复杂媒质目标电磁散射问题的有限元分析

采用有限元方法分析含有各向异性、双各向同性以及双各向异性的复杂媒质目标的电磁散射问题.建立了具有通用形式的线性媒质——双各向异性媒质的有限元泛函公式,并推导了其有限元矩阵方程的具体表达式.通过对铁氧体球、手征球、等离子球和Ω媒质体等四类复杂媒质结构的数值分析,证明了本文给出的复杂媒质散射问题有限元分析方法的准确性以及通用性.     

各向异性材料部分涂覆导体的散射特性研究

利用物理光学法(PO)与有限元法(FEM)混合方法,研究了有各向异性媒质局部涂覆的电大导体目标的电磁散射问题.在有复杂媒质涂覆的电小结构区域采用有限元法,在未涂覆媒质的电大导体区域采用物理光学法结合等效电磁流法.将两部分区域的边界进行消隐处理,考虑耦合效应,并利用共同的等相位面,将不同区域产生的散射场矢量叠加得到总散射场.文中的实例结果与传统的FEM很好的一致,说明了该方法的有效性和精确性.     

两媒质半空间复杂形体电磁散射

本文利用矢量波函数变换方法讨论了两媒质半空间的电磁散射问题，从Ｍａｘｗｅｌｌ方程出发，讨论了单矩法在三维复杂形体散射问题上的实施。并在数学球面上将内部区域的有限元解与外部区域矢量波函数变换的结果相匹配，从而得到复杂埋入体的电磁散射特性。作为检验和示例，本文计算了在平面波照射下自由空间导体球，埋入导体球，埋入介质覆盖钝锥等的散射场，其中一些结果与可供比较的经典解或其它算法的结果进行了比较，吻合较好。     

双各向异性色散介质电磁波传播Z-时域有限差分分析

基于一种改进的Z变换-时域有限差分(Z-Finite-Difference Time-Domain,Z-FDTD)方法,即将双各向异性色散介质的频域本构方程先转化到Z域中,再利用Z变换的性质将其转换到时域,得到离散时域的FDTD迭代式,分析了双各向异性色散介质电磁波传播特性.由于Omega媒质是一种典型的双各向异性色散介质,以此为例编程计算了垂直入射在Omega介质板情形下产生的同极化和交叉极化电磁波的反射和透射情况,并通过算例和解析解对比验证了算法的正确性,最后对其电磁散射特性进行了分析.     

求解各向异性介质涂覆的薄壳元-边界积分法

为了克服传统有限元－边界积分方法在分析薄涂敷目标时采用四面体单元离散导致未知量非常多及需要大量的计算机存储量的缺点,采用薄壳单元（SHELL）与边界积分方法相结合分析各向异性涂敷目标的电磁特性.薄壳单元可以大大减少未知量数目,并可将体积分转化为面积分,使计算量大为减少.用薄壳元－边界积分方法考察了不同厚度及媒质涂敷时对电磁散射特性的影响,证明了该方法是精确的,在减少未知量、存储量和计算时间上具有极大的优势.     

FEM/BEM混合法计算各向异性不均匀介质柱电磁散射

应用有限元-边界元(FEM/BEM)混合法计算二维各向异性不均匀介质柱电磁散射,对介质柱内、外区域分别采用有限元和边界元法进行分析,然后应用边界条件建立部分稀疏部分满填充的矩阵方程.应用内观法结合多波前法求解该矩阵方程,分别计算了均匀分布和不均匀分布的各向异性介质柱的雷达散射截面.数值计算表明,有限元-边界元混合法在分析和计算不均匀开放域电磁问题时有一定的优势.     

电各向异性介质FDTD并行算法的研究

基于一种改进的Z变换-时域有限差分(Z-Finite-Difference Time-Domain, Z-FDTD)方法, 即将双各向异性色散介质的频域本构方程先转化到Z域中, 再利用Z变换的性质将其转换到时域, 得到离散时域的FDTD迭代式, 分析了双各向异性色散介质电磁波传播特性.由于Omega媒质是一种典型的双各向异性色散介质, 以此为例编程计算了垂直入射在Omega介质板情形下产生的同极化和交叉极化电磁波的反射和透射情况, 并通过算例和解析解对比验证了算法的正确性, 最后对其电磁散射特性进行了分析.

     

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。     

类回旋各向异性媒质电磁特性及参数反演研究

讨论了类回旋各向异性媒质参数在对称、共轭对称以及反对称等条件下的有耗性、互易性.然后利用不同极化、不同角度入射条件下类回旋各向异性材料平板的自由空间反射、透射系数及其与媒质参数的特点,通过设计不同的目标函数,提出了在对称、共轭对称以及反对称条件下分步反演该类媒质参数的方法.算例中考虑了有噪声条件下的反演,并讨论了频率的选择、初始值的正确选择以及纵向参数的反演.结果表明,分步反演方法是可行的,为任意复杂电磁媒质的反演提供了一条新的思路.     

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向异性媒质柱的电磁散射，文中给出了一些典型数值算例，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。     

Generalized material models in TLM .II. Materials with anisotropicproperties

For pt. I see ibid., vol.47, no.10, p.1528-34 (1999). Transmission-line modeling (TLM) can be used for the time-domain simulation of electromagnetic wave propagation in anisotropic and bi-anisotropic media. In this paper, Z-transform methods are utilized to obtain the time-domain iteration procedures for propagation in anisotropic and bi-isotropic materials. For clarity, the method is first developed for one-dimensional (1-D) propagation and then extended to the three-dimensional (3-D) case     

Finite-element method coupled with method of lines for the analysis of planar or quasi-planar transmission lines

A full-wave analysis incorporating the finite-element method (FEM) and the method of lines (MoL) is presented in this paper to investigate a planar or quasi-planar transmission-line structure containing complex geometric/material features. For a transmission-line structure being considered, the regions containing complex media are modeled by the FEM while those consisting of simple media with simple geometry are analyzed using the MoL. From the field solutions calculated by MoL, the boundary conditions are constructed. The boundary integrals involved in finite-element analysis are then carried out using these boundary conditions. Since the finite-element analysis is employed only in the complex parts of the structures, while other parts are handled by the MoL, this approach not only retains the major advantage of the FEM in simulating complex structures but also becomes more efficient than the conventional finite-element analysis. Good agreement between the calculated results and those reported in the available literature is obtained and thus validates the present approach. Furthermore, proficient computational efficiency of this method is demonstrated by examining its convergence property. Finally, a number of relevant transmission-line structures are analyzed to illustrate the applications of this approach.     

A simplified formulation to analyze inhomogeneous waveguides withlossy chiral media using the finite-element method

In this paper, an efficient finite-clement formulation is presented for the analysis of the propagation characteristics in arbitrarily shaped lossy inhomogeneous waveguides loaded with chiral media. It is a simplified form of the one proposed for the bi-anisotropic media. In this formulation, showing no spurious modes, the frequency or the propagation constants may be treated as eigenvalues of a resulting sparse quadratic eigenproblem. However, in order to handle losses easily and to facilitate computation of complex modes, the frequency is specified as an input parameter and the eigensystem is solved for the complex propagation constant as the eigenvalue. This sparse eigensystem is further transformed into a generalized one, thus maintaining the sparse properties of the matrices. New numerical finite-element results are presented     

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     

Properties of and generalized full-wave transmission line modelsfor hybrid (Bi)(an)isotropic waveguides

In this paper single and coupled equivalent transmission lines are developed for the propagation of modes in reciprocal and nonreciprocal, anisotropic, bi-isotropic, and bi-anisotropic waveguides. The transmission lines are described by the generalized telegrapher's equations. In order to develop these transmission line models some properties related to reciprocity, bi-directionality, and mirroring, of general waveguides and generalized transmission lines are investigated. The transmission line models are based on the reciprocity theorem and are valid for arbitrary frequencies     

A brief review of a new development for constitutive relations oflinear bi-anisotropic media

While physical restrictions on the constitutive parameters of linear bi-anisotropic media are well known, attention has been meager on the issue of mathematical consistency, when specializing the Maxwell equations for material media. The authors show that such a consistency requirement results in a mathematical constraint: an algebraic relation between the constitutive parameters. Repercussions for specific types of linear media are discussed, most importantly, the consequence that bi-isotropic media must be reciprocal     

General theory of Maxwell-Garnett model for particulate composites with bi-isotropic host materials

A self-consistent derivation is given for the Maxwell-Garnett model for a very general particulate composite. The bi-anisotropic inclusions are supposed to be randomly embedded in a bi-isotropic host medium. It is seen that the effective medium is also bi-anisotropic in general.     

Finite-Element Formulation in Terms of the Electric-Field Vector for Electromagnetic Waveguide Problems

A vector finite-element method for the analysis of anisotropic waveguides with off-diagonal elements in the permeability tensor is formulated in terms of all three components of the electric field. In this approach, spurious, nonphysical solutions do not appear anywhere above the "air-line." The application of this finite-element method to waveguides with an abrupt discontinuity in the permittivity is discussed. In particular, we discuss how to use the boundary conditions of the electic field at the interface between two media with different permittivities. To show the validity and usefulness of this formulation, examples are computed for dielectric-loaded waveguides and ferrite-loaded waveguides.     

Generalized spectral-domain analysis for multilayered complex mediaand high-Tc superconductor applications

An efficient algorithm for rigorously deriving the spectral-domain impedance dyadic Green's function for MMICs on general complex anisotropic or bi-anisotropic substrates is developed. Its main advantage is that it provides closed-form expressions for transverse propagation constants and related immittances in the spectral domain and, therefore, allows the following parameters to be taken into account: dielectric and magnetic losses of anisotropic or bi-anisotropic media without restrictions to the magnitude of tensor elements, alternative directions for magnetic bias, and the finite metallization thickness of conventional conductors and/or superconductors including their losses. Microstrip and coplanar waveguide structures in open, shielded, and conductor-backed technology can be treated. The theory is verified by comparison with previously published data, and its flexibility is demonstrated for both superconductor and conventional conductor (M)MIC structures