A triple‑band metamaterial graphene-based absorber using rotated split-ring resonators for THz biomedical sensing

A triple-band tunable polarization insensitive graphene-based metamaterial perfect absorber with the ability to be used as a THz biomedical sensor has been proposed. A graphene ring and four circular split-ring resonators with 90-degree rotations are used to design the polarization-insensitive metamaterial sensor. Simulation results based on finite element method show that the designed absorber has absorption efficiencies above 99.2% and tunable sensing features. Due to the confinement of the field, caused by the graphene's surface plasmon resonances, three perfect narrow absorption peaks are generated at the frequencies of 4.92 THz, 6.65 THz, and 8.58 THz with absorption efficiencies of 99.2%, 99.99%, and 99.2%, respectively. In addition, the ability to change the resonance frequencies along with improving the absorber performance by modifiying the chemical potential of the graphene layer has been demonstrated. The designed refractive index sensor, shows a maximum sensitivity, Q-factor and figure-of-merit of 1760 (GHz/RIU), 15.23 and 3.41 RIU−1 for an analyte thickness of 3 μm, respectively. Due to its rotational symmetry, the proposed THz RI sensor has the same response for TE and TM polarizations, and also has angular stability (up to 60°). The quality of RI sensor performance is investigated for two biomedical samples of healthy skin and a cancerous skin tissue. Based on the obtained results, it is clear that the THz sensor is applicable for biomedical applications.