Temporal wavelet analysis for deformation and velocity measurement in speckle interferometry

When a continuously deforming object is measured by electronic speckle pattern interferometry (ESPI), the speckle pattern recorded on a camera sensor changes constantly. These time-dependent speckle patterns would provide the deformation history of the object. Various objects are applied with both linearly and nonlinearly varying loads and speckle patterns are captured using a high-speed CCD camera. The temporal intensity variation of each pixel on the recorded images is analyzed by a robust mathematical tool—Morlet wavelet transform instead of conventional Fourier transform. The transient velocity and displacement of each point can be retrieved without the necessity of the temporal or spatial phase unwrapping process. The displacements obtained are compared with those from a temporal Fourier transform, and the results show that the wavelet transform minimizes the influence of noise and provides better results for a linearly varying load. System error in the wavelet analysis for nonlinear load is also discussed.

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