Structural Optimization of Single-Layer Graphene Metamaterial for Ultra-Broadband Terahertz Absorber

We propose and validate an approach to obtain an ultra-broadband terahertz absorber by taking the advantages of the absorption of the surface plasmon resonance in combination with the absorption of the intrinsic mode. The absorber is composed of a gold (Au) bottom layer and a patterned graphene embedded in TOPAS polymer, exhibiting ultra-broadband absorption by coupling the surface plasmon resonance and the intrinsic modes. The single-layer graphene is patterned to C4 symmetric regular polygons which are arranged in circle circumscribed polygons (CUPs) or circle inscribed polygons (CIPs) at the same periodicity for comparison. With the increase of the side number (
N
), the strongest and weakest coupling of the surface plasmon resonance and the intrinsic modes was achieved at
N
= 4 (square) and ∞ (circle) for CUP and CIP arrangements, respectively. The optimum absorption bandwidth of 2.54 THz with relative absorption bandwidth of 109.5% above 90% absorption efficiency has been achieved for the circles with a diameter of 12.4 μm arranged at a gap distance of 1.0 μm. This design shows broader relative absorption bandwidth than previously reported single-layer graphene THz absorbers. Therefore, the proposed method would be highly valuable to design and manufacture ultra-broadband THz absorbers.