Georgios D. Kolezas

Fast Solution of the Electromagnetic Scattering by Composite Spheroidal–Spherical and Spherical–Spheroidal Configurations

The electromagnetic scattering of a plane wave by composite spheroidal-spherical and spherical-spheroidal configurations is studied in this work. The spheroidal-spherical configuration consists of a spheroidal dielectric shell coating a spherical metallic core, while the spherical-spheroidal configuration consists of a spherical dielectric shell coating a spheroidal metallic core. Initially, the formal series solution is constructed by using analytical expansions connecting the spheroidal with the spherical eigenvectors. The solution of the problem is then obtained following two independent paths: first, asymptotic expansions are applied on all related quantities leading to a solution for the fields and the scattering cross sections, which is given by closed-form expressions, and is valid for small eccentricities of the spheroid. Second, the formal full-wave series solution is solved numerically by truncation. Both the full-wave and the closed-form solutions are validated by numerous comparisons with numerical simulations. The accuracy of the closed-form solution is then compared to the full-wave solution. The closed-form solution has very low computational cost. The spheroid can be one of prolate or oblate type. Both TE and TM incidence are studied and numerical results are given for various values of the parameters.

Scattering by an inhomogeneous gyroelectric shell coating a PEC spherical core

In this work we investigate the electromagnetic scattering by a perfect electric conductor (PEC) sphere coated by an inhomogeneous gyroelectric spherical shell. We develop a method based on the surface-volume integral equation (SVIE) approach, in conjunction with Dini series expansion (DSE). An orthogonal set of Dini-type spherical vector wave functions (SVWFs) is constructed that directly satisfies the boundary conditions on the conductors surface, and allows the reduction of the SVIEs to an algebraic form. Validity tests are performed for the developed method and numerical results are given for radar cross section (RCS) computations.

Acoustic scattering from inhomogeneous spheres with impenetrable cores

In this work, we develop a full wave solution for the acoustic scattering by inhomogeneous compressibility spheres having an impenetrable core. The solution is developed by following two alternative mathematical formulations: one through a volume integral equation where a modified Greens function is needed to describe the scattering by the impenetrable core, and one through a surface-volume integral equation where the equivalent surface sources due to the impenetrable core are described via a surface integral. We prove analytically that these two alternative paths lead to the same set of nonhomogeneous equations for the evaluation of the total acoustic field. We investigate both Dirichlet and Neumann boundary conditions. Our developed method is then numerically validated by comparison with other techniques, including the exact solution for core-mantle spheres with constant compressibility function. Furthermore, we construct a solution which is valid for a special inhomogeneous compressibility profile bas...

Electromagnetic Scattering by Inhomogeneous Conducting—Gyroelectric Objects

The electromagnetic scattering by an inhomogeneous conducting-gyroelectric object is investigated. A rigorous full-wave method based on the surface-volume integral equation (SVIE), in conjunction with Dini series expansion, is developed. A new orthogonal set of Dini-type spherical vector wave functions is constructed that allows the direct satisfaction of the boundary conditions on the conductors surface, and in sequence, the reduction of the SVIE to an algebraic form. We investigate the validity of the developed method, which is next applied to radar cross section and interior field computations.

Efficient and Accurate Calculation of the Cutoff Wavenumbers of Coaxial Elliptical-Circular and Circular-Elliptical Metallic Waveguides

In this paper, we propose an efficient method for the calculation of the cutoff wavenumbers of coaxial elliptical-circular and circular-elliptical metallic waveguides. The cutoff wavenumbers are obtained through closed-form expressions making the evaluation efficient, and moreover, very accurate even for large values of the eccentricity of the elliptical boundary. The resulting formulas are free of Mathieu functions, including only simple algebraic expressions with Bessel functions, and are valid for every different value of the indices n and m, corresponding to every higher order TMnm or TEnm mode. The validation of the method is performed by comparing to the general exact solution. The efficiency and accuracy of our method is presented by illustrative examples. Numerical results are given for the cutoff wavenumbers of various higher order modes.

Complex resonances of composite PEC-gyroelectric resonators using SVIE method

In this work we investigate the resonant frequencies of composite metallic-anisotropic open resonators. The open resonator is formed by a perfect electric conductor (PEC) sphere coated by a gyroelectric spherical shell. We develop a surface-volume integral equation (SVIE) method, in conjunction with Dini series expansion. An orthogonal set of Dini-type spherical vector wave functions (SVWFs) is employed for the expansion of the field quantities, and allows the reduction of the SVIE to an homogeneous algebraic linear system. The validity of the developed method is tested by comparison to the separation of variables method (SVM), and numerical results are given for the normalized resonant wavenumbers and quality factors.

CFVIE Formulation for EM Scattering on Inhomogeneous Anisotropic—Metallic Objects

The coupled-field volume integral equation-Dini series expansion (CFVIE-DSE) method is employed for electromagnetic scattering on inhomogeneous anisotropic-metallic objects. The anisotropic coating is both of gyroelectric and gyromagnetic type. Unlike traditional methods that describe the metallic core through a surface integral, a full-wave method is developed based on VIEs only, in conjunction with modified tensorial Green’s functions, taking into account the electric boundary condition (BC) on core’s perfect electric conducting surface. CFVIE-DSE is then solved using entire domain basis functions of Dini-type. New orthogonal sets in the domain of anisotropy are developed for the proper satisfaction of the physical BCs, along with the reduction of the CFVIE to algebraic form. The method is fully validated, and numerical results regarding radar cross section (RCS) computations for various anisotropic configurations are presented.

Electromagnetic scattering by a conducting sphere with anisotropic coating

The electromagnetic (EM) scattering by a conducting sphere with anisotropic coating is investigated. A surface-volume integral equation (SVIE) method is developed, in combination with Dini series expansion (DSE). Appropriate orthogonal sets of spherical vector wave functions (SVWFs) are employed that directly satisfy the boundary conditions on the conductors surface, and allow the transformation of the SVIEs to a simple algebraic system. The validity of the developed method is examined and numerous radar cross section (RCS) computations are performed.

Scattering and Radiation by Perturbed Spherical Metallic Bodies of Revolution

A general theory, based on asymptotic expansions, for the electromagnetic scattering by rotationally symmetric bodies, whose boundary is considered as a shape perturbation of the sphere, is constructed in this work. The parametric expression of the arc that generates the body by rotation is asymptotically expanded applying Maclaurin series. Next, the fields are expressed in asymptotic expansions using the spherical vector wave functions (SVWFs). The boundary conditions are then satisfied and lead to infinite nonhomogeneous sets for the evaluation of the unknown expansion coefficients. Depending on the body of revolution (BoR), these sets are solved analytically, in asymptotic closed form, and finally the whole procedure enables a closed-form evaluation of the scattering quantities. An application of the general theory for the scattering by a body of revolution is presented.

Study of radiation characteristics of prolate or oblate spheroidal antennas using shape perturbation method

In this work we present a closed-form solution for the electromagnetic radiation of a prolate or oblate spheroidal antenna. The problem is solved using a shape perturbation technique, allowing a closed-form solution which is valid for small eccentricities of the spheroid. We validate our approach by comparing with the full wave solution and present numerical results for radiation patterns.