A kind of graphene film metamaterial for terahertz absorbers

Abstract

A kind of functional graphene thin film metamaterial on a metal-plane separated by a thick dielectric layer is designed for terahertz (THz) absorbers. We investigate the properties of the graphene metamaterial with different interlayers in the 0-3 THz range. The simulation results show that the absorption rate reaches up to 99.9% at the frequency of 1.917 THz. Changing the period to 80 μm×18 μm can get a narrow-band high quality factor (Q) absorber. We present a novel theoretical interpretation based on the standing wave field theory, which shows that the coherent superposition of incident and reflection rays produces standing waves, and the field energy is localized inside the thick spacers and dissipates through the metal-planes.Recent researches have demonstrated that graphene is an efficient terahertz (THz) modulator [1][2][3][4] . The optical properties of graphene have attracted particular interest in the metamaterial and plasmonic polaritons [5][6][7][8][9] . More recently, graphene-based metamaterials with perfect absorption have been theoretically and experimentally studied, including the effective surface conductivity investigations of graphene micro-ribbon metamaterials and structured graphene metamaterials [10][11][12][13][14] .In this paper, we design a perfect absorber based on graphene, and demonstrate that the perfect absorption can be achieved by the patterned graphene microstructural arrays on a thick spacer deposited on a reflecting metal substrate. Numerical simulations and analytical calculations are used to investigate the perfect absorption and the surface current resulting from a local energy field in the absorber induced by CST 2009 and a standing wave effect.We design a graphene metamaterial absorber with unit cell consisting of a graphene metamaterial and a thick dielectric interlayer deposited on the metal plane, as shown in Fig.1. One graphene micro-circle array and a metallic ground plane are separated by a thick dielectric spacer. The ground plane and the dielectric layer are copper metal and silicon (Si), respectively. The metagraphene has a radially periodic structure with period of 36 μm×36 μm, and the center of the circle is (0, 0). The Si dielectric with refractive index of n= d ε =3.45 is deposited on a copper metallic ground plane, and the thickness of Si dielectric spacer is d=33.4 µm. The copper metallic ground plate with conductivity of σ=5.9×10 7 S/m and thickness of t 2 =0.2 µm has perfect reflection property in the THz regime. The graphene is numerically modeled by a thin layer with thickness of t 1 =0.5 nm and permittivity of ε eff =1+σ s /ε 0 ωΔ (Δ=t 1 ), where σ s represents the conductivity of graphene, which can be derived using the well-known Kubo formula. The conductivity of graphene is described with interband and intraband parts as σ s =σ s intra +σ s inter , where σ s inter and σ s intra are interband and intraband conductivities, respectively. At THz frequencies, the photon energy is hω<<E F , and the interband contribution is negligible compared with the int...