Reciprocity in perfectly matched absorbers

In the numerical solution of electromagnetic scattering and/or radiation problems by finite methods, a mesh truncation scheme must be employed in order to obtain a bounded computational domain. The perfectly matched layer (PML) concept, is an efficient mesh truncation technique in finite difference time domain (FDTD) applications. Basically, PMLs are designed such that a plane wave with arbitrary frequency and direction of incidence is absorbed by the layer without any reflection. Although the PML concept has been originally introduced for FDTD simulations, it has also been used in the solution of frequency domain electromagnetic boundary value problems by the finite element method. We discuss the reciprocity issue in PML media. We show that the satisfaction of reciprocal depends upon the choice of the decay behavior within the medium. We also demonstrate that the non-local character of the bianisotropic PML plays an important role in determining whether or not the reciprocity-criterion is met.