Figure 1: Schematic diagram of the three media considered. The upper medium is a dielectric, characterized by its electric permittivity 𝜖 𝑑 and magnetic permeability 𝜇 𝑑 in the frequency region of interest. Similarly, the metals 1 and 2 are characterized by 𝜖 1 , 𝜇 1 and 𝜖 2 , 𝜇 2 , respectively.