Method of locating ultrasound-powered nerve stimulators

We have previously shown a small simple ultrasound-powered nerve stimulator. The piezoelectric implant receives power from an external driving ultrasound transducer. Focusing the ultrasound beam improves power transfer efficiency, but the implant location must be known to aim the focus. We show that currents driven by the stimulator might be detectable on the skin. By scanning the ultrasound focus and measuring the electrical response, we form an image of the implant location. This could give a feedback signal for aiming the beam, and allow multichannel addressing of several stimulators with no added circuitry in the implant.