Graphene-based metamaterial ultrawideband absorber with enhanced terahertz performance

In this paper, we present a graphene-based metamaterial ultrawideband absorber operating in the terahertz regime. The absorber is composed of two patterned and continuous graphene layers, a bottom gold layer, and a SiO₂ substrate that separates the continuous graphene layer from the gold layer. The absorption spectrum is enhanced by integrating a graphene resonator with water, which has frequency-dependent permittivity. The water is encapsulated in polytetrafluoroethylene (PTFE) in the form of a circular ring sandwiched between the two graphene layers. Simulation results show that the absorber attains a 90 % absorption bandwidth of about 14.55 THz. The proposed absorber is polarization-insensitive under normal incidence. For TE polarization, the absorption level remains stable for incident angles θ from 0° to 55° across the entire frequency band (14.55 THz), except for the 5–8 THz range. For TM polarization, the absorption level remains stable for θ ranging from 0° to 60° over the entire bandwidth. Additionally, the absorption level is consistent for both TM and TE polarizations across the entire bandwidth for incident angles φ from 0° to 90°.