Design and optimization of graphene based wideband programmable coding metasurface for beam steering of terahertz waves

In this manuscript, a graphene based optimized wideband 2-bit unit cell is proposed for THz beam steering. The proposed structure, may be utilized in THz communication networks including 6G wireless applications. The proposed structure has two distinct graphene parts where the corresponding chemical potential of each part may be varied separately. Therefore, a 2-bit controllable unit cell is realized. Moreover, the Random Hill Climbing optimization algorithm is used to improve the bandwidth of the 2-bit unit cell. A prescribed link between CST and MATLAB softwares is employed to define and simulate various graphene patch constructions. The optimization is done simultaneously on pattern of graphene patch and chemical potentials of graphene parts. The relative bandwidth of the proposed unit cell is 23.9 % (1.4-1.78 THz) whereas the corresponding size is 0.22 lambda at 1.6 THz. Two proposed metasurfaces are designed for arbitrary azimuthal angles of 0 degrees and 45 degrees . The reflected beam for two configurations is simulated at different beginning, middle, and end frequencies of 1.4 THz, 1.6 THz, and 1.78 THz. According to simulation results, the direction of the reflected beam is fixed over the operating frequency band. Therefore, the proposed structures are good candidates for wideband wireless communication networks.