Analysis of Wireless Power Transfer Efficiency and Specific Absorption Rate for a Distributed Brain Implant System

Wireless sub-mm sized distributed brain implants have been proposed as the next frontier of Brain-Machine Interface (BMI) design to achieve untethered, high-density neural recording and stimulation. Simultaneously improving the wireless power transfer (WPT) efficiency and reducing the specific absorption rate (SAR) will be crucial for its clinical success. Towards these goals, we present an EM simulation method, a lumped equivalent circuit model, and a theoretical analysis to accurately predict the power delivered to the recording/ stimulating nodes, as well as the power dissipated in biological tissues and all other lossy elements within the system. This comprehensive framework also explains how increasing the distance between the transmit coil and the scalp can beneficially reduce the SAR without undermining the WPT efficiency. This work presents a rigorous prediction technique for transmission loss and tissue heating towards performance optimization.