Matrix formulation of electromagnetic scattering

A new method is proposed for the computation of the radar cross section and other associated field quantities arising when a smooth, perfectly conducting obstacle is illuminated by an incident electromagnetic wave. The scattered wave is first represented by a distribution of electric dipoles over the surface in question, with the response from any dipole proportional to the induced surface current density at that point. The surface current is then determined by the "boundary condition" that the scattered wave, through interference, precisely cancels the incident wave inside the obstacle. One obtains in this mariner a pair of coupled (infinite) matrix equations for the surface current. Green's identity permits decoupling of the equations, reducing the problem to roughly the equivalent of two independent scalar problems. The equations have been specialized to axially symmetric obstacles and then solved numerically on the IBM 7094 for several examples of interest. Reciprocity and energy conservation are also examined and the resonant mode (interior) problem set up explicitly in matrix form.     

Electromagnetic scattering by nonplanar junctions of resistivesheets

Approximate uniform asymptotic expressions are provided to determine the field scattered by a penetrable wedge illuminated at normal incidence. The wedge is formed by two resistive sheets or two thin dielectric slabs definable as resistive sheets having identical geometric and electromagnetic characteristics. The solution is limited to wedge angles and source positions where internal reflections cannot occur. It is obtained by using a geometrical optics (GO) approximation for the field internal to the slabs and by performing a uniform asymptotic evaluation of the physical optics (PO) radiation integral in the hypothesis that a resistive sheet condition is valid. Samples of numerical results so obtained are presented and compared with other methods to demonstrate the effectiveness of the proposed technique     

Transform approach to electromagnetic scattering

In this paper, we present a comprehensive review of the Fourier transform technique as applied to the problem of high-frequency scattering and introduce the concepts of the spectral theory of diffraction (STD). In contrast to the more commonly employed ray-optical method for high-frequency scattering, viz. the geometrical theory of diffraction (GTD), the STD approach interprets the scattered field as the spectrum, or the Fourier transform of the induced current on the scatterer. Such an interpretation offers several important advantages: uniform nature of representation, capacity to improve and extend the ray-optical formulas in a systematic manner, and convenient accuracy tests for the results. Methods for combining integral equation methods with the Galerkin procedure and asymptotic techniques in the transform domain are described, and representative examples illustrating the application of the spectral approach are included.     

Ultra-wide-band transient electromagnetic scattering laboratory

A unique free-field transient scattering facility is described which employs a dual-channel ultra-wide-band impulsive source. A brief historical review is presented, and the theory and operational characteristics of the laboratory are discussed. Technical implementations which have yielded significant improvement in effective bandwidth and signal-to-noise ratio (SNR) are described. High-quality experimental validations are shown, and consideration is given to future enhancements     

TM electromagnetic scattering by a transparent wedge with resistivefaces

The Sommerfeld-Maliuzhinets (1958) method is used to calculate the total fields in the interior and exterior regions of an arbitrarily angled resistive wedge. A E-plane wave (TM mode) normally illuminates the two-dimensional resistive wedge. Two spectral functions are introduced to represent the fields in both regions. By imposing the resistive boundary conditions on the wedge faces, a system of coupled functional equations is obtained for the two unknown spectral functions. The functional equations are reduced to singular integral equations for the auxiliary functions. The predictions for a right-angled resistive wedge are shown to be in good agreement with measurements     

Determination of volume and surface scattering from saline iceusing ice sheets with precisely controlled roughness parameters

Experiments were performed at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, NH, to precisely determine the relative contributions of surface and volume scattering from saline ice that has well-known surface roughness characteristics. The ice growth phase of the experiment made use of two 6-ft diameter tanks and a 6-ft diameter mold with known roughness statistical parameters of rms height=0.25 cm and Gaussian correlation (correlation length=2.0 cm). One tank was used for growing a moderately thick saline ice sheet with very smooth surface, and the other was used for growing a thin layer of freshwater ice over the surface mold. The latter resulted in a layer with one statistically known rough boundary and one smooth boundary. Wide-bandwidth, multiple incidence angle backscattering measurements were performed, first on the bare saline ice sheet and then on the same sheet after the thin freshwater ice sheet was placed on top of it. Results indicate that the surface scattering dominates over saline ice volume scattering at all frequencies for low incidence angles for both the very smooth and Gaussian rough surfaces. The significance of volume scattering depends strongly on angle of incidence, frequency, volume scattering albedo, surface roughness, and surface correlation function     

The tolerance method for electromagnetic scattering

The original electromagnetic field will be disturbed when the parameter of a local region is changed. To find the distribution of the disturbed electromagnetic field a boundary value problem, which is different from the original one, must be solved. A method to find the disturbed electromagnetic field from the known original one with a minimum amount of computation would be very significant. In this paper, we present a method, tolerance method, which can save significant computer time in the computation of the disturbed electromagnetic field. This method can be used for many complicated boundary value problems as well as for optimum design in engineering. An example of the computation of an electromagnetic scattering problem is given in this paper     

A FAFFA-MLFMA algorithm for electromagnetic scattering

Based on the multilevel fast multipole algorithm (MLFMA), an efficient method is proposed to accelerate the solution of the combined field integral equation in electromagnetic scattering and radiation, where the fast far-field approximation (FAFFA) is combined with MLFMA. The translation between groups in MLFMA is expensive because spherical Hankel functions and Legendre polynomials are involved and the translator is defined on an Eward sphere with many k/spl circ/ directions. When two groups are in the far-field region, however, the translation can be greatly simplified by FAFFA where only a single k/spl circ/ direction is involved in the translator. The condition for using FAFFA and the way to efficiently incorporate FAFFA with MLFMA are discussed. Complexity analysis illustrates that the computational cost in FAFFA-MLFMA can be asymptotically cut by half compared to the conventional MLFMA. Numerical results are given to verify the efficiency of the algorithm.     

Dual-surface integral equations in electromagnetic scattering

A brief review is given of the derivation and application of dual-surface integral equations, which eliminate the spurious resonances from the solution to the original electric-field and magnetic-field integral equations applied to perfectly electrically conducting scatterers. Emphasis is placed on numerical solutions of the dual-surface electric-field integral equation for three-dimensional perfectly electrically conducting scatterers.     

Non-uniform wavelets in electromagnetic scattering analysis

Non-uniform wavelets are constructed to benefit from both adaptively refined grids for modelling edge singularities and compression of moment matrices with wavelet bases. They are applied to the analysis of electromagnetic scattering problems     

Neighboring-patch integrals in transient electromagnetic scattering

The integrals over patches that are close to the self-patch are calculated by expanding the factors in the integrand in power series. The values are computed analytically up to first order in the linear size of the patch. This procedure applies to patches for which the distance between the centers is of the same order of magnitude as the size of the patch. The same formulas are useful in steady-state scattering problems.     

Self-patch integrals in transient electromagnetic scattering

The self-patch integrals that arise in the integral equations of electromagnetic scattering are evaluated analytically for general orthogonal coordinate systems to first order in the linear size of the patch. There are terms that contain spatial derivatives of the surface fields, and these terms may not be negligible. Although the formulas are derived for transient waves, the same integrals appear for monochromatic waves.     

Analyses of electromagnetic scattering from wire-mesh structures

Various analytical and numerical methods have been developed recently to calculate the interaction of wire-mesh structures with electromagnetic waves. An intercomparison of these methods is reported for the two cases where the wire junctions are bonded and unbonded. In particular, it is found that the average boundary condition method of Kontorovich and Astrakhan appears to give valid results only if the interwire spacing of the mesh is small compared with a wavelength. However, we may safely conclude from both their work and ours that bonding the wire junctions may degrade the shielding performance of such meshes.     

A state-space formulation of transient electromagnetic scattering

For a perfectly conducting scatterer, a state-space formulation for the transient scattered field is given for single-input and multiple-output. The formulation is based on the meromorphic property of the scattered field and includes the constraint that the natural body resonances are invariant with observation point.     

Numerical second-kind-integral-equation solutions of electromagnetic scattering problems

A new, highly accurate numerical method based on second-kind integral equations has been developed to solve electromagnetic scattering problems for closed conducting bodies in two dimensions. The method is approximately fourth-order convergent, owing to the use of accurate new quadrature formulas.<>     

Approximate 3D model of electromagnetic modes in waveguide cross-shaped junctions with dielectric filling

Athree-dimensional electrodynamic model of hybrid electromagnetic modes in a waveguide junction of cylindrical and rectangular waveguides with dielectric filling of a cylindrical waveguide is proposed in this study. To solve the vector problem, the mode matching technique (MMT) is applied with the separation of the common waveguide junction region and the representation of the field in this region in the form of superposition of the fields of the partial eigenwaves of waveguides. Classification of eigenmodes is carried out: intrinsic resonances of junction based on transcendental modes and resonances of a waveguide-dielectric type. The investigated structure can be used for measuring the electrical parameters of dielectric samples of both cylindrical and rectangular cross-section shape. Since the spectral characteristics of the junction are determined mainly by the size of the central coupling region of the waveguides and the electrical parameters of the dielectric in the junction, the measurements are of a local nature.     

大尺度电磁散射与逆散射问题的深度学习方法

大尺度电磁散射与逆散射一直是科学研究和工程应用的热点和难点,亟待发展将电磁模型与数据挖掘有机融合的高性能求解方法,针对此,提出了一种针对大尺度电磁散射与逆散射问题的深度学习模型.该模型不仅继承了深度神经网络结构简单、运算速度快等优点,而且还能高精度地解决大尺度电磁散射与逆散射问题.实验结果表明:文中提出的深度学习方法可为解决现有大尺度电磁测算融合和电磁逆散射的计算成本昂贵的难题提供新思路、开辟新方向.     

Analyzing low-frequency electromagnetic scattering from a compositeobject

In this paper, we present a method for solving electromagnetic scattering from a composite object at low frequencies using the method of moments (MoM) and loop-tree basis. Many applications involve composite objects which consist of several homogeneous regions. The loop-tree basis used for analyzing scattering from a homogeneous body at low frequencies could not be directly applied to analyze the low-frequency scattering from a composite object. In general, it is very difficult, if not impossible, to find a set of loop-tree basis functions that is valid for the structures on both sides of the interfaces. In this paper, we treat a composite object as a limiting case of multibody problem so that we could setup the MoM equation using the loop-tree basis found on each single body. A process is then developed to eliminate the redundant unknowns. The proposed method makes it possible to analyze low-frequency scattering from an arbitrary composite object. The validity and applications are illustrated with representative numerical examples     

The bymoment method for two-dimensional electromagnetic scattering

The bymoment method is presented for analyzing two-dimensional electromagnetic wave scattering in an unbounded region. The method introduces a conforming surface to geometrically decouple the interior region containing the scatterer from the exterior region extending to infinity. The solution in the interior is generated using the standard finite-element solution of an interior Dirichlet boundary-value problem. The interior solution is then coupled to the exterior using Green's theorem in the unbounded exterior region. The validity of the method and the associated computer program is demonstrated by comparing the results to those of other methods for scattering by various cylindrical geometries