Ana C. L. Cabeceira

Modelling dispersive dielectrics in TLM method

The TLM method, being a time domain method, cannot deal directly with frequency dispersive media. A way for modelling such media, for instance, dielectric dispersive ones, is proposed, starting from the causality relationship between field vectors D and E, which is discretized over the same space–time mesh as the three-dimensional TLM mesh (in our case, with HSCN node). This leads to adding, at each node on the network, three voltage sources (one for each field component), their value depending on the previous instants. The method is validated by computing the reflection (magnitude and phase) coefficient at normal incidence at an air–dielectric interface, for different dispersive behaviours of the dielectrics. Copyright

Two-dimensional extension of a novel FDTD technique for modeling dispersive lossy bi-isotropic media using the auxiliary differential equation method

This letter describes a two-dimensional (2-D) extension of a recently developed finite-difference time-domain (FDTD) scheme to model wave propagation in bi-isotropic media. To our knowledge this method is the only one successfully generalized to modeling transient microwave signals in general lossy dispersive bi-isotropic media. The new 2-D cell built and computational procedure of the FDTD algorithm developed is described. Condon and Lorentz dispersion models have been included for modeling the frequency dependence of the medium parameters and the auxiliary differential equation (ADE) method is considered to deal with dispersion in order to avoid defining complex back-stored numbers to compute the convolutions recursively. Finally the oblique incidence of a wave on a chiral medium and the propagation in a general lossy bi-isotropic medium have been successfully simulated.

Reinterpreting Four-Stage Split-Step FDTD Methods as Two-Stage Methods

In recent years, split-step finite-difference time-domain (SS-FDTD) methods have attracted much attention and many implementations have been developed to improve their accuracy and efficiency. In this communication the equivalence between some of these recently reported techniques and conventional schemes is shown. More specifically, we prove that there are four-stage split-step (4SS)-FDTD algorithms that can be reinterpreted as classic two-stage split-step (2SS)-FDTD schemes yielding the same local truncation errors and numerical dispersion relationships. The analytical results are validated by numerical simulations.

A Multiresolution Model of Transient Microwave Signals in Dispersive Chiral Media

A multiresolution in time domain method is used to model the propagation of transient signals through dispersive chiral media. The modeling of these media requires the computation of convolution integrals, whose resolution level may be increased by introducing wavelets in the time dependence of the fields

Quasi-Planar Chiral Materials for Microwave Frequencies

The growing development in the new communication technologies requests devices to perform new features or to improve the old ones. The trend is to develop new artificial materials reproducing well-known properties already present in other frequency ranges (such as optics) or materials with properties inexistent in the nature. Among the first kind, artificial chiral media, based on the random inclusion of metallic particles with chiral symmetry into a host medium are worth to mention (Fig. 1). Nevertheless, the fabrication techniques up-to-date are quite expensive and produce samples not easy to be tailored and with imperfections, such as intrinsic anisotropy and non-homogeneity (non-uniform density and orientation of inclusions), as well as heavy losses.

Application of Schelkunoff's Method for Simulating Isotropic Chiral free Propagation: Clarifying Some Common Errors

Schelkunoffs method, also commonly refered to as Coupled Mode Method (CMM), is a numerical method which gives the propagation constants and the electromagnetic field in a general homogeneous medium bounded by perfect electric walls. In this paper, we test Schelkunoffs method for a waveguide filled with an isotropic chiral material (chirowaveguide) where the dimensions of the walls are electrically large compared with the wavelength. It is reasonable to foresee that, in this case, the results given by Schelkunoffs method must approach to the corresponding ones for the chiral unbounded medium. Effectively, we obtain the solutions for both circular polarized waves (right-handed and left-handed) in free propagation in a single calculation. These results are in opposition with those of other authors analyzing analogous cases.

Chiral Media Based on Printed-Circuit Board Technology: A Numerical Time-Domain Approach

The common design of artificial chiral media for microwave frequencies is based on the inclusion of particles with chiral symmetry (i.e., specular symmetry or handedness) into a host medium. Recently, we have considered new fabrication techniques based on printed-circuit board technology, because the use of via holes gives us great additional flexibility to select the type of chiral inclusions from helix to cranks. In this paper, a numerical study in the time domain of the electromagnetic-wave propagation through these types of structures is achieved by using the commercial software MEFiSTo, a time-domain electromagnetic simulator based on the transmission-line matrix method.

Metamaterials, a chance for high frequency electronics?

Metamaterials are a new kind of artificial media, exhibiting electromagnetic properties not found in nature. In fact, the word “meta” comes from the Greek word meaning “beyond”. Among them, the class of “Left Handed” (LH), also known as “Double Negative” (DNG) metamaterials shows unusual characteristics such as backward waves, negative refraction or reverse Doppler effect. In this paper we will present the fundamentals of metamaterials: structure, electromagnetic properties, characteristics of wave propagation and some applications in high frequency (ranging from GHz to THz) passive circuits. Also, a brief scope of prospective applications in electronic circuitry will be discussed.

2D-TLM model for propagation in biisotropic media

A TLM model suitable to model the propagation of electromagnetic waves in biisotropic media is presented. The main characteristic of the electromagnetic response of such complex media is the cross coupling of the electromagnetic field vectors in its constitutive relationships. In this work, the angle tilt between electric and magnetic field vectors, the intrinsic impedances, the effective parameters of the medium, and the rotation of the polarization plane are computed. The results for a monochromatic source are in very good agreement with the theoretical solution.