ShaZam: Charge-Free Wearable Devices via Intra-Body Power Transfer from Everyday Objects

In this work, we investigate a wireless power transfer technology that can unobtrusively charge wearable devices while users interact with everyday objects, such as an office desk, laptop, or car. We design and develop our solution, ShaZam, that exploits the human body as a medium to transfer Radio Frequency (RF) energy-carrier signals from minimally-instrumented daily objects to wearable devices. We 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. To showcase the feasibility of our technology, we investigate three different use scenarios---i.e., interacting with a keyboard on a desk, a laptop, and the steering wheel of a car---to transfer power to a wrist-worn device. Using data obtained from ten healthy individuals within a setting where uncontrolled electromagnetic interference was relatively low, we demonstrate that we can transfer approximately 0.5 mW - 1 mW of DC power to the wrist-worn device. We also investigate several critical environmental and design parameters that could affect the power transfer and offer design guidelines that optimize performance. Our initial results suggest the potential for a new design paradigm towards completely charge-free wearable devices.