Planar Multiple-Antiparallel Square Transmitter for Position-Insensitive Wireless Power Transfer

In this letter, a new kind of transmitter for uniform magnetic field distribution over relatively long-distance wireless charging plane is proposed. The transmitting coil is composed of multiple series square windings. Each winding consists of a set of concentric square loops. The spiral directions of two adjacent windings are opposite. The theoretical analysis shows, compared with conventional unidirectional square spiral coil, the proposed multiple-antiparallel square spiral coil can effectively enhance the height of the charging plane with uniform magnetic field. Furthermore, two planar wireless power transfer (WPT) systems adopting the proposed and conventional square transmitters are set up. The charging height is 5 cm. The ratio between the charging height and the transmitter's side length is 0.25. The experimental results show that, owing to the better uniform magnetic field produced by the proposed transmitter, the maximum transfer efficiency without coil misalignment is 91.4%. The reduced efficiency is less than 3% regardless of the location of the receiver. Additionally, the load power significantly maintains stability compared with the case of the conventional coil. As a result, the proposed coil can be a good candidate for practical planar WPT applications.