A central characteristic feature of an important class of hyperbolic PDEs in odddimension spaces is the presence of lacunae, i.e., sharp aft fronts of the waves, in their solutions. This feature, which is often associated with the Huygens' principle, is employed to construct accurate non-local artificial boundary conditions (ABCs) for the Maxwell equations. The setup includes the propagation of electromagnetic waves from moving sources over unbounded domains. For the purpose of obtaining a finite numerical approximation the domain is truncated, and the ABCs guarantee that the outer boundary be completely transparent for all the outgoing waves. The lacunae-based approach has earlier been used for the scalar wave equation, as well as for acoustics. In the current paper, we emphasize the key distinctions between those previously studied models and the Maxwell equations of electrodynamics, as they manifest themselves in the context of lacunae-based integration. The extent of temporal nonlocality of the proposed ABCs is fixed and limited, and this is not a result of any approximation, it is rather an immediate implication of the existence of lacunae. The ABCs can be applied to any numerical scheme that is used to integrate the Maxwell equations. They do not require any geometric adaptation, and they guarantee that the accuracy of the boundary treatment will not deteriorate even on long time intervals. The paper presents a number of numerical demonstrations that corroborate the theoretical design features of the boundary conditions. Key words: Electromagnetic waves, Maxwell's equations, unsteady propagation, unbounded domains, truncation, finite computational domain, lacunae, non-deteriorating method, long-term numerical integration.Email address: tsynkov@math.ncsu.edu (S. V. Tsynkov). URL: http://www.math.ncsu.edu/∼stsynkov (S. V. Tsynkov).1 The author gratefully acknowledges support by AFOSR, Grant F49620-01-1-0187, and that by NSF, Grant DMS-0107146.
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