Biologically inspired coupling pixilation for position independence in capacitive power transfer surfaces

A common problem with wireless/contactless power transfer is that the coupling factor is often position dependent, particularly in mobile applications. For both inductive and capacitive power transfer (IPT and CPT respectively) techniques, the transmitter and receiver usually require ideal positioning for maximum power transfer, which limits practicality. This paper aims to reduce this impediment for CPT applications. CPT is straightforward to implement with low material requirements, therefore it is very attractive for applications that require non-contact and galvanic isolation under the constraint of short distances and low cost. However, misalignment of the coupling surfaces severely impedes throughput power capability. This paper presents a nearly position-independent capacitive coupler design for CPT applications. A plant leaf cell inspired hexagon capacitor receiver array paired with multiple half bridge rectifiers achieves nearly uniform capacitance and coupling factor. Design considerations of cell shape, size, etc. for this “capacitive leaf” are developed and experimental results for a mobile phone charging application demonstrate <; 20% capacitance variation and ~12% load voltage variation regardless of position or orientation.