Efficiency tunable broadband terahertz graphene metasurface for circular polarization anomalous reflection and plane focusing effect

In this paper, a broadband reflective metasurface (MS) with patterned graphene is proposed and investigated numerically, which can realize wavefront manipulation dynamically in terahertz (THz) region. The unit-cell of the proposed reflective MS is composed of a dielectric substrate sandwiched with a single layer oval-hollow-structure (OHS) graphene and a metal ground-plane, which can achieve the cross-polarization conversion of the circularly polarized (CP) waves in reflection mode. The full 2π phase shifts of the reflected orthogonal CP wave can be obtained by changing the orientation angle of the OHS graphene in a broadband frequency range with different Fermi energy level (EF). Moreover, it has been verified that the reflection CP conversion efficiency is highly dependent on the variation of the EF. In particular, the efficiencies of the anomalous reflection and focusing effect of the reflective MS can be adjusted dynamically by changing EF. It has great prospects in the THz application fields such as communication and imaging.