Application of Terahertz metamaterials for Low-concentration sensing of premium explosives like RDX and TNT

In the present study, we have studied the applicability of terahertz (THz) metamaterials for sensing low concentrations of premium explosives like RDX and TNT. A parallel metal-pair-based metamaterial has been investigated. The structure exhibits a Fano resonance at 0.627 THz in reflection geometry within the 0.1 to 1 THz range. The unit cell of the metamaterial comprises two asymmetric aluminium rod-like structures on an intrinsic silicon wafer with dimensions of 100 mu m and 80 mu m, respectively, and a silicon wafer thickness of 40 mu m. The structure's periodicity is 120 mu m along the x and y directions. We have also performed COMSOL-based simulations of metamaterial structures with different analyte thicknesses in conjunction with experimental verification. In the experiment, for an analyte thickness of 0.5 mu m, the structure exhibits a refractive index-dependent sensitivity (S) of 5.1 GHz/RIU. For explosives, resonance peak shifts of 0.031 THz for TNT (refractive index 1.61) and 0.043 THz for RDX (refractive index 1.85) were observed from their respective resonance positions at 0.627 THz. These findings underscore the efficacy of THz metamaterials for detecting trace amounts of explosives.