Wireless power transfer by inductive coupling for implantable batteryless stimulators

This study investigated wireless power transfer with inductive coupling at a distance addressing the power requirement for chronic gastrostimulator implants. The energy harvesting system was designed to collect 3 to 20 mW power to operate an implantable stimulator to deliver 1 to 6 mA electric current into stomach tissues. The power transfer system efficiencies were investigated with different dimensions and turn numbers in coil antennas, distances between the two antennas, and variable loads. Clinical practicality and patient comforts were considered for implanting in the stomach through endoscopic procedures. Thus, the antenna size of the transmitter was configured to be between 4 and 6 cm in diameter, to increase portability while the implant coil was fixed at 10×35 mm². The distance between the two antennas varied from 4 to 10 cm in air. The system efficiency measured as the ratio of output power to input power included tuning a class-E amplifier in the transmitter at 1.3 MHz carrier frequency. A maximum efficiency was achieved at 9.59%. At all distances measured, the delivered power to the implant was more than 3 mW which was the minimal requirement for the operation of the implant.