Moreover, some theoretical analyses of problems involving metamaterials have shown that simple frequency-domain waveguide discontinuity problems can be ill-posed  even in the presence of lossy media and of absorbing boundary conditions .
Accordingly, the proposed stabilization algorithm is preliminary numerically validated (by exploiting a commercial FE solver ) against a wide set of electromagnetic problems belonging to two canonical classes: a waveguide discontinuity problem, and a multi-layer sphere scattering problems.
Indeed, it has been recently demonstrated that waveguide discontinuity problems can become ill-posed even in the presence of lossy media and absorbing boundary conditions .
[24.] Raffetto, M., "Ill posed waveguide discontinuity problem involving metamaterials with impedance boundary conditions on the two ports," IET Proc.