Multifocus Techniques for Reconfigurable Intelligent Surface-Aided Wireless Power Transfer: Theory to Experiment

• Published in: IEEE internet of things journal Vol. 9; no. 18; pp. 17157 - 17171
• Main Authors: Tran, Nguyen Minh, Amri, Muhammad Miftahul, Park, Je Hyeon, Kim, Dong In, Choi, Kae Won
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 15.09.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Antenna arrays; Beamforming; Channel estimation; Energy harvesting; Focusing; Fresnel reflection; Fresnel zones; Internet of Things; Phased arrays; Power management; Receivers; reconfigurable intelligent surface (RIS); Reconfigurable intelligent surfaces; Reflection; Unit cell; wireless power transfer (WPT); Wireless power transmission
• ISSN: 2327-4662; 2327-4662
• DOI: 10.1109/JIOT.2022.3195948

Recently, reconfigurable intelligent surface (RIS) with passive beamforming capability is emerging as a potential technology for wireless power transfer (WPT) applications thanks to its cost-effective and energy-efficient features. This work studies multifocus techniques for RIS-aided WPT systems to simultaneously and adaptively charge multiple Internet of Things (IoT) devices in the Fresnel zone. In particular, we propose three multifocus methods, which are pattern addition (PA), random unit cell interleaving (RUI), and RIS tile division (RTD), for enabling multifocus RIS-aided WPT applications. We elaborate the algorithms for computing the RIS reflection phases for all methods. The proposed methods can balance the power levels of beams focused on multiple receivers by controlling weight factors. Furthermore, we have implemented a real-life RIS-aided WPT testbed to verify these proposed methods. The system consists of a phased antenna array transmitter, two receivers, and a 1-bit RIS with 512 unit cells. The WPT experiments have been performed in several test scenarios to show the effectiveness of the proposed techniques. The experiment results demonstrate that the proposed schemes effectively generate multiple focusing beams with adjustable power levels toward the desired receivers.