Signal Processing And Visualization Of Thermal Wave Detection Based On Infrared Lock-in Thermography

Thermal wave detection based on infrared Lock-In thermography is one of theinfrared nondestructive testing technologies. It has been widely used in the detection ofaerospace materials, solar, nuclear industry and other high-tech industries with theadvantage of noncontact, nondestructive and being used in large area detections. But wecan’t get a vivid understanding of the defects with the2D image of phase. So that it’snecessary to do some works on3D reconstruction of the defects using computertechnology based on the analysis of theoretical model.After studying on the previous research, this paper gives explain to the conductionof sinusoidal heat flaw in solids, establishes the1D heat conduction model of singlemedium plate and composite plate of three medium and solves the problem using Fouriertransform and Green function method, obtains the relationship between the phase ofsurface thermal wave signal and the depth of the plates. At last it gives a briefintroduction of lock-in algorithm.In Matlab environment, we make local smoothing to the phase image. Then we getthe depth of every pixel using the solution above and do3D reconstruction of the depth.After that we process denoising in the two value image getting from the3D datareconstruction of the depth and do the3D drawing using surface rendering method inMatlab. At last we complete the GUI programme for2D processing and3D drawing sothat we can do some basic interactive operations.To analyze the reconstruction method above, we do experiments using Q235platewith artificial defects. Analyzing the phase image getting from the experiments and doing3D reconstruction of the plate, it points out the reason of the difference between theoryand practice. We also make reconstruction of the phase image of SiC plate with artificialdefects. The results show that the reconstruction method introduced in this paper cancomplete the3D reconstruction of the defects.