EMDS Analysis of Dielectric Layers and Coatings

This paper first describes a software package that was recently introduced by Cray Research for electromagnetic analysis, EMDS (ElectroMagnetic Design System), based on the Finite-Difference, Time Domain code developed by A. Taflove. This package allows the user to specify scatterers by means of a Computer Aided Design (CAD) interface. The scatterers are modeled using a conformal, curved-surface method. This package has been validated by comparison of results obtained for a double sphere problem with GMT results, and results from an almond-like object with measured results. An EMDS demonstration in July 1992 involved modeling of an entire airplane.

It is highly desirable to use EMDS to model scatterers which have high density dielectric layers and coatings. The wavelength of a wave in these layers is generally very small, in relation to the freespace wavelength. This would imply that a very fine mesh would be needed for the FD-TD method to be used. For very small problems, however, this can require storage and running times which are not practical.

The surface impedance boundary condition (SIBC) developed by Beggs, et.al. (J. H. Beggs, et. al., "Finite-Difference Time-Domain Implementation of Surface Impedance Boundary Conditions," IEEE Trans. on Ant. and Prop., vol. 40, pp. 49-56, January, 1992) in one dimension and in two dimensions for a stepped-edge object is extended to model curved-surface objects in two and three dimensions, and is used with EMDS to allow these and more complex scatterers to be input in a simple manner. Validations are given for 2-D circular cylinders and 3-D spheres against both alternative numerical and analytic methods, as well as measured data.