Optimized Rectangular Planar Coil Design for Wireless Power Transfer with Free-Positioning

This paper introduces a new method for optimizing the efficiency of two planar coils for a wireless power transfer system, assuring a specific pre-defined efficiency over the entire given charging surface. The referred efficiency is calculated from the transmitter's source to the receiver's load. This study is based on rectangular shaped coils. The electrical parameters, coupling and efficiency of the system are calculated and optimized as function of their physical dimensions. Thus, taking those parameters into account a useful design tool is proposed here. One of many possible designs is presented as example, which proves by theoretical and simulation results that the receiver might be free-positioned over the surface of charging without losing efficiency. Results for a 13.56 MHz system show that more than 82 % of efficiency (load to transmitter coil) can be achieved for a 4 cm x 4 cm receiver moving over a 12 cm x 8 cm surface.