“…In theory, the background medium can be of any homogeneous linear non-dissipative material and is chosen here to be free space for convenience. The material considered within the discontinuity region can also be linear, non-linear, dissipative, frequency dependent and/or a combination of them [36][37][38][39][40], however, for simplicity it is considered here to be linear, isotropic and nondissipative of relative permittivity ε 1 . For this case, the associated polarization function is defined by…”