Time of flight improved thermally grown oxide thickness measurement with terahertz spectroscopy

 Zhang, Zhenghao, Yi Huang, Shuncong Zhong, Tingling Lin, Yujie Zhong, Qiuming Zeng, Walter Nsengiyumva, Yingjie Yu, and Zhike Peng. "Time of flight improved thermally grown oxide thickness measurement with terahertz spectroscopy." Frontiers of Mechanical Engineering 17, no. 4 (2022): 1-11.

for full paper see https://link.springer.com/article/10.1007/s11465-022-0705-3

As a nondestructive testing technique, terahertz time-domain spectroscopy technology is commonly used to measure the thickness of ceramic coat in thermal barrier coatings (TBCs). However, the invisibility of ceramic/thermally grown oxide (TGO) reflective wave leads to the measurement failure of natural growth TGO whose thickness is below 10 µm in TBCs. To detect and monitor TGO in the emergence stage, a time of flight (TOF) improved TGO thickness measurement method is proposed. A simulative investigation on propagation characteristics of terahertz shows the linear relationship between TGO thickness and phase shift of feature wave. The accurate TOF increment could be acquired from wavelet soft threshold and cross-correlation function with negative effect reduction of environmental noise and system oscillation. Thus, the TGO thickness could be obtained efficiently from the TOF increment of the monitor area with different heating times. The averaged error of 1.61 µm in experimental results demonstrates the highly accurate and robust measurement of the proposed method, making it attractive for condition monitoring and life prediction of TBCs.