Time-Multiplexed Beam-Steering Antenna Arrays for Programmable-Coverage RF Powering of mm-Scale CMOS Brain Implants

This paper introduces a wireless powering system for multiple implantable devices located across a wide region of the human brain, addressing the spatial coverage challenges in traditional powering methods. We present an RF phased-array time-multiplexing technique that extends the powering coverage to as far as one hemisphere. The TX array is designed with optimal surface currents at 915 MHz to reach and beam-steer deep brain tissue. With transmitting 1 W, this method ensures safe and consistent power delivery over 18 cm lateral span and provides at least 250 $\mu$W to 6-cm deep RX implants. In addition, we developed a dynamically-biased 65 nm CMOS rectifier, featuring peak power conversion efficiency of 72.6\% at -2 dBm input power. The integration of phased-array multiplexing and an efficient CMOS rectifier offers a pathway towards arrays of smaller, battery-free neurostimulation implants, capable of simultaneous operation under stringent safety requirements and limited wearable power source size.