R.G. Martin

FDTD Modeling of Graphene Devices Using Complex Conjugate Dispersion Material Model

Graphene-based devices constitute a pioneering field of research for their extraordinary electromagnetic properties. The incorporation of appropriate models into numerical simulators is necessary in order to take advantage of these properties. In this work, we propose a method to incorporate graphene-sheet models into the FDTD method. The use of vector-fitting techniques expands the permittivity of graphene into a rational function series of complex conjugate pole-residue pairs, which is implemented into FDTD by an auxiliary differential equation formulation. Simple waveguiding problems validate our approach.

A hybrid technique combining the method of moments in the time domain and FDTD

This letter presents a new hybrid method that efficiently combines two versatile numerical techniques, viz., the finite difference time domain (FDTD) and the method of moments in the time domain (MoMTD). The hybrid method is applicable to complex geometries comprising arbitrary thin-wire and inhomogeneous dielectric structures. It employs the equivalence theorem to separate the original problem into two subproblems: (1) the region containing the wires, which is analyzed by using the MoMTD, and (2) the dielectric zone that is modeled with the FDTD. The application of the method is illustrated by analyzing two canonical problems involving thin wires and inhomogeneous media.

Time-domain integral equation methods for transient analysis

Some recent developments and extensions of the method of moments for analyzing, in the time domain, the interaction of transient electromagnetic waves with perfect electric conductors are described. The electric and magnetic time-domain integral equations (TDIEs) are formulated and their characteristics briefly discussed. Some issues involved in the formulation and solution of the thin-wire electric-field integral equation are examined. The solution of the magnetic- and electric-field integral equations for bodies modeled by patches is considered. The problem of the instabilities that appear in the solution of the TDIEs is addressed. The possibilities of using postprocessing of the time-domain data to visualize the history of electromagnetic phenomena are illustrated.<<ETX>>

Extension of the ADI-FDTD method to Debye media

This paper describes an extension of the alternating direction implicit finite-difference time-domain (ADI-FDTD) method to analyze problems involving Debye media.

A hybrid time-domain technique that combines the finite element, finite difference and method of moment techniques to solve complex electromagnetic problems

This paper describes a hybrid technique directly operating in time domain that combines the finite element time domain (FETD), the finite-difference time-domain (FDTD) and the integral-equation-based method of moments in the time domain (MoMTD) techniques to analyze complex electromagnetic problems involving thin-wire antennas radiating in the presence of inhomogeneous dielectric bodies whose shape can be arbitrary. The method brings together the ability of the FDTD scheme to deal with arbitrary material properties, the versatility of the FETD to accurately model curved geometries, and that of the MoM to analyze thin-wire structures. Working in the time domain provides wide-band information from a single execution of the marching-on-in-time procedure and simplifies the interfacing of the FE and MoM methods with the FDTD, an approach specifically designed for time domain analysis. Numerical results that validate the hybrid method and show its capabilities are presented in the paper.

On the application of finite methods in time domain to anisotropic dielectric waveguides

This paper presents some general ideas for the construction of explicit finite algorithms to study wave propagation in dielectric anisotropic waveguides. The goal is to facilitate the development of different finite schemes through the extension of the finite-difference time-domain (FDTD) method to study anisotropic media. Some of these schemes are particularized and applied to the simulation of the propagation of electromagnetic waves through planar dielectric anisotropic waveguides.

GA design of a thin-wire bow-tie antenna for GPR applications

A microgenetic algorithm has been applied to design a new ultrawideband thin-wire bow-tie antenna for ground-penetrating radar applications. The broadband performance of the antenna is achieved by resistive loading and by optimizing the number of wires and the angular distances between those wires. The radiation characteristics of the optimized antenna are discussed, and its performance is compared to that of a resistively loaded Wu-King dipole.

Benchmark Antenna Problems for Evolutionary Optimization Algorithms

A set of antenna-optimization problems is presented that satisfies the necessary requirements to form a test suite useful for measuring and comparing the performance of different evolutionary optimization algorithms (EAs) when they are applied to solve complex electromagnetic problems. The ability of the proposed test suite to find strong and weak points of any EA is illustrated by a complete study of four broadly used evolutionary algorithms carried out with the aid of the new test functions

Some thoughts about transient radiation by straight thin wires

The paper discusses, from a physical point of view, several basic features related to the transient radiation of electromagnetic waves by straight thin-wire antennas.

On the dispersion relation of ADI-FDTD

In this letter, we analyze the alternating direction implicit finite-difference time-domain (ADI-FDTD) dispersion relation and find the numerical plane-wave relationship between the magnetic and electric fields, showing that the scheme is not divergence-free. We also show that negative-group-velocity modes with positive phase velocities may appear for high Courant numbers. A parallel comparison is made with the behavior of the classical Yee FDTD and the Crank-Nicolson schemes.