Tunable broadband terahertz absorber based on a single-layer graphene metasurface

In this paper, a broadband and tunable terahertz absorber based on a graphene metasurface in a sandwiched structure is introduced. A single-layered graphene patterned with hollow-out squares is applied in this design, which is continuously connected to provide convenience for electrical tuning and fabrication. Plasmonic coupling and hybridization inside the graphene pattern can significantly enhance the absorption bandwidth. Moreover, polarization-insensitive and omnidirectional performances are also guaranteed by the symmetrical design. Full wave simulations demonstrate that the absorber exhibits over 90% absorbance within 1.14∼3.31 THz with a fractional bandwidth up to 97.5%. The device reveals tunable absorbance from 14% to almost 100% by manipulating the graphene chemical potential from 0 to 0.9 eV. When the incident angle sweeps up to 55°, the absorbance remains more than 90% from 1.77 to 3.42 THz for TE polarization, while over 90% absorbance maintains around 3.3 THz for TM polarization. These superior abilities guarantee the applicability of the presented absorber in THz cloaking, tunable sensor and photovoltaic devices.