Constantinos A. Valagiannopoulos

ELECTROMAGNETIC SCATTERING FROM TWO ECCENTRIC METAMATERIAL CYLINDERS WITH FREQUENCY-DEPENDENT PERMITTIVITIES DIFFERING SLIGHTLY EACH OTHER

The interaction between a metamaterial cylindrical structure and an incident plane wave is investigated. The structure is comprised of two cylinders, one embedded into the other, whose effective characteristics vary with the operating frequency following similar laws. Such a model can be used to describe periodic structures, constituting metamaterials, with slightly different features. The well- known eigenfunction expansions are adopted, while the boundary conditions are manipulated with help of the translation theorem for cylindrical coordinates. A first-order perturbation solution is obtained leading to simple and computationally efficient formulas. The fluctuations of near-field and far-field responses with respect to the position of the internal cylinder, the permittivities and the frequency are observed and discussed.

Electromagnetic scattering of the field of a metamaterial slab antenna by an arbitrarily positioned cluster of metallic cylinders

The operation of a slab antenna with low-index metamate- rial substrate is afiected by a cluster of metallic cylinders positioned in the near-fleld area. A semi-analytical solution of the deflned boundary value problem is obtained based on the small size of the rods. Several difierent conflgurations are found to possess beneflcial features con- cerning the total radiated power and the angle of directive emission. The deduced diagrams are independently validated and discussed, re- vealing certain conclusions.

Total absorption in asymmetric hyperbolic media

Finite-thickness slabs of hyperbolic media with tilted optical axes exhibit asymmetry properties for waves propagating upward and downward with respect to slab interfaces. Under certain conditions, asymmetric hyperbolic media acquire extreme permittivity parameters and the difference between upward and downward propagating waves becomes very large. Furthermore, both waves can be perfectly matched with the free space; such a feature makes possible the development of optically ultra thin perfect absorbers. The proposed approach is unified and allows the use of different -negative materials. Of particular interest is the asymmetric hyperbolic medium, made of silicon nanowires, since it can be directly applicable to solar cell systems.

EFFECT OF CYLINDRICAL SCATTERER WITH ARBITRARY CURVATURE ON THE FEATURES OF A METAMATERIAL SLAB ANTENNA

The metamaterial slab with low refractive index exhibits directive properties which make it suitable to work as antenna. The characteristics of such a device are affected under the presence of a conducting rod of arbitrary shape placed over the slab. A qualitative and quantitative approach is presented which is possible by implementing the method of auxiliary sources. For the evaluation of the far field quantities the method of stationary phase is employed. A validation example considering a circular rod is solved rigorously with use of the method of moments. Several numerical results are shown and discussed.

STUDY OF AN ELECTRICALLY ANISOTROPIC CYLINDER EXCITED MAGNETICALLY BY A STRAIGHT STRIP LINE

An infinite homogeneous circular cylinder with full permittivity tensor is excited by a straight strip flowed by arbitrary axial magnetic current. A nontrivial differential equation is derived for the single axial magnetic component which is assigned a plane wave representation. The boundary conditions lead to an integral equation with nonsingular kernel which is solved by supposing a Dirac comb representation for the unknown function. The resultant Greens function multiplied by the current distribution is integrated numerically over the source to give the total field. Various numerical examples are presented and discussed.

CLOSED-FORM SOLUTION TO THE SCATTERING OF A SKEW STRIP FIELD BY METALLIC PIN IN A SLAB

A tiny metallic cylinder placed into a planar dielectric waveguide scatters the field developed by a current-carrying skew strip centralized at the middle of the slab. Due to the small size of the scatterer, the induced surface current is taken independent of the azimuthal angle. The Greens function of the problem is expressed in closed form and it is inserted to the scattering integral after the polar equation of the strip has been determined. The behavior of near- field quantities in the slab, with respect to geometrical and material parameters, is observed and examined.

AN OVERVIEW OF THE WATSON TRANSFORMATION PRESENTED THROUGH A SIMPLE EXAMPLE

One of the methods developed for accelerating the convergence speed of infinite series is the Watson transformation. It is a technique with an interesting theoretical background which is applied in a restricted number of cases due to its complexity. Most of the papers using this method do not extensively analyze every step of implementation. In this work we apply Watson transformation in a simple case and we focus on each aspect of the procedure.

Arbitrary Currents on Circular Cylinder with Inhomogeneous Cladding and RCS Optimization

The perfectly conducting circular cylinder is a simple type of radiator and scatterer. The effects of coating the cylinder have been studied in a number of papers. In the present work arbitrary magnetic and electric axial surface currents are considered on the cylinder, while the coating is radially inhomogeneous following a power-law. The Helmholtz equation possesses a closed-form solution in such materials involving Bessel functions of non-integer order. After the determination of the scattered field the coating that optimizes the backscattering reflection is determined. Several numerical results are presented and discussed.

Electromagnetic cloaking of cylindrical objects by multilayer or uniform dielectric claddings

We show that dielectric or even perfectly conducting cylinders can be cloaked by a uniform or a layered dielectric cladding, without the need of any exotic or magnetic material parameters. In particular, we start by presenting a simple analytical concept that can accurately describe the cloaking effect obtained with conical silver plates in the visible spectrum. The modeled structure has been originally presented in [S. A. Tretyakov, P. Alitalo, O. Luukkonen, C. R. Simovski, Phys. Rev. Lett., vol. 103, p. 103905, 2009], where its operation as a cloak in the optical frequencies was studied only numerically. We model rigorously this configuration as a multi-layer dielectric cover surrounding the cloaked object, with excellent agreement to the simulation results of the actual device. The concept of using uniform or multilayer dielectric covers, with relative permittivities larger than unity, is then successfully extended to cloaking of impenetrable objects such as conducting cylinders.

A Novel Methodology for Estimating the Permittivity of a Specimen Rod at Low Radio Frequencies

Capability in accurately determining the permittivity of a dielectric specimen is significant for a number of reasons. In this study, a new method is proposed to estimate the texture of the test rod with negligible error. It is based on the assumption that the specimen rod possesses electrically small dimensions, under which the scattering integral is simplified. The obtained formula is suitable for a variety of measuring configurations and has been tested for a particular one, with satisfying results.