Electrically tunable graphene-based bifunctional terahertz metasurface for absorption and polarization conversion

In this paper, an electrically tunable bifunctional terahertz metasurface based on graphene that can be switched between absorption and broadband polarization conversion (PC) functions is proposed. The metasurface operates in a broadband PC with a PC rate over 90% in 1.45-3.15 THz when the Fermi level of graphene is 0 eV, and it exhibits good absorption performance with the absorptivity of over 90% in 2.79-3.15 THz and more than 80% in 1.52-3.28 THz when the Fermi level of graphene is 1 eV. Moreover, the operational mechanisms for PC and absorption are elucidated through investigating the surface current and electric field distributions at resonant frequencies, in conjunction with impedance matching theory. The influence of structural parameters and oblique incidence angles is analyzed to explore their performance stability. In addition, its tunable performance can be dynamically regulated via graphene-based electrical modulation, demonstrating application potential in electromagnetic shielding and terahertz devices such as absorbers and polarizers.