Influence of Heterogeneous Human Body on Midfield Wireless Power Transfer for Implantable Heart Devices

Midfield wireless power transfer (WPT), using frequencies ranging from sub-GHz to 2 GHz, has recently been introduced as an efficient method to wirelessly transmit power to compact implanted devices. The operating frequency plays a vital role in enhancing the power transfer efficiency (PTE) of such WPT systems. However, the currently developed WPT transmitters and implantable receiver antennas have been designed to operate at frequencies determined by a mathematical equation based on a homogeneous model. Consequently, they are not specifically optimized to accommodate the diverse characteristics of the real human body. To address this issue, more than 30 multilayered tissue realistic models based on real CT images of humans were simulated to define the optimal frequency for real scenarios. The coupling parameter and a newly defined specific absorption rate (SAR) efficiency for each model were calculated by the formula derived from the theory of midfield WPT. The results were then compared with those obtained numerically from realistic body models and validated by experimental measurements using biological phantoms. The results showed that the optimal frequency of midfield WPT for implantable heart devices is significantly influenced by the tissue composition and thickness between the transmitter and the receiver.