Determination of curvature and twist by digital shearography and wavelet transforms.

A new technique based on digital shearography for determining the transient curvature and twist of a continuously deforming object from a series of speckle patterns is presented. The intensity variation of each pixel is analyzed along the time axis by using a complex Morlet wavelet transform. The absolute sign of the phase variation is determined by introduction of a temporal carrier when the speckle patterns are captured by a high-speed camera. A high-quality spatial distribution of the deflection derivative is extracted at any instant without the need for temporal or spatial phase unwrapping. The continuous Haar wavelet transform is subsequently processed as a differentiation operator to reconstruct the instantaneous curvature and twist of a continuously deforming object.

[1]  C. J. Tay,et al.  Multiple-image shearography: a direct method to determine curvatures. , 1995, Applied optics.

[2]  L R Watkins,et al.  Determination of interferometer phase distributions by use of wavelets. , 1999, Optics letters.

[3]  Y. Y. Hung.  Shearography for non-destructive evaluation of composite structures , 1996 .

[4]  Siew Lok Toh,et al.  Direct determination of second-order derivatives in plate bending using multiple-exposure shearography , 1994 .

[5]  Hans J. Tiziani,et al.  NOVEL TEMPORAL FOURIER TRANSFORM SPECKLE PATTERN SHEARING INTERFEROMETER , 1998 .

[6]  Yu Fu,et al.  Wavelet analysis of speckle patterns with a temporal carrier. , 2005, Applied optics.

[7]  Y. Y. Hung.  A speckle-shearing interferometer: A tool for measuring derivatives of surface displacements , 1974 .

[8]  Junqing Cao,et al.  Realization of optical image differentiation by means of wavelet transform and power spectrum nonlinear processing , 1995, Optics & Photonics.

[9]  Jing Fang,et al.  Digital transform processing of carrier fringe patterns from speckle-shearing interferometry , 2001 .

[10]  Y. Y. Hung.  Digital shearography versus TV-holography for non-destructive evaluation , 1997 .

[11]  Yu Fu,et al.  Temporal wavelet analysis for deformation and velocity measurement in speckle interferometry , 2004 .

[12]  P. Rastogi,et al.  Measurement of curvature and twist of a deformed object by electronic speckle-shearing pattern interferometry. , 1996, Optics letters.

[13]  Fook Siong Chau,et al.  Direct measurement of curvature and twist of plates using digital shearography , 2003 .

[14]  Pramod Rastogi,et al.  Trends in optical non-destructive testing and inspection , 2000 .

[15]  J. Leendertz,et al.  An image-shearing speckle-pattern interferometer for measuring bending moments , 1973 .

[16]  Y. Y. Hung.  Shearography: A New Optical Method For Strain Measurement And Nondestructive Testing , 1982 .