Reconfigurable Intelligent Surfaces: Design, Implementation, and Practical Demonstration

Metasurfaces, ultrathin two-dimensional version of metamaterials, have attracted tremendous attention due to their exotic capabilities to freely manipulate electromagnetic waves. By incorporating various tunable materials or elements into metasurface designs, reconfigurable metasurfaces and related metadevices with functionalities controlled by external stimuli can be realized, opening a new avenue to achieving dynamic manipulation of electromagnetic waves. Recently, based on the tunable metasurface concept, reconfigurable intelligent surfaces (RISs) have received significant attention and have been regarded as a promising emerging technology for future wireless communication due to their potential to enhance the capacity and coverage of wireless networks by smartly reconfiguring the wireless propagation environment. Here, in this article, we first focus on technical issues of RIS system implementation by reviewing the existing research contributions, paying special attention to designs in the microwave regime. Then, we showcase our recent attempts to practically demonstrate RIS systems in real-world applications, including deploying reflective RIS systems in indoor scenarios to enhance the wireless network coverage and utilizing intelligent omni-metasurfaces to improve both indoor and through-wall wireless communication quality. Finally, we give our own perspectives on possible future directions and existing challenges for RISs toward a truly commercial intelligent technology platform.