INTRA-BODY POWER TRANSFER AND BACKSCATTER COMMUNICATION

Abstract

In recent years, Capacitive Intra-Body Power Transfer (C-IBPT) technology has emerged as a promising solution to enable battery-free wearable sensor application. This innovative approach utilizes the human body as a conductive medium to facilitate wireless power transfer and communication via capacitive coupling. In the first part of this dissertation, I investigate the feasibility and performance of a C-IBPT system that can unobtrusively charge wearable devices while users interact with everyday objects. I design and develop a custom solution, ShaZam, that exploits the human body as a medium to transfer Radio Frequency (RF) signals from minimally instrumented daily objects to wearable devices. I focus on establishing the technical groundwork of the proposed technology by incorporating the capacitive coupling mechanism, in which the forward signal path is established through the human body, and the return path is established via capacitive coupling to the surrounding environment. Using data obtained from ten healthy individuals, the system can transfer approximately 0.5 mW of DC power to the wrist-worn device. I also investigate several design parameters that could affect the power transfer and offer design guidelines that optimize performance. The initial results suggest the potential for a new design paradigm towards completely charge-free wearable devices. Localized capacitive coupling (LCC) in intra-body power transfer (IBPT) is a promising technology that enables wearable devices to be powered by a body coupled transmitter without relying on external infrastructure. In the second part of this dissertation, I designed and developed a new wearable hardware system to measure capacitive power gains at multiple anatomical locations on ten healthy individuals. Through controlled laboratory experiments, I discovered that mean path gains range from -44 dB to -48 dB for body channel lengths of 5 cm to 12 cm. Based on these findings, I developed a batteryless ring sensor that can record finger movements and store motion data on local memory by using a capacitor. The experimental outcomes confirm the channel gain measurement accuracy and the hardware system’s potential to support ultra-low-powered wearable sensing within a short body channel. Utilizing the human body as a communication channel is an innovative alternative to traditional air-based communication methods, providing a more effective path gain for communication among wearable devices. In the final part of this dissertation, I introduce capacitive backscatter communication in the human body to enable low-powered communication for batteryless identification and sensing. The experimental results demonstrate the hardware system’s ability to interrogate 16-bit binary IDs seamlessly using 40 MHz pulsed RF carrier. In addition, I developed a modular transceiver system and intra-body channel gain emulator. This hardware system optimizes transceiver architecture and tag systems, enabling a functional intra-body backscatter system for a batteryless ring sensor.National Science Foundation (NSF) (Grant Number: 016419-00001) National Institutes of Health (NIH) (Grant Number: R01HD114147)Doctor of Philosophy (Ph.D.