Study On Identification Of Product Oil Using Terahertz Time-domain Spectroscopy

Product oils, transported sequentially in the pipeline, can be easily mixed, identification of which is important to ensure the oil quality, prevent security risks, and achieve full utilization of energy. Optical methods with high sensitivity, accuracy and security no pollution as well as various measuring ways, have become a new research direction in the field of mixed oil interface detection. And terahertz spectroscopy, because of its high time resolution, ability to reflect nuances of molecules, low energy and harmlessness, strong penetrability through the non-polar liquids, turns into a hot spot in the aspects of biological medicine, physical chemistry, material science and security detection. The amplitude and phase information of terahertz pulse through oils can be acquired simultaneously from terahertz time-domain spectra, which is convenient to extract oils’optical parameters, and to achieve the purpose of identifying different oils.In this article, terahertz time-domain spectroscopy was used for mixed product oils recognition, and its principle for detection was studied. The calculating formulas were derived, through which optical parameters of product oil can be extracted using terahertz time-domain spectroscopy technology. Five types of THz-TDS system were expounded and the transmission one used for detecting product oil was given in detail. The response characteristics of the product oils in the terahertz band in different optical paths and the terahertz spectrums of mixed oils compounded in different proportions were studied systematically. Matlab and Origin were used to get spectroscopic data analyzed and processed. Relation curves about concentration with refractive index on average, and with absorption coefficient on average were fitted respectively. And based on the linear relationship between concentration and absorption coefficient on average, the mixed oil identification was programmed in Labview.Experiments show that, refractive index spectrums and absorption coefficient spectrums of mixed oils from the terahertz time-domain spectrums for the same type of oil mixtures are distinct and for the two types of oil mixtures, they are significantly different, which confirm that THz-TDS technology is a satisfactory means to identify different proportion of mixed oils.