Ultrasensitive THz Refractive Index Sensor Based on a Controllable Perfect MTM Absorber

In this paper, a perfect metamaterial (MTM) absorber with simple design has been proposed and investigated in terahertz (THz) region. The suggested absorber has the controllability of the resonance frequency to have a perfect absorption at different frequencies by tuning the graphene chemical potential. The structure has near-unity absorption for the incident angles up to 70°. Strong coupling of the graphene surface plasmon resonance (GSPR) and the resonance of the structure result in a narrow and sensitive absorption peak. Therefore, the suggested absorber can be used as a sensor to detect sensing media with different refractive indices. The simulation results show the capability of the proposed structure to detect glucose with an ultra-high sensitivity of 22.72 THz per refractive index unit (THz/RIU) and diagnose malaria with high sensitivities of 4.7 and 10.58 THz/RIU and good figure of merits (FOM) of 13.84 and 36.51 1/RIU, at the frequencies of 5.71 and 9.88 THz, respectively. Moreover, the equivalent circuit model of the structure has been derived to verify the FDTD simulation results. The proposed plasmonic sensor is a good candidate for biomedical applications in diagnosis of cancer, malaria, anemia and bacterial infection.