Terahertz Refractive Index Sensor Based on Tunable Graphene Metamaterial Absorber

A terahertz refractive index sensor constructed with graphene metamaterial absorber has been proposed. The sensor features a patterned graphene structure, consisting of an independent circular ring and a special structure formed by intersecting cross and square patterns. Under normal incidence of TM and TE polarized light, the sensor exhibits a low-frequency peak at 1.55 THz with maximum absorption rates of $\mathbf{9 9. 4 5 \%}$ and a high-frequency peak at 3.83 THz with maximum absorption rates of $\mathbf{9 9. 5 0 \%}$. The quality factors (Q factor) of the two peaks are 31 and 65, respectively. Unlike traditional metal sensors, the absorption peaks of this sensor can achieve dynamic tunability through adjusting the graphene’s Fermi level. By varying the analyte’s thickness and refractive index, the maximum sensitivity of the two absorption peaks can reach $495 \mathrm{GHz} / \mathrm{RIU}$ and 895 $\mathrm{GHz} /$ RIU. The corresponding figures of merit (FOM) are 9.9 and 15.2, respectively. The sensor proposed here are applied to detect hemoglobin biomolecule content and has shown excellent sensing performance in our simulations. Therefore, the present work has broad potential for applications in biomedical and medical diagnostic fields.