In cigarette manufacturers, the detection of cigarette quality has always been the key problem in the entire industry's production chain. The efficiency and accuracy of detection technology are directly related to product quality and furthermore, it will affect the credibility and economic benefits of the entire enterprise. For the cigarettes with blasting beads, in order to ensure the safety of smokers during smoking and to obtain a better experience, determining the presence or absence, location, and damage condition of beads in the cigarette filter is critical. Therefore, it is necessary to test the beads in the manufacturing process of the cigarette, thereby timely remove the unqualified product. In this paper, a nondestructive testing method based on reflective terahertz time-domain spectral imaging system is proposed, which can easily evaluate the presence or absence approximate position and damage condition of beads in the cigarettes filter. To lay a foundation for further accurate and effective measurement of the positional offset of beads and to evaluate the damage condition of beads, it is of great significance to improve the production efficiency and tobacco quality of the tobacco factory.
In this paper, we demonstrated a quasi-optical method for extracting electromagnetic parameters of materials in free space. This contactless and non-destructive method shows the great value and significance in detecting the materials that is hard to process. The system contains a high-precision vector network analyzer and a quasi-optical system, a pair of high-gain corrugated horn antennas and an off-axis parabolic mirror system for beam shaping and focus controlling of transmitting and receiving electromagnetic waves. The measurement frequency can reach the range of 220GHz~325GHz as the frequency conversion module ZVA-Z325 matches with the vector network analyzer. The scattering parameter matrix of Teflon and a porous ceramics are measured. Fourier transform of the measured signal and time domain gating are used to eliminate multiple reflections and diffraction interference. The complex permittivity of the materials, including the complex permeability and complex refractive index, are derived from classical Fresnel formula. The differences between the results in this experiment and classical THz-TDS measurements in the same frequency range are compared to analyze the errors and make further explanations.
Alcohol is a kind of flammable substance. It is strictly forbidden in public places such as airports and high-speed railway stations. So the non-destructive testing of the alcohol is very crucial. In this paper, we used the reflective terahertz (THz) time-domain spectrometer to measure THz signals of alcohol aqueous solutions in different concentrations, the relationship between the pulse peak and concentration is obtained. And then reflectance spectra were obtained by using Fourier transform. Linear regression was employed to fit the relationship between the terahertz reflectance and the alcohol concentration at different frequencies. This pilot work has preliminarily formed a testing method for the detection of liquids concentration by using THz reflectance spectra. In the future, we can establish the THz spectral library for dangerous and inflammable liquids.