Konstantinos P. Prokopidis

AN FDTD ALGORITHM FOR WAVE PROPAGATION IN DISPERSIVE MEDIA USING HIGHER-ORDER SCHEMES

A fourth-order accurate in space and second-order accurate in time, Finite-Difference Time-Domain (FDTD) scheme for wave propagation in lossy dispersive media is presented. The formulation of Maxwells equations is fully described and an elaborate study of the stability and dispersion properties of the resulting algorithm is conducted. The efficiency of the proposed FDTD(2,4) technique compared to its conventional FDTD(2,2) counterpart is demonstrated through numerical results.

A Unified FDTD/PML Scheme Based on Critical Points for Accurate Studies of Plasmonic Structures

A generalized auxiliary differential equation (ADE) finite-difference time-domain (FDTD) dispersive scheme is introduced for the rigorous simulation of wave propagation in metallic structures at optical frequencies, where material dispersion is described via an arbitrary number of Drude and critical point terms. The implementation of an efficient perfectly matched layer for the termination of such media is also discussed and demonstrated. The models validity is directly compared with both analytical and numerical results that employ known dispersion schemes, for the case of two benchmark examples, transmission through a thin metal film and scattering from a metallic nanocylinder. Furthermore, the accuracy of the proposed method is also demonstrated in the study of the optical properties of Ag and Au metal-insulator-metal waveguides, filters, and resonators, which also involve dielectrics whose material dispersion is described by the Sellmeier model.

Numerical modeling of an indoor wireless environment for the performance evaluation of WLAN systems

A site-specific numerical model, based on the finite-difference time-domain method, is developed in this paper for the indoor radio channel. The scenario of interest is concerned with wave propagation in a typical office environment, for which several simulations are performed considering different placements of the transmitting antenna. Both the 2- and 5-GHz bands are examined, where contemporary wireless local area networks operate. Important channel characteristics are evaluated via the estimation of received power levels, as well as the examination of small-scale fading and time dispersion

Investigation of the Stability of ADE-FDTD Methods for Modified Lorentz Media

This letter addresses the stability problem of two auxiliary differential equation (ADE) finite-difference time-domain (FDTD) methods for the case of modified Lorentz media, using the combination of the von Neumann method and the Routh-Hurwitz criterion. A rigorous investigation supported by FDTD simulations designates that the stability criterion of the conventional FDTD method can be preserved via the proper selection of the difference and averaging operators. A set of conditions for the dispersive medium parameters is derived, providing the stability limit for both FDTD schemes with practical guidelines for evaluating the fitting of experimentally studied materials.

Time-domain modeling of dispersive and lossy liquid-crystals for terahertz applications

A numerical framework based on the finite-difference time-domain method is proposed for the rigorous study of electro-optically tunable terahertz devices based on liquid crystals. The formulation accounts for both the liquid-crystal full-tensor anisotropy and the dispersion of its complex refractive indices, which is described via modified Lorentzian terms. Experimentally characterized liquid-crystalline materials in the terahertz spectrum are fitted and modeled in benchmark examples, directly compared with reference analytical or semi-analytical solutions. In addition, the efficiency of broadband time-domain modeling of the proposed technique is also demonstrated by accurately reproducing time-domain spectroscopy measurements.

Rigorous broadband investigation of liquid-crystal plasmonic structures using finite-difference time-domain dispersive-anisotropic models

A finite-difference time-domain scheme is proposed for the rigorous study of liquid-crystal photonic and plasmonic structures. The model takes into account the full-tensor liquid-crystal anisotropy as well as the permittivity dispersion of all materials involved. Isotropic materials are modeled via a generalized critical points model, while the dispersion of the liquid-crystal indices is described by Lorentzian terms. The validity of the proposed scheme is verified via a series of examples, ranging from transmission through liquid-crystal waveplates and cholesteric slabs to the plasmonic response of arrays of gold nanostripes with a liquid-crystal overlayer and the dispersive properties of metal–liquid-crystal–metal plasmonic waveguides. Results are directly compared with reference analytical or frequency-domain numerical solutions.

FDTD Algorithm for Microstrip Antennas with Lossy Substrates Using Higher Order Schemes

Higher order spatial schemes are applied to approximate the derivatives of the conducting Maxwells equations and an analytical study regarding the stability properties and the numerical dispersion of the N-order-in-space and second-order-in-time technique is considered. The hard-to-model effect of dielectric losses on microstrip antennas is investigated and their performance is demonstrated using a fourth-order-in-space and second-order-in-time, finite-difference time-domain scheme in three-dimensional calculations.

Modeling of ground-penetrating radar for detecting buried objects in dispersive soils

A three-dimensional (3-D) time-domain numerical method is used for simulation of ground penetrating radar (GPR) on Debye-dispersive soil. The radar unit is modeled with two transmitters and one receiver in order to eliminate undesired signals. The impact of radar frequency, soil parameters and object depth upon the ability to detect buried targets is investigated through several FDTD simulations.

Performance optimization of the PML absorber in lossy media via closed-form expressions of the reflection coefficient

A robust closed-form expression of the reflection coefficient concerning the discrete uniaxial finite-difference time-domain/perfectly matched layer (FDTD/PML) for the termination of lossy materials is presented in this paper. The novel formulation introduces an advanced procedure in the optimized derivation of layer conductivities involving medium parameters, spatial or temporal increments, and excitation frequencies. Numerical results indicate that the proposed technique greatly diminishes artificial reflections and therefore achieves a significant accuracy.

An ADE-FDTD Formulation for the Study of Liquid-Crystal Components in the Terahertz Spectrum

An anisotropic auxiliary differential equation finite-difference time-domain formulation is presented in detail for the time-domain study of nematic liquid crystal devices in the terahertz spectrum. The termination of the computation domain is achieved by employing a properly designed convolution perfectly matched layer. The material dispersion and dichroism of the LC complex permittivities is modeled via a modified Lorentzian function that is demonstrated to provide an accurate description for a series of state-of-the-art materials used in LC-THz technology.