Study On Spectral Response Of Terahertz Spectra For Foreign Bodies Of Insects Hidden In Tea

Foreign body is one of the three major pollution sources of tea.In order to solve the problem of high frequency of insect foreign body mixing and lack of effective detection methods,the spectral response information in THz band of famous tea with foreign body like insects contained was excavated.And the nondestructive detection method for famous tea with insect foreign body was constructed,so as to explore the field of food safety detection where THz has outstanding advantages.The main research results and conclusions are as follows:(1)Study on experimental sample preparation and THz spectral information acquisition.The sample preparation method and process were designed to reduce the influence of interfering factors such as tablet thickness,pressure and sample moisture on THz spectral response characteristics of tea substrate and insect foreign body.The extraction method of THz absorption coefficient,refractive index,dielectric constant,dielectric loss and other physical parameters was proposed,which improved the accuracy of THz spectrum.(2)Research on THz spectrum response of tea and foreign body like insects.Take crickets-as the representative of insects with an exoskeleton-and barley worm-as the representative of worms-as samples,and extracted physical parameters of different samples such as THz absorption coefficient,refractive index,permittivity,dielectric loss.Then observed and analyzed which THz wave band can best reflect the differences between tea and foreign body,and it was found that THz physical parameters in the 0.3-1.5THz and 1.5-1.8THz has bigger difference;Principal component analysis(PCA)in this band could distinguish tea from foreign bodies,but the difference between cricket exoskeleton and polystyrene was not obvious.(3)THz spectral discriminant study on foreign bodies in tea: PCA,support vector machine(SVM)and least squares discriminant(PLS-DA)models were established in the bands of 0.3-1.5THz,1.5-1.8THz and 0.3-1.8THz respectively.The SVM discrimination model based on the absorption coefficients of three bands above has the best performance and can correctly identify the foreign bodies contained in green tea.The SVM discrimination model based on the absorption coefficients of 1.5-1.8THz has the best recognition effect for foreign bodies contained in black tea,with a misjudgment rate of 8.1%.The PCA discriminant model of three bands can effectively identify barley worms mixed with green tea,cricket meat,barley worms mixed with black tea and polystyrene,but other foreign bodies were not able to be identified.The PLS-DA discriminant model based on the data of dielectric loss in the band of 0.3-1.5THz is able to identify insect foreign bodies in black tea and green tea,and the misdiagnosis rate was 3.0% and 11.4% respectively.The research in this paper shows that there are differences between the THz physical property parameters of tea substrate and insect foreign bodies,which can be used for nondestructive detection of insect foreign bodies in tea.The research in this paper provides theoretical support for online detection of foreign bodies in tea...