Corrosion of steel materials (such as rebars and steel plates) usually occurs under coating materials . It is, with the existing non-destructive testing (NDT) technologies, difficult to accurately determine the corrosion of steel materials. The terahertz (THz) electromagnetic waves can penetrate the non-polar materials, and theoretically experience an absorption resonance with some corrosion products crystals ( i.e. , iron oxides). The THz spectroscopy has, therefore, a great application potential to characteristically identify the corrosion of steel materials. In the present study, the optical parameters and, especially, the positions of the characteristic absorption peaks of the corrosion products were systematically investigated and identified using the THz system. The experimental results showed that the refractive index of the different corrosion product samples was in the range of 2.7–3.4 in the effective frequency range of 0 THz - 1.2 THz, and the content of Fe 3 O 4 had a large influence on the optical parameters in the corrosion product mixtures. To measure the characteristic absorption peaks of the corrosion products, the effective frequency range was extended to 0 THz - 10 THz by an assembled broadband THz system. Within this range, the positions of the characteristic absorption peaks were identified as 3.4 THz, 4.2 THz, 4.85 THz, and 5.8 THz for Fe 2 O 3 , and as 3.6 THz, 4.05 THz, 5 THz, and 5.45 THz for α-FeOOH. For Fe 2 O 3 and α-FeOOH, the intensities of the absorption peaks at 4.85 THz and 3.6 THz, respectively, showed a linear relationship with the mass content. Furthermore, the THz spectroscopy could accurately identify Fe 2 O 3 and α-FeOOH in the corrosion product mixtures by comparing with the results from IR spectroscopy and Raman spectroscopy. This means that the occurrence of steel corrosion could be detected according to the characteristic absorption peaks of Fe 2 O 3 and α-FeOOH. The experimental results provide a basis for the application of THz spectroscopy in the NDT of the corrosion of steel materials.
Water vapor noise in the air affects the accuracy of optical parameters extracted from terahertz (THz) time-domain spectroscopy. In this paper, a numerical method was proposed to eliminate water vapor noise from the THz spectra. According to the Van Vleck–Weisskopf function and the linear absorption spectrum of water molecules in the HITRAN database, we simulated the water vapor absorption spectrum and real refractive index spectrum with a particular line width. The continuum effect of water vapor molecules was also considered. Theoretical transfer function of a different humidity was constructed through the theoretical calculation of the water vapor absorption coefficient and the real refractive index. The THz signal of the Lacidipine sample containing water vapor background noise in the continuous frequency domain of 0.5–1.8 THz was denoised by use of the method. The results show that the optical parameters extracted from the denoised signal are closer to the optical parameters in the dry nitrogen environment.
In response to the research demand in spatial frequency domain techniques at continuous wavelengths in the field of agricultural and food products, a line scan hyperspectral spatial frequency domain combined imaging (LSH-SFDI) system was developed for quantitative hyperspectral optical imaging in the spatial frequency domain for detecting absorption ( μ a ) and reduced scattering ( μ′ s ) parameters of tissues in the continuous spectral range. Systematic calibration of the LSH-SFDI system was performed using the configured liquid phantoms, and the average errors of μ a and μ′ s at 56 wavelength bands between 450 and 740 nm were obtained as 9.24% and 6.08%, respectively. The optical parameters of milk were measured using the LSH-SFDI system, and the μ a and μ′ s values of milk samples at continuous wavelengths were analyzed by linear regression with the fat and protein contents of the corresponding milk, and the final results verified the correlation between the fat content and μ′ s and the protein content and μ a of milk. The developed system can be further used for milk quality evaluation and classification subsequently, as well as for other agricultural products and foods.
危险品化学品经营许可证（带存储）