The use of carrier fringes and FFT in holographic nondestructive testing

ConclusionIn this paper, the spatial carrier fringe technique has been applied to holographic deformation measurement. The spatial carrier across the object can be easily generated by moving the optical fibre which illuminates the object. The use of the fibre optics greatly facilitates the carrier fringe technique and FFT fringe analysis. The carrier fringe technique not only benefits the automatic fringe analysis using FFT approach, but also removes the sign ambiguity of the displacement, since the direction of translating the light source is pre-determined. The Fourier transform method of fringe analysis combined with the carrier fringe technique can be used to extract deformation information automatically from complex interferograms. Unlike the phase-stepping method, only one frame is needed to form the fringe information using FFT method. The FFT approach has considerable potential for solving images in its ability to extract data despite pixels noise. The results presented in this paper have illustrated that, despite the use of generous assumptions and simple equations without a full knowledge of the experimental parameters, a reasonably accurate estimation of deformation was achieved.