Reduced-Fringing-Field Multi-MHz Capacitive Wireless Power Transfer System Utilizing a Metasurface-based Coupler

This paper introduces a multi-MHz large air-gap capacitive wireless power transfer (WPT) system that achieves substantial fringing field reduction by utilizing metasurface-based coupling plates (referred to as `metacoupler'). The metasurface in the proposed coupler has an impedance property that restricts the electric field lines from emanating outwards from the coupler, leading to a more focused near-field energy transfer compared to a system with a conventional capacitive coupler. Physical implementations of the metacoupler in a capacitive WPT system using different types of metasurfaces are investigated. A design methodology for the metacoupler is presented that enables substantial fringing field reduction while maintaining high efficiency. Two 13.56-MHz 12-cm air-gap capacitive WPT prototypes, one with the conventional coupler and another with the proposed metacoupler, are designed, built, and tested. The prototype system with the proposed metacoupler is shown to achieve 40% reduction in fringing electric field levels compared to its conventional counterpart.