From Fixed to Fluid: Unlocking the New Potential with Fluid RIS (FRIS)

Abstract: Owing to its flexible and intelligent electromagnetic signal manipulation, the technology of reconfigurable intelligent surfaces (RISs) has attracted widespread attention. However, the potential of current RISs can only be partly unlocked due to their fixed geometry and element patterns. Motivated by the concept of the fluid antenna system (FAS), a novel RIS system, termed fluid RIS (FRIS), has been developed. Unlike traditional RISs, FRIS allows the element positions or radiation patterns to exhibit ``fluid" properties, i.e., dynamic reconfigurability, to adapt to the wireless environment, offering enhanced beamforming flexibility and environmental adaptability. Given that research on FRIS is still in its infancy, this paper provides a comprehensive overview of its current developments and future prospects. Specifically, the key features of FRIS are first presented, including its classification, fundamental mechanisms, and advantages. Next, potential application scenarios of FRIS are analyzed and discussed, followed by two illustrative case studies demonstrating its potential. Finally, the main open challenges and future research directions related to FRIS are highlighted.