Generation of Wideband Tunable Orbital Angular Momentum Vortex Waves Using Graphene Metamaterial Reflectarray

In this paper, a wideband tunable reflectarray consisting of a graphene-based metamaterial structure has been developed to generate an orbital angular momentum (OAM) vortex wave in terahertz. In the proposed reflectarray, a multi-layer graphene metamaterial unit cell is designed, and through varying chemical potentials of the graphene sheets, reflection phase range of 360° and reflection magnitude better than −2.5 dB can be achieved. By suitably choosing the chemical potentials of the graphene layers, the designed reflectarray can produce the OAM vortex waves with $l$ = ±1, ±2, and ±3 modes. Moreover, the OAM beams operating in a wide frequency band from 1.8 to 2.8 THz can be generated with the adjustment of the chemical potentials. Simulation results demonstrate good performance of the proposed reflectarray in the efficient generation and manipulation of the OAM vortex waves, which is promising to be used in wireless communication.