Nondestructive detection technology of THz time-domain spectroscopy technology

The terahertz time-domain spectroscopy (THz TDS) system was developed in the 1980s by T.J.Wastson Research Center of AF&T, Bell Labs and IBM Corporation. The system utilizes THz pulse transmission or reflection on the sample surface to measure the resulting terahertz electric field over time. The amplitude and phase variation of the terahertz pulse obtained in the Fourier transform are used to extract sample information. THz-TDS system can effectively detect a variety of materials, such as dielectric materials, semiconductor materials, gas molecules, biological macromolecules and superconducting materials in the terahertz wave band dispersion and absorption of information. According to the absorption peak frequency in the absorption spectrum of the sample, the energy level difference of the sample can be judged and its chemical composition and structure can be analyzed. The THz-TDS technology is mainly used for studying the properties and physical phenomena of the material in the terahertz band and also for terahertz wave imaging. Terahertz time-domain spectroscopy detection system is mainly composed of PC, the terahertz source, launchers, receivers, collinear adapters, two-dimensional motion guide XY Gantry and motion controller, as shown in Fig.


Transmission THz time-domain spectrum detection system


    Institute of Photoelectric Measurement and Control Technology, Changchun University of Science and Technology, based on terahertz imaging, infrared thermal imaging, laser dislocation speckle interference imaging, ultrasonic imaging and other detection techniques for ceramic matrix composites, laminates, carbon fiber composites, multi-cemented composites, honeycomb composite materials and other composite materials for full three-dimensional quantitative non-destructive testing technology to carry out in-depth study. The THz time domain spectral imaging system was established and the optical parameter extraction technology was studied, the simplex optimization algorithm was proposed. Focusing on terahertz time and frequency domain signal preprocessing techniques, in the terahertz time domain signal preprocessing, a de-convolution filtering algorithm is proposed to improve the quality of the THz signal. According to the position of the echos noise signal before and after the main pulse, the apodization function filtering and wavelet filtering technique were proposed to remove. In the terahertz frequency domain signal processing, a fast and efficient Savitzky-Golay filter smoothing and wavelet smoothing technique is proposed to improve the quality of THz frequency domain signal. At the same time, for large-size global coordinate system adaptive robot automatic NDT imaging technology to carry out engineering applications. In terahertz non-destructive testing, the Institute conducted in-depth study of time-domain and frequency-domain terahertz non-destructive testing, breaking through key technologies such as THz signal processing, THz propagation simulation, THz high resolution imaging and defect intelligent image recognition. Fingerprint database, to achieve THz nondestructive testing of engineering, intelligent applications. As a new non-destructive testing technology, THz non-destructive testing technology provides a solution for non-destructive testing of various new composite materials compared with ultrasonic testing. Compared with ultrasonic testing, THz Of the energy only millivolt volts, no harm to the human body, in line with the development trend of non-destructive testing green; laser dislocation speckle, infrared non-destructive testing, less affected by the detection environment for a variety of adverse detection Environment. Compared with the electromagnetic detection such as eddy current, the THz wave can penetrate the non-polar material and provide a new idea for non-destructive testing of non-polar materials. Based on the actual needs of different detection, four methods of THz nondestructive testing were proposed to identify and determine the defects of the material. In this paper, researchers propose an imaging technique of region of interest in THz frequency domain and time domain signal in reflective imaging, which improves the image resolution. According to whether the optical properties of the material are known or not, the terahertz reflection tomography was studied. Multispectral imaging and hyperspectral imaging technology were studied, and a multi-feature parameter terahertz imaging technique was proposed. According to the defect characteristics of different materials, the different THz characteristic parameters were given to the R, G, B three color channels, to achieve the THz likely color imaging.

 

About team
Institute of Photoelectric Measurement and Control Technology, Changchun University of Science and Technology and "Jilin Province photoelectric precision measurement and digital assembly technology innovation center", mainly for assembly of digital measurement system of the basic structure and key technologies, integration of laser scanning, laser tracking, laser projection, too Terahertz testing, infrared thermal flaw detection, laser speckle flaw detection and other advanced measurement techniques, the use of digital measurement theory with independent intellectual property rights, technology and methods, through the multi-sensor fusion measurement network and collaborative measurement system, people, machine, measuring equipment and other environments, for the user to establish a full three-dimensional model of the digital assembly and detection system to achieve parts, components, systems, rapid and accurate detection and assembly. There are more than 20 people in the research team, focusing on instrument science and technology, optical engineering, mechanical engineering, computer science and technology and other multi-disciplinary talents, "Science and Technology Department of Jilin Province Science and Technology Innovation Team" and "Jilin Provincial Department of Education Innovation Team". The team has applied for 21 invention patents and published over 30 papers. The team undertook research on 863 major national projects and key state projects, and obtained many innovative achievements with independent intellectual property rights, forming a stable research direction and mature products. 

Article
Hou C H, Zhu Y D, Li L J, et al. Optical parameter extraction and error analysis of terahertz time domain spectrum detection[J]. Opto-Electronic Engineering, 2018, 45(2): 170534.
DOI:10.12086/oee.2018.170534