John A. Roumeliotis

Electromagnetic scattering from an eccentrically coated infinite metallic cylinder

In this work the scattering from an eccentrically coated infinite metallic cylinder is considered. The problem is solved using classical separation of variables techniques combined with translational addition theorems. For small eccentricities κd, where d is the distance between the two axes and κ the wave number of the dielectric coating, exact closed‐form expressions of the form S(d)=S(0)[1+g′(κd)+g″(κd)2+O(κd)3] are obtained for the scattered field and the various scattering cross sections of the problem. Both polarizations are considered for normal incidence. Numerical and graphical results for various values of the parameters are also discussed.

Enhancement factor of open thick-wall carbon nanotubes

We have calculated the electric field around and on the surface of an open thick-wall carbon nanotube (CNT) of height h, external radius R, and wall thickness w. To accomplish that we simulate the CNT as a vertical array of touching toroids, each of external radius R and cross section radius w/2, and then we express the problem in toroidal coordinates. From our calculations we obtain the enhancement factor γ as a function of h, R, and w. By fitting to our numerical results we obtain an empirical but simple formula for γ, which extrapolates to that of a closed CNT in the limiting case of w=R.

Electromagnetic Scattering by a Metallic Spheroid Using Shape Perturbation Method

The scattering of a plane electromagnetic wave by a perfectly conducting prolate or oblate spheroid is considered analytically by a shape perturbation method. The electromagnetic field is expressed in terms of spherical eigenvectors only, while the equation of the spheroidal boundary is given in spherical coordinates. There is no need for using any spheroidal eigenvectors in our solution. Analytical expressions are obtained for the scattered field and the scattering cross-sections, when the solution is specialized to small values of the eccentricity h = d/(2a), (h 1), where d is the interfocal distance of the spheroid and 2a the length of its rotation axis. In this case exact, closed-form expressions, valid for each small h, are obtained for the expansion coefficients g(2) and g(4) in the relation S(h) = S(0)[1 + g(2)h2 + g(4)h4 + O(h6)] expressing the scattering cross-sections. Numerical results are given for various values of the parameters.

Scattering of plane waves from an eccentrically coated metallic sphere

Abstract In this paper the scattering of plane electromagnetic waves from eccentrically coated metallic spheres is considered. Inhomogeneous, surface, singular integral equations are used to formulate the problem. Their solution is obtained in terms of spherical vector wave functions in conjunction with related addition theorems. Analytical, closed-form results are obtained in the case of small eccentricities kd , where d is the distance between the two centers and k the wave number of the dielectric coating. Thus the scattered field and the various scattering cross-sections of the problem are given by expressions of the form: S(d) = S(0)[1+g’(kd)+g”(kd) 2 +0(kd) 3 ] . Numerical and graphical results for various values of the parameters are also discussed.

Acoustic scattering by an impenetrable spheroid

The scattering of a plane acoustic wave from an impenetrable, soft or hard, prolate or oblate spheroid is considered. Two different methods are used for the evaluation. In the first, the pressure field is expressed in terms of spheroidal wave functions. In the second, a shape perturbation method, the field is expressed in terms of spherical wave functions only, while the equation of the spheroidal boundary is given in spherical coordinates. Analytical expressions are obtained for the scattered pressure field and the various scattering cross-sections, when the solution is specialized to small values of the eccentricity h = d/(2a) , where d is the interfocal distance of the spheroid and 2a is the length of its rotation axis. In this case, exact, closed-form expressions are obtained for the expansion coefficients g(2) and g(4) in the relation S(h) = S(0)[1 + g(2)h2 + g(4)h4 + O(h6)] expressing the scattered field and the scattering cross-sections. Numerical results are given for various values of the parameters.

Scattering from an infinite cylinder of small radius embedded into a dielectric one

In this paper the scattering from an infinite metallic or dielectric cylinder of electrically small radius, embedded into a dielectric cylinder, is considered. The problem is solved by the method of separation of variables, in conjunction with translational addition theorems. Analytical expressions are obtained for the scattered field and the various scattering cross-sections, when the radius of the inner cylinder is electrically small. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters and for metallic or dielectric inner cylinder. >

Acoustic scattering by a circular cylinder parallel with another of small radius

The scattering of a plane acoustic wave by an infinite penetrable or impenetrable circular cylinder, parallel with another one, also penetrable or impenetrable, of acoustically small radius, is considered. The method of separation of variables, in conjunction with translational addition theorems for cylindrical wave functions, is used. Analytical expressions are obtained for the scattered pressure field and the various scattering cross sections, for normal incidence. Numerical results are given for penetrable and impenetrable cylinders.

Cutoff wavenumbers and the field of surface wave modes of an eccentric circular Goubau waveguide

Abstract The cutoff wavenumbers knm and the field of surface wave modes of a circular cylindrical conductor eccentrically coated by a dielectric are determined analytically. The electromagnetic field is expressed in terms of circular cylindrical wave functions referred to both axes, in combination with related addition theorems. When the solutions are specialized to small eccentricities kd, where d is the distance between the two axes, exact closed-form expressions are obtained for the coefficients gnm in the resulting relation knm(d)=knm(0)[1+gnm(knmd)2+...] for the cutoff wavenumbers of the waveguide. Similar expressions are obtained for the field. Numerical results for all types of modes are given. For certain values of the parameters, it is possible to enhance the operating bandwidth of the basic hybrid mode HE11 over the conventional concentric guide.

Acoustic scattering from a sphere of small radius coated by a penetrable one

The scattering of a plane acoustic wave from an impenetrable or a penetrable sphere of acoustically small radius coated by another penetrable sphere, is considered in this work. The method of separation of variables is used, combined with translational addition theorems for spherical wave functions. Analytical expressions are obtained for the scattered pressure field and the various scattering cross sections. Numerical results are given for various values of the parameters and for both an impenetrable or a penetrable inner sphere.

Acoustic eigenfrequencies in a spheroidal cavity with a concentric penetrable sphere

The acoustic eigenfrequencies fnsm in a spheroidal cavity containing a concentric penetrable sphere are determined analytically, for both Dirichlet and Neumann conditions in the spheroidal boundary. Two different methods are used for the evaluation. In the first, the pressure field is expressed in terms of both spherical and spheroidal wave functions, connected with one another by well-known expansion formulas. In the second, a shape perturbation method, this field is expressed in terms of spherical wave functions only, while the equation of the spheroidal boundary is given in spherical coordinates. The analytical determination of the eigenfrequencies is possible when the solution is specialized to small values of h=d/(2R2),u2009(h≪1), with d the interfocal distance of the spheroidal boundary and 2R2 the length of its rotation axis. In this case exact, closed-form expressions are obtained for the expansion coefficients gnsm(2) and gnsm(4) in the resulting relation fnsm(h)=fns(0)[1+h2gnsm(2)+h4gnsm(4)+O(h6)]. ...