Study of Displacement Current Effect for Planar Coils in Layered Medium

Abstract—In this paper, a full-wave semi-analytical solution of self and mutual impedances for a coil-based system is proposed. It consists of two concentric circular coils with rectangular cross sections. Traditionally, the calculation of self and mutual impedances of these coils are based on eddy current approxima-tion, where a simple background is assumed to achieve analytical and semi-analytical solutions. As the system operates at higher frequencies and with inhomogeneous media, the displacement current has to be taken into account. By deriving Maxwell’s equations without eddy current assumption, the impedances of coils immersed in the layered medium can be obtained analytically. The results show a considerable discrepancy at sub-GHz frequencies, indicating the significant effect of displacement current at higher frequencies for a coil-based wireless power transfer link. I