On the interior resonance problem of FEM/BEM-hybrid- and BEM-approaches

The interior resonance problem usually states the fact that certain surface integral equation techniques (boundary element methods (BEM)) used to describe exterior electromagnetic field problems may produce wrong solutions if applied to closed structures also representing resonant cavities. The situation is quite similar in the case of hybrid techniques splitting a field problem into an interior and an exterior problem, where the exterior problem is described by the BEM and the interior problem is formulated by a local technique like the finite element method (FEM). In this case not only the BEM can have an interior resonance problem, but also the FEM. The authors extend the BEM-model of the exterior field problem by one or more additional lossy bodies in the interior region to remove the corruptions of the solution by interior resonances. Illustrations are given for the two-dimensional case.