Human-aware Beamforming Method Based on Electromagnetic Field Strength Estimation

This study proposes a beamforming (BF) method to maximise the received power at the receiver (Rx) in microwave wireless power transfer (MWPT) under the constraint that the human exposure power is maintained below a standard value. The proposed method first estimates the electromagnetic field strength (EMFS) of a human based on a combination of i) equivalent channel estimation between the human and transmitter and ii) human localisation using the same frequency as that of MWPT. Subsequently, a convex optimisation problem was formulated to maximise the received power of the Rx under the constraint that the estimated EMFS on the human must be maintained below the standard value. Solving this problem enables the determination of the optimum BF weight that enables null steering by considering the human area, suppression of human exposure, and high transfer efficiency. The results of full- wave simulations show that the ratio of the received power to the human exposure power of the proposed method is 5.11 dB higher than that of the conventional method, with maximum transfer efficiency that does not consider human exposure, enabling both high transfer efficiency and human avoidance. Furthermore, it is shown that if the angle between the receiver and the human is equal to or greater than 20°, it is possible to suppress human exposure below the standard value in the human body area while maintaining high transfer efficiency.