Review Paper on Hardware of Reconfigurable Intelligent Surfaces

Abstract

Recently reconfigurable intelligent surface (RIS) has attracted great attention because it can create a smart wireless environment. Hence it can enhance the capacity and coverage of the wireless network significantly. A thorough review of RISs has been presented in this paper focusing on the hardware aspect of the RIS. Beyond-5G/6G communication will have a smart propagation environment, where RIS can be used for such communications. RIS consists of various small unit cells. The unit cells should have some tunning mechanism so that the incoming waves can be reflected or transmitted in the desired direction. It is possible to tune the impedance of the unit cells using PIN diodes, varactor didoes, microelectromechanical (MEMS), thermal, and other ways. In this paper, initially, the background of RIS has been discussed where RIS is going to play a significant role in beyond-5G/6G communications. We have also added the theoretical background of RIS and motivations to writing this paper. After that several published papers in the literature have been presented so that the readers can get an overall idea about the RIS and its hardware. Hence, this paper will be very useful for practitioner engineers and researchers. RISs have been presented in various tables and various parameters have been presented. We have discussed challenges and solutions for the hardware of the RIS design. We have also discussed potential research and research gap that can be explored in the future. Lastly, we have added a conclusion for this review paper.INDEX TERMS Reconfigurable intelligent surface (RIS), beyond-5G/6G communication, reflectarray, PIN diode, varactor diode.

Joint Beamforming Optimization Design and Performance Evaluation of RIS-Aided Wireless Networks: A Comprehensive State-of-the-Art Review

“…There have been numerous studies in the literature that have introduced RISs and their applications [11], [40], [78], [79], [80], [81], [82], [83], [84], [85], [86]. However, the focus and scope of these papers differ from our work.…”

“…Additionally, RIS hardware can be composed of metastructures [74], nanoparticle-based structures [75], near-zeroindex materials [76], and multi-functional structures [77], each providing innovative ways to control electromagnetic waves. More in-depth information on RIS hardware can be found in [78]. The selection of materials and technologies depends on specific requirements, operating frequencies, and application goals.…”

“…Additionally, it highlights the relationships between these methods and conducts simulations to compare their properties. Moreover, the authors in [78] focused on the hardware aspect of RIS, offering valuable insights for the design of future RIS hardware and providing a solid theoretical foundation. In [79], the authors provided a comprehensive survey on optimization techniques for RIS-aided wireless systems, covering model-based, heuristic, and ML algorithms.…”

Empowering the Vehicular Network with RIS Technology: A State-of-the-Art Review

“…Some surveys and tutorials [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ] introduced RISs and their variants. An overview of the RIS with a particular focus on hardware aspects is provided in reference [ 23 ].…”

Passive Type Reconfigurable Intelligent Surface: Measurement of Radiation Patterns

“…RIS is emerging as one of the main technologies for beyond-5G/6G communications. By changing the properties of the surface of the RIS, a programmable structure can be conceived to control the electromagnetic waves [1]. This programable structure can be placed in the desired locations to improve the performance of wireless communications.…”