Multiple-half-wave resonator for wireless power transfer using magnetic resonant coupling

In order to extend the transfer distance in wireless power transfers using magnetic resonant coupling, it is necessary to increase the quality factor of resonators. In general, resonators with a larger number of turns may have a higher quality factor; however, the number of turns is limited by the half wavelength. To overcome this frequency limitation, we propose a multiple-half-wave resonator that consists of several half-wave resonators in order to provide an overall larger number of turns. An electromagnetic simulation shows that the proposed structure improves the transfer efficiency by 14%, 30%, and 40% over transfer distances of 50 cm, 75 cm, and 100 cm, respectively, when compared to a conventional helical resonator at 13.56 MHz.