Active Control of THz Waves in Wireless Environments Using Graphene-Based RIS

The active and dynamic controls of the terahertz (THz) waves are highly demanded due to the rapid development of wireless communication systems. Recently, reconfigurable intelligent surface (RIS) has gained significant attention due to their tremendous potential in controlling electromagnetic (EM) waves. Particularly, RIS-based wireless communications are promising for improving the system's performance by properly designing the reflection coefficient of the unit cell. In this work, we investigate a graphene-based RIS for active and dynamic controls of THz waves. The RIS design consists of a rectangular graphene meta-atoms periodic array placed over a metallic grounded silicon substrate. An equivalent circuit modeling of the RIS design and its solution is provided. The RIS performance is numerically analyzed. The graphene-based RIS achieves nearly 100% reflection in the operational frequency ranging from 0.1 to 4 THz. The perfect reflection is insensitive to the polarization and the incident angles. Moreover, 100% absorption in the graphene-based RIS is achieved by electrically reconfiguring the meta-atom response via the chemical potential of the graphene. The graphene RIS also achieves the anomalous reflection performance by controlling the number of unit cells and phase gradient of RIS. In view of the effective THz wireless communication environment, this article finally presents a simple RIS-aided communication model to study the impact of the proposed graphene-based RIS on the signal-to-noise ratio (SNR). The results reveal that the proposed THz RIS with graphene meta-atoms is promising for efficient and intelligent THz wireless communications.