SOLUTION OF MAXWELL EQUATIONS IN TIME-DOM AIN

This article presents two numerical methods used to solve 3D Maxwell's equations in the time domain. The first one is a finite difference me thod which has been implemented in a numerical code called ALICE. This method generally used for scatterers having an infinite conductivity, has been extended to take into account electromagnetic coupling throu gh composite materials. The thickness of these materials can be thin o r thick compared to the skin depth: the first formalism, based on the ''sheet impedance' concept, is devoted to electromagnetic sources havi ng a low frequency content (lightning for example), the second one, mo re general, is however time and memory consumming. A new stability cri terion has been established to calculate currents flowing on wires of arbitrary radius compared to the cell size. The second one is a time d omain integral method. After a shea presentation of the method, a solu tion to solve numerical instability problems is proposed. New formalis ms have been developed to calculate electromagnetic fields on scattere rs covered with thin sheets of materials having a finite conductivity. Furthermore wire structures can be taken into account in the computer code. Results obtained by both methods are compared for modeling the Radar Cross Section (RCS) of a perfectly conducting sphere in free spa ce and for the computation of the current flowing on a wire located in side a cavity; this current is induced by a plane wave impinging the c avity and penetrating through the walls of finite conductivity (compos ite material).