Quatrefoil-loop metamaterial absorber with polarization-independent and wide angular stable response for dual-band explosive gas sensing

A quatrefoil-loop-shaped metamaterial is designed in this paper to detect explosive gases in the C and X bands. It achieves three resonance frequencies at 6.5 GHz, 7.58 GHz, and 8.7 GHz with absorption rates of 99.9 %, 93.2 %, and 96.5 %, respectively. The absorber shows the same absorption at different polarization angles from 0° to 90° in both transverse electric (TE) and transverse magnetic (TM) modes. The absorber can sense explosive gases such as propane and butane. The sensitivity of the propane and butane is 0.47 GHz/RIU and 0.5 GHz/RIU with a quality factor of 130 and 216, respectively. The Figure of Merit values are 10 for propane and 16.67 for butane. The sensing occurs based on the refractive index. The design is based on a cost-effective FR-4 (lossy) dielectric substrate. The unit cell dimensions are 8 × 8 × 1.6 mm 3 . Analysis of surface current, electric fields, and magnetic fields confirms strong resonance at each band. Additionally, the design's equivalent circuit is modeled and validated in Advanced Design System (ADS). The fabricated design is measured, and the measurement results agree well with the simulated response.