Ginseng drugs are reported to have multiple health benefits, which are believed to boost energy, lower blood sugar and cholesterol levels. However, ginseng products can vary in their components and medicinal properties. Panax ginseng, American ginseng and radix pseudostellariae are different medical substances. Therefore, it is of great significance to accurately and quickly identify them for the quality control and clinical medication safety of TCM (traditional Chinese medicine). However, the identification of the botanical origins of crude drugs through anatomical and chemotaxonomical studies is limited. It is noted that the effective identification of the herbal species can be interpreted by terahertz wave. The frequency range of the terahertz wave is from 100 GHz to 3 THz. Most of the vibrational and rotational energy levels of biological macromolecules are in the terahertz band. Terahertz time-domain spectroscopy (THz-TDS) is used to obtain the time-domain spectrum of ginseng drugs at room temperature. It was shown that we can discriminate different ginseng samples by the terahertz waves.
Metamaterials are artificial materials with unique electromagnetic properties not found in nature and could exhibit a strong electromagnetic resonance with frequency. These characteristics depending on the geometry, dimensions, compositions of the structure, and even the symmetry. In this study, we demonstrated a highly sensitive detection method of glycerol-water solutions using terahertz metamaterials fabricated on silicon substrate with metal arrays of the asymmetric double split-ring resonator structure. We measured the transmitted spectra of the metamaterial to detect the water-glycerol solutions at different concentrations by the terahertz time-domain spectroscopy system. With the increasing of glycerol concentration, resonant dips of metamaterial exhibit the blue-shift phenomena and transmittance at the resonance frequency simultaneously enhance. The movement of resonant dips and the change of transmittance shows that these resonators are sensitive to the variation of glycerol concentration. The finite-difference time-domain simulation agree well with the experimental data, and the simulation of surface current and electric field distribution at resonance dips can further understand the resonance modes in transmission spectra. Our study provides new prospect into the application of terahertz metamaterials in detecting glycerol proportions of solution.
Melamine is an organic base and a trimer of cyanamide, with a 1, 3, 5-triazine skeleton. It is usually used for the production of plastics, glue and flame retardants. Melamine combines with acid and related compounds to form melamine cyanurate and related crystal structures, which have been implicated as contaminants or biomarkers in protein adulterations by lawbreakers, especially in milk powder. This paper is focused on developing an available method for quantitative detection of melamine in the fields of security inspection and nondestructive testing based on THz-TDS. Terahertz (THz) technology has promising applications for the detection and identification of materials because it exhibits the properties of spectroscopy, good penetration and safety. Terahertz time-domain spectroscopy (THz-TDS) is a key technique that is applied to spectroscopic measurement of materials based on ultrafast femtosecond laser. In this study, the melamine and its mixture with polyethylene powder in different consistence are measured using the transmission THz-TDS. And we obtained the refractive index spectra and the absorption spectrum of different concentrations of melamine on 0.2-2.8THz. In the refractive index spectra, it is obvious to see that decline trend with the decrease of concentration; and in the absorption spectrum, two peaks of melamine at 1.98THz and 2.28THz can be obtained. Based on the experimental result, the absorption coefficient and the consistence of the melamine in the mixture are determined. Finally, methods for quantitative detection of materials in the fields of nondestructive testing and quality control based on THz-TDS have been studied.
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