Electromagnetic wave scattering from a random medium layer with a random interface

Abstract

The problem of electromagnetic wave scattering from a random medium layer with a random interface is considered. The layer has planar boundaries on average. Assuming that both the random perturbations of the interface and the random fluctuations of permittivity of the medium are small, a first-order perturbation solution to the scattered field is obtained. Using this solution, the bistatic scattering coefficients γ_αβ are calculated and expressed in a compact and meaningful form. The various terms that constitute γ_αβ are identified with distinct scattering processes. Since it is often of particular interest, the special case of backscattering is considered. Finally, the results are compared with those of others.     

Electromagnetic wave propagation from a point source in air through a medium with a negative refractive index

Refraction of an electromagnetic wave from a point source to a medium with a negative refractive index is considered. An electric Hertz dipole that is located in air and directed parallel to a plane interface is considered as the point source. It is rigorously shown that the electromagnetic radiation propagated from the dipole into the medium with the negative refractive index is focused within a certain region in this medium. The sizes of the focusing region are determined. As a result, it is pointed out that the diffraction limit cannot be overcome by using homogeneous materials with negative refractive indices.     

Monte Carlo simulation for millimeter wave propagation and scattering in rain medium

As the operating frequencies of communications systems more higher into the millimeter wave range, the effects of multiple scattering in precipitation media become more significant. This paper treats the problems of electromagnetic multiple scattering in rain medium by the Monte Carlo method. The em wave is regarded as a Markov chain of photon collisions in a medium in which it is scattered and absorbed. For the sake of simplicity, the polarization is not taken into account, the above mentioned problems are described by the scale integro-diffierential equation of transfer. When the plane wave through a random medium with particle size distribution, the technique of weighted average is used to characterize the radiation intensity, including average scattering, absorption coefficients and phase function. The Monte Carlo simulation algorithms are done for the rain attenuation and reflectance at millimeter wavelength region. Our computational results are in good agreement with experimental data of rain attenuation.     

Electromagnetic wave propagation in a medium with defects

The equations of the electromagnetic field in a solid with defects were obtained and an approximate wave solution was found by the Debye–Rytov method.     

Reverse wave propagation in a randomly-inhomogeneous medium

Conclusion Therefore, it has convincingly been demonstrated in this paper that the so-called RWF mirror that reverses the radiation wave front even when using a finite aperture will assure elimination of field fluctuations during propagation in media with large-scale scatterers. Both reproduction of the mean intensity distribution and suppression of the intensity fluctuations are assured here in two-pass schemes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 51–63, November, 1985.     

Markovian non-Gaussian approximation for light propagation in a random medium

A theory is presented for wave propagation in a random medium that generalizes the Markovian-Gaussian approximation to the case of a non-Gaussian probability distribution of refractivity fluctuations. A Poissonian model of refractivity fluctuations that are statistically independent in non-overlapping intervals in the x-direction is used. This model turns out to be Gaussian under appropriate conditions. General solutions are obtained for the mean field and the mutual coherence function of a plane, partially coherent incident wave. These solutions contain a new functional parameter, a characteristic function of the amplitude of dielectric permittivity fluctuations, that affects the shape of the coherence function as well as its spectrum.     

A mixture theory for wave propagation in a laminated medium with debonding

In this paper wave propagation in the direction of the layering of a bi-laminated medium with the presence of imperfect bonding at the interfaces is investigated. The debonding mechanism is represented by a model which allows imperfect bonding both in the normal and tangential directions. A mixture theory is formulated in which every constituent has its own motion but is allowed to interact with the others. The resulting theory is applied to transient wave propagation in the laminated composite. It is shown that debonding in the tangential direction is significant in modifying the shape and amplitude of the propagating wave.     

二维随机介质中柱面波传播及其局域性的随机泛函分析

分析了二维各向同性均匀随机介质中柱面波的传播特性及局域化现象.用随机泛函理论,在频域内将随机介电起伏展开成柱坐标系下的Wiener积分式,将波场表示为内外行柱面波的线性和,求解二维Helmholtz波动方程,得到随机介电起伏对柱面波幅度与相位调制的解析表达.由柱面波能量的空间分布验证了波的局域化现象,并求解局域化长度.二维随机介质中平面波按柱面波展开的波转换方程与非随机介质中的情形有相似的表达,但具有随机介电起伏对幅度和相位的调制,并给出数值模拟结果.     

The reference wave solution for a two-frequency wave propagating in a random medium

In this work a new reference wave method for solving parabolic-type equations is proposed. The performance of the method is demonstrated by applying it to the equation governing the propagation of the two-frequency mutual coherence function in a random medium. An analytic solution is presented for arbitrary correlation properties of the medium. It is shown that when approximating the transverse structure function of the medium by a quadratic form, the solution reduces to the exact result derived previously. Extensions to more general types of media are considered.     

色散介质电磁特性时域有限差分分析的Newmark方法

根据Debye模型、Drude模型和Lorentz模型3种常见色散介质模型频域极化率的特点,利用频域到时域的转换关系jω→?/?t,将极化矢量P与电场强度E的频域关系转换成时域内关于P的二阶微分方程,其对3种色散介质模型皆适用,具有统一的形式.然后采用相比于中心差分具有更高精度的Newmark两步算法(Newmark-β-γ法)求解该方程,进而得到E→P的递推公式,再结合本构关系得到D→E的时域递推式.实现了色散介质电磁场量的时域有限差分迭代计算.数值计算结果表明该方法是适用于3种色散介质模型的通用算法,并且相比于移位算子时域有限差分方法等以中心差分为基础的离散方案具有更高的计算精度.     

Wave scattering in a multiscale random inhomogeneous medium

In this paper, using the Fock method of the fifth parameter and weighted Fourier-transform with respect to the coordinates of the source and observer, an integral representation is obtained for the wave field in a randomly inhomogeneous medium without invoking the assumption about small-angle propagation. Random trajectory variations to a first approximation are taken into account in calculating the partial wave phase (the expression under the integral sign). The expressions for the field in a medium with different-scale irregularities and for the scintillation index, obtained using this integral representation, are compared with known results. The good agreement with results from the theory of single scattering in a medium with background irregularities, and with investigations of the scintillation index made in terms of Rytov's method and path integrals, indicates that it is possible to use the approach developed in this study to describe the effects of simultaneous influence of different-scale irregularities.     

On the temporal power spectra of scintillations by propagation through a moving random medium with wave turbulence

The formation of the temporal spectrum of scintillations is considered for electromagnetic waves propagating in a moving continuous random medium with wave turbulence. The relative contributions of the motion of the medium and turbulent wave propagation to the transformation of the spatial spectrum into a temporal one are discussed. Some results obtained from radio occultation by solar wind plasma at small solar elongations are used for choosing a suitable model for wave turbulence.     

Electromagnetic wave propagation in random media

The propagation of a narrow frequency band beam of electromagnetic waves in a medium with randomly varying index of refraction is considered. A novel formulation of the governing equation is proposed. An equation for the average Green function (or transition probability) can then be derived. A Fokker-Planck type equation is contained as a limiting case. The results are readily generalized to include the features of the random coupling model and it is argued that the present problem is particularly suited for an analysis of this type.     

Adiabaticity and random wave propagation

We examine the assumption of adiabaticity that underlies mode-coupling analysis of stochastic phenomena such as roughness and inhomogeneity in passive photonics devices such as couplers, gratings, and simple waveguides. We show that although the adiabaticity condition is formally violated by such phenomena, only the low spatial frequencies actually contribute significantly to such phenomena, thus preserving the validity of the analysis.     

Signal propagation in two-layer medium with random large-scale inhomogeneities

A formula is derived for the average intensity of a signal propagated in a medium with a semitransparent layer and random large-scale inhomogeneities. A solution is obtained by the interference-integral method and the resulting formula is represented as an integral with respect to the sines of the partial-wave exit angles. The case in which the emitted pulse has a Gaussian form is examined as an example. Results of numerical modeling of the average signal intensity and the width of the semitransparency frequency band are given.Institute of Applied Physics at Irkutsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 6, pp. 475–483, June, 1993.