SCAPE: Safe Charging with Adjustable Power

Wireless power transfer technology is considered as one of the promising solutions to address the energy limitation problems for end-devices, but its incurred potential risk of electromagnetic radiation (EMR) exposure is largely overlooked by most existing works. In this paper, we consider the Safe Charging with Adjustable PowEr (SCAPE) problem, namely, how to adjust the power of chargers to maximize the charging utility of devices, while assuring that EMR intensity at any location in the field does not exceed a given threshold R_t. We present novel techniques to reformulate SCAPE into a traditional linear programming problem, and then remove its redundant constraints as much as possible to reduce computational effort. Next, we propose a distributed algorithm with provable approximation ratio (1 - ε). Through extensive simulation and testbed experiments, we demonstrate that our (1 - ε)-approximation algorithm outperforms the Set-Cover algorithm by up to 23%, and has an average performance gain of 41.1% over the SCP algorithm in terms of the overall charging utility.