Constantinos A. Valagiannopoulos

Learn More
—In this paper, two different neural models are proposed for calculating the quasi-static parameters of multilayer cylindrical coplanar waveguides and strip lines. These models were basically developed by training the artificial neural networks with the numerical results of quasi-static analysis. Neural models were trained with four different learning(More)
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.(More)
—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,(More)
Several wave scattering phenomena in optics are modeled by the method of fictitious sources (MFS). Despite its interesting features, the effectiveness of the MFS and its applicability are restricted by open issues, including the placement of the fictitious sources (FS) and the fields' convergence. Concerning these issues, we investigate here the MFS(More)
—The permittivity tensor of an anisotropic material can be predicted with use of the presented technique. A slab of this substance possessing infinitesimal thickness is illuminated by a normally incident plane wave and rigorous expressions for the transmission coefficients are obtained. The derived formulas are linearly expanded with respect to the small(More)
A grounded dielectric film-slab is externally excited by a normally-incident Gaussian beam. A single superstrate dielectric layer, with suitably selected parameters, is placed on top of the film-slab in order to increase the power concentration inside the slab. A basic quantity of interest, called “enhancement factor” is defined, which(More)
A ground-penetrating radar (GPR) antenna excites a perfectly electric conducting inclusion buried inside the ground. The scattering problem is solved semi-analytically via integral equation techniques. The permittivity and thickness of a superstrate deposited atop the ground are determined such that the detectability of the inclusion is significantly(More)
The electromagnetic response of a two-dimensional metal embedded in a periodic array of a dielectric host can give rise to a plasmonic Dirac point that emulates Epsilon-Near-Zero (ENZ) behavior. This theoretical result is extremely sensitive to structural features like periodicity of the dielectric medium and thickness imperfections. We propose that such a(More)
* These authors contributed equally to this work Lens design for focusing and imaging has been optimized through centuries of developments; however, conventional lenses, even in their most ideal realizations, still suffer from fundamental limitations, such as limits in resolution and the presence of optical aberrations, which are inherent to the laws of(More)