Numerical Approximation of Asymptotically Disappearing Solutions of Maxwell's Equations

TL;DR

This paper develops a finite-element numerical method to approximate asymptotically disappearing solutions of Maxwell's equations in polyhedral domains, demonstrating exponential decay of solutions over time.

Contribution

It introduces a finite-element approach with divergence-free initial conditions for approximating ADS in complex geometries, extending prior analytical results.

Findings

Finite-element approximation accurately models ADS decay.

Numerical solutions exhibit exponential energy decay.

Method is effective for practical polyhedral domains.

Abstract

This work is on the numerical approximation of incoming solutions to Maxwell's equations with dissipative boundary conditions whose energy decays exponentially with time. Such solutions are called asymptotically disappearing (ADS) and they play an importarnt role in inverse back-scatering problems. The existence of ADS is a difficult mathematical problem. For the exterior of a sphere, such solutions have been constructed analytically by Colombini, Petkov and Rauch [7] by specifying appropriate initial conditions. However, for general domains of practical interest (such as Lipschitz polyhedra), the existence of such solutions is not evident. This paper considers a finite-element approximation of Maxwell's equations in the exterior of a polyhedron, whose boundary approximates the sphere. Standard Nedelec-Raviart-Thomas elements are used with a Crank-Nicholson scheme to approximate the electric and magnetic fields. Discrete initial conditions interpolating the ones chosen in [7] are modified so that they are (weakly) divergence-free. We prove that with such initial conditions, the approximation to the electric field is weakly divergence-free for all time. Finally, we show numerically that the finite-element approximations of the ADS also decay exponentially with time when the mesh size and the time step become small.