Incident Power and Relative Phase Distribution Mapping in Reconfigurable Intelligent Surfaces Using Energy Harvesting

One of the major challenges of reconfigurable intelligent surfaces (RISs) is the large state-selection search space that demands real-time programmability and fast processing. The knowledge of incident power and relative phase distribution across an RIS can potentially simplify the state-selection process. Herein, we present a novel method of obtaining incident power and relative phase distribution using energy harvesting circuits (rectifiers) that can be integrated into the RIS. Four versions of the energy harvesting circuit are proposed that offer great control over the sensitivity of the system. The sensitivity of the proposed rectifier circuit is -42 dBm for direct rectification. The inclusion of direct current (dc) bias and radio frequency (RF) amplifiers greatly increases the sensitivity of the rectifiers. The received power and phase distribution across the unit dipoles of RIS are simulated to demonstrate the potential of the proposed method. Experiments are performed in an indoor environment at 2.1 GHz. Experimental results show that the proposed energy harvesting method can successfully predict the received power distribution for angular and perpendicular incidence of the incident radio waves.