Nondestructive evaluation of multilayered paint films in ambient atmosphere using terahertz reflection spectroscopy

• The reliability of layered material evaluation with terahertz (THz) waves is easily compromised.
• We suggest a THz signal decomposition scheme to analyze angled THz reflection measurements in ambient atmosphere.
• The extracted spectrum from each decomposed THz signal enables individual identification of each constituent layer.

The reliability of material characterization with terahertz (THz) waves is typically compromised by irrelevant signals present in the THz measurements. These are well observed in the investigation of layered materials in humid environments, causing difficulty in accurate analyses. In this article, we suggest a realistically employable method of analyzing angled THz reflection measurements in ambient atmosphere for qualitative monitoring and evaluation of multilayered paint films. In particular, we present successive decomposition of THz sample signals for individual identification of each constituent layer in the samples. It is shown that the extracted spectrum of each paint layer presents sufficient information for effective monitoring of the multilayered structures. In this process, THz spectra of the marine paints EH2350, Interthane 989, BEA777, and ENA300 are reported for the first time. Our experimental findings show promise in highly effective nondestructive inspection of layered structures for real-world evaluation applications.