Analysis of electromagnetic scattering from dielectric cylinders using a multifilament current model

A moment solution is presented for the problem of transverse magnetic (TM) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary currents to simulate both the field scattered by the cylinder and the field inside the cylinder and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the cylinder surface. The procedure is simple to execute and is general in that cylinders of arbitrary shape and complex permittivity can be handled effectively. Metallic cylinders are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure.     

Analysis of electromagnetic scattering from dielectrically coatedconducting cylinders using a multifilament current model

A method of moments solution is presented for the problem of transverse magnetic scattering from dielectrically coated conducting cylinders. The solution uses fictitious filamentary electric sources of yet unknown currents to simulate both the field scattered by the cylinder and the field inside the dielectric coating. The simulated fields obey the boundary conditions, namely, the continuity of the tangential components of the electric and magnetic fields across the air-dielectric interface and the vanishing of the tangential component of the electric field at the perfect conductor, at selected sets of points on these respective surfaces. The result is a matrix equation that is readily solved for the unknown current. The currents can be used to determine approximate values for the fields and field-related parameters of interest. The procedure is simple to implement and is general in that cylinders of smooth but otherwise arbitrary shape and coating of arbitrary complex permittivity can be handled. Illustrative examples are considered and compared with available data, demonstrating the efficiency of the solution     

Analysis of TE scattering from dielectric cylinders using amultifilament magnetic current model

A moment solution is presented for the problem of transverse electric (TE) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary magnetic currents to simulate both the field scattered by the cylinder and the field inside the cylinder and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the cylinder surface. The procedure is simple to execute and is general in that cylinders of arbitrary shape and complex permittivity can be handled effectively. Metallic cylinders are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure     

Oblique scattering from inhomogeneous cylinders using a coupledintegral equation formulation with triangular cells

A novel method of moments formulation for scattering from penetrable two-dimensional cylinders illuminated by an obliquely incident excitation is presented. The permittivity and permeability profiles may have arbitrary piecewise-constant dependence on the transverse variables. Regardless of the polarization of the incident field, the response of the scatterer is a combination of transverse electric (TE) and transverse magnetic (TM) waves. Coupled integral equations for the longitudinal electric and magnetic fields are used in conjunction with a triangular-cell discretization, a piecewise linear representation for E_z and H_z, and point-matching. Numerical results for the internal fields and scattering cross-section are presented to illustrate the accuracy of the approach     

Accurate analysis of two-dimensional electromagnetic scattering from multilayered periodic arrays of circular cylinders using lattice sums technique

A very efficient and accurate method to characterize two-dimensional (2-D) electromagnetic scattering from multilayered periodic arrays of parallel circular cylinders is presented, using the lattice sums technique, the aggregate T-matrix algorithm, and the generalized reflection and transmission matrices for a layered system. The method is quite general and applies to various configurations of 2-D periodic arrays. The unit cell of the array can contain two or more cylinders, which may be dielectric, conductor, gyrotropic medium, or their mixture with different sizes. The periodic spacing of cylinders along each array plane should be the same over all layers, but otherwise the cylinders in different layers may be different in material properties and dimensions. The numerical examples validate the usefulness and accuracy of the proposed method.     

Transient scattering from conducting cylinders

A method for determining the fields scattered by arbitrarily shaped cylindrical conducting structures with a transient incident wave is described. The transient scattering problem is reduced to the solution of a time domain integral equation which in turn is solved directly in the time domain by means of a digital computer. The approximate electromagnetic impulse response for a number of cylindrical scatterers is calculated using this method.     

Electromagnetic scattering from longitudinally corrugated cylinders

The scattering of plane electromagnetic waves from circular cross-section cylinders, longitudinally corrugated to realize anisotropic structures, is analyzed. The solution is devised at oblique incidence and for an arbitrary polarization of the incident wave using a rigorous Floquet modal expansion of the field. The implementation of the procedure is discussed with emphasis to its numerical efficiency     

Electromagnetic scattering from two adjacent cylinders

The problem of electromagnetic scattering from two adjacent cylinders is considered. The approximate analytical scattering solutions up to second order are derived for two adjacent, long finite length cylinders. The method used can avoid the complex evaluation of scattering field under nonplane wave illustrated when calculating the secondary scattering fields. The bistatic specular scattering is discussed, and the results are compared with numerical computations based on the method of moments     

Bistatic scattering from a vegetative medium simulated by cylinders

By considering the vegetation as a regular homogeneous distribution of individual scatterers and thus modeling it as an array of perfectly conducting finite thin circular cylinders over a ground plane, bistatic cross section is determined using the image principle and its variation with the angle of incidence, length, and diameter is studied.     

High frequency scattering from corrugated stratified cylinders

Interest in applying radar remote sensing for the study of forested areas led to the development of a model for scattering from corrugated stratified dielectric cylinders. The model is used to investigate the effect of bark and its roughness on scattering from tree trunks and branches. The outer layer of the cylinder (bark) is assumed to be a low-loss dielectric material and to have a regular (periodic) corrugation pattern. The inner layers are treated as lossy dielectrics with smooth boundaries. A hybrid solution based on the moment method and the physical optics approximation is obtained. New expressions for the equivalent physical-optics currents are used which are more convenient than the standard ones. It is shown that the bark layer and its roughness both reduce the radar cross-section. It is also demonstrated that the corrugations can be replaced by an equivalent anisotropic layer     

Forward scattering from cylinders of triangular cross section

The induced-field ratios (IFR) of conducting cylinders of a triangular cross section have been calculated. When the width of the cross-section is in the range of 1-2 wavelengths, theE-wave IFR's are substantially less than the corresponding values for square or circular cross sections. From the standpoint of RF aperture blocking of a reflector antenna, the triangular cross section thus offers an advantageous cross section for feed-support struts.     

A partitioning technique for the finite element solution ofelectromagnetic scattering from electrically large dielectric cylinders

A finite element partitioning scheme has been developed to reduce the computational costs of modeling electrically large geometries. In the partitioning scheme, the cylinder is divided into many sections. The finite element method is applied to each section independent of the other sections, and then the solutions in each section are coupled through the use of the tangential field continuity conditions between adjacent sections. Since the coupling matrix is significantly smaller than the original finite element matrix, it is expected that both the CPU time and memory costs can be significantly reduced. The partitioning scheme is coupled to the bymoment method to account for the boundary truncation. Numerical results are presented to demonstrate the efficiency and accuracy of the method     

High frequency scattering from polygonal impedance cylinders andstrips

An analysis is presented for the high-frequency diffraction by convex polygonal cylinders with arbitrary side impedances. The authors extend their solution for the multiply diffracted fields associated with a double wedge (see ibid., vol.36, no.5, p.664-678, 1988). The analysis thus utilizes the extended spectral ray method (ESRM) that is applicable to nonray optical regions. Diffraction coefficients yielding a uniform total field are given for up to and including all fourth-order mechanisms. An important aspect of this analysis is the rigorous and uniform incorporation of the surface-wave effects in the resulting diffraction coefficients. A general polygon computer code was written that includes up to a third-order mechanisms. Based on this code, backscatter and bistatic patterns are given for impedance cylinders with triangular and square cross sections. The results are found to be in remarkable agreement with corresponding moment method data. As a matter of completeness, uniform diffraction coefficients are presented for a strip (which is a special case of a cylinder) that can have unequal face impedances     

Boundary element method for electromagnetic scattering from cylinders

The computation of low frequency scattering of electromagnetic fields by solid/hollow dielectric or conducting cylinders using the boundary element method (BEM) is considered. A general computer program has been developed for both transverse electric and magnetic cases. Numerical examples are given for conducting circular cylinders, and solid and hollow dielectric cylinders. The computational accuracy is checked by comparing the results with the analytic solution or computing an error defined from the optical theorem. In addition some problems at an interior resonance of the scatterer are discussed. The method can be directly applied to more complicated geometries.     

Transient scattering from two-dimensional dielectric cylinders ofarbitrary shape

The problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the surface equivalence principle. Two coupled integral equations are derived by enforcing the continuity of the electric and magnetic fields which are solved by using the method of moments. Numerical results are presented for two cross sections, viz. a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution     

Application of point-matching method to scattering from quadrilateral cylinders

The possibility of constructing computer programs with the capability of generating detailed information on the scattering characteristics of a wide class of perfectly conducting cylinders of arbitrary cross-section in the `resonance? range has made further investigation of the `point-matching? technique of some interest. In the letter, the utility of the point-matching method is explored for a class of quadrilateral cylinders when the region exterior to the scatterer can be described by a set of overlapping domains within which the field can be expanded in terms of complete eigenfunction expansions.     

Mode uncoupling in oblique scattering from radially inhomogeneous cylinders

A class of radially inhomogeneous cylindrical scatterers is given, for which the TM and TEfields produced by an obliquely incident plane wave are uncoupled.     

Surface integral representations for electromagnetic scattering from dielectric cylinders

The surface integral representations are derived for electromagnetic wave scattering from dielectric bodies. Several kinds of integral equations are given for dielectric cylinders immersed in an obliquely incident wave. The interior resonant solutions, the cause of erroneous solutions, accompanied with the equations presented here and the removal of these solutions are briefly discussed.     

Electromagnetic scattering from anisotropic plasma-coated perfect electromagnetic conductor cylinders

The scattering of electromagnetic waves by a perfect electromagnetic conductor (PEMC) cylinder coated with a homogeneous plasma anisotropic material is studied in this paper. Both of the transverse electric and the transverse magnetic polarizations of the incident waves have been analyzed and formulated. The presented analysis and formulations are general for any perfect conductor cylinder (PEC, PMC, or PEMC) with general isotropic/anisotropic material coatings that include plasma and metamaterials. The co-polarized and the cross-polarized components of the scattered fields are computed for different cases of the anisotropic plasma coated PEMC cylinders and for an anisotropic plasma column. Bistatic echo widths for the cases of PEMC, PEC (perfect electric conductor) and PMC (perfect magnetic conductor) cores have been computed and compared. The behavior of the monostatic echo width with the variation of the admittance parameter for the co-polarized and the cross polarized fields is also investigated. The comparisons of the computed results of the presented formulations with the published results of some special cases confirm the accuracy of the presented analysis.     

RESEARCH ON ELECTROMAGNETIC SCATTERING FROM PARTIALLY COATED CONDUCTING CYLINDERS

In this paper,moment methods are applied to solving the electromagnetic scatteringproblems(for both E-and H-polarizations)involving partially coated conducting cylinders.Thecomputer programs have been compiled for general use.They can be used to solve the electro-magnetic scattering from uncoated,partially coated or entirely coated cylinders of arbitrary crosssectional shape.Numerical examples are also presented to show the validity and versatility of themethod.