Polarization-independent tunable multi-band terahertz absorber based on graphene structure to design the ultra-high sensitive biosensors

Abstract

In this paper, we investigated the heterogeneous structure of a multi-band perfect absorber based on graphene in the terahertz range, benefiting from polarization independence. The proposed structure comprises three layers: copper, silicon dioxide, and an inhomogeneous graphene structure with an analyte. By altering the sub-layers dimensions and the graphene slices' geometric shape, we can modify the number of bands, quality, and absorption levels. Additionally, adjusting the chemical potential of graphene enables the customization of absorption frequencies as needed. The application of this structure in biological sensors extends to the detection of proteins, viruses, and cancer cells, as well as filtering telecommunication waves and imaging. Through geometrically shaping the graphene cuts at frequencies of 4.89 THz, 9.14 THz, and 10.76 THz, absorption values of 99.54%, 99.64%, and 98.3% have been achieved, respectively. Introducing the analyte to the biosensor structure causes a shift in absorption frequency values due to varying refractive index values in different materials. This property has been utilized for biosensor design. Within the refractive index range of biological analytes (e.g., 1.3), the first band achieved a sensitivity value of 2700 GHz/RIU and FoM = 13.08, while the second band achieved a sensitivity value of 2200 GHz/RIU and FoM = 14.02. An important characteristic of this structure is its insensitivity to polarization. Simulations were conducted using Computer Simulation Technology (CST) Microwave Studio Suite 2023.