Time reversal beamforming for powering ultrasonic implants

Efficient ultrasonic beamforming to millimeter-scale neural implants can reduce implant volume, improve tolerance to misalignment, and allow multiple implants to be operated simultaneously. This work proposes the use of time reversal, a computationally simple approach to beamforming that is robust despite scattering and inhomogeneity of the acoustic medium. A custom ultrasound phased array system is used to demonstrate beam focusing and steering both in a liquid phantom and through tissue. Time reversal is experimentally compared with other beamforming techniques by measuring energy transfer efficiency at varying depths and angles. Simultaneous power delivery to multiple implants is also demonstrated.