Electromagnetic scattering from an extended laminar plasma column

This paper is concerned with examining in the laboratory the backscattering from a simplified ionized target in the form of an extended laminar plasma column. Measured results, compared with calculations based on a homogeneous model approximation that incorporates the measured electrical parameters of the column, show that the column scatters electromagnetic energy that is polarized with the electric vector along the axis of the column in the same manner as a homogeneous column of critical density with the column radius equal to that of the critical electron density contained within the column.     

Electromagnetic reflection from a curved dielectric interface

The reflection of a high-frequency electromagnetic field from an arbitrarily curved dielectric interface is considered. The fields are expanded in asymptotic series ofk^{-1}, known as Luneburg-Kline expansions. Based on a ray method the zero- and first-order terms ofk^{-1}of the reflected and transmitted field are evaluated at the interface. Associated with the fields at the interface, effective surface current densities can be used to determine the reflected and transmitted field at points away from the interface, which is done analytically for the reflected far field in the case of plane wave incidence. The result consists of a frequency-independent term, which is related to geometrical optics solution, and a term ofk^{-1}, which is a useful extension of geometrical optics solution in some cases.     

Electromagnetic reflection from a conducting surface: Geometrical optics solution

The reflection of electromagnetic waves from a smooth conducting surface at high frequencies is studied in this paper. Both the incident and reflected fields are expanded in asymptotic series of the formE = exp [iks(r)]Sigmamin{m=0}max{infty}(ik)^{-m}e_{m}(r), wheresis the phase function, and {e_{m}} are amplitude vectors. Explicit formulas based on a ray technique are given for calculating the first two orders of the electric field, magnetic field, and surface current. When the conducting surface is a paraboloid (or a sphere) and the incident field is a plane wave in its axial direction, our solution recovers the exact solution (or the first two orders of the exact asymptotic solution), As a special case, our result is compared with the work of Schensted. It appears that the latter is only partially correct.     

Transient reflection of an electromagnetic signal from a stratified conducting medium†

The reflection characteristics of an electromagnetic pulse from a stratified conducting medium is analysed. For the case of a plane-wave signal with a Gaussian envelope, n simple expression for the reflected signal is obtained. The results show that the envelope of the reflected signal is not Gaussian any more. If there is a large number of carrier cycles in the envelope, it is found that the amplitude of the reflected signal is negligibly small as compared to that of incident signal.     

Discussion of radiative-transfer methods applied to electromagnetic reflection from turbulent plasma

The reflected energy flux of electromagnetic waves incident upon an underdense turbulent plasma recently has been extended beyond the weak-scattering Born approximation by two different methods. One approach is based upon summing cumulative small-angle propagation effects between successive large-angle scatterings. A heuristic application of radiative-transfer methods under the same approximations and conditions yields a backscatter cross section that differs by a factor of up to one-half at given plasma thickness. It is shown that the cross section can be made to agree with that of the selective-summation approach by including a class of contributions that appears to have been omitted in the radiative-transfer approach.     

The scattering from curved rough surfaces of an EM wave transmitted through a turbulent medium

A generalized analysis of electromagnetic (EM) wave scattering from rough surfaces yields an expression for mean scattered power flux which is the spatial Fourier transform of the product of three transfer functions: 1) the optical transfer function (OTF) of the propagating medium; 2) the joint characteristic function of the surface roughness; and 3) a coherence involving the mean surface and the wave profile. The solution is applicable to moderately rough surfaces which have rms slopes less than a few degrees. The solution is applied to laser scattering from aluminum and titanium surfaces where the medium is the atmosphere. The randomly rough surface consists of independent "roughness" and "waviness" components which possess a Gaussian autocorrelation. The deterministic surface is quadratic; the laser profile, Gaussian. The atmospheric OTF is modeled into a Gaussian form. For typical parameters, the result decouples into a specular term (depending on turbulence, wave profile, and known surface) and a diffuse component (depending on rough and known surfaces). A slightly spherical incident wave affects only the coherent term.     

Electromagnetic scattering from extended wires and two- and three-dimensional surfaces

Efficient numerical solutions for the electromagnetic scattering for classes of electrically large one-, two-, and three-dimensional perfectly conducting scatterers are presented. The formulation is based on solution of the electric field integral equation (EFIE) using the method of moments (MM). An entire domain Galerkin representation is used for wires and two-dimensional surfaces and a combination of entire and subdomain representations is applied to surfaces in three dimensions. The analysis is extendable to corrugated surfaces formed from sections of surfaces of translation or rotation. Numerical results are presented for wires, infinite strips, and finite strips (or plates). The behavior of the solutions with the number of terms in the entire domain expansion is examined. The reconstruction of the traveling-wave contribution to the scattering cross section using various approximations is discussed, and representative examples are given.     

Electromagnetic beam propagation in turbulent media: An update

In 1975, we reviewed the recent developments on wave propagation in turbulent media. In this paper, we update that paper to include recent results on adaptive optics, intensity scintillations, pulse propagation, atmospheric measurements at visible, IR, and millimeter wave frequencies, speckle interferometry, and other related topics.     

Electromagnetic spherical wave reflection from a perfectly conducting surface of revolution

The problem of electromagnetic spherical wave reflection from a perfectly conducting surface of revolution is considered. The expressions for the first two terms of the high frequency asymptotic expansion for the reflected field are found. The analysis is based on Lee's theory of electromagnetic reflection from a conducting surface.     

Electromagnetic reflection and tramsission for a dielectric-Ω interface and an Ω slab

A time-harmonic electromagnetic plane wave obliquely incident on a half-space or a slab consisting of a so-called Ω medium is considered. The up- and down-going eigenmodes in the Ω medium are derived and used to calculate the reflection and transmission coefficients for TE and TM modes. The Brewster angles for an Ω half-space are computed. Numerical results for the co- and cross-polarized reflection and transmission coefficients for an Ω slab are presented.     

Electromagnetic scatter from small dielectric gradients in a continuous medium

A new approach is presented to the formulation and understanding of the problem of electromagnetic scatter from a slightly perturbed continuous medium. The problem is expressed in terms of periodic functions instead of conventional power series. From this formulation, specular properties are observed that are not obtainable from older considerations. The approach was verified with a laboratory experiment using microwave transmission lines with length-dependent, slowly varying dielectric cross sections. Further experiments were carried out using backscatter from a radar designed to detect clear air turbulence. The primary result shows that a turbulent medium can be replaced for the purposes of scatter calculation by a structure of finite periodicities because the medium acts as a lumped insertion loss, the stopping characteristics being determined by a spectral scale in the turbulence. The formulation defines the limits of knowledge about the medium and shows that, although it is not unique, some knowledge of the structure is obtainable. Insight is gained into the work needed to understand and interpret remote probe experiments.     

高斯介质粗糙面电磁散射的小斜率近似方法

基于小斜率近似方法推导了极坐标系下介质粗糙面的双站散射系数和后向散射系数计算公式.为验证小斜率近似方法的准确性,针对二维高斯介质粗糙面,计算了双站散射系数并将得到的数值结果与实验测量数据和基尔霍夫近似方法计算结果进行了对比分析,结果表明:小斜率近似方法的结果和实验数据吻合较好.同时对不同入射角下散射系数的角分布及粗糙度和均方根斜率对散射系数的影响进行了讨论分析.     

湍流大气中含镜反射点漫射目标的电磁散射

基于广义惠更斯 -菲涅尔原理 ,研究了波束入射到湍流大气时 ,考虑漫射目标上包含一个或多个镜反射点 (该镜反射点半径远小于束宽 )时的散射统计特性 ,导出了散射场的互相关函数、平均强度、强度协方差和强度方差的公式 ,讨论了镜反射点的半径和离轴远近对归一化强度方差的影响。     

Electromagnetic reflection and transmission from a new version of Cantor fractal nonlinear multilayers

In this paper, we put forward a new version of Cantor fractal multilayers, which are nonlinear medium, and investigate its properties of reflection and transmission when a plane wave is obliquely incident upon it. A new exact self-similarity algorithm that make use of the self -similarity of these structure are developed. The results for different stages of fractal growth within the first-order nonlinear approximation are found. Compared with the traditional chain-matrix approach, the scheme provides the reflection and transmission coefficients for any stage (S) with much less calculation time on a personal computer.     

The bilocal approximation for the effective dielectric constant of an isotropic random medium

The bilocal approximation in strong fluctuation theory leads to an expression for the effective dielectric constant of a random medium. A detailed study of this expression is made for the case of a medium characterized by an isotropic correlation function. The effective dielectric constant is shown to obey an equation involving an integral containing the correlation function, the free space propagation constant, the quasistatic dielectric constant, and the effective dielectric constant itself, Numerical methods for solution are suggested. The low frequency behavior is also examined. The leading correction term to the quasistatic dielectric constant is shown to be different than previously deduced expressions.     

Electromagnetic scattering from a wire grid parallel to a planar stratified medium

The theory for electromagnetic scattering from a special periodic structure adjacent to a stratified medium is given. The configuration consists of a parallel grid of thin wires that are located in a plane parallel to a planar stratified region. The case where the grid is outside the stratified half-space is considered first. Subject to the restriction on the thinness of the grid wires, an exact solution for the scattered fields is obtained. The final result, for the far-field scattering and transmission, can be interpreted clearly in terms of an equivalent transmission line circuit. In this case, the grid is represented as a shunt element. Finally, the theory is generalized to allow for the situation where the grid is within the stratified region.     

Electromagnetic scattering from an eccentric multilayered circularcylinder

Electromagnetic scattering from an eccentric multilayered, homogeneous, circular cylinder is derived rigorously by using a boundary value mode-matching approach. The layers are assumed to be infinite in length and their axes are parallel to each other but their centers may have arbitrary coordinates. The composite arrangement is illuminated by a cylindrical wave from a line source of infinite extent in a direction parallel to the cylinder axis. The problem is two-dimensional and the solution to both types of polarization is presented. The effects of various geometrical and electrical parameters on the near- and far-field patterns are examined     

Electromagnetic scattering from an inhomogeneous object by raytracing

A shooting and bouncing ray (SBR) formulation is presented for treating the electromagnetic scattering from electrically large, inhomogeneous objects. A dense grid of rays representing the incident plane wave is shot toward the inhomogeneous objects. At the scatterer boundary, reflected rays and refracted rays are generated due to the discontinuity of the medium parameters. The trajectory, amplitude, phase and polarization of the rays inside the inhomogeneous object are traced based on geometrical optics. Whenever the rays cross the scatterer surface, additional reflected/refracted rays are generated and are tracked. This is repeated until the intensities of the refracted/reflected rays become negligible. The contributions of the existing rays to the total scattered field are calculated using the equivalence principle in conjunction with a ray-tube integration scheme. The ray formulation is applied to calculate the backscattering from cylinders and spheres and good agreement with the exact series solutions is observed in the high-frequency range. In addition, the backscattering mechanisms in penetrable objects are interpreted in terms of simple ray pictures     

On the reflection of light from an inhomogeneous shell

The main contribution to the reflected field from a radially inhomogeneous spherical shell is determined. It is shown that it is much smaller in amplitude than the field reflected by a perfectly conducting sphere coated with the same type of radially inhomogeneous dielectric.     

星际湍流介质中二阶矩方程的数值差分方法及其应用

详细分析了湍流介质中二阶矩方程的数值差分方法。利用不同的波结构函数模型,计算了平面脉冲波在湍流介质中传播的双频互相关函数的实部和虚部,直接应用于脉冲展宽,脉冲强度等问题的计算中。为应用于脉冲波传播特性分析,提供必要的理论基础和方法。同时,也可以推广就用到处理复宗量函数的同类偏微分方程问题中。