Safe Charging For Wireless Power Transfer

Wireless charging 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 order to control the risk of EMR in wireless charging,in this paper,we study two charging utility optimization problems with considering the EMR safety.The main contents are as follows:1.This paper firstly study the safe charging problem under wireless charging technol-ogy,which guarantees the certain EMR safety.That is to say,we consider how to adjust the power of wireless chargers to maximize the overall charging utility of de-vices,while assuring that EMR intensity at any location in the field doesn't exceed a given threshold Rr.To solve this problem,we first reformalize the problem into a linear program by area discretization and propose a fully distributed approximation algorithm.The approximation ratio of this algorithm is(1-?).The communication complexity of the distributed approximation algorithm does not increase with the enlargement of the network scale,thus alleviating the communication bottleneck brought by the centralized algorithm.After that,we carry out simulation experi-ments to verify the effectiveness of our algorithm.Compared with the greedy algo-rithm,the performance of the distributed approximation algorithm is better than the greedy algorithm by 10.24%,and the gap between the distributed approximation algorithm and the optimal solution is only 8.23%.2.This paper then study the robust safe charging problem under wireless charging technology.We carry out some experiments and find that the jitter characteristic of EMR in the charging area.Thus this problem guarantees the uncertain EMR safety,that is,we consider how to adjust the power of wireless chargers so that the overall charging utility for all rechargeable devices is maximized while the proba-bility the EMR anywhere doesn't exceed Rt is no less than a given confidence ?.To solve this problem,we first build a probabilistic charging model according to the data collected from the actual charger,reformalize the problem into a Second-Order Cone Program by area discretization,and obtain a(1-?)-approximation central-ized algorithm and(1-?)-approximation fully distributed algorithm scalable with network size.Then we carry out both simulation experiments and field experi-ments to verify the correctness and effectiveness of our algorithms.The simulation results show that the output of the centralized approximation algorithm is nearly same to the optimal solution.Although the performance of the distributed approxi-mation algorithm is not as good as that of the centralized approximation algorithm,the communication complexity of the distributed approximation algorithm does not increase with the expansion of the n etwork scale.Field experiments show that the performance of centralized approximation algorithm and distributed approximation algorithm are better than greedy algorithm by 391.09%.