D. S. Katz, M. J. Piket-May, and A. Taflove

EECS Department

McCormick School of Engineering

Northwestern University

Evanston, IL 60208

This paper describes the EMDS (*E*lectro*M*agnetic
*D*esign *S*ystem) software package that we have developed in
collaboration with Cray Research, Inc. EMDS implements conformal
curved-surface FD-TD modeling of electromagnetic wave interactions with
electrically large 3-D structures of complex shape. EMDS aims to
minimize computational burdens by using an almost-completely-structured
FD-TD mesh, with rectangular Yee cells everywhere except for the
relatively few finite-volume stretched or cut cells adjacent to the
target surface. It allows the user to rapidly specify complicated
structures via the General Dynamics ACAD (*A*dvanced
*C*omputer *A*ided *D*esign) system, or import
appropriate files from other CAD systems. And, using Cray's MPGS
(*M*ulti*P*urpose *G*raphics *S*ystem,) it provides
tools to visualize the dynamics of electromagnetic wave scattering and
surface current flow via color animations.

A number of examples will be presented which provide validations of EMDS modeling for perfectly electrically conducting 3-D targets. These will include the double sphere (validated versus generalized multipole theory) and the NASA almond (validated versus measurements). EMDS results for a complete General Dynamics fighter aircraft prototype will be shown and compared to scale-model scattering measurements (if the latter are available in time for this symposium).

This paper will also discuss EMDS modeling of metal scatterers with thin, high-density dielectric layers and coatings. To avoid the numerical storage, running time and stability problems experienced in directly resolving these thin layers, a "smart-cell" strategy is used wherein a surface impedance boundary condition is applied at the finite-volume stretched or cut cells adjacent to the target surface. For this case, validations will be provided for canonical 2-D and 3-D curved target shapes.