Terahertz Based Thickness Measurement of Thermal Barrier Coatings Using Long Short-Term Memory Networks and Local Extrema

The terahertz (THz)-based thickness measurement of thermal barrier coatings (TBCs) demands smart determination of THz peaks instead of human intervention for efficiency and accuracy, especially in the case of uneven microstructure due to imperfect spraying conditions. To this end, in this article, a long short-term memory (LSTM) framework driven by a theoretical model of THz signals is proposed to locate peaks automatically and location errors are eliminated by finding the maximum around the originally located results. Then, the local extrema are used to extract peaks for calculating refractive index online to remove the influence of the change in refractive index on thickness measurement. Finally, the simulations and experiments were carried out to verify the proposed method. The results show that our method generated identical results with those from the manual intervention, while the efficiency is significantly improved.