A moment method solution for the shielding properties of three-dimensional objects above a lossy half space

In this paper, a moment method (MM) solution for analyzing the electromagnetic (EM) shielding properties of three-dimensional (3-D) lossy dielectric and magnetic objects over a lossy half space is presented. An MM, based on a volume formulation and a special Green's function in the spectral domain, is developed. Plane waves with TMz and TEz polarizations incident upon 3-D lossy material structures are demonstrated for the shielding effects of those bodies in the presence of a lossy ground. Some of the results are compared with those evaluated by applying the finite difference time domain method, and good agreements are obtained. The MM solution can be used to study the shielding problems for 3-D objects located above a lossy ground.     

Solution of combined-field integral equation using multilevel fastmultipole algorithm for scattering by homogeneous bodies

We present an accurate method of moments (MoM) solution of the combined field integral equation (CFIE) using the multilevel fast multipole algorithm (MLFMA) for scattering by large, three-dimensional (3-D), arbitrarily shaped, homogeneous objects. We first investigate several different MoM formulations of the CFIE and propose a new formulation, which is both accurate and free of interior resonances. We then employ the MLFMA to significantly reduce the memory requirement and computational complexity of the MoM solution. Numerical results are presented to demonstrate the accuracy and capability of the proposed method. The method can be extended in a straightforward manner to scatterers composed of different homogeneous dielectric and conducting objects     

Scattering by arbitrarily cross-sectioned layered, lossy dielectric cylinders

The scattering properties of TM or TE illuminated lossy dielectric cylinders of arbitrary cross section are analyzed by the surface integral equation techniques. The surface integral equations are formulated via Maxwell's equations, Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by flat-pulse expansion and point matching. Once the surface fields are found, scattered field in the far-zone and radar cross section (RCS) are readily determined. RCS thus obtained for circular homogeneous dielectric cylinders and dielectric coated conducting cylinders are found to have excellent agreements with the exact eigenfunction expansion results. Extension to arbitrary cross-sectioned cylinders are also obtained for homogeneous lossy elliptical cylinders and wedge-semicircle cross-sectioned cylinders, with and without a conducting cylinder in its center. RCS dependences on frequency and conductivity as well as the matrix stability problem of this surface integral equation method are also examined.     

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     

Integral equation analysis of dielectric and conducting bodies ofrevolution in the presence of arbitrary surfaces

A formulation is developed to treat radiation from structures consisting of conducting and/or dielectric bodies of revolution (BOR) in the presence of multiple arbitrary shaped three-dimensional objects. A set of integral equations is developed on the surfaces of the combined structure and the resulting integro-differential equations are solved using the method of moments. On the BOR, harmonic entire domain expansion functions are used for the circumferential dependence, while overlapping sub-domain functions are used to model axial curvature. The arbitrary shaped portions of the structure are modeled using triangular surface patch basis functions. The resulting matrix has a partial block diagonal nature which provides a more economical solution for structures which have some rotational symmetry. The accuracy of the BOR and arbitrary surface formulation is verified using the self-consistency method and measured data     

The finite difference method for S-parameter calculation ofarbitrary three-dimensional structures

Describes the application of the finite-difference method for the determination of scattering parameters of passive, arbitrary three-dimensional, lossy structures. Maxwell's equations are solved in the frequency domain by solution of a boundary value problem. The generalized S-parameters can be computed for any one port or two port structure, while dielectric and conductor losses are taken into account. Higher order mode coupling can be considered and different geometries are allowed at the input and output ports. Verification calculations are given and results are presented for typical structures     

时域有限差分法在有耗介质电磁能量吸收问题中的应用

本文论述了用时域有限差分法计算平面电磁波照射下有耗介质中电磁能量的吸收问题。讨论了影响计算精度的各种因素。计算了均匀和分层均匀球体中能量的吸收和分布,并把计算结果与精确的解析分析进行了比较。还讨论了理想导电面的模拟问题,并把结果与镜象理论进行了对比。所有的结果都说明,在一定条件下,时域有限差分法能给出满意的结果。     

Numerical analysis of H-plane waveguide junctions bycombination of finite and boundary elements

A numerical method is formulated for the analysis of H-plane waveguide junctions with arbitrary cross sections. The junctions are loaded with arbitrarily shaped dielectric or ferrite. The method is a combination of the finite-element method and the boundary-element method, and is applied to the regions with and without dielectric or ferrite, respectively. To show the validity and usefulness of the method, a lossy dielectric post and a ferrite slab in a rectangular waveguide are investigated in detail, and the computed results are compared with earlier theoretical and experimental results     

FDFD full-wave analysis and modeling of dielectric and metalliclosses of CPW short circuits

A finite-difference method in the frequency domain (FDFD) is used to analyze the influence of lossy materials on the scattering behavior of CPW short ends. Not only dielectric losses but also realistic metallic losses are taken into account for the first time in an FDFD method. Both, the numerical results for the three-dimensional structure and the complex propagation constants of the homogeneous waveguide are presented. These are compared with those yielded by an analytical method and shown to be of good agreement. Finally, a simple model is presented, which describes the CPW short end with good accuracy     

Space-time integral equation approach to dielectric targets

A time-domain integral equation technique is presented for computing the response of arbitrarily shaped three-dimensional nondispersive homogeneous dielectric solids. The method is an extension of the previously reported space-time integral equation (STIE) approach to scattering from conducting solids. It consists of the simultaneous solution of four integral equations by a procedure of marching in time. The incident pulse-width is of the order of a target dimension. The result is a "smoothed impulse response," or, after deconvolution, a frequency response valid from dc through the resonance region. While applicable to arbitrary shapes, the numerical solution was implemented for smooth solids with plane symmetry. Results for a sphere and a sphere-capped cylinder are given and verified, respectively, by comparison with the Mie series solution and with measurements.     

Diffraction tomographic algorithm for the detection ofthree-dimensional objects buried in a lossy half-space

A diffraction tomographic (DT) algorithm has been proposed for detecting three-dimensional (3-D) dielectric objects buried in a lossy ground, using electric dipoles or magnetic dipoles as transmitter and receiver, where the air-earth interface has been taken into account and the background is lossy. To derive closed-form reconstruction formulas, an approximate generalized Fourier transform is introduced. Using this algorithm, the locations, shapes, and dielectric properties of buried objects can be well reconstructed under the low-contrast condition, and the objects can be well detected even when the contrast is high. Due to the use of fast Fourier transforms to implement the problem, the proposed algorithm is fast and quite tolerant to the error of measurement data, making it possible to solve realistic problems. Reconstruction examples are given to show the validity of the algorithm     

USE OF FINITE-DIFFERENCE TIME-DOMAIN METHOD FOR CALCULATING EM ABSORPTION IN LOSSY DIELECTRIC SCATTERER

The problem for calculating EM energy absorption by lossy dielectric scatterer ir-radiated by plane wave are discussed.The factors affecting the accuracy of computation arediscussed.The calculated results of EM energy absorption and its distribution in homogeneousand layered homogenous lossy dielectric spheres are presented,and a comparison of these resultswith analytical solution is given.The calculation is carried out for dielectric cylinder on conduct-ing ground as well,and the results are compared with the image theory.All the computationsshew that the finite-difference time-domain method can give satisfactory results.     

Electromagnetic Modeling for Microwave Imaging of Cylindrical Buried Inhomogeneities

Many diagnostic techniques in geophysics and civil engineering are based on the interaction of electromagnetic waves with objects buried in homogeneous or stratified media. Most of the investigations are concerned with the detection of buried objects, but a few papers have dealt with the problem of identifying the objects. The proposed method is based on the integral representation for a plane wave incident on a lossy half-space containing a cylindrical object of arbitrary cross section and electrical properties. The induced current distribution in the object is obtained from the backscattered field measurement in amplitude and phase. In order to improve the spatial resolution of the image, the scattered field is measured for different plane wave incidence and frequencies. Results of numerical simulations concerning the shape and size of the object for different values of soil electromagnetic parameters are presented in this paper.     

Importance of normal field continuity in inhomogeneous scatteringcalculations

The finite-element method with conventional scalar bases is coupled with the moment method to handle the three-dimensional scattering and/or absorption from inhomogeneous, arbitrarily shaped objects. The C⁰ finite-element basis enforces continuity of both normal and tangential E at element boundaries within homogeneous regions. At dielectric interfaces, the continuity of normal D and tangential E are enforced in a strong sense. Excellent agreement between the numerical solution and the Mie series is obtained for both internal and scattered fields for homogeneous and layered spheres under plane wave illumination. Compared to an alternative finite-element method using edge elements which lack strong enforcement of normal field continuity, the present method produces higher-order approximations, especially at dielectric interfaces, with no penalties in computational effort     

Complex resonances of conducting spheres with lossy coatings

The electromagnetic scattering amplitude for metal objects coated with a lossless dielectric exhibits a large number of resonances versus real frequency. These resonances are a function of the object shape and size, coating thickness, and coating electrical properties. Previously, it was shown that for coated spheres and nonspherical bare objects, these resonances can be understood in terms of phase matched circumnavigating surface waves and the objects' complex eigenfrequencies. The effect of dielectric loss in the coating on the complex eigenfrequencies and phase velocities of these surface waves is presented for a metal sphere coated with a uniform homogeneous dielectric coating. It is seen that the positions of the complex resonance frequencies move away from the real frequency axis under the influence of dielectric loss in the coating. The effect of this is shown to correspond to the changes in the backscatter spectrum versus real frequency as computed using a Mie series expansion. The significant difference between the lossless and lossy dielectric-coated sphere cases is seen to be due to a modification of the phase velocities of surface waves, particularly the whispering gallery types, and the increased attenuation of the surface wave modes     

Mixed-potential integral expression formulation of the electricfield in a stratified dielectric medium-application to the case of aprobe current source

The well-known procedure for determining the electric field in a structure consisting of an arbitrary number of planar dielectric layers is modified in order to obtain a form specially suited for the analysis of multiprobe multipath configurations. In general, the field is generated by arbitrary currents in the layers and arbitrary sheet currents in the transitions between the layers. The currents may be electric as well as magnetic, and the dielectric layers are isotropic, homogeneous, and lossy. The procedure results in Green's functions especially suited for the analysis of multiprobe multipatch configurations. They can be used in an efficient mixed-potential integral expression formulation. The theoretical procedure is applied in the case of a probe current source situated in one of the dielectric layers of the structure. For this probe current a highly efficient attachment current distribution is derived. Comparison of measured and calculated results for example structures proves the accuracy of both the approach and the attachment mode     

Electromagnetic scattering by a mixture of conducting and dielectric objects: analysis using method of moments

In this paper, the method of moments is employed to solve the combined field integral equation for characterizing electromagnetic scattering by large three-dimensional structures of arbitrary shape. Unlike those discussed in the literature, these structures consist of mixed conducting and homogeneous dielectric objects. To improve the matrix conditioning number, the basis functions used to represent magnetic currents are also chosen as the popular Rao-Wilton-Glisson functions, but are multiplied by a constant number. A Galerkin's procedure is implemented, i.e., the testing functions are chosen to be the same as the basis functions.     

An absorber tip diffraction coefficient

The UTD corner diffraction solution for a perfectly conducting corner is empirically modified for the case of a dielectric corner. The dielectric may be lossless or lossy, but is assumed to be homogeneous. This modified solution is used to calculate the bistatic scattering from the tip of a dielectric pyramid. Sample calculations display some features of the scattering from a single lossy dielectric pyramid. To verify the solution, calculations are compared with backscatter measurements of a single pyramid that is cut from a homogeneous lossless dielectric (polyethylene). Calculations are then compared with measurements for the more pertinent case of bistatic scattering from a wall of pyramidal radar absorbing material     

地下目标的瞬态电磁散射

本文运用时域有限差分法(FDTD)计算埋地物体的瞬态电磁散射,研究了目标的电磁脉冲响应与介质参数和地下结构的关系,为时域探地系统的目标检测和识别提供了一定的理论依据。本文的方法适用于任意形状的柱体目标以及任意二维地下结构,也易于推广到三维的情形。     

Distinctive features of a pulsed beam scattering on a plane surface (two-dimensional case)

A two-dimensional problem of scattering of pulsed beams having arbitrary time and spatial form on a plane surface of a lossy dielectric halfspace is solved. A pulsed beam has been modeled by letting an E- or H-polarized plane pulse with homogeneous front pass through a space filter. The reflected pulse is found using an expansion of the incident pulsed beam over time-harmonic plane waves.