Triple-band metamaterial perfect absorber for refractive index sensing in THz frequency

A triple-band metamaterial perfect absorber (MPA) is presented in monolayer graphene in the THz region, which is adjustable and polarization-independent. The first layer of the structure from the top is patterned graphene which contains a graphene ring at the center of the frame with four graphene wheel-shaped around it and four graphene triangles in the corner. This proposed structure has caused the absorber to achieve 98.64%, 99.97%, and 99.98% perfect absorption peaks at 8.17 THz, 9.74 THz, and 11.95 THz, respectively. We can vary the absorption peak frequencies to our desirable frequencies by changing graphene's Fermi level. This absorber has good tolerance for up to 60-degree change in the angle of incident waves. Moreover, a significant matter about the suggested absorber structure design is that it is polarization independent, so by tuning the polarization angle, the frequency peaks and absorption value remain unchanged. These aspects make the suggested absorber proper for imaging, detecting, filtering, and sensing applications. We have investigated the application of the MPA in refractive index sensing. The refractive index of unknown material can be measured by measuring the shift of the frequency peaks. The perfect metamaterial absorber is a good candidate for biosensor application based on the obtained results.