Wavelet-based subsurface defect characterization in pulsed phase thermography for non-destructive evaluation

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5 Citations (Scopus)


Active infrared thermography is a method for non-destructive testing (NDT) of materials and components. In pulsed thermography (PT), a brief and high intensity flash is used to heat the sample. The decay of the sample surface temperature is detected and recorded by an infrared camera. Any subsurface anomaly (e.g. inclusion, delamination, etc.) gives rise to a local temperature increase (thermal contrast) on the sample surface. Conventionally, in Pulsed Phase Thermography (PPT) the analysis of PT time series is done by means of Discrete Fourier Transform producing phase images which can suppress unwanted physical effects (due to surface emissivity variations or non-uniform heating). The drawback of the Fourier-based approach is the loss of temporal information, making quantitative inversion procedures tricky (e.g. defect depth measurements). In this paper the complex Morlet-Wavelet transform is used to preserve the time information of the signal and thus provides information about the depth of a subsurface defect. Additionally, we propose to use the according phase contrast value to derive supplementary information about the thermal reflection properties at the defect interface. This provides additional information (e.g. about the thermal mismatch factor between the specimen and the defect) making interpretation of PPT results easier and perhaps unequivocal.

Original languageEnglish
Title of host publicationProceedings of SPIE - Wavelet Applications Volume 7248
Number of pages8
Publication statusPublished - 2009
EventWavelet Applications in Industrial Processing VI - San Jose, CA, United States
Duration: 21 Jan 200922 Jan 2009

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


ConferenceWavelet Applications in Industrial Processing VI
Country/TerritoryUnited States
CitySan Jose, CA


  • Active thermography
  • NDT
  • Pulsed phase thermography
  • Thermal reflection
  • Wavelet analysis


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