Theodoros I. Kosmanis

A comparative study of the biological effects of various mobile phone and wireless LAN antennas

This paper presents a comprehensive electromagnetic and thermal analysis of radiation and its impact on human beings, due to the use of various types of commonly used mobile phones and communication antennas. This is one of the first studies that deals with a wide-range comparative investigation of modern cell phones, unlike the majority of existing work, which do not extend beyond the obsolete generic phone case. The rather severe, although overlooked, case of wireless local area network antennas is also considered, due to their increasing use and the large times of exposure associated with them.

A comparative FDTD study of various PML configurations for the termination of nonlinear photonic bandgap waveguide structures

A comparative investigation of high-performance nonlinear, homogeneous and periodic, perfectly matched layers (PMLs) for the termination of two-dimensional (2-D) nonlinear photonic bandgap waveguides is conducted. The absorbing configurations are combined with an appropriate Z-transform-based finite difference time domain (FDTD) technique for the numerical treatment of the nonlinear materials. As in the linear case, a remarkable reduction of the reflected waves is achieved when the periodic dielectric motif of the waveguide is continued inside the absorbing layers.

A systematic and topologically stable conformal finite-difference time-domain algorithm for modeling curved dielectric interfaces in three dimensions

A systematic conformal finite-difference time-domain (FDTD) algorithm for the direct modeling of dielectric interfaces in three dimensions is presented in this paper. The straightforward procedure is based on the proper reformation of the grid cells in the vicinity of the dielectric surface, leading thus to the creation of five-faced prisms on the primary grid, apart from the standard hexagonal ones. The new scheme overcomes any topological deficiency that forbids the contour path FDTD and conformal FDTD technique to directly simulate dielectric boundaries, since it maintains the lattice duality. Therefore, no instabilities, even late-time ones, are observed. On the other hand, the accuracy obtained, even with very coarse meshes, is very good as is proved by the numerical analysis of various resonance problems.

Perfectly matched anisotropic layer for the numerical analysis of unbounded eddy-current problems

An extension of the perfectly matched layer (PML) technique in quasi-static fields is developed. The new low frequency PML is based on a fictitious medium with diagonal tensor anisotropy. On the basis of a theoretical investigation, the material properties of the anisotropic layer are specified, so that it will be reflectionless for an arbitrary eddy-current field that may exist in free space. Furthermore, the PML is designed in such a way that outgoing eddy-current fields are sufficiently absorbed. The effectiveness of the low-frequency PML is validated by the implementation of the finite-element solution of a simple two-dimensional eddy-current problem as well as a more complicated three-dimensional one.

A hybrid FDTD-wavelet-Galerkin technique for the numerical analysis of field singularities inside waveguides

A novel hybrid finite difference time domain-wavelet-Galerkin (FDTD-WG) technique is presented for the accurate representation of electromagnetic field solutions in regions of fast field transitions. Its fundamental concept lies in the combination of the robust FDTD method with the wavelet-Galerkin formulation, which in its turn can efficiently treat highly varying phenomena. The computational domain is, therefore, divided into regions of smooth and fast field variations. Proper determination of these two areas leads to improved simulations and significantly reduced computational burden, turning the proposed scheme into a powerful tool. Numerical results derived from the manipulation of various waveguides, proves the validity and efficacy of the new scheme.

EMC Analysis of High-Speed on-Chip Interconnects via a Mixed Quasi-Static Finite Difference - FEM Technique

We present a new technique to investigate electromagnetic compatibility/electromagnetic interference (EMC/EMI) interactions in high-speed transmission lines on the chip level. The time-domain method is based on the different nature of the problem in conductors and semiconductors, compared to the insulating media that separate them. Therefore, the static problem in the silicon oxide is separated from the diffusion problem in conductors. The latter one is solved by an efficient DuFort-Frankel technique, while the static problem is solved in a coarse finite element method (FEM) mesh. In each step, the two problems are appropriately coupled by means of the interface conditions. The time-domain nature of this method permits the use of proper fast Fourier transform (FFT)-based postprocessing procedures to calculate the per unit length parameters in a fast and efficient manner

A systematic conformal finite-difference time-domain (FDTD) technique for the simulation of arbitrarily curved interfaces between dielectrics

A systematic, three-dimensional methodology is presented in this paper for the finite-difference time-domain modeling of curved dielectric interfaces. Prism cells, appropriately arranged around the interface in order to preserve the duality of the overall lattice, are utilized for the accurate geometrical representation of the arbitrarily shaped dielectrics. The new scheme is enhanced by projection coefficients for the connection of field fluxes and field intensities, and appropriately computed effective permittivity values along the interface between the two media. The minor percentage of these cells in relation to the classical ones that complete the computational grid, minimizes the algorithms complexity and resource requirements. Its efficiency is proved via the analysis of partially filled resonant cavities.

Nondiagonally anisotropic PML: a generalized unsplit wide-angle absorber for the treatment of the near-grazing effect in FDTD meshes

A new generalization of the PML with wide-angle absorption is presented, for the efficient truncation of FDTD lattices. The proposed unsplit-field layer uses a nondiagonal symmetric tensor anisotropy and via an appropriate parameter selection achieves notable attenuation rates in the case of near-grazing angles. Hence, it can be placed much closer to large structures. Improved accuracy and lower dispersion errors are attained via higher-order FDTD schemes with regular and non-Cartesian lattices constructed by hexagonal or tetradecahedral cells. Finally, Ramahi ABCs are invoked for the absorbers termination. Numerical results, addressing wave attenuation at grazing incidence, prove the efficiency of the proposed PML.

Analysis of multiport waveguide structures by a higher-order FDTD methodology based on non-orthogonal curvilinear grids

A generalized methodology for the construction of nonstandard higher-order finite-difference time-domain schemes, as well as their application to complex electromagnetic problems in curvilinear non-orthogonal coordinate systems, are presented in this paper. As a consequence, a new class of low-dispersion operators is designed for the approximation of spatial and temporal derivatives. Their extension to curvilinear non-orthogonal coordinates is attained by a higher-order variation of the covariant and contravariant vector component theory, in which all metric terms are taken into account. Finally, the proposed method is validated by the analysis of diverse multiport microwave structures with realistic features.

Beam Propagation Method Based on the Iterated Crank–Nicolson Scheme for Solving Large-Scale Wave Propagation Problems

An explicit vectorial beam propagation method, based on the iterated Crank-Nicolson scheme is developed and utilized to solve electromagnetic wave propagation problems in large-scale structures. A full wide-angle extension is studied, based on a direct calculation of the one-way differential operator only in the first propagation step, together with a fast modification along the propagation axis, to account for material and structure variations.