Capacitively Coupled Resonator Models for Investigating Spatial Impedance Variation in WPT Systems

An analysis of a capacitive wireless power transfer system is presented to investigate the relationship between spatial impedance variation between the transmitter and receiver. The capacitively coupled link is modeled by an equivalent circuit that includes all coupling paths between the four conductors which make up the link. The analysis shows that a low Q resonator circuit is desirable to minimize impedance changes from spatial variation. On the other hand, the presence of crosslink capacitances can increase the Q which can be obtained after matching the circuit. Therefore cross-link capacitances should be minimized for spatially robust systems. Experimental results for ISM band frequencies of 13.56 MHz, 27.12 MHz, and 40.68 MHz are shown to verify the analysis.