A high-order accurate scheme for Maxwell's equations with a Generalized Dispersive Material (GDM) model and material interfaces

Abstract

A high-order accurate scheme for solving the time-domain dispersive Maxwell's equations and material interfaces is described. Maxwell's equations are solved in second-order form for the electric field. A generalized dispersive material (GDM) model is used to represent a general class of linear dispersive materials and this model is implemented in the time-domain with the auxiliary differential equation (ADE) approach. The interior updates use our recently developed second-order and fourth-order accurate single-stage three-level space-time finite-difference schemes, and this paper extends these schemes to treat interfaces between different dispersive materials. Composite overlapping grids are used to treat complex geometry, with Cartesian grids generally covering most of the domain and local conforming grids representing curved boundaries and interfaces. Compatibility conditions derived from the interface jump conditions and governing equations are used to derive accurate numerical interface conditions that define values at ghost points. Although some compatibility conditions couple the equations for the ghost points in tangential directions due to mixed-derivatives, it is shown how to decouple the equations to avoid solving a larger system of equations for all ghost points on the interface. The stability of the interface approximations is studied with mode analysis and it is shown that the schemes retain close to a CFL-one time-step restriction. Numerical results are presented in two and three space dimensions to confirm the accuracy and stability of the schemes. The schemes are verified using exact solutions for a planar interface, a disk in two dimensions, and a solid sphere in three dimensions.