Fig. 1. The principle of infrared pulse thermal wave optical flow imaging based on THFS technology

Fig. 2. Schematic diagram of THFS and FFT coupling algorithm

Fig. 3. (a) Geometry of simulated specimen; (b) Finite element mesh

Fig. 4. (a) Power density distribution; (b) Heat flow field

Fig. 5. (a) Normalized FFT amplitude; (b) Normalized FFT-THFS amplitude; (c) Normalize FFT phase; (d) Normalized FFT-THFS phase

Fig. 6. (a) Optical images; (b) Geometry diagram

Fig. 7. The schematic diagram of infrared pulsed thermal imaging

Fig. 8. Infrared pulse thermal imaging detection experimental platform

Fig. 9. (a) Normalized heat flow field for 5 s; (b) Comparative analysis of thermal image and thermal image-THFS

Fig. 10. (a) The regression curve of the original defect diameter and normalized contrast; (b) The regression curve of THFS-enhanced defect diameter and normalized contrast

Fig. 11. (a) Comparative analysis of FFT phase and FFT-THFS phase; (b) Comparative analysis of FFT amplitude and FFT-THFS amplitude

Fig. 12. Definition of defect area and non-defect area

Fig. 13. (a) FFT amplitude SNR vs defect diameter and depth; (b) FFT-THFS amplitude SNR vs defect diameter and depth; (c) FFT phase SNR vs defect diameter and depth; (d) FFT-THFS phase SNR vs defect diameter and depth

Fig. 14. Relationship between FFT/FFT-THFS amplitude SNR and defect diameter-to-depth ratio

Fig. 15. Relationship between FFT/FFT-THFS phase SNR and defect diameter-to-depth ratio

Fig. 16. (a) FFT amplitude segmentation; (b) FFT-THFS amplitude segmentation