Influence of boundary conditions on statistical characteristics of the wavefield in a layered randomly inhomogeneous medium

Abstract

We consider the problem of the oblique incidence of a wave on the half-space of a layered randomly inhomogeneous medium without absorption and analyse the influence of boundary conditions on the probability distribution of the reflection coefficient phase, and the statistical behaviour of the wavefield intensity moments inside the medium.     

Influence of boundary conditions on statistical characteristics of the wavefield in a layered randomly inhomogeneous medium

We consider the problem of the oblique incidence of a wave on the half-space of a layered randomly inhomogeneous medium without absorption and analyse the influence of boundary conditions on the probability distribution of the reflection coefficient phase, and the statistical behaviour of the wavefield intensity moments inside the medium.     

Statistical characteristics of waves in a layered randomly and regularly inhomogeneous medium

Pacific Ocean Oceanographic Institute, Far East Region, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 2, pp. 191–195, February, 1990.     

Temporal characteristics of communications channels between source and receiver in inhomogeneous medium

The temporal translation properties of communications channels between a source and receiver in an inhomogeneous medium are investigated. For this, special characteristics are introduced: the average propagation time, the time variance of signal arrival, the probability of normal arrival, and the probability of division of direct and scattered signals by inhomogeneities. Spatial maps of the distributions of the characteristics are constructed for the example of a bilinear layered waveguide. Recommendations on the use of these maps for the solution of various practical problems are provided.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 11, pp. 1373–1387, November, 1994.     

Permittivity of a randomly inhomogeneous medium

A theory of permittivity of suspension-type systems is developed that allows one to calculate such optical parameters of inhomogeneous systems as the length of scattering and the transport length. It is shown that, in the Born approximation, which takes into account two-particle correlations in the arrangement of scattering particles, the theoretical and experimental data are in agreement only to within tens of percent. The contribution of three-particle correlations to the permittivity of a system of solid spheres is determined. It is shown that, in describing the optical properties of suspensions with a large difference between the refractive indices of the medium and the particles, it does not suffice to replace the Rayleigh-Gans form factor by the Mie form factor, even under a restriction to two-particle correlations.     

Beam propagation in a randomly inhomogeneous medium

An integrodifferential equation describing the angular distribution of beams is analyzed for a medium with random inhomogeneities. Beams are trapped because inhomogeneities give rise to wave localization at random locations and random times. The expressions obtained for the mean square deviation from the initial direction of beam propagation generalize the “3/2 law.”     

Wave propagation in a weakly inhomogeneous medium

We develop an asymptotic method to describe the n-dimensional wave propagation through nonlinear inhomogeneous media characterized by dissipative and (or) dispersive systems of partial differential equations. This method is used to study the bidimensional propagation of surface water waves of varying depth.     

Model of a nanoparticle in the theory of inhomogeneous medium

Basic thermodynamic characteristics (density distribution profile near the surface of a nanoparticle, adsorption, and interfacial surface tension) of the structureless nanoparticle-vapor/liquid equilibrium system are calculated using a unified approach. A joint solution of the basic equation in the Van der Waals theory of an inhomogeneous medium for the density distribution profile in the spherical system of coordinates and the Gibbs equation for the interfacial tension and absorption is obtained. The features of nucleation of nanoparticles are considered. The results generalize some familiar formulas and provide a more adequate interpretation of experimental results.     

Focused antenna array in a strongly inhomogeneous medium

A focused acoustic antenna array is considered in a strongly inhomogeneous stationary medium. An opportunity is indicated to determine the coordinates of a number of objects by active location. It is assumed that, in insonifying the objects by a wave with an arbitrary wave front, they scatter spherical waves and are sufficiently separated in distance and angle to be resolved by the same array in a homogeneous medium. The procedure of determining the coordinates of the objects involves a wave front inversion for distinguishing between the signals from different objects. The coordinates are determined by estimating the parameters for each individual object. The parameter estimation procedure is shown to provide a high efficiency of extracting the argument of a complex signal. The results of the numerical modeling and solution of the problem are presented.     

Radiation transfer in a three-dimensionally inhomogeneous stochastic medium

Within the framework of a small-angle iteration method the propagation of radiation in a three-dimensionally inhomogenous stochastic scattering medium is considered. The results of the analysis show a significant dependence of the average light field on the statistical structure of scattering parameters of the medium. Deceased. Institute of Applied Optics, National Academy of Sciences of Belarus, 11, Belynitskii-Birulya Str., Mogilev, 212793. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 234–240, March–April, 1999.     

Energy characteristics of coupling channels between points of an inhomogeneous medium

The translational characteristics of points of a continuous medium are studied for a source and receiver with fixed locations and given properties. Within the framework of geometrical optics, the energycoupling coefficient (AC) and anisotropy coefficient (AC) are introduced, which determine the size and angle distribution of the coupling channels between the source and observation region through a point of the inhomogeneous medium. The spatial structures of the AC and AC are investigated for some typical waveguides encountered in practice. The possibilities of using the AC and AC in systems for viewing and tomographic monitoring of inhomogeneous media are analyzed.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 5, pp. 443–455, May. 1993.     

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.     

Mechanical resistance of a compact nanoparticle in a gaseous medium

Resistance of fullerenes in air is investigated under standard conditions. The general problems of resistance of compact nanosized particles in gaseous media are solved at different temperatures and pressures. The resistance of the nanosized particle moving in a gaseous medium is calculated using the deterministic approach, direct methods of molecular dynamics, and main theorems of classical mechanics (including the theorem on the momenta of a particle and a particle ensemble). Theoretical results obtained are in complete agreement with the Lapple experimental data on the resistance of ultradispersed particles. Moreover, they describe well the resistance of particles having much larger sizes for which the molecular dynamics model disregarding collisions of molecules seems to be inapplicable.