Liquid-Crystal-Driven Reconfigurable Intelligent Surface With Cognitive Sensors for Self-Sustainable Operation

For the first time, this article describes the concept of a sustainable reconfigurable intelligent surface (RIS) for random wireless propagation channel management at millimeter-wave (mmWave) bands. Reconfigurable beam scanning capabilities are obtained by modifying the permittivity of liquid-crystal (LC) molecules. In order to configure a self-sustainable feedback loop for the proposed RIS operation, a lens-based beamforming circuit is embedded in the LC-driven reconfigurable beamforming surface. This sensing circuit enables the acquisition of channel estimation information without additional hardware implementation and signal processing costs. The proposed RIS is verified by link-level field trials for near-field indoor and far-field outdoor environments, satisfying the 5G new radio specifications for proof-of-concept purposes. This proposed RIS is expected to be applied in energy-efficient wireless channel management for mmWave radios.