High Sensitivity of Metasurface-Based Five-Band Terahertz Absorber

In this paper, we present a simple design of a sensing scheme based on a plasmonic metamaterial absorber operating at THz frequencies. The unit cell of the designed structure consists of a gold (Au) cross-bar-patch structure, and a polyimide dielectric spacing layer located on an Au grounded plane. Simulations are carried out using the finite element method and subsequently validated through the calculation using the interference model. We discuss optimized designs that enable the achievement of five resonance modes and high sensitivity. The mechanism of absorptance spectrum is studied, revealing that the coupling effect between the Au cross bars of the metasurface and the sandwiched Au ground surface, separated by a polyimide dielectric spacer, gives rise to the five absorptance modes. The analysis of localized surface plasmon resonance modes are conducted through examination of electric field distributions and surface current density streamlines. Furthermore, the impact of various geometry parameters of the top Au crossbar layer on the resonance frequencies is explored. This work makes a significant contribution to the design of a straightforward plasmonic metamaterial absorber based on a metasurface, which exhibits five distinct absorption bands ranging from 0.4 to 3.2 THz. The calculated refractive index sensitivity and the figure of merit (S (THz/RIU), FOM (RIU-1)) for five resonance frequency modes are (2.00, 1.67), (14.00, 140.00), (14.00, 28.00) (14.00, 11.67), and (12.00, 10.00), respectively. The designed plasmonic device offers valuable insights for future developments in metamaterial absorber-based devices, particularly in the fields of THz nanophotonic applications.