Broadband polarization insensitive and tunable terahertz metamaterial perfect absorber based on the graphene disk and square ribbon

Designing broadband absorbers with only one metamaterial layer operating in the terahertz band is a relatively difficult challenge. In this paper, we proposed and investigate a broadband metamaterial perfect absorber (MPA) based on the graphene disk and square ribbon. The conductive substrate of this structure is made of gold and the middle dielectric layer of this structure is made of Rogers RT5880LZ, which acts as a spacer layer between the gold and graphene layers. This structure, while having only one metamaterial layer, also has the advantage of easy implementation because the graphene embedded on the dielectric surface does not have a complex design. The simulation results show that the proposed absorber can provide absorption above 90% with a bandwidth of 2.173 THz (1.482-3.655 THz). The fractional bandwidth ratio of the proposed structure is 85% for absorption greater than 90%. The absorption mechanism of this structure based on electric fields has been investigated. Since the design of the proposed broadband MPA is symmetrical, this structure is not sensitive to polarization and has a good bearing angle in the range of 0-30 degrees. The proposed structure is tunable because we can shift the absorption frequency by changing the Fermi level of graphene (mu(c)). The proposed absorber with these properties is suitable and flexible for applications such as sensing, imaging, and spectroscopy.