Abstract

Energy beamforming is fundamental to overcome the coverage limitations of radio frequency (RF) wireless energy transfer. Indeed, multi-antenna energy transmitters, also known as power beacons (PBs), can leverage spatial degrees of freedom to boost energy efficiency, motivating large-antenna array implementations. However, practical implementations based on traditional analog, digital, and hybrid analog-digital architectures are difficult to scale when the number of antennas increases because of the increasing number of power-hungry RF chains and the lossy and complex interconnection networks that carry the signal to the antenna array. In this work, we studied a costeffective single RF chain PB architecture embedding a reflecting intelligent surface and a single antenna feeder. Herein, we model the PB's average power consumption and obtain a closed-form approximation for the point-to-point charging scenario where the device position varies randomly. Moreover, we estimate the local electromagnetic field radiation (EMF) exposure in the device's vicinity by leveraging a Monte Carlo integration method. Our results show the increasing trend of the PB's average power consumption as the operating frequency increases, as well as the power savings obtained by increasing the directivity of the radiating elements. Moreover, we show the optimal position of the feeder for different operating frequencies and antennas' boresight gain. We also illustrate that EMF exposure decreases with the increased operating frequency and the measuring distance from the device.