Individually frequency and amplitude tunable metamaterial absorber with sensing functions based on strontium titanate and graphene

A terahertz metamaterial absorber with sensing function based on strontium titanate (STO) and graphene is designed. The optical characteristics of the designed structures are simulated and numerically calculated by the finite difference time domain (FDTD) and coupled mode theory (CMT) method. The results show that the temperature of STO is 300 K and Fermi level of graphene is 1.0 eV, the absorptance achieves 99.8 % and 92.7 % at 0.36 THz and 2.18 THz, respectively. When the temperature of the STO is set from 250 K to 400 K, the center frequency is moved from 0.32 THz and 1.96 THz to 0.43 THz and 2.54 THz. When the temperature is stable at 300 K, the dual narrow band absorption can be converted to single narrow band absorption by tuning the Fermi level from 1.0 eV to 0 eV. The physical mechanism of the dual narrow band absorptions and active tuning is analyzed by electric field distribution and impedance matching theory. The effect of polarization direction and incident angle on the absorber performance is also investigated. In addition, we also investigated the sensing characteristics of the absorber when the Fermi level of graphene is 0 eV, and the sensitivity and figure of meritis of the structure for detecting different refractive indices is 50 GHz/RIU and 0.33/RIU. The proposed structure provides new ideas for future multifunctional terahertz device design.