High-efficiency self-resonant transmitters and receivers for wireless power transfer

Dartmouth College, Hanover NH

Investigators

Abstract

Wireless power transfer has emerging and potential applications such as charging personal electronics and electric vehicles, and powering wireless sensors. However, at present, the capabilities in terms of distance and efficiency are limited. This work will develop a new self-resonant structure to replace the transmit and receive coils now used, and enable improvements in distance and efficiency. The structure can be fabricated using low-cost non-toxic recyclable materials, and is scalable for a wide range of power levels, frequencies and sizes. The increased efficiency of this new approach can allow migration from conventional wired connections to wireless power transfer with minimal loss of efficiency, while expanded use of wireless power can facilitate beneficial new technologies such as low-cost sensor networks and electric vehicles. The quality factor Q of the resonant circuits used for transmitting and receiving wireless power is an essential figure of merit that determines the achievable distance and efficiency. The new resonant structures developed in this work are expected to achieve higher Q and therefore make longer distance and higher efficiency power transfer feasible. Beyond the application to wireless power transfer, the approach developed in this work may lead to more efficient resonant structures applicable to more conventional power and energy applications. Two geometries of the resonant structure will be developed. A planar version uses a stack of thin foil conductors separated by thin polymer dielectric layers. Each foil is much thinner than a skin depth, thereby overcoming skin-effect losses. The capacitance between the foil layers resonates with the inductance of the current loop at the frequency of operation, such that the main high-current path is completely within the coil, eliminating the need for high-current connections exiting the coil, as well as eliminating the need for external resonant capacitors. The capacitors formed by the layers also act as ballast impedance in order to achieve equal current sharing between layers, a critical and difficult challenge in more conventional layered-foil windings. The planar technology works best in conjunction with a magnetic core that shapes the field to achieve the most effective coupling between the transmitter and receiver, and to minimize losses by making the field parallel to the foil layers. For higher frequency applications, where soft magnetic material performance is not as good, similar structures deposited in multiple steps on a toroidal substrate will be used to effect the same advantages without the need for a magnetic core.