SAR distribution for a strongly coupled resonant wireless power transfer system

Abstract

Tissue heating is a key safety consideration in wireless power transfer (WPT) systems. Heating is regulated in the form of specific absorption rate (SAR) limitations to prevent dangerous conditions when wireless power transfer is used in proximity to people. Implanted biomedical devices which depend on wireless power transfer for their operation are particularly of interest, as a high potential for tissue heating exists in these systems. Finding ways to reduce SAR for a given load power requirement enables reduced tissue heating and/or increased limits on power transmission. This work explores SAR heating in the two resonant modes (in-phase and out-of-phase) of a strongly coupled wireless power transfer system, where the power receiver is implanted in tissue. Results based on full EM simulation with realistic planar transmit/receive coil model near 13.56 MHz and simplified tissue model indicate that the higher frequency mode (out-of-phase mode) of strongly coupled wireless power transfer results in significantly lower peak and average SAR heating.