The present study introduces an innovative approach for a real-time detection of concealed metallic objects using a SiGe 300 GHz radar source. It has achieved remarkable precision distances up to 2.0 m. The system employs a miniaturized 300 GHz Industrial, Scientific, and Medical (ISM) band frequency-modulated continuous wave (FMCW) radar system. This setup includes a SiGe single-chip radar sensor and Liquid Crystal Polymer (LCP) off-chip antennas integrated into a Quad Flat No-Lead (QFN) package, breaking a new ground with millimeter-level accuracy. The system is linked to a user-friendly graphical interface (WebGUI) software, which help the users for fine-tuning the baseboard parameters to visualize radar data, and make real-time adjustments. The strength of reflected signal exhibits a nuanced second-order polynomial nature intricately correlated with signal bandwidth and the target's distance. Notably, the system provides maximum and minimum peak power at 289 and 329 GHz, respectively and helping us to achieve a Signal-to-Noise Ratio (SNR) of the order of 3.78 at a detection distance of 2.0 m. A detailed frequency bandwidth-based analysis reveals the system’s detection range. The maximum target distance was obtained 2.0 m at 20 GHz bandwidth range. Similarly, bandwidth of 30, 40 50 and 60 GHz were able to achieve the target range of 146, 100, 80 and 63 cm range, respectively. The 300 GHz SiGe radar source outperforms the lower-frequency (in microwave range) in terms of excellent spatial resolution and minimum interference from microwave devices which are some essentially requirements for radar based imaging and sensing applications. This adaptive radar system act as a powerful tool for enhancing the homeland security and defense system where concealed objects pose threats to public safety.
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 μm and 80 μm, respectively, and a silicon wafer thickness of 40 μm. The structure's periodicity is 120 μm 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 μm, 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.
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