by an interior advanced composite material. The backing material considered is a graphite-fiber-reinforced plastic composite (GFRPC), which is treated as a laminated electrically anisotropic medium. In this model, a recursive eigenfunction theory is derived for describing the electromagnetic fields in the bi-isotropic layers of the cylinder, while a state-equation approach is employed for governing the fields in the anisotropic layers of the cylinder. On the basis of this model, echo widths were computed and, wherever possible, were compared with data available in the literature to validate this model. Particularly, the distinct scattering properties of obliquely incident cases are observed and discussed in detail     

Application of extended boundary conditions and the Haar wavelets in the analysis of wave scattering by thin screens

A recent approach to solution of 2D scattering problems for electromagnetic waves scattered by thin screens is analyzed. With the use of examples of scattering by a strip and an unclosed cylindrical surface, it is shown that the proposed approach has no advantages in terms of the efficiency of numerical solution over a well-known approach based on exact integral equations for currents that have singular kernels and that are solved with the Krylov-Bogoliubov method.