Signal to Noise Ratio Threshold in Active Thermography

In this study an approach to determine the Signal to Background Contrast, by using a threshold level as a suitable measure for Active Thermography is given. Carbon Fiber Reinforced Plastic specimen with artificial defects in random positions and depths were manufactured and analysed. These artificial defects were fabricated by using folded Teflon foil pieces to enclose a small amount of air, which acts as a delamination. Measurements were carried out in reflection as well as in transmission mode with data analysis in time and frequency domain. For thermal excitation two high power flash lamps were used. After processing of the temperature-time history diffusion time images as well as phase images were given to different inspectors to search for defects and mark them. From their results a hit/miss matrix was derived and a Probability of Detection analysis was carried out.