A STUDY OF ELECTROMAGNETIC SCATTERING FROM A DIELECTRIC-COATED CONDUCTING CYLINDER

In order to solve the problem of electromagnetic scattering by a dielectric-coated conducting circular cylinder, the total field excited by an electric and amagnetic dipoles exterior to the cylinder is derived in terms of dyadic Green's function (DGF) technique. Then, the scattering problem can be solved on basis of the relation between the total and the scattered. field. The solution of the scattered field can be obtained directly from the general formula of the scattered field as the cylinder is illuminated by a spherical wave. For a plane wave of arbitrary polarization incident to the cylinder from the direction (theta-0, phi-0), the scattered field can be given by the solution of the scattered field with a spherical wave incident as the center of the spherical wave moves to infinity. For an astigmatic wave incident to the cylinder, the scattered field can be derived by superposing or integrating of the scattered field with the special spherical wave incident.

Scattering characteristics of conducting cylinder coated with nonuniform magnetized ferrite

An analytical technique, referred to as the scattering matrix method （SMM）, is developed to analyse the scattering of a planar wave from a conductolution for the nonuniform fering cylinder coated with nonuniform magnetized ferrite. The SMM srite coating can be reduced to the expressions for the scattering and penetrated coefficients in four particular cases： nonuniform magnetized ferrite cylinder, uniform magnetized ferrite-coated conducting cylinder, uniform ferrite cylinder as well as homogeneous dielectric-coated conducting cylinder. The resonant condition for the nonuniform ferrite coating is obtained. The distinctive differences in scattering between the nonuniform ferrite coating and the nonuniform dielectric coating are demonstrated. The effects of applied magnetic fields and wave frequencies on the scattering characteristics for two types of the linear profiles are revealed.

Pure elastic resonance scattering of an obliquely incident plane acoustic wave by a submerged infinite cylinder

Although sound scattering by submcrged elastic cylinders was extensively studied,only a few works aimed at the case of obliquely incidence. In this paper, we derive a simple and explicit expression of the pure clastic resonance scattering function of a submerged infinite cylinder excited by a plane wave at obliquely incidcnce. For backscattering of a solid aluminum cylinder we calculated (a) the partial resoriance spectra n=0 to 7, (b) the far field total form functions and the pure elastic resonance form the functions, (c) the complex resonance poles in the normalized complex frequency plane and (d) the dispersion curves of the first several families of helical waves, at various incident angles in details. It was discussed that the generation mechanism and properties of the complementary resonance modes are existed only at oblique incidence. Our attention is also focused on the variance of the resonance spectra with the incident angle, particularly near several critical angles.

Band structure calculations of in-plane waves in two-dimensional phononic crystals based on generalized multipole technique

A numerical method, the so-called multiple monopole（MMoP） method,based on the generalized multipole technique（GMT） is proposed to calculate the band structures of in-plane waves in two-dimensional phononic crystals, which are composed of arbitrarily shaped cylinders embedded in a solid host medium. To find the eigenvalues（eigenfrequencies） of the problem, besides the sources used to expand the wave fields, an extra monopole source is introduced which acts as the external excitation. By varying the excitation frequency, the eigenvalues can be localized as the extreme points of an appropriately chosen function. By sweeping the frequency range of interest and the boundary of the irreducible first Brillouin zone（FBZ）, the band structures can be obtained. Some typical numerical examples with different acoustic impedance ratios and with inclusions of various shapes are presented to validate the proposed method.

The resonance scattering of underwater elastic cylinders

If the frequency of the incident sound wave coincides with one of the eigenfrequencies of the underwater elastic cylinder, the corresponding eigenvibration will be excited by incident sound wave and strongly reradiate sound wave towards surronding water. It has been revealed by previous investigations that the amplitude of backscattering sound appears to be minimum at the eigenfrequencies of the underwater metallic cylinders because of the destructive interference between reradiated wave of the eigenvibration and the geometrical reflected wave from surface of the cylinders. In this paper, a new phenomenon has been revealed. The amplitude of backscattering sound appears to be maximum at the eigenfrequencies of a cylinder made from nonmetallic material in which the velocity of elastic transverse wave is less than the sound velocity in water.

SCATTERING OF SOUND FROM A PAIR OF FINITE CYLINDERS——A PRELIMINARY STUDY APPLICABLE TO SOUND INTENSITY TECHNIQUE

In this paper, it is studied that the scattering effect is caused by microphones itself, on both wave magnitude and phase. The experimental method was found difficult to do this. We will apply the Boundary Element Method(BEM) to the problem and explain the results obtained. The numerical method seems to be a powerful tool in this situation.