Investigation On Terahertz Spectroscopy Technology For Edible Oil Detection

Terahertz wave refers to a kind of electromagnetic wave,the frequency of which ranges from 0.1 to 10 THz.It has some characteristics of microwave and infrared wave,including low photon energy,selective penetration,fingerprint and water sensitivity,which makes terahertz wave have great application prospect in biomedical science,security check,industry inspection,food safety and other fields.Edible oil is a significant source of human nutrition and energy,providing essential fatty acids for human body.The investigation on the optical properties of edible oils in THz region is considered to be of great importance for component analysis and quality evaluation.In this paper,focusing on terahertz spectroscopy technology for edible oil detection,we investigated the key technologies of terahertz time-domain attenuated total reflection spectroscopy and terahertz frequency-domain transmission spectroscopy.Combined with density functional theory and regression algorithm separately,the absorption characteristics were analyzed and the identification of edible oils was realized.The main innovations of this paper include:1.A new method for measuring the optical parameters of edible oils by terahertz timedomain attenuated total reflection spectroscopy was investigated,which solved the oscillation of spectra induced by the FP effect of sample cell when using terahertz time-domain transmission spectroscopy,and realized an accurate measurement of optical parameters of edible oil.We deduced the optical parameter calculation model theoretically and measured the spectra of refractive index and absorption of soybean oil,walnut oil and grape seed oil experimentally.They had obvious absorption peaks in the range of 1~1.8THz,showing that terahertz time-domain attenuated total reflection spectroscopy can obtain the spectral characteristic of edible oils effectively.2.We analyzed the low frequency vibration and rotation mode of fatty acid molecules of edible oils in terahertz region using the density functional theory.The theoretical results were consistent well with the experimental results obtained by the terahertz time-domain attenuated total reflection spectroscopy.It was proved that the absorption peaks resulted from their vibration and rotation modes.3.A terahertz frequency-domain spectroscopy system based on tunable terahertz parametric oscillator was studied.We deduced the optical parameter calculation model theoretically and measured the absorption spectra of rapeseed oil,soybean oil and corn oil experimentally.The oscillation of transmission spectra was explained by a transmission model of a three-layer structure.A partial least squares multivariate regression model based on terahertz spectra was established and optimized,and the accuracy of prediction was 100%.