Resonant Coupler Designs for Subcutaneous Implants

Abstract

A tuning element is utilized in a planar inductive resonant coupler to improve resonance for monolithic subcutaneous implants. The concept is to enhance the impedance matching for the implant chip at the desired operating frequencies under the practical constraints for subcutaneous implants, such as the requirements within the regulated frequency bands, the limited thickness of overall package, uncertainty of surrounding tissues in individual’s implant site, and inability of antenna tuning after implantation. Two designs are demonstrated with planar ring antennas, targeting the two industrial, scientific and medical (ISM) bands at 903 MHz and 2.45 GHz, with improved reflection coefficients for the implant circuitry. The effects of implantation depths and tissue permittivities are investigated. Measurements with hydrated pork compared with theory utilizing documented human skin tissue permittivities find discrepancies. Experiments and simulations are conducted to explain the discrepancies and validate the designs for human uses. The proposed planar resonant wireless power and signal coupler shows good performance and promise for small subcutaneous implant applications.