Electromagnetic scattering from vibrating penetrable objects using a general class of time-varying sheet boundary conditions

Calculation of electromagnetic (EM) scattering from vibrating penetrable cylinders of arbitrary cross-section is presented using a general class of time-varying sheet boundary conditions (SBCs) in conjunction with the method of moments (MoM). Sheet impedance and admittance expressions are first derived from the exact scattering solution for a penetrable circular cylinder with perturbed radius. Then, using the SBCs, integral equations are derived and solved numerically so that vibrating cylinders with arbitrary cross-section can be treated. Cylinder vibrations are assumed to be non-relativistic, allowing a simplified calculation of the scattered Doppler spectrum. A critical factor in the calculation of the potentially small Doppler components is that the time-varying nature of the cylinder boundary, contained within the sheet impedance and admittance expressions, can be isolated from the unperturbed terms in the scattered field. Comparison with exact and analytical perturbation solutions are presented to demonstrate the accuracy of the numerical solution.     

Scattering from an infinite cylinder of small radius embedded intoa dielectric one

In this paper the scattering from an infinite metallic or dielectric cylinder of electrically small radius, embedded into a dielectric cylinder, is considered. The problem is solved by the method of separation of variables, in conjunction with translational addition theorems. Analytical expressions are obtained for the scattered field and the various scattering cross-sections, when the radius of the inner cylinder is electrically small. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters and for metallic or dielectric inner cylinder     

An Alternative Theory of Optical Waveguides with Radial Inhomogeneities

The field equations are solved for an inhomogeneous dielectric cylinder with azimuthaf symmetry. The solutions are shown to satisfy particular orthogonality relations and allow derivation of simple, generally valid expressions for dispersion relation, power flow, energy density, and group delay. A method for numerical solution of the equations, the modified staircase method, is proposed. It is shown that it leads to expressions similar to those of the Wentzel-Kramer-Brillouin (WKB) method, but,     

Radiation pattern of square patch mounted diagonally on cylinder

The radiation pattern of a square patch mounted diagonally on a cylinder is computed using the cavity model. Analytical expressions for the far field are presented and calculations are compared with measurements     

TM scattering by an impedance sheet extension of a paraboliccylinder

An integral equation and method of moments (MM) solution are presented for the two-dimensional (2-D) problem of transverse magnetic (TM) scattering by an impedance-sheet extension of a perfectly conducting parabolic cylinder. An integral equation is formulated for a dielectric cylinder of general cross section in the presence of a perfectly conducting parabolic cylinder. It is then shown that the solution for a general dielectric cylinder considerably simplifies for the special case of TM scattering by a thin multilayered dielectric strip that can be represented as an impedance sheet. The solution is termed an MM/Green's function solution, where the unknowns in the integral equation are the electric surface currents flowing in the impedance sheet; the presence of the parabolic cylinder is accounted for by including its Green's function in the kernel of the integral equation. The MM solution is briefly reviewed, and expressions for the elements in the matrix equation and the scattered fields are given. Sample numerical results are provided     

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.     

Uniform physical theory of diffraction equivalent edge currents fortruncated wedge strips

New uniform closed-form expressions for physical theory of diffraction equivalent edge currents are derived for truncated incremental wedge strips. In contrast to previously reported expressions, the new expressions are well behaved for all directions of incidence and observation and take a finite value for zero strip length. This means that the expressions are well suited for implementation in general computer codes. The new expressions are expressed as the difference between two terms. The first term is obtained by integrating the exact fringe wave current on a wedge along an untruncated incremental strip extending from the leading edge of the structure under consideration. The second term is calculated from an integration of the asymptotic fringe wave (FW) current along another untruncated incremental strip extending from the trailing edge of the structure. The new expressions are tested numerically on a triangular cylinder and the results are compared with those obtained using the method of moments and the previously reported expressions     

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.     

Plane-wave scattering by a magnetoplasma cylinder

The scattering of H-polarised plane waves by an infinitely long axially magnetised cylinder of uniform plasma is investigated for the case in which the radius of the cylinder is small in comparison with the wavelength of the incident wave. The scattering amplitude is found to be a maximum at two frequencies, which are shown to be related to the familiar dipolar resonant frequency of an isotropic plasma column. Approximate expressions for the two resonant frequencies are derived.     

A ray representation of surface diffraction by a multilayer cylinder

The exact expressions for the field produced by a point source radiating in the presence of an infinitely long cylindrical structure comprising layers of different materials is evaluated asymptotically for source and observation points that are widely removed from the cylinder surface and related so that the cylinder shadows the source from the observer. The diffracted field is interpreted in a ray-optic format. It is observed that surface-propagating waves along the layers can be slowed significantly as compared with those on an impenetrable cylinder of the same radius. This wave slowing requires that rays attaching to the cylinder refract into a layer-guided mode and refract a second time as the curved structure sheds energy into the scattered field. Consequently, rays attaching to and shedding from the cylinder are not tangent to it when the layer profile slows the surface-propagating waves. The analysis applies for both metallically backed and open-shell layers. Computed diffraction coefficient results are given for a coated metallic cylinder as a function of coating thickness.     

Scattering by an infinite circular dielectric cylinder coatingeccentrically an elliptic metallic one

The scattering of a plane electromagnetic wave by an infinite-circular dielectric cylinder, containing eccentrically an elliptic metallic one is considered. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions, connected with one another by well-known expansion formulas. Translational addition theorems for circular cylindrical wave functions are also used for the satisfaction of the boundary conditions in the dielectric cylinder. When the solution is specialized to small values of h=k₁c/2, with k₁ the wavenumber of the dielectric cylinder and c the interfocal distance of the elliptic conductor, semianalytical expressions of the form S(h)=S(0)[1+gh²+O(h ⁴)] are obtained for the scattered field and the various scattering cross sections of this configuration. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters     

Electromagnetic scattering by buried objects of low contrast

The Born approximation is used to derive the plane-wave scattering matrix for objects of low dielectric contrast. For general shapes a numerical integration over the volume of the scatterer is required, but analytical expressions are derived for a sphere, a circular cylinder and a rectangular box (parallelepiped). The plane-wave scattering-matrix theory is used to account for the air-Earth interface. Numerical results are presented for the scattered field and far field for plane-wave excitation. The scattered field are weak for low-contrast objects, but the near-field results have application to electromagnetic detection of buried objects     

Numerical evaluation of the derivative of the parabolic cylinderfunction

We have presented numerically useful expressions for calculating the derivative of the parabolic cylinder function D_p'(z) for the argument z=xe^-iπ/4 and order p=-1/2+iy, with x and y real. This case is needed for calculating the currents excited on a perfectly conducting parabolic cylinder by a TE plane wave and for calculating the scattered far-field pattern     

椭圆柱面结耗尽层分析

本文证明了椭圆柱面Schottky结的耗尽层边缘也是一个与结共焦的椭圆柱面.给出了耗尽层宽度与偏压之间的关系.     

单层和双层手征介质柱域的并矢格林函数理论及其应用

本文应用散射叠加法,分别导出了单层和双层手征介质圆柱区域中的并矢格林函数。由此分析了位于手征介质圆柱和手征介质圆柱罩中心轴线上点偶极天线的辐射特性。结果表明,通过改变手征介质圆柱的尺寸和手征介质圆柱罩的厚度,可以任意调节辐射场的极化特性。另外,本文给出的并矢格林函数公式还可用于分析柱形手征微带天线的辐射特性。     

Transient currents on a cylinder illuminated by an impulsive plane wave

An analytical and numerical study of the transient current density induced on a perfectly conducting circular cylinder has been carried out. Both TE and TM incident plane waves with impulsive time dependence are considered. Complete closed form expressions for the TE and TM current density at all points on the cylinder and for all time values are obtained by a functional interpolation of both large and small time asymptotic solutions. The complete expressions should he useful in future transient radar scattering problems for approximating the transient current behavior on portions of a complex scatterer. The numerical results are presented in the form of "snapshots" of the current density at specific instants of time. The results are interpreted in terms of specular reflection and creeping waves. The creeping wave pulses are seen to be a continuation of pulses generated on the illuminated surface; their propagation into the shadow region is a highly dispersive phenomenon. The natural mode spectrum is seen to have both discrete and continuous components with the response at very large times determined by the latter.     

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.     

一种甚低频PVDF压电内贴复合圆管水听器的研究＊

一种新型PVDF压电内贴复合圆管水听器巳研制成功。它具有耐高静水压、灵敏度高及加速度响应低等优点,宜在水下拖曳线阵中使用。文中提出的理论公式与实验数据相符。     

Electromagnetic scattering interaction between a dielectriccylinder and a slightly rough surface

An electromagnetic scattering solution for the interaction between a dielectric cylinder and a slightly rough surface is presented in this paper. Taking the advantage of a newly developed technique that utilizes the reciprocity theorem, the difficulty in formulating the secondary scattered fields from the composite target reduces to the evaluation of integrals involving the scattered fields from the cylinder and polarization currents of the rough surface induced by a plane wave. Basically, only the current distribution of isolated scatterers are needed to evaluate the interaction in the far-field region. The scattered field from the cylinder is evaluated in the near-field region using a stationary phase approximation along the cylinder axis. Also, the expressions for the polarization current induced within the top rough layer of the rough surface derived from the iterative solution of an integral equation are employed in this paper. A sensitivity analysis is performed for determining the dependency of the scattering interaction on the target parameters such as surface root mean square (RMS) height, dielectric constant, cylinder diameter, and length. It is shown that for nearly vertical cylinders, which is of interest for modeling of vegetation, the cross-polarized backscatter is mainly dominated by the scattering interaction between the cylinder and the rough surface. The accuracy of the theoretical formulation is verified by conducting polarimetric backscatter measurements from a lossy dielectric cylinder above a slightly rough surface. Excellent agreement between the theoretical prediction and experimental results is obtained     

The radiation from rectangular microstrip antennas mounted on two-dimensional objects

The radiation patterns for a quadratic microstrip antenna mounted on two-dimensional objects, the circular cylinder and the strip, have been calculated using both the transmission-line model and the resonator model. Analytical expressions for the far field are presented, and calculations are compared with measurements. All measurements clearly indicate that the resonator model is better than the transmission-line model in radiation pattern calculations outside the principal planes of the antenna.