Reducing the Effect of Surface Emissivity Variation in Eddy Current Pulsed Thermography

Manually selected frames have been used for both defect detection and quantification in Eddy current pulsed thermography. Defects are indicated by high/low temperatures within frames. However, variation of surface emissivity sometimes introduces illusory temperature inhomogeneity and results in detection false alarms. To improve the probability of detection, this paper proposes a two heat balance states-based method. For each pixel, a surface emissivity coefficient is extracted from the two heat balance states and is used to correct the transient response. The temperature and emissivity is thus separated. A verified experiment was carried out on a steel sample having both a polished and black strip painted surface, and the image quality was improved significantly.