Design and Experimentation of a Novel Five Coil Asymmetric Magnetic Resonance Wireless Power Transfer System

This paper introduces a wireless power transfer system using a 5-coil asymmetric topology to mitigate range limitations when powering devices requiring small coils. The efficiency of a traditionally coupled wireless power transfer system falls sharply at distances beyond the diameter of the coils used. In order to power devices requiring small packaging at a distance, this limitation must be eliminated. Magnetically coupled coils have demonstrated the ability to extend power transfer distances beyond that of traditional coupling techniques; however, power transfer is still limited by coil size. We utilized the power transfer capabilities demonstrated by a 4-coil magnetic resonant transfer system and introduced a fifth coil to extend the transfer range. Coil asymmetry was then introduced to overcome coils radius limitations. This power transfer technique was demonstrated by charging a cell phone at a distance of 61 cm. The 5-coil transfer system operates at 40% efficiency from amplifier output to rectifier input. We develop an end-to-end power transfer system including a power amplifying source, 5-coil transfer system, and load including rectification to feed the cell phone. Circuit models and equations are introduced for all three stages with an emphasis on the asymmetric 5-coil system. Key parameters characterizing the 5-coil wireless transmission segment are also derived. Individual and system-wide efficiency limitations are discussed, and areas of future work are presented.