Spoof Surface Plasmon Polariton Enables Ultrawideband THz Absorption Enhancement of Multilayer Graphene Excited by a Double Circular Metal Ring Array

Abstract

Although graphene's THz absorption rate increases with number of graphene layers, the absorbance is limited and unsatisfactory as a practicable absorber. Patterned graphene or graphene‐based surface plasmon resonance has been proved to enhance THz absorption, but the performance is prone to be affected by graphene defects and local multilayer stacks. In this paper, we proposed to use a double circular metal ring (DCMR) array to enhance both the graphene's THz absorption with an ultrawide bandwidth and the tolerance of graphene's physical impurities. A DCMR array is patterned on the top surface of graphene layer with dielectric substrates, which excites a broadband spoof surface plasmons polaritons (SPPs) in the THz frequency range. The broadband spoof SPPs locally confine and strengthen THz wave interaction with graphene, and further enhance graphene's THz absorption, which is confirmed by numerically simulated dispersion relations. A four‐layer graphene composite structure is fabricated to validate the scenario, which consists of graphene, a SiO2‐capped doped‐silicon substrate covered by graphene, and the DCMR array on the top surface of graphene. Time domain spectroscopy test shows that the THz absorption enhancement of the graphene composite with DCMR array covers the frequency range from 0.3 to 1.1 THz with 110% bandwidth. The THz absorption of the proposed graphene composite increases to more than 70% over a wide bandwidth of 77% at 0.65 THz compared with the graphene composite without DCMR array.