A Sub-millimeter, Inductively Powered Neural Stimulator

Daniel K. Freeman, Jonathan M. O'Brien, Parshant Kumar, Brian Daniels, Reed A. Irion, Louis Shraytah, Brett K. Ingersoll, Andrew P. Magyar, Andrew Czarnecki, Jesse Wheeler, Jonathan R. Coppeta, Michael P. Abban, Ronald Gatzke, Shelley I. Fried, Seung Woo Lee, Amy E. Duwel, Jonathan J. Bernstein, Alik S. Widge, Ana Hernandez-Reynoso, Aswini Kanneganti, Mario I. Romero-Ortega, Stuart F. Cogan

Wireless neural stimulators are being developed to address problems associated with traditional lead-based implants. However, designing wireless stimulators on the sub-millimeter scale (<1 mm3) is challenging. As device size shrinks, it becomes difficult to deliver sufficient wireless power to operate the device. Here, we present a sub-millimeter, inductively powered neural stimulator consisting only of a coil to receive power, a capacitor to tune the resonant frequency of the receiver, and a diode to rectify the radio-frequency signal to produce neural excitation. By replacing any complex receiver circuitry with a simple rectifier, we have reduced the required voltage levels that are needed to operate the device from 0.5 to 1 V (e.g., for CMOS) to ~0.25-0.5 V. This reduced voltage allows the use of smaller receive antennas for power, resulting in a device volume of 0.3-0.5 mm3. The device was encapsulated in epoxy, and successfully passed accelerated lifetime tests in 80°C saline for 2 weeks. We demonstrate a basic proof-of-concept using stimulation with tens of microamps of current delivered to the sciatic nerve in rat to produce a motor response.