A New State-space-based Algorithm to Assess the Stability of the Finite-difference Time-domain Method for 3D Finite Inhomogeneous Problems

The finite-difference time-domain (FDTD) method is an explicit time discretization scheme for Maxwell's equations. In this context it is well-known that explicit time discretization schemes have a stability induced time step restriction. In this paper, we recast the spatial discretization of Maxwell's equations, initially without time discretization, into a more convenient format, called the FDTD state-space system. This in turn allows us to derive a new algorithm in order to determine the stability limit of FDTD for lossy, inhomogeneous finite problems. It is shown that a crucial parameter is the spectral norm of the matrix resulting from the spatial discretization of the curl operator. In a rectangular simulation domain the time step upper bound can be calculated in closed form and results in a time step limit less stringent than the Courant condition. Finally, the validity of the technique is illustrated by means of some pertinent numerical examples.     

Desquamating intersitial pneumonia (author's transl)

A rare case of desquamating interstitial pneumonia, in a 15-year-old boy, is reported. Symptoms consisted of dry cough, progressive dyspnoea and chest pain. The chest X-ray revealed bilateral basal opacities. There were hypoxaemia and restrictive ventilatory changes. Bacteriological, virological and serological tests were all negative. An open lung biopsy established the diagnosis and corticosteroids were given as the drug of first choice. Other drugs, such as cytostatic ones, should only be given if steroids are ineffective. Arterial blood gases proved to be the most sensitive indicator of improvement, while the chest X-ray remained abnormal for several months.     

Analysis and modeling of coupled dispersive interconnection lines

A standard method is presented for the analysis and the simulation of coupled dispersive interconnection structures. A high-frequency circuit model which is well-suited for CAD applications is proposed. Considerable attention is paid to the physical interpretation of the full-wave parameters     

High-frequency transmission line models for a thin wire above aconducting ground

Full-wave transmission line models are constructed for a thin wire above a conducting ground. The transmission line models are based on a reciprocity theorem rather than on power assumptions. Different models are considered where the current or the voltage in the transmission line model has physical significance. The models describe the propagation of the fundamental mode in the waveguide structure consisting of the wire and the conducting ground. The characteristics of this mode, needed for the models, are determined with a spectral domain technique     

Green's function for layered lossy media with special applicationto microstrip antennas

Suitable Green's dyadics are determined for the fields generated by a surface current density in a plane parallel to the interface of a layered isotropic structure. Special care is taken to ensure that Green's function can still be calculated in the source region by circumventing the numerical problems using analytical procedures. The obtained Green's function is used to calculate the power deposition from a microstrip antenna inside a layered biological tissue, the media involved can be highly lossy. An analytical method is developed to avoid numerical problems arising from the exponential decay of the fields due to these losses     

Low-frequency reflectivity approximation for two- andthree-dimensional EM absorbers

Large-size electromagnetic absorbers are mainly used in anechoic and semi-anechoic chambers for electromagnetic compatibility testing. Therefore, the determination of the reflectivities in the low-frequency range (30-300 MHz) are of paramount importance in the performance evaluation of the absorber and, finally, in a “dark room” design. We here present a low-frequency approximation of the reflectivity based on a boundary and surface integral equation technique. This approach makes it possible to compare the approximation to the rigorous integral equation approach and to other approximations in the literature. The validity of the new low-frequency approximation is discussed based on reflectivity calculations of representative two- (2-D) and three-dimensional (3-D) absorber structures     

Rigorous full-wave space-domain solution for dispersive microstriplines

The eigenmode problem for the open microstrip line is analyzed in the space domain starting from the calculation of a dyadic Green's function in the spectral domain. The transverse and the longitudinal current are discretized using the method of moments. A point-matching technique is used to impose the boundary condition, i.e., zero tangential electric field, on the strip. The edge conditions at the end points of the strip are explicitly incorporated and special care is taken to accurately retain the static behavior of the field on and near the strip. Special attention is given to the variation of the current distribution as a function of frequency