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In this work, an efficient numerical method is proposed for three-dimensional (3D) electromagnetic scattering from multiple coated targets buried under a two-dimensional dielectric rough surface. In the proposed method, the interior region of each coated target is regarded as an independent subregion. The field within each coated target is modeled by 3D vector finite element method (FEM). The multiple scattering interactions between the buried targets and between targets and rough surface are considered by the electric field integral equation and the Poggio–Miller–Chang–Harrington–Wu integral equations, respectively. The fields inside and outside the targets are coupled together via boundary conditions on the boundary of each target. To improve the calculation efficiency and reduce the memory requirement, the fast multipole technique is used in our method. The presented method is numerically validated by comparing it with method of moments and conventional FEM-boundary integral method (BIM). The results indicate that, compared with traditional FEM-BIM, our method has significant advantages in computational efficiency and memory requirements. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid method for computing electromagnetic scattering from target above composite rough surface of ground and near sea in adjacent region. First, a kind of composite rough surface for simulating ground and near sea in adjacent region is modeled by utilizing the Monte Carlo method, in which the ground region is modeled by adopting Gauss spectral function; the near sea region is modeled by adopting JONSWAP spectral function combined with shallow coefficient; diverse weighted inverse tangent functions are introduced to structure different boundaries and connect regions. Second, aiming at fast and accurately computing composite scattering from target above this kind of composite rough surface, a hybrid method with several acceleration strategies is proposed by combining adaptive iterative physical optics (AIPO) with method of equivalent currents (MEC), in which MEC meliorates edge diffraction. Finally, some examples verify the validation of the proposed hybrid method showing that: this hybrid method is an effective tool for analyzing the composite scattering characteristics of target above practical environment during radar detection and SAR imaging, and we also give the composite scattering from target above composite rough surface with different incident angle, shape of boundary and statistic parameters. Moreover, composite scattering from different targets above this kind of composite rough surface model is studied in order to provide some useful conclusions. [ABSTRACT FROM AUTHOR]

A novel implementation of the integral equation discontinuous Galerkin (IEDG)-based domain decomposition method (DDM), named as the IEDG-DDM, is developed for the efficient analysis of electromagnetic scattering from large and complex perfect electrically conducting (PEC) objects. Due to the nature of the IEDG scheme, the proposed DDM is nonconformal and nonoverlapping. Therefore, each sub-domain can be meshed independently according to the local geometrical feature, leading to a flexible discretization and a minimum number of unknowns. Different from the IEDG formulation in the skew-symmetric interior penalty DDM, the current continuity at the sub-domain boundaries is enforced through a properly defined interior penalty term, where the error energy from the electric potential is minimized. Consequently, the troublesome implementation of the stabilization term, which requires complex geometrical operations to find the intersection of edges in a nonconformal mesh, can be totally avoided. The proposed DDM results in an effective nonoverlapping domain decomposition preconditioner and a fast convergence of Krylov sub-space iterative solvers can be achieved. This method can be easily applied to curved sub-domain boundaries or curvilinear discretizations. Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed method. [ABSTRACT FROM PUBLISHER]

This article proposes a hybrid iterative solver for modeling composite rough surface electromagnetic scattering. First, a kind of divisional rough surface with the shape of a round water zone embedded in a larger land rough surface is modeled, in which the former is built by Pierson-Moscowitz spectrum; the latter is by Gauss spectrum. Second, aiming at fast computing scattering from this kind of composite rough surface with large scale and fast waving, a hybrid iterative solver is based on forward-backward iterative physical optics with several acceleration strategies, as well as impedance boundary condition. Finally, numerical results show that this hybrid iterative solver can satisfy the requirement for high efficiency, reliable precision in computing scattering from large scale composite rough surface. [ABSTRACT FROM PUBLISHER]

The single-source equivalence principle algorithm has been proposed as an efficient solution for analyzing large array structures. However, due to the discretization error of the identity operator, the accuracy of single-source equivalence principle algorithm is not good. In this paper, a single-source tangential equivalence principle algorithm is proposed to improve the accuracy by using the tangential field projection scheme. Based on this scheme and extinction theorem, a new relation between equivalence electric current and magnetic current can be established which has more accurate discretization. Moreover, it is demonstrated that the single-source equivalence principle algorithm can be derived from one type of single-source tangential equivalence principle algorithm. Numerical examples are designed to demonstrate the accuracy improvement of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, a simply constructed overlapped domain decomposition method is presented for analyzing electromagnetic scattering from perfect electric conducting objects with limited memory. In contrast to the conventional overlapped methods, the buffer regions in this method are limited to only a single layer of jagged triangular mesh cells. Furthermore, the overlapped currents belonging to adjacent sub-domains are expanded into different linear combinations of basis functions and enforced to be equal by a continuity condition. Then, a well-posed linear system is obtained, and an inner-outer iteration scheme is employed to solve the sub-domain problems one after another. In this method, the number of extra unknowns only increases with artificial boundaries. Numerical examples are presented to investigate the accuracy and robustness of the proposed approach. [ABSTRACT FROM PUBLISHER]

With the increase of block size, the amount of calculation and storage of the recently developed sparsified adaptive cross approximation for compressing the impedance submatrix of well-separated blocks will become as large asO(s2M) andO(sM), respectively, whereMis the number of unknowns in each block, andsis the effective rank of the impedance submatrix. To address this issue, an improved sparsified adaptive cross approximation, termed as sparsified multi-level adaptive cross approximation, is presented in this article. The sparsified multi-level adaptive cross approximation uses the multi-level adaptive cross approximation to exhibit a faster and sparser compression of the sparsified adaptive cross approximation inner matrices. As a result, the computational time and storage can be reduced toO(s3) +O(sM) andO(s2) +O(Mlogs), respectively, where logs«s«M. Furthermore, the characteristic basis function method is used to further reduce the storage of the sparsified multi-level adaptive cross approximation by compressing its outer matrices. Numerical results about the electromagnetic scattering are given to verify the advantages of the proposed sparsified multi-level adaptive cross approximation-characteristic basis function method. [ABSTRACT FROM PUBLISHER]

The alternate direction implicit scheme is introduced to the wide-angle parabolic equation method for the analysis of electromagnetic scattering from electrically large targets. Modified non-homogeneous boundary conditions are added on the surface of the scattering target. In this way, a marching solution is used along the paraxial direction and the fields in each marching plane can be calculated direction by direction in a parallel manner. The accurate results can be obtained at wider angles than the traditional narrow-angle alternate direction implicit–parabolic equation method within 30° along the paraxial direction by the proposed method. Moreover, encouraging accuracy can be obtained with fewer computing resources than the traditional wide-angle Crank–Nicolson–parabolic equation method. Numerical results are given to demonstrate the validity, stability, and efficiency of the proposed method, and the parallel efficiency is given at the same time. [ABSTRACT FROM AUTHOR]

This article proposes to solve the extra-large-scale (e.g., larger than 1,000 square lambda) electric electromagnetic scattering problem on a wind-driven sea surface at a low grazing angle directed against a shore-based radar with an iterative physical optics model. In order to accelerate the convergence of the iterative physical optics model and improve its robustness, the forward–backward methodology and its modification with under-relaxation iteration are developed first to simulate the rough sea surface scattering. Meanwhile, according to the scattering characteristics of rough sea surface, the local iteration methodology and the fast far-field approximation in the matrix-vector product are proposed to reduce greatly the computational complexity. Through these techniques, this model can solve effectively the extra-large-scale electric scattering problem from the randomly rough sea surfaces. [ABSTRACT FROM PUBLISHER]

Aiming to accurately solve the extra-large-scale electric and composite electromagnetic scattering from an object above a randomly rough surface, a bi-iteration model is proposed in this article that includes outer iteration and inner iteration. The outer iteration, based on the analytical/numerical methods, is used to calculate the electromagnetic scattering from the rough surface and the object due to their respective computational costs and accuracy. The inner iteration is applied to solve the scattering simulation of a complicated rough surface and to improve its computational precision by using the iterative physical optics. Meanwhile, to accelerate the convergence of the iterative physical optics, the forward–backward methodology and its modification with an under-relaxation iteration method are applied to solve the scattering of the complicated rough surface states. The efficiency and accuracy are demonstrated by some experiments. Therefore, compared with the common methods, the proposed model can effectively solve the more complicated scattering problem from a 3D object above a 2D rough surface. [ABSTRACT FROM PUBLISHER]

A shadowing test technique for analysis of practical objects by a non-uniform rational B-spline based high-frequency asymptotic method is presented in this article. A hierarchical space volumetric partitioning data structure is proposed for the shadowing test. The surface area heuristic strategy is employed to govern the construction of the hierarchical space volumetric partitioning in an adaptive and optimized way. The fast ray-patch intersection solving algorithm with linear complexity is developed based on the hierarchical space volumetric partitioning. Finally, using the proposed hierarchical space volumetric partitioning in combination with the methods of the uniform theory of diffraction or physical optics, some electromagnetic scattering and radiation problems are solved successfully. [ABSTRACT FROM AUTHOR]

A dyadic Green's function of a wedge with anisotropic impedance faces, excited by an electric dipole source, is derived for the paraxial region where the source and observation points are in proximity to the apex but widely separated. The principal anisotropy axis is the edge axis, and surface impedances parallel and transverse to this axis are considered. Following a “separation of variables” derivation, final dyadics involve eigenfunction solutions over an angular wave number and a longitudinal spectral integral, which is evaluated asymptotically assuming that k|z – z′| is large. It is observed that derived forms reveal three distinct scattering mechanisms: edge-guided waves, surface waves, and guided waves in the classical sense. Numerical simulations limited to paraxial region show that edge-guided and guided-wave terms are dominant at points away from the wedge surface, whereas surface waves are dominant near impedance surfaces. Both capacitive, inductive, and mixed (one face capacitive and the other inductive) reactive surface impedances are numerically analyzed. The resulting expressions can be used in the analysis of antennas located near the apex of a wedge and electromagnetic scattering from artificially hard and soft surfaces. [ABSTRACT FROM PUBLISHER]

A closed-form approximation for the current induced on a thin resistive strip by an incident plane wave is presented. The formula provides a significant improvement in accuracy over the traditional physical optics approximation. A closed-form result for the radar cross-section is also derived for the case of uniform surface resistance. A comparison is given to the standard physical optics approximation, to the results found by solving integral equations, and to the experiment. Finally, efficient methods are provided for computing the special functions appearing in the closed-form approximation. [ABSTRACT FROM AUTHOR]

This article presents a noniterative and parallel finite element technique that is tailored for a wide class of electromagnetic boundary problems, covering both quasi-static and time-harmonic regimes. This approach, called the characteristic basis finite element method, combines the domain decomposition technique with the use of characteristic basis functions that are generated by employing a finite number of point charges or dipole-type sources, depending upon whether work is being done in a quasi-static or a time-harmonic regime. Two major advantages of this method are considerable reduction in the matrix size and convenient parallelization, both of which make possible the direct solution of multi-scale problems in an efficient manner. For the static case, the problem of computing the capacitance matrices of 3D interconnects in integrated circuit packaging is considered. For the time-harmonic case, the proposed method is applied to 3D electromagnetic scattering problems. The accuracy of the proposed technique has been validated via a number of numerical simulations, covering a wide variety of configurations. [ABSTRACT FROM AUTHOR]

In this article, the microwave backscattering from 3-D rough sea surfaces has been numerically studied. Due to the advantages of the memory and CPU savings of the rigorous multilevel fast multipole algorithm, it was employed to calculate the radar cross-section of the sea surface at large incident angles. Usually, the sea surface can be regarded as a planar scatterer comparing the roughness height with the domain; therefore, an algorithm, called the fast Fourier transform multilevel fast multipole algorithm, was applied in the calculation of this case for a nearly planar scatterer. The difference of the fast Fourier transform multilevel fast multipole algorithm is the use of fast Fourier transform for the translation operator, which can further reduce the computational memory and the CPU time compared with the common multilevel fast multipole algorithm. In the calculation, the Thorsos window and Gaussian window were used in the azimuthal and range direction, respectively, to suppress the edge effects. This fast Fourier transform multilevel fast multipole algorithm provides a useful tool to test the effectiveness of classic analytical methods in computing the backscattering of large sea surfaces at very large incident angles. Some numerical examples are presented to test the accuracy and efficiency of the fast Fourier transform multilevel fast multipole algorithm. It shows that the results of the small perturbation method agree very well with the fast Fourier transform multilevel fast multipole algorithm results at moderate incident angles. [ABSTRACT FROM AUTHOR]

This article presents the implementation of the rigorous method of regularization to the scattering of an E-polarized plane wave by the classical airfoil described by the Zhukovski transform. The accurate computation of the scattering patterns and the radar cross-section are performed in a wide frequency band for different incident angles. [ABSTRACT FROM AUTHOR]

We present scattering computations performed with a newly developed stable hybridization of the finite element method (FEM) and the finite-difference time-domain (FDTD) scheme, which is based on Nitsche's method. This hybrid has not been tested on scattering problems previously, and here we compute the radar cross-section (RCS) for three different targets: (i) the perfect electric conducting (PEC) sphere, (ii) the NASA almond, and (iii) a generic aircraft called RUND. In order to assess the discretization errors associated with the hybrid, we provide comparisons with established results and techniques: (i) the Mie-series for the PEC sphere, (ii) the method of moments (MoM) implemented in the commercial code FEKO, and (iii) a stable FEM-FDTD hybrid that exploits pyramids and a curl-conforming representation of the electric field. The bistatic RCS for the PEC sphere shows second order convergence towards the analytical solution and a relative error of 2% is achieved for about 20 points per wavelength. The NASA almond has a low monostatic RCS in its horizontal plane, which makes it a good benchmark problem for scattering computations. It features a sharp tip and, as a consequence, the order of convergence for the RCS is lowered. Given a careful convergence study for the NASA almond, we achieve a highly accurate monostatic RCS by means of extrapolation and this result is state-of-the-art in the open literature. [ABSTRACT FROM AUTHOR]

This article considers the numerical simulation of three-dimensional electromagnetic wave scattering problems and describes the construction of a reduced-order approximation that enables the rapid prediction of the monostatic radar cross section (RCS). Associated certainty bounds ensure confidence in the results of the computed approximation. Numerical examples are included to demonstrate the performance of the proposed procedure. [ABSTRACT FROM AUTHOR]

This paper presents an efficient approach to quantifying the variation of electromagnetic scattering due to an uncertain geometrical deviation of the scattering surface. This approach employs a stochastic collocation method to decouple the collocation nodes, which permits the direct use of a deterministic solver to compute the solution to electromagnetic scattering for each collocation point. The multidimensional integral introduced by the stochastic collocation method is then evaluated using Stroud's cubatures, which require significantly fewer samples than does the traditional Monte-Carlo method. The accuracy and efficiency of this approach are demonstrated through a few numerical examples, where the results are obtained using the Monte-Carlo method and Stroud's cubatures. [ABSTRACT FROM AUTHOR]

The scattering of a plane electromagnetic wave by an infinite elliptic metallic cylinder is considered. Two different methods are used for the evaluation. In the first the electromagnetic field is expressed in terms of elliptical-cylindrical wave functions. In the second, a shape perturbation method, the field is expressed in terms of circular-cylindrical wave functions only, while the equation of the elliptical boundary is given in polar coordinates. Analytical expressions are obtained for the scattered electromagnetic field and the various scattering cross-sections, when the solution is specialized to small values of the eccentricity h = c/2a, (h ≪ 1), with c the interfocal distance of the elliptic cylinder and 2a the length of its major axis. In this case exact, closed form expressions are obtained for the expansion coefficients g(2) and g(4) in the relation S(h) = S(0)[1 + g(2)h2 + g(4)h4 + O(h6)] expressing the scattered field and the scattering cross-sections. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters. [ABSTRACT FROM AUTHOR]

A hybrid technique is presented that combines the finite element and boundary integral methods for simulating electromagnetic scattering from discrete body-of-revolution (DBOR) geometries. The inherent angular periodicity present in a DBOR is utilized to decompose the system matrix into several smaller modal problems, which can be solved efficiently with sparse direct solvers. The proposed method has been validated numerically and provides an efficient tool for the simulation of the scattering by DBOR geometries in electromagnetics. [ABSTRACT FROM AUTHOR]

In this contribution, a fast iterative method to solve for the fields scattered by thin layers of particles is presented. The particles are randomly positioned within the layer and are characterized by means of their T -matrix. The memory complexity of the problem is reduced by dividing the layer into uniform cells. Different preconditioning techniques are applied to yield an iterative solution. The speed and the memory requirements of the presented algorithm are compared to a direct calculation approach. As an example, the scattered fields of up to 6000 dielectric spheres that are excited with a gaussian beam are calculated. [ABSTRACT FROM AUTHOR]

The scattering from a metal plane with a ridge is considered for the cases of plane wave and line source illumination and both polarizations. Exact analytical results are expressed using series that contain products of radial and angular Mathieu functions. The exact analytical results are computed and compared with high-frequency approximations and with measurements. [ABSTRACT FROM AUTHOR]

Recently, a new type of infinite elements (IFEs) was proposed as an accurate and efficient mesh truncation method for the finite element analysis of open-region acoustic scattering. These IFEs are based on the radial expansion of the scattered field and are used to model the scattered field outside a separable surface characterized by a constant radial coordinate (such as a spherical or a spheroidal surface in three dimensions). In this paper, spherical infinite elements are formulated and implemented for the finite element (FE) analysis of time-harmonic electromagnetic scattering from a complex body of revolution (BOR), and their performance is studied by comparison with the finite element solution using conventional absorbing boundary conditions (ABCs). Numerical results are presented to demonstrate that the new type of infinite elements is indeed more accurate than both the first- and second-order ABCs. [ABSTRACT FROM AUTHOR]

This paper presents a rigorous accuracy analysis of the method of auxiliary sources (MAS) for the problem of oblique incidence plane wave scattering by a perfectly conducting, infinite circular cylinder. For this particular scattering geometry, it is shown that the MAS matrix is inverted analytically, via eigenvalue analysis, and an exact mathematical expression for the discretization error is derived. Furthermore, the computational error, resulting from numerical matrix inversion, is calculated and compared to the analytical one, showing perfect fit for a wide range of the auxiliary sources' locations. The irregular behavior of the computational error for small values of the auxiliary sources' radii is explained by the corresponding high values of the linear system's condition number. It is also demonstrated that specific source locations, associated with the characteristic eigenvalues of the scattering problem, should be avoided, because then both computational and analytical error increase very abruptly. The dependence of the computational and analytical error on the angle of incidence is thoroughly investigated. Finally, the optimal location of the auxiliary sources is determined on the grounds of error minimization. [ABSTRACT FROM AUTHOR]

This paper describes a finite element analysis of finite-by-infinite arrays with arbitrary composition. The analysis employs higher order tetrahedral elements for discretization and imposes appropriate boundary conditions on the unit cell boundaries. The radiation boundary condition imposed on the array aperture is derived through a spectral- and a mixed-domain formulation. The two formulations are found to produce consistent numerical results. In addition to a general code using tetrahedral elements, a special code is also developed based on brick element discretization, which utilizes the conjugate gradient fast Fourier transform (CG-FFT) method. Both computer codes are applied to the analysis of several finite-by-infinite arrays and numerical examples are presented to demonstrate their accuracy and capability. [ABSTRACT FROM AUTHOR]

In this paper, a high-order technique based on a locally-corrected Nyström scheme is applied to the solution of electromagnetic scattering problems via the volume electric field integral equation. The locally corrected Nyström method is detailed for the solution of the vector polarization currents. It is demonstrated that this scheme converges in a high-order manner for the scattering cross section of a dielectric cylinder of arbitrary cross section, and is computationally efficient. [ABSTRACT FROM AUTHOR]

A physical-optics (PO) solution to the three-dimensional problem of dipole radiation over an arbitrary-angled wedge is presented. The medium beneath each face of the wedge is nonmagnetic, lossy, and not necessarily the same for both faces. Excitation is provided by an electric dipole that is parallel to the edge of the wedge. The analytical formulation is based on the Stratton-Chu formula. The electromagnetic (EM) field due to a horizontal electric dipole over a lossy half-space is used on the faces and a charge distribution along the edge is introduced to account for the discontinuity of the EM field across the edge. The integral expression for the electric-field intensity far from the edge is evaluated asymptotically, thus resulting in a formula that is uniformly valid. The validity of this edge-corrected PO solution is established through a reciprocity check and comparisons with other solutions. [ABSTRACT FROM AUTHOR]