Reflection of electromagnetic waves from rough waveguides

The reflection coefficient of a section of randomly rough waveguide is calculated using a coordinate transformation developed by A.K. Mallick and G.S. Sanyal (ibid., vol.26, no.4, p.243-9, 1978). A perturbed analysis which assumes that the amplitude of the roughness is small compared to the average width of the waveguide is performed. A drastic difference at long wavelengths between TEM on the one hand and TE and TM on the other has been found     

Scattering of electromagnetic waves from moving surfaces

Electromagnetic wave scattering from moving objects is considered. Use is made of the reformulated current method in which the object is replaced by a current distribution radiating into an unbounded media. Cylindrical and spherical profiles in nondeterministic motion are considered. Results are obtained for far-field and steady-state cases when the radii of curvature are large compared to the wavelength.     

Reflection and transmission of electromagnetic plane waves from an uniaxial chiro-omega slab

Chiro-omega medium is a combination of the reciprocal chiral and omega media, and can be obtained by mixing helical and Ω — shaped wire elements in the host medium. In this article the most general uniaxial chiro-omega medium is studied. The solutions for the dispersion equations and corresponding eigenwaves are derived. Transmission and reflection properties of a chiro-omega slab at a normal incidence are studied, and the polarization, direction of the polarization ellipse, and relative powers of transmitted and reflected waves are given. The results are applied to find suitable parameters for designing a polarization transformer. These results are compared with those obtained in earlier studies on wave propagation in a free uniaxial chiral space, where the effect of the boundaries of a proposed polarization transforming device have been neglected.     

Reflection of electromagnetic waves from a ferromagnet/nonmagnetic-conductor/ferromagnet layered structure

The effect of the exchange interaction between ferromagnet (FM) layers via conduction electrons of conducting interlayers on the equilibrium conditions, reflectivity, and integral susceptibility of an FM/nonmagnetic-conductor/FM layered structure is theoretically investigated. Frequency and field dependences of the reflection coefficient of electromagnetic waves and the integral susceptibility are obtained and analyzed for structures containing different numbers of layers and for the cases of interacting and noninteracting FM layers. It is shown that the resonant behavior of the structure’s reflection coefficient can be controlled through variation of the values of the exchange interaction between the layers and the layers’ thicknesses.     

Reflection and transmission of plane electromagnetic waves in uniaxial bianisotropic materials

Electromagnetic waves in the most general linear reciprocal uniaxial media are considered. The theory is appropriate for novel reciprocal microwave materials which have properties of chiral composites and omega structures (or both) and can be modeled by uniaxial bianisotropic constitutive relations. Field coupling terms in the media equations are assumed to be the most general uniaxial dyadics with symmetric and antisymmetric components. Plane eigenwaves in unbounded media are studied and the theory of reflection and transmission in plane layers is constructed.     

Isofrequency surfaces and dependences of electromagnetic waves in infinite ferromagnetic space

Isofrequency surfaces and dependences of various (spin, nonresonant, and postresonant) electromagnetic waves that propagate in infinite ferromagnetic space under saturated magnetization are calculated. In a frequency interval of ω_H < ω < ω_⊥, the propagation of spin waves is characterized by open isofrequency dependences and the cutoff angles that depend on the frequency and material parameters. When the conditions are not satisfied, closed dependences are obtained. The properties of the isofrequency dependences that determine specific features of the reflection and diffraction divergence of waves are analyzed. The spin wave that propagates perpendicularly to the uniform magnetic field may exhibit zero angular width of the beam in the plane that is parallel to the magnetic field vector. In the same plane, the nonresonant wave with linear dispersion may have the diffraction divergence that is significantly less than that of the wave in isotropic media. In the presence of a plane interface, the reflection of the wave to the ferromagnetic material may give rise to two reflected beams.     

Depolarisation of electromagnetic waves backscattered by finitely conducting gently curved surfaces

The vector solution for the field backscattered by a finitely conducting surface with radii of curvature much larger than the incident wavelength obtained by the Stratton-Chu method is expressed in a form which gives insight into the dependence of depolarisation on angle of incidence, incident polarisation and on the electrical and geometrical properties of the backscattering surface.     

Reflection of signals from a randomly oscillating conducting plane

The problem of signal reflection from a conducting plane in random oscillation is considered. The mean reflected signal is found to depend, in general, on the characteristic function of the stochastic process that describes the random oscillation of the conducting plane. Asymptotic expressions for the mean reflected signal are derived. For a monochromatic signal it is shown that the amplitude of the reflected signal depends on the ratio between the wavelength and the rms displacement of the conducting plane from its mean position. Also, from the mean reflected signal, information about the statistical properties of the random oscillation may be obtained under certain conditions.     

电磁波在媒质分界面上的反射与透射特性

由于不同媒质的参数不同,电磁波入射到媒质分界面会产生反射和透射现象.通过对电磁波在分界面上反射和透射的理论分析,讨论了反射波透射波振幅、方向随入射角的变化特性.     

Scattering of waves from periodic surfaces

The scattering of waves from periodic surfaces is studied. We give a general review of this problem and compare three analytical methods for a conducting sinusoidal surface in detail for both TE and TM polarized waves. The three methods are: 1) the method developed by Masel, Merrill, and Miller (MMM); 2) the Modified Physical Optics (MPO) method; and 3) Waterman's Plane Harmonics (WPH) approach. We find the MMM method to be the most efficient one in terms of the rate and range of convergence. For dielectric media with periodic rough surfaces, an improved method is developed for calculating the reflected and transmitted powers. The results are used to compare with experimental data obtained at optical frequencies. It is shown that good agreement is achieved when the complex permittivity of the metal for the grating at the corresponding frequency is used.     

Reflection and transmission of electromagnetic waves on the interface of uniaxial chiral media

The reflection and transmission properties of plane waves on the interface of uniaxial chiral media with the optical axis parallel to the interface are investigated. The formulas of the reflected and transmitted power are derived. The curves of the group refractive angles, power of the reflected and transmitted waves for TE and TM incident waves are presented for three cases of dielectric constant combinations and for non-chiral, weak chiral and strong chiral media. Some new results are obtained, which are different from those in the uniaxial chiral media with the optical axis per-pendicular to the interface.     

A new theory for scattering of electromagnetic waves fromconducting or dielectric rough surfaces

The problem of electromagnetic scattering from a conducting or dielectric rough surface with arbitrary shape is studied. An exact solution, using a differential method, is provided for a plane wave with one-dimensional irregularity of the interface. The problem is reduced to the resolution of a linear system of partial differential equations with constant coefficients, and to the computation of eigenvalues and eigenvectors of a truncated infinite matrix. Numerical application is made to show the angular distribution of energy density in the case of an arbitrary profile of the scattering surface and its evolution when the nonperiodic profile tends to become periodic. The near field is computed on the interface and its enhancement in the illuminated region is observed. It increases with the height of the irregularity and with the frequency     

Reflection of electromagnetic wave from a time-varying medium

For the purpose of radiowave propagation in the ionosphere, in a plasma and in other media, the reflection and transmission of an electromagnetic wave from a suddenly changed conductivity, when a plane wave is normally incident upon an interface separating two conducting media, are studied. The field expressions are exactly obtained through the use of the Laplace transform. The discussion is primarily on the time behaviour of the reflected wave.     

The reflection of electromagnetic waves from stratified anisotropicmedia

A direct approach to the investigation of the reflection of electromagnetic waves from a plane interface separating a vacuum half-space and a stratified anisotropic layer is presented. The formulation involves the generation of a Riccati differential equation for a certain 2×2 reflection matrix. The approach is already well established for scalar problems, but its implementation in cases which allow mode conversion is believed to be new. The reflection matrix concerned is unitary when the anisotropic layer is nondissipative, and an efficient numerical method to solve the equation is outlined. Sample results are presented to illustrate the theory     

Mode-expansion method for calculating electromagnetic waves scattered by objects on rough ocean surfaces

A mode-expansion method that needs less than 6% the number of unknowns required by conventional method of moments is introduced in calculating two-dimensional electromagnetic wave scattering from perfectly conducting objects on rough ocean surfaces. Modes are selected for dominant propagation waves so that the number of unknowns in the matrix equation are minimized. In the numerical examples, ocean surfaces are modeled as perfectly conducting rough surfaces described by the Pierson-Moskowitz power spectrum. Bistatic radar cross-sections (RCS) of various objects, such as ship-like and low-observable targets, are calculated for a 1-GHz incident plane wave and are validated for accuracy against an iterative MoM solution.     

Reflection and transmission of electromagnetic waves by anisotropic plasma half-space moving in longitudinal direction

The reflection and transmission coefficients for the incidentHwave on an anisotropic plasma half-space moving normal to the interface are investigated theoretically. Several numerical results are presented and it is found that the behavior of the transmission coefficient is a strong function of the motion of the anisotropic plasma half-space.     

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.     

Scattering of electromagnetic waves from nonlinear thin dielectric coatings

In this paper the reflection and diffraction properties of nonlinear thin dielectric coatings are investigated. A quite simple geometry consisting of two semi-infinite homogenous linear spaces separated by a non-linear coating is considered. An incident plane wave propagating along the z direction towards the nonlinear thin coating is taken. The nonlinear thin coating is divided into elementary sectors, within each one of which one propagating and one reflected wave exists. The boundary conditions are then applied in order to develop an efficient numerical alogirthm to study the properties of the nonlinear thin coating.     

Parallel analysis of electromagnetic scattering from random rough surfaces

An efficient approach for simulation of random rough surface scattering is developed based on using a single integral equation formulation and a multilevel sparse-matrix canonical-grid method. Merits of the scheme are demonstrated using two wind-driven ocean surfaces, one which is very rough and the other large in size.