Through transmission thermography- A review of the state-of-the-art

Nondestructive Testing (NDT) covers a wide range of testing methods in which a component can be inspected without affecting its functionality. Infrared thermography is an NDT technique that has gained rapid popularity in recent years for structural integrity assessment, especially in the aerospace and oil & gas industries. Pulsed thermography, a subset of IR thermography is one of the active thermography techniques that uses flash lamps to thermally excite the specimen under observation. Thermal measurements can be taken in the reflection, or the transmission mode based on the positioning of the IR Camera and the flash lamps with respect to the specimen. Currently, estimating the defect depth using IR thermography remains a challenge as the reflection mode cannot accurately characterise defects that are deeper than 3mm. A major advantage of the throughtransmission technique lies in its ability to detect defects that are deeper than the 3mm depth with higher levels of precision and accuracy. This makes through-transmission a suitable candidate for measuring defect depths using IR thermography. However, unlike the reflection mode, through-transmission has a limited number of image post-processing algorithms for defect detection and characterisation. This paper presents the state-of-the-art in the development of through-transmission thermography together with the technique’s know-how and limitations currently available in the scientific committee.