An All-Metal Terahertz Metamaterial Absorber Using Concentric Octagonal Rings for Refractive Index Sensing

This article introduces an all-metal THz metamaterial absorber (MA) featuring triple concentric octagonal rings optimized to detect the refractive index of brain tissues. Constructed entirely from stainless steel, the absorber achieves dual-band absorption rates of 99.45% and 96.72% at 3.7149 and 3.8695 THz, respectively. Simulations reveal that the device exhibits sensitivities of 2.45 and 2.70 THz per refractive index unit (RIU) as the refractive index shifts from 1.30 to 1.40. The corresponding quality factors (Q-factor) are 571 and 1488, while the figures of merit (FoM) are 376 and 1038. These exceptionally high Q-factors and FoM values highlight the absorber’s potential for high-precision sensing applications. Moreover, a parametric analysis was performed to optimize the geometric dimensions of the structure. Physical mechanisms, including impedance matching, current distribution, and sensitivity, were also explained in detail. This stainless steel-based absorber simplifies fabrication and significantly reduces costs compared to conventional metal-dielectric-metal designs. This work finds its application in biomedical sensing, which requires highly sensitive sensors.