High FoM quad‐band THz perfect metamaterial absorber‐based RI sensor for gas sensing applications

Here, a novel design of a microstructured quad‐band terahertz metamaterial absorber is presented consisting of a copper‐based merged circular and square split ring resonator‐integrated over a lead glass substrate intended to detect changes in the surrounding medium's refractive index for gas sensing applications through THz spectroscopy. Outstanding performance is shown by the suggested absorber, which achieves a maximum absorption rate of 99.4%, 98.7%, 99.2%, and 99.4%, at resonance frequencies of 8.055 (f1$f_1$), 8.423 (f2$f_2$), 9.257 (f3$f_3$), and 9.507 (f4$f_4$) THz, respectively. The quality factors (Q‐factors) attained are 201, 129, 298, and 271 for these four absorption bands. The obtained sensitivity values at these four distinct bands are 3898, 2927, 4719, and 4102 GHz per refractive index unit with high figure of merits (FoM) of 97, 95, 152, and 117, respectively, throughout a range of refractive indices from n = 1.00 to n = 1.05 (with a step size of 0.005). The study's novelty lies in its novel design and remarkable ability to excel in gas sensing with high sensitivity and high FoM across not just one but four distinct THz bands. Furthermore, each band demonstrates significantly superior performance in sensitivity, Q‐factor, and FoM, among other parameters compared to prior research in both gas detection and RI monitoring scenarios, hence exhibiting its potential across a wide range of applications. In order to detect changes in the refractive index of the surrounding medium, a novel quad‐band terahertz metamaterial absorber design is developed that exhibits outstanding performance, with maximum absorption rates surpassing 98% for resonance frequencies spanning from 8.059 to 9.512 THz. The absorber demonstrates high quality factors and sensitivity values, making it suitable for detecting harmful gases with figure of merits ranging from 95 to 152 across a range of refractive indices from 1.00 to 1.05. This versatile design exhibits efficacy in both gas detection and refractive index monitoring, highlighting its potential for diverse applications in sensing technologies.