Wireless Power Transfer Through Biological Tissue: The Role of The Interface

Wireless power transfer (WPT) is challenging when the receiver is located in biological tissues. We theoretically study a basic WPT system of two coaxial loops operating when both transmitting and receiving antennas are inside the tissue and when the transmitting antenna is outside it. Our main goal is to understand how the air-tissue interface and the depth of the Rx antenna influence the optimal frequency bands of maximal efficiency and maximal transferred power. We reveal that the impact of the interface is critical. Due to relocation of the transmitter to the air, the frequencies of the maximal WPT efficiency increase by two orders of magnitude. The frequencies of maximal transferred power increase by 1-2 orders of magnitude. This increase occurs for all depths of the Rx coil below the interface. Its reason is the absence of huge electromagnetic absorption around the Tx coil that is inherent to the WPT between two coils located in the medium.