Optimal Frequencies for Wireless Power Transfer through Biological Tissues

Wireless power transfer (WPT) encounters challenges when the receiver is located in biological tissues, which are lossy and dispersive. Recent studies have paid significant attention to the mechanism of WPT in unbounded lossy media and between multiple media, such as at air-biological tissue interfaces. We present a comparative theoretical study of a basic WPT system for two cases: when both transmitting and receiving loops are inside a biological tissue (human body) and when the transmitting loop is outside while the received loop is inside. The study aims to find and compare optimal frequency ranges of WPT, distinguishing the regimes of maximal efficiency and maximal transferred power for both of these cases. We have found that the impact of the interface results in a significant increase in the frequencies that are optimal for the maximum power transfer efficiency: from dozens of MHz for a WPT system entirely located in the medium to the GHz range for a WPT system with the transmitting antenna in free space. Though the bands of the maximal efficiency and maximal power transfer never coincide, they overlap if the transmitting loop is in the air.