J. Van Hese

Modeling of discontinuities in general coaxial waveguide structures by the FDTD-method

The finite-difference time-domain (FDTD) method is used to model generalized coaxial waveguide structures with discontinuities. The cross section of the waveguide consists of a closed outer conductor and one or two inner conductors of arbitrary shape. The cross section can have any number of dielectric materials with losses. The singular field-behavior near sharp edges is explicitly included in the finite-difference scheme. Any kind of discontinuity can be handled: changes in cross-section as well as changes of material parameters. From the time-domain data, frequency-domain data (S-parameters) are obtained using Fourier-transform techniques. >

Generalised Space Domain Green's Dyadic for Multilayered Media with Special Application to Microwave Interconnections

The eigenmode problem for multilayered structures with coplanar or non-coplanar strips is analysed using the space domain Greens dyadic of these structures as the kernel of an integral equation. The integral equation is solved using the method of moments combined with point-matching. The calculation of the Greens dyadic starts in the spectral domain. First, an efficient solution technique is presented to determine the spectral Greens dyadic. Special attention is then devoted to its behaviour for large values of the Fourier variable and to the contribution of this asymptotic part to the space domain Greens dyadic. The behaviour of the fields in the vicinity of the excitation is determined explicitly. The method is illustrated by two typical examples.

Electromagnetic field calculations used for exposure experiments on small animals in TEM-cells

Three-dimensional electromagnetic calculations for loaded transverse electromagnetic (TEM) transmission cells are presented. Based on those calculations a prediction of the perturbation of the standard uniform field in the TEM-cell, due to the scattering by inhomogeneous structures placed inside the cell cavity, is given. The influence of the dimensions of a lossy structure and its position in the TEM-cell on its absorption of the electromagnetic fields is presented. Knowing the perturbation of the uniform field is important for good interpretation of the biological experimental results.

Simulation of the effect of inhomogeneities in TEM transmission cells using the FDTD-method

The finite-difference-time-domain (FD-TD) method is applied to model transverse electromagnetic (TEM) transmission cells in three dimensions. The perturbation of the TEM mode and the standard field distribution in the TEM cell, due to inhomogeneous materials placed inside the cell cavity, is evaluated. Particularly, the dependence of the disturbance of the TEM mode on the dimensions of the material and its position in the TEM cell is studied. The absorption of the electromagnetic fields in the lossy materials, placed in the cell, is also calculated. >

A Calderón multiplicative preconditioner for the electromagnetic Poincaré-Steklov operator of a heterogeneous domain with scattering applications

In the context of hybrid formulations, the Poincare-Steklov operator acting on traces of solutions to the vector Helmholtz equation in a heterogeneous interior domain with a smooth boundary is regularized by a well-known boundary integral operator related to the homogeneous exterior domain. For the first time, this property allows us to simultaneously construct a Calderon multiplicative preconditioner for the discretized operator and for a 3-D hybrid finite/boundary element method formulation, applicable to electromagnetic scattering problems. Numerical examples demonstrate the effectiveness of this novel preconditioning scheme, even for heterogeneous domains with non-smooth boundaries.

Frequency derivatives of the Green's functions of a stratified medium

We present an exact method for calculating the frequency derivatives of the Greens functions (FDGF) or Sommerfeld potentials for microstrip structures in a laterally infinitely extending, stratified medium. By applying the adjoint network concept in the spectral space domain, the PDGF are easily calculated. The inversion of these FDGF from the spectral space domain to the space domain is discussed and several examples are presented. These FDGF can be used in the mixed potential integral equation (MPIE) for obtaining frequency derivatives of the surface currents on the microstrip.

Method of moment solution of multilayered microstrip structures with thin layers using quasi-static images

A method of moment solution for multilayered microstrip structures with thin layers is described. The effect of the thin layers is taken into account properly by the use of quasi-static images. These images are extracted and treated analytically throughout the whole solution proces. This results in an efficient and accurate simulation technique for microstrip structures with thin layers. Numerical results are shown for a microstrip line covered by a thin passivation layer and for a thin film capacitor.

Electromagnetic Calculations using the FDTD-Method for the Analysis of Waveguide Applicators for Microwave Hyperthermia

Electromagnetic calculations for waveguide applicators using the Finite Difference Time Domain (FDTD) method are presented. The algorithm is applied to a water-filled applicator and the computed results are compared to experimental results in a phantom of saline-solution. Influence of the loading on the near field of the applicator is illustrated in the case where a thin plexi-glass plate is inserted between the applicator and the phantom.

Application of the FDTD method in the modeling of bent coaxial structures

An extended finite difference time domain (FDTD) method is presented to model a typical interconnection structure consisting of a closed three-dimensional bent coaxial waveguide. In order to obtain a faster, more accurate, and more elegant implementation, some aspects of the FDTD method were studied. A transition formula to connect meshes with difference cell size is proposed. The derived formula was tested in a one-dimensional case, but is applicable in more-dimensional discretization schemes. A formula to correctly describe a transition between a discretization scheme in a Cartesian system and in a cylindrical coordinate system is obtained. This is a second-order discretization formula for the first-order derivatives in Maxwells equations. The validity of this approach is illustrated by a three-dimensional example. >

Modelling of high-speed interconnection lines and discontinuities

For the design and simulation of high speed interconnection systems and fast digital computers it is imperative to consider both the two-dimensional modelling of bus structures in different technologies and to take the presence of so-called discontinuities (e.g. via-holes, line crossings, packages and connectors) into account. The paper presents quasi-TEM capacitance calculations based on an integral equation technique. As typical examples we studied the effect of etching on the impedance of striplines and impedance calculations for the shielded wire configuration. Furthermore, we considered the capacitance of via-holes and of line crossings.