Characterization of simple wireless neurostimulators and sensors

Abstract

A single diode with a wireless power source and electrodes can act as an implantable stimulator or sensor. We have built such devices using RF and ultrasound power coupling. These simple devices could drastically reduce the size, weight, and cost of implants for applications where efficiency is not critical. However, a shortcoming has been a lack of control: any movement of the external power source would change the power coupling, thereby changing the stimulation current or modulating the sensor response. To correct for changes in power and signal coupling, we propose to use harmonic signals from the device. The diode acts as a frequency multiplier, and the harmonics it emits contain information about the drive level and bias. A simplified model suggests that estimation of power, electrode bias, and electrode resistance is possible from information contained in radiated harmonics even in the presence of significant noise. We also built a simple RF-powered stimulator with an onboard voltage limiter.

Remote Stimulation of Sciatic Nerve Using Cuff Electrodes and Implanted Diodes

“…This approach to using volume-conducted currents to power implanted diodes and other devices in tissue was first explored by Palti [ 17 ] and others more recently [ 18 , 19 , 20 , 21 ] for direct stimulation of muscles [ 18 ] and nerves [ 19 , 20 , 21 ]. But a careful assessment of nerve activation using smaller microscale diodes as a function of the AC stimulation parameters such as frequency, peak-to-peak voltage amplitudes and diode parameters such as diode–dipole lengths, feature size and relative position of the diodes with respect to the stimulation electrodes has not yet been done.…”