Split Frequency and Load-Shift Keying Based Bi-directional Data Transfer Technique in Wireless Implantable Medical Devices

Abstract

The 'power frequency splitting' phenomenon is widely observed over critical coupling conditions in the wireless power transfer system. Frequency splitting occurs in the voltage gain and power delivered to the load (PDL) curve but not in the end-to-end power transfer efficiency curve. This brief has considered the mutual inductance model to analyze the relationship between characteristic frequencies and circuit parameters in the wireless series-parallel system. Here authors have proposed a novel co-simulation platform using ANSYS MAXWELL and SIMPLORER for dynamic modeling of frequency-dependent resistance in a flexible polymer coil setup. The wireless power and bidirectional data transmission protocol were developed over a single link using Frequency shift keying (FSK) based forward data transfer (downlink) and Load shift keying (LSK) based backward data transfer (uplink) technique. The split frequency-based FSK modulation scheme helps in continuous wireless power transmission without disrupting the carrier amplitude for large power delivery, high data rate, and high-power transfer efficiency. The trade-off between link gain, bandwidth, and efficiency limits the application of the 'frequency splitting based data transfer technique' after a certain distance. A detection (tertiary) coil co-planar with the transmitter coil receives and decodes backscattered data from the receiver side using LSK. The three-coil architecture does not affect the split point locations of the two-coil system and slightly reduces link gain.