Dual Receiver Coils Wireless Power Transfer System With Interleaving Switching

This letter presents a wireless power transfer (WPT) system for wristband device charging. By using dual receiver coils with power switches in an interleaved manner, the proposed WPT system can simultaneously operate to accumulate energy from the primary coil and transfer the previously accumulated energy to the battery in each coil. As a result, the WPT efficiency can be increased with the small coils, even at high load resistance. The proposed WPT system is theoretically analyzed by a lumped circuit model and verified by measurement using prototype boards. Compared with the conventional WPT structure that uses one receiver coil (
$\text{2}\,{\text{cm}}\,\times \,\text{5}\,{\text{cm}}$
), the proposed WPT system with two receiver coils (each
$\text{2}\,{\text{cm}}\,\times \,{\text{2.5}}\,{\text{cm}}$
) achieved a 6.67% end-to-end power efficiency improvement at the output resistance of 100 Ω under the same condition of the coil dimension and the resonant frequency of 140 kHz.