Inductive Power Transfer Efficiency Limit of a Flat Half-Filled Disc Coil Pair

The efficiency limit for an inductive power transfer between two flat half-filled disc coils is derived based on a model for the eddy current losses in the coils and the losses due to electromagnetic radiation. Analytic approximations for the coupling factor of the coils and eddy current losses are proposed and experimentally verified. It is shown that the approximative terms allow us to express the maximum efficiency of the coil pair analytically. If the strand diameter of the coil is sufficiently small, the efficiency depends only on the strand diameter, diameter of the coils, and the gap between the coils—but not on the operating frequency. Therefore, increasing the frequency does not result in higher efficiency but allows to reduce the coil thickness.

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