Ultrasonic Beamforming System for Interrogating Multiple Implantable Sensors

In this paper, we present an ultrasonic beam-forming system capable of interrogating individual implantable sensors via backscatter in a distributed, ultrasound-based recording platform known as Neural Dust [1]. A custom ASIC drives a 7 x 2 PZT transducer array with 3 cycles of 32V square wave with a specific programmable time delay to focus the beam at the 800 mu m neural dust mote placed 50mm away. The measured acoustic-to-electrical conversion efficiency of the receive mote in water is 0.12% and the overall system delivers 26.3% of the power from the 1.8V power supply to the transducer drive output, consumes 0.75 mu J in each transmit phase, and has a 0.5% change in the backscatter per volt applied to the input of the backscatter circuit. Further miniaturization of both the transmit array and the receive mote can pave the way for a wearable, chronic sensing and neuromodulation system.