Phased array beamforming methods for powering biomedical ultrasonic implants

TL;DR

This paper presents a phased array ultrasound system with beamforming techniques, including time reversal, to improve wireless power transfer to biomedical implants, enhancing alignment tolerance and enabling multiple implants.

Contribution

It introduces a custom planar phased array system with time reversal beamforming, optimized for deep-tissue biomedical implants, and demonstrates simultaneous power delivery to multiple targets.

Findings

Time reversal beamforming improves energy transfer efficiency.

The system can steer and focus ultrasound within a 3D volume.

Multiple implants can be powered simultaneously.

Abstract

Millimeter-scale implants using ultrasound for power and communication have been proposed for a range of deep-tissue applications, including neural recording and stimulation. However, published implementations have shown high sensitivity to misalignment with the external ultrasound transducer. Ultrasonic beamforming using a phased array to these implants can improve tolerance to misalignment, reduce implant volume, and allow multiple implants to be operated simultaneously in different locations. This paper details the design of a custom planar phased array ultrasound system, which is capable of steering and focusing ultrasound power within a 3D volume. Analysis and simulation is performed to determine the choice of array element pitch, with special attention given to maximizing the power available at the implant while meeting FDA limits for diagnostic ultrasound. Time reversal is proposed as a computationally simple approach to beamforming that is robust despite scattering and inhomogeneity of the acoustic medium. This technique is demonstrated both in active drive and pulse-echo modes, and it is experimentally compared with other beamforming techniques by measuring energy transfer efficiency. Simultaneous power delivery to multiple implants is also demonstrated.