School of Information and Control Engineering,China University of Mining and Technology;
[Objective] The signal of thin coatings overlaps in the time domain, making it challenging to directly apply the time-of-flightmethod for thickness detection. The accuracy of model-based methods combined with optimization algorithms depends on both theprecision of the coating's optical parameters and the modeling precision. These methods must also address the anisotropic properties ofcarbon fiber composite materials. However, in practice, the propagation path of terahertz signals changes only at the interface, and thesample response to terahertz signals can be regarded as approximating a linear system. [Methods] Since the front part of the terahertzsignal waveform already contains critical interface information of the coating, and the response of the sample behaves as an approximatelinear system, the propagation path of the terahertz signal changes only at the interface. Therefore, signal sparse decomposition combinedwith the time-of-flight method was employed to detect thin coating thickness on carbon fiber composite substrates. First, a comprehensiveanalysis of compressive sensing theory was conducted, identifying the spectral projection gradient algorithm with L1 norm as suitable, asit has been validated on isotropic bases. Experimental evidence clarified that the reflective terahertz time-domain systems are preferablefor detecting coatings on substrates. Subsequently, based on practical coating thickness measurements, the principle of the SPGL1 algorithm was derived, and a perception matrix was constructed using reference signals. A coating thickness detection scheme combiningsignal sparse decomposition and time-of-flight method was proposed by analyzing the conditions required for solving convex optimalproblems.[Results] Experimental data demonstrated that when coating refractive indices differ significantly and the thickness is greaterthan or equal to 100 μm, the results, even with added noise, align well with ideal expectations. When coating refractive indices are similarbut the thickness is greater than or equal to 100 μm, the SPGL1 method exhibits strong anti-interference capability. [Conclusions] Thiscomplete experimental design promotes a deeper understanding of fundamental theories and methods, such as time-domain spectroscopy,sparse decomposition, and the time-of-flight method. It bridges theoretical knowledge and practical application, fostering students' abilityto connect the two while cultivating their interest and skills in scientific research.
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Basic Information:
DOI：10.16791/j.cnki.sjg.2025.04.016
China Classification Code:G642;TB306-4
Citation Information:
[1]李海港,黄宇蕾,朱美强等.基于SPGL1算法的CFRP涂层厚度检测方法研究[J].实验技术与管理,2025,42(04):127-135.DOI:10.16791/j.cnki.sjg.2025.04.016.
Fund Information:
国家自然科学基金项目(62273348); 教育部产学合作协同育人项目(2022030014); 中国矿业大学研究生教育教学改革研究与实践项目(2025JSJG054);中国矿业大学教学研究项目(2020ZD05,2022KCSZ03)