Dynamically tunable broadband absorber with a single ultra-thin layer of graphene in the terahertz regime

We have proposed a broadband near perfect terahertz absorber based on a single ultra-thin layer of graphene with incident polarization angle and oblique incidence angle insensitivity. The absorber consists of a patterned graphene metasurface, a polyethylene cycloolefin copolymer (TOPAS) dielectric layer, and a gold film. The structure of the graphene metasurface includes a cross-shaped graphene patch with four corners cut off at the center of the unit cell, and four arc-shaped graphene patches at the four corners of the unit cell. Numerical simulations show that the proposed absorber can achieve absorbance higher than 97% in the wideband frequency range of 1.45-2.99 THz under normal incident conditions with an absolute bandwidth reaches to 1.54 THz. For oblique incidence, the absorber remains the same absorbance over a wide frequency range, which infers that the proposed broadband absorber is incident angle insensitive. Moreover, the tunable property of graphene was also studied, which indicated that absorbance can be tuned from 11% to nearly 100% by changing the chemical potential of the graphene via external bias voltage. Furthermore, we introduced the impedance matching theory and interference theory to verify the absorption rate of the absorber. The calculated results are nearly the same as the simulated results. Due to its simple structure and flexible tunability, the proposed metamaterial absorber has potential application prospects in modulators, sensors, and other multispectral devices.