Design Strategy of Off-Resonant Tertiary Coils for Uplink Detection in Biomedical Implants

A detection (tertiary) coil co-planar with the transmitter coil receives and decodes backscattered data from the receiver using load shift keying (LSK). Tertiary coil parameters such as the number of turns, compensation capacitance and quality factor are studied for maximizing voltage gain and end-to-end efficiency through novel analytical modelling, SPICE simulations and measurement results. A novel “inside-tertiary coil structure” is suggested to save the overall coil area, and two variations are discussed. Voltage gain and efficiency are improved by ~197% and ~15%, respectively, at a transmitter-receiver distance of15 mm. Design strategy improves the operating distance of implant by 50%, from 12 mm to 18 mm.