Terahertz wave is the electromagnetic spectrum situated between microwave and infrared wave. Quantitative analysis
based on terahertz spectroscopy is very important for the application of terahertz techniques. But how to realize it is still
under study. L-tartaric acid is widely used as acidulant in beverage, and other food, such as soft drinks, wine, candy,
bread and some colloidal sweetmeats. In this paper, terahertz time-domain spectroscopy is applied to quantify the tartaric
acid. Two methods are employed to process the terahertz spectra of different samples with different content of tartaric
acid. The first one is linear regression combining correlation analysis. The second is partial least square (PLS), in which
the absorption spectra in the 0.8-1.4THz region are used to quantify the tartaric acid. To compare the performance of
these two principles, the relative error of the two methods is analyzed. For this experiment, the first method does better
than the second one. But the first method is suitable for the quantitative analysis of materials which has obvious terahertz
absorption peaks, while for material which has no obvious terahertz absorption peaks, the second one is more
appropriate.
Terahertz time-domain spectroscopy (THz-TDS) is a newly developed technique in the last decade. A new method to
classify tea is proposed based on THz-TDS and pattern recognition method. Four kinds of tea are investigated to study its
feasibility. Their absorption spectra are measured using the THz-TDS system. Then a pattern recognition method,
support vector machine (SVM), is employed to differentiate the investigated tea based on their terahertz data. The
absorption spectra between 0.2 and 2.0 THz of the investigated tea samples are selected as the feature to classify them.
The correct rate of recognition for the SVM classifier is 96.88%. The results give evidence that different tea varieties can
be distinguished based on their terahertz spectra. In this respect, the spectral method provides enough information to
differentiate different kinds of tea.
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