Digital treatment of thermal data by quantitative pulsed phase thermography for the non-destructive evaluation of materials

Pulsed phase thermography (PPT) is a technique for material inspection by which the thermal sequences in the temporal domain are treated by Fourier transformation, giving access to the phase data in the frequency spectrum. It is well known that the phase data is little disturbed by the problems typically affecting the thermal signals, notably the variations of emissivity at the surface, the presence of complex shapes and non-uniform reheating. There is thus great research interest in utilising these characteristics in quantitative calculation (or inversion). The basic theory behind PPT is described in detail and a new inversion technique for depth, starting from the phase, is presented.