In this paper a semi-analytical representation of the coupling impedance between coils composed of filamentary turns located between two layered media is provided on the basis of the spectral expansion of the fields involved in the system. Both media are composed of several layers of homogeneous materials characterized by their physical properties occupying, respectively, a half-space bounded by a plane. The domain in the middle, where the coils are placed, has vacuum properties. The development is focused on misaligned circular coils placed in parallel planes with respect to the media boundaries. Two different behavioral descriptions have been considered: first, the system is made up entirely of magnetic insulators and the coupling impedance is therefore purely inductive; second, at least one medium is an electrical conductor and, as a consequence, an additional resistive component emerges when the coupling impedance is evaluated. In the latter case, the coupling impedance exhibits a frequency dependence due to the dispersive effects associated with the induced currents generated in the conductive media. The model developed is verified by means of a comparison between numerical and experimental results.
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