Active Thermography Nondestructive Testing Going Beyond Camera’s Resolution Limitation: A Heterogenous Dual-Band Single-Pixel Approach

Active thermography nondestructive testing (ATNDT) has a broad application in the quality control of novel materials while its resolution is strictly constrained by the principle of microbolometer-based infrared cameras. Single-pixel image approach can free thermal images in thermography theoretically but is limited by the cost of long-wave infrared spatial light modulators (SLMs). This article has proposed a heterogeneous dual-band imaging system to solve this issue. This study has both theoretically and experimentally demonstrated that the surface temperature field can still carry the spatially encoded information of the excitation source to some extent after it diffuses naturally in ATNDT, which means the defect reconstruction can be achieved using single-pixel imaging. Such a subsurface defect can be revealed with a resolution independent of the camera. A spectral analysis tool is developed and validated for the excitation design and the detectability prediction.