Wireless power transfer for a miniature gastrostimulator

In this work, wireless power transfer issues were investigated for a gastroparesis management system consisting of an endoscopically-implantable miniature batteryless/rechargeable wireless gastrostimulator and a wearable battery-operated transmitter module. Output power for stimulation and input power consumption in the transmitter as well as the wireless power transfer efficiency of two coil antennas with significantly different sizes were examined. With an implant antenna coil of 1×3.5 cm² and 5-cm radius transmitter antenna coils of varying coil turns, power transfers and efficiencies at the individually-tuned resonance of 1.3MHz were experimentally obtained at various coil separation distances from 4 to 10 cm between two coils. Taking power consumption in the wearable module and tolerance of parasitic capacitance in the environment into consideration, a 17-turn transmitter coil was chosen. RF losses through tissues were also examined with saline mimicking the abdomen tissues. At a distance of 10 cm as the worst scenario, a load current 3.02 mA was achieved which was still sufficient for gastrostimulation. Measurements of output voltage and efficiency distribution were mapped in 3-D to examine the effects of antenna misalignment due to body and stomach motion. This work provided insights into a complete system design for an endoscopically-implantable gastrostimulator that could relieve the suffering of many gastroparesis patients.