Ultrasensitive refractive index sensor based on stainless steel metamaterial.

Terahertz metamaterial technology, as an efficient nondestructive testing method, has shown great development potential in biological detection. This paper presents a stainless steel terahertz metamaterial absorber that achieves a near-perfect absorption of incident metamaterial waves with a 99.99% absorption at 2.937 THz. We demonstrate the theoretical discussion about the absorber and the application in sensing. The effect of the metamaterial absorber's structural parameters on the sensing performance is also analyzed. Simulation results show that the sensor can detect analytes with a refractive index between 1.0 and 1.8. Additionally, the performance of the sensor in detecting analytes in three states (solid, liquid, and gas) is analyzed in detail, and the sensitivity and the FoM of the sensor to detect methane are 22.727 THz/RIU and 568.175 , respectively. In addition, the terahertz sensor has the advantage of wide incident angle insensitivity, maintaining a good sensing performance within a wide manufacturing tolerance range of -10 to 10%. Compared to metal-dielectric-metal or dielectric-metal structures, the proposed sensor adopts stainless steel as the only manufacturing material, which has the advantages of simple structure, low manufacturing costs, and high sensitivity, and has potential application prospects in label-free high-sensitivity biomedical sensing.