A Filter Theory Approach to the Synthesis of Capacitive Power Transfer Systems

Resonant-coupled wireless power transfer (WPT) systems are typically modeled as circuits with inductively or capacitively coupled resonators. In a two-resonator system, the transmit and receive resonators are linked by a coupling coefficient, and the coupling can be adjusted for critical coupling, overcoupling, and undercoupling. In this work, we show that the coupled-resonator structure is equivalent to a filter structure and provide a demonstration of how filter theory can be used to design a capacitive WPT system. An advantage of this approach is that it provides access to a wide range of canonical structures and methods of impedance scaling to realize matched links. We show a maximally flat filter has a critically coupled response and an equiripple Chebychev filter has an overcoupled response. There is a relationship between frequency bandwidth in a filter design and spatial bandwidth in a WPT link. Therefore, the filter context can be used to synthesize wideband filters that are more robust to spatial variation than narrowband filters.