Scattering from a chirally coated DB elliptic cylinder

An exact analytic solution to the problem of scattering of a plane electromagnetic wave from a chirally coated elliptic cylinder defined by a DB boundary has been obtained, by expanding the different electromagnetic fields associated with the problem in terms of suitable elliptic vector wave functions and a set of expansion coefficients. The incident field expansion coefficients are known, but the expansion coefficients associated with the fields scattered outside the coated cylinder and the fields transmitted inside the coating are unknown. These unknown coefficients are obtained by imposing appropriate boundary conditions at the two boundaries. Results have been presented as normalized bistatic and backscattering widths for a variety of admittances, permeabilities, and permittivities of the chiral materials used for the coating, to show their effects on scattering from the chirally coated cylinder.     

Scattering of electromagnetic waves from dielectric coated conducting spheres

Several series of rigorous numerical calculations of the backscatter cross section of a conducting sphere with a thin lossless dielectric coating were carried out. The ratio of the radius to wavelength was varied from about 0.02 to 10.0; the dielectric constant of the coating was taken to be 2.56, 4.0, or 6.0; and the thickness of the coating was 0.1 or 0.05 times the outer radius of the coated sphere. Curves of the results are presented which indicate that the backscatter cross section of a coated sphere may be increased by as much as a factor of ten over that of an uncoated sphere of the same size, and, due to interference effects, an even greater decrease may be obtained. Further, small changes (less than one per cent) in the thickness or dielectric constant of the coating, or in the wavelength, may bring about large changes in the cross section. The numerical results are also compared with some experimental measurements, and with predictions of a "creeping-wave" type of analysis carried out by Helstrom.     

Plane wave scattering by a conducting elliptic cylinder coated by anonconfocal dielectric

The scattering properties of a dielectric-coated nonconfocal conducting elliptic cylinder are investigated. The theoretical treatment of such a problem is based on the boundary value solution, which is an exact treatment of the problem. Only the transverse magnetic (TM) case is considered, although the transverse electric (TE) case can be treated in the same way. It is shown that this solution is much more general than all previous solutions because it can handle a variety of scattering geometries. Numerical results are presented in graphical form for the echo width pattern of various geometries     

Scattering from dielectric-coated impedance elliptic cylinder

The scattering properties of an impedance elliptic cylinder coated with a homogeneous material are investigated analytically. The method of separation of variables together with the impedance boundary condition (IBC) are used to determine the field distributions in each region for both the TM and TE excitations. The technique can be easily extended to handle any number of layers. The behavior of the scattered field in the far zone is illustrated with numerical results for different core and coating material types, axial ratio, and electrical sizes     

Scattering from a conducting cylinder above a lossy medium

Scattering from conducting objects above a lossy medium is a problem of current interest concerning the radar detection and identification of targets near the ground. Using a Green's function approach, in a way similar to that used to treat scattering from underground objects, the problem of electromagnetic scattering from conducting cylinders located above the ground is considered. The unknown surface current J(r) of the conducting cylinder is determined through the resulting integral equation and the far-field in the air is evaluated employing the steepest descent method of integration. Numerical results for the far-field region of the overground scatterer are plotted and some useful conclusions concerning the influence of the various parameters of the problem are also discussed.     

Scattering of electromagnetic waves by an anisotropic plasma-coated conducting cylinder

This paper considers the scattering of electromagnetic waves by an infinitely long anisotropic plasma-coated conducting cylinder. The source is assumed to be a magnetic current filament which gives rise to an incident magnetic field with only an axial component. Complete expressions for the scattered electric and magnetic fields are obtained. Scattering by an anisotropic plasma column and that by an isotropic plasma-coated conducting cylinder are special cases of the present problem.     

Scattering of electromagnetic waves by a layer of air plasma surrounding a conducting cylinder

In this paper, the total scattering and back-scattering cross-sections (respectively represented by σ and σ_b) of an air plasma layer surrounding a conducting cylinder are studied. The plasma layer can be turned ON and OFF to allow for a comparison between the scattering cross-section of the bare cylinder and the plasma covered cylinder. The plasma layer is generated at atmospheric pressure, which results in a very highly collisional case. The scattered fields are calculated using a cylindrical expansion, with coefficients satisfying the appropriate boundary conditions, and which are a function of the refractive index of the air plasma. The results of our study are presented as plots of the total scattering cross-section, σ, and back-scattering cross-section, σ_b, versus frequency. The scattering cross-section gives an average characteristic of the scattering process from obstacles. Once the scattering cross-section is known, the actual scattered energy per unit length per second can be calculated by multiplying σ by the incident energy per unit area per second.     

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.     

Scattering and coupling properties of a slotted elliptic cylinder

Near-field analysis and coupling of a perfectly conducting slotted elliptic cylinder excited by an electric line source placed inside or outside the cylinder is considered. The solution can be easily extended to account for a z-polarized incident plane wave excitation. The separation of variables technique is used to express external and internal fields in terms of Mathieu and modified Mathieu functions with unknown expansion coefficients. The problem is then reduced to an integral equation in terms of the aperture field. The solution of the integral equation is carried out by expressing the aperture field in terms of a Fourier series expansion with unknown coefficients. Then Galerkin's technique is introduced to solve for the unknown aperture field coefficients. Results for the penetrated and near fields are given in terms of different parameters such as location and type of the excitation, aperture width, cylindrical axial ratio, and the loading of the cylinder     

Radiation from an aperture in a conducting cylinder coated with a moving plasma sheath

The electromagnetic radiation from an aperture on a conducting cylinder coated with a moving isotropic plasma sheath is considered. Numerical results are presented to illustrate the radiation patterns as functions of sheath velocity and plasma frequency for the circumferential slot and axial slot apertures. It is found for the circumferential slot aperture that the radiation is enhanced in the direction of sheath motion when the plasma is overdense and that relatively little change occurs when the sheath is underdense. For the axial slot, it is found that an electromagnetic field is radiated whose polarization is normal to that of the field radiated under stationary conditions, in addition to a field of the usual polarization. Significant alterations of radiation patterns from their form when the sheath is stationary can occur at relatively small velocities if the wave frequency is near the plasma frequency.     

FINITE DIFFERENCE METHOD FOR ELECTROMAGNETIC SCATTERING FROM PERFECTLY CONDUCTING CYLINDER

A numerical method of solving electromagnetic wave scattering problem is described.Radiation boundary condition(RBC)is applied to confine EM scattering problem in unboundedregion into problem in finite region.Combined with RBC and scatterer surface boundary condi-tion,Helmholtz equation in the finite region is solved numerically by the finite difference method.Thus the distribution of induced surface current on conducting cylinder and near field can beobtained.Computational results for both polarizations for circular,elliptic and square cylindersare presented.These results are in excellent agreement with those obtained by the eigenfunctionexpansion method or moment method and much better then the results of OSRC method.     

Scattering of electromagnetic plane waves by a circular cylinder

Numerical investigation of scattering electromagnetic plane waves by a circular conducting cylinder is considered. The results presented are 1) validity of asymptotic far-field expressions when it is applied to calculate near-field around the cylinder and 2) equicontours of amplitude and phase of total field around the cylinder.     

The inverse electromagnetic scattering problem for a perfectly conducting cylinder

The problem of determining the shape of the cross section of a simply connected perfectly conducting infinite cylinder from a knowledge of the far-field pattern for all angles of observation and small values of the wavenumber is considered. The method proposed relies heavily on conformal mapping techniques. In particular it is shown that if the transfinite diameter is known each Fourier coefficient of the far-field pattern of the electric field determines a Laurent coefficient of the conformal mapping taking the exterior of the unit disk onto the exterior of the unknown cross section. The transfinite diameter is determined by changing the polarization of the incoming wave and measuring the far-field pattern of the resulting magnetic field. Of particular interest is the case when only a finite number of the Fourier coefficients of the far-field pattern are known. In this situation error estimates are obtained by using results on coefficient estimates for univalent functions.     

Scattering from a perfectly conducting cube

The cube epitomizes the complex, three-dimensional scatterer with its multiple interactions and vertex diffraction playing a critical part in the far-field patterns of some bistatic planes. the results presented are for a cube on the order of 1.5-3 wavelengths on edge which is illuminated by a plane wave at broadside incidence. The method employed is the hybrid iterative method (HIM) which utilizes an initial approximation of the surface currents on the cube faces. These currents are inserted into the magnetic-field integral equation (MFIE) to produce improved or updated approximations to these surface currents. This process is repeated to convergence by the method of successive approximations. These currents are then used to find the bistatic radar cross section (RCS) for an arbitrary plane of measurement (emphasis has been placed upon the H-plane and the E-plane). Of particular interest is the development of cross-polarized currents, which are initially approximated by zero. As the iteration process progresses, it is seen that all physical scattering processes present in this body are introduced by enforcing the MFIE     

Scattering by an infinite circular dielectric cylinder coating eccentrically an elliptic dielectric cylinder

Scattering of a plane electromagnetic wave by an infinite circular dielectric cylinder coating eccentrically an elliptic dielectric one, is under consideration. Both E and H polarizations are treated for normal incidence. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions. Using proper transformation theorems between the field expressions in different coordinate systems, for the satisfaction of the boundary conditions, we obtain two infinite sets of linear nonhomogeneous equations for the expansion coefficients of the field. In case of small values of h=k/sub 2/c/2, where c is the interfocal distance of the elliptic cylinder and k/sub 2/ the wavenumber of the dielectric coating, the former sets of equations provide, by truncation, semianalytical expressions of the form S(h)=S(0)[1+gh/sup 2/+O(h/sup 4/)] for the scattered field and the various scattering cross sections. The coefficients g are independent of h. Graphical results for the scattering cross sections are given for various values of the parameters.     

Scattering by a perfectly conducting and a coated thin wire using aphysical basis model

A traveling-wave model is used in conjunction with a Galerkin's solution of the exact integral equation to solve for the scattering by a thin perfectly conducting and a thin dielectrically coated wire. The proposed current model consists of three weighted traveling-wave components; one is associated with the current on the infinite wire whereas the other two describe the reflected traveling waves from the wire terminations. Several current distribution and scattering patterns are presented which serve to validate the accuracy of the model and the derived analytical formulas     

JEC-FDTD for 2-D conducting cylinder coated by anisotropic magnetized plasma

The JE convolution finite-difference-time-domain (JEC-FDTD) method is extended to the anisotropic magnetized plasma which incorporates both anisotropy and frequency dispersion at the same time, enabling the transient solution of the electromagnetic wave propagation in anisotropic magnetized plasmas. Two-dimensional JEC-FDTD formulations for magnetized plasma are derived. The back scattering radar cross section (RCS) of a perfectly conducting cylinder coated by a layer of magnetized plasmas is calculated.     

Scattering of electromagnetic waves by rough perfectly conducting circular cylinders

A numerical method is proposed for computing the normalized correlation functions of the real and imaginary parts of the field scattered from a statistically rough perfectly conducting circular cylinder. The deviation of the surface from its mean radius is assumed to be small. The correlation function of the far-field is related to the correlation function of the scattering object by an integral equation. Far-field correlation functions are found for two types of surface correlation functions: the delta function and a periodic exponential function.