Development of a Novel Metal Grating and Its Applications of Terahertz Spectroscopic Detection of CuSO4 in Fruit

As a novel detection method of CuSO4, terahertz (THz) spectroscopy detection has great application prospects, but the terahertz detection with the tablet method has low sensitivity, and with the metamaterials has complicated manufacture. This work has proposed a high-sensitivity pesticide THz spectroscopic detection method with a novel metal grating. The metal grating was composed of a circular hole array. It was made by laser micromachining technology to provide a simplified but improved measurement and had a strong transmission peak at the 0.4–1.0 THz band. The results indicated that the addition of copper sulfate (CuSO4) solutions to different concentrations caused the transmission peak frequency to shift red. The detection limit was about 103 times higher than that of CuSO4 measured on the polyethylene (PE) film substrate, which reached 0.375 mg/L. The method was applied for detecting CuSO4 in apple and grape, and the relative error was less than 5.8%. The metal grating combined with Terahertz time-domain spectroscopy (THz-TDS) can improve the sensitivity of sample detection and realize the detection and analysis of trace elements.