Research On The Technology Of Pulsed Phase Thermography

Pulsed Phase Thermography (PPT) is a new developed photothermal radiometry technology. This technology method combines Pulsed Thermography technology (PT) and Lock-In thermography technology (LT), so the method has the speed as fast as PT and the strong ability to restrain noise as LT. During these years PPT has been payed more and more attention for its convenience for detection.Based on the theory of PPT, the sampling parameters'effect on frequency spectrum computed by fourier is analyzed. Enlarging sampling window can enhauce frequency spectrum resolution, and enlarging sampling frequency can enlarge the range of frequency spectrum. In appropriate range enlarging sampling window and frequency can both improve accuracy of phase detection. In actual computition fitting expandation and insertion is used to enlarge sampling time and sampling frequency. Fitting the time signal data of infared sequence images can not only improve phase image's contrast but also compress data storage. PPT is used to analyze the undersurface defect detection of metallic and nonmetallic sample.Defect's quantitative analysis methods are discussed. The influnce of thermodiffusion on phase image in PPT is analyzed and selecting appropriate short sampling time can improve phase image's detection effect. Research shows that, phase image shows higher ability to quantitative detect and analyze undersurface defect than amplitude image and contrast image because of its better defect contrast. Two methods are used to detect the depth of defect: one is computing contrast and concluding defect's depth through the functional relation between maximal value of contrast (Cimg) and the value of defect's depth (d), another is computing the maximal contrast of phase image obtained by wavelet transform and get depth through the approximately linear relation between translation factor T and depth. An active photothermal radiometry image process system is also designed in this paper. This system includes image process fuction of PPT based on Fourier Transform, contrast image computing, image matching and image fuse. It provides a convenient data process platform for Pulsed Phase Thermography.