Tissue Depth Study for a Fully Implantable, Remotely Powered and Programmable Wireless Neural Stimulator

Miniature, remotely powered and programmable neural stimulators were implanted on the sciatic nerve in nine pig hind limbs. An external dipole antenna was used to transmit power and waveforms to the implant at 915 MHz. For each placement location, external power was swept until motor threshold was achieved. Thresholds were determined via visual observation of muscle twitches in the lower leg. The external antenna was placed at several different distances from the implant and the threshold power was recorded as a function of the tissue thickness overlying the implant. Verification of the current was measured by: 1) optical recording electrodes and 2) Random validation using wired recording electrodes. Both methods recorded the current required to reach motor threshold. Results from these tests confirmed that wireless neural stimulation could effectively excite motor nerves remotely in up to 12 cm of soft tissue of a mixed medium. Propagation losses for this verification also agreed with simulation models. These measurements verified that ample current densities could be achieved at significant tissue depths and therefore, a wireless neural stimulator can be potentially be utilized in existing neural stimulation therapeutic treatments.