An Intra-Body Power Transfer System via Localized Capacitive Coupling.

Intra-body power transfer (IBPT) enables batteryless wearables by using the human body as a conductive medium. This work introduces Localized Capacitive Coupling (LCC), a new IBPT technique that uses a 40 MHz RF carrier to provide power transfer without relying on external grounds or environmental infrastructure. We evaluate LCC using computational modeling and human subject experiments with ten participants across multiple short-range capacitive body channels. Laboratory measurements with an isolated electrode system show mean path gains of 44 dB to 48 dB for channel lengths of 5 to 12 cm, closely matching our computational model with deviations under 3 dB. Circuit analysis indicates that air-gap coupling capacitance, typically in the femtofarad range, dominates channel gain, highlighting the importance of short-range fringing fields. To demonstrate practical energy harvesting, we designed and evaluated multistage Dickson charge pump (DCP) receivers. A five-stage impedance-matched DCP produced 3 V DC at 13.5 [Formula: see text] 0.5 dBm of incident RF power across a load in the tens of megaohms. A single-stage DCP paired with a battery manager generated a regulated 1.8 V output by charging a 100 [Formula: see text] capacitor from RF peak powers as low as 18.5 dBm. These results enabled a fully batteryless ring-worn motion sensor that uses an ultra-low-power accelerometer and non-volatile memory for offline activity logging, demonstrating that LCC is a practical approach for powering short-range wearable sensor networks. All hardware designs and simulation configurations will be open-sourced upon publication.