This paper describes feasibility study of temporal phase analysis techniques using wavelet transform. In electronic speckle pattern interferometry (ESPI), a series of speckle patterns is captured during the deformation or vibration of the test specimen. The intensity variation on each pixel is analyzed along time axis. Phase values are evaluated point by point using complex Morlet wavelet transform. To demonstrate the validity of the proposed method, two experiments based on ESPI are conducted. These include instantaneous velocity and displacement measurement on continuous deformed objects; and absolute displacement measurement on vibrating objects using temporal carrier technique. Compared to temporal Fourier transform, wavelet analysis detects the optimized instantaneous frequency and performs an adaptive band-pass filtering of the measured signal, thus limits the influence of noise sources and increases the resolution of measurement significantly. It was observed that continuous wavelet transform (CWT) on each pixel generates a smoother spatial displacement distribution at different instants compared to a Fourier transform. The maximum displacement fluctuation due to noise is around 0.04 μm in Fourier transform, but only 0.02 μm in wavelet analysis. The wavelet transform proposed in this paper demonstrates a high potential for robust processing of continuous image sequences. The deep exploration on wavelet phase analysis techniques will broaden the applications in optical and non-destructive testing field.

Date Published: 17 September 2005
PDF: 8 pages
Proc. SPIE 5914, Wavelets XI, 59140B (17 September 2005); doi: 10.1117/12.613224

Published in SPIE Proceedings Vol. 5914:
Wavelets XI
Manos Papadakis; Andrew F. Laine; Michael A. Unser, Editor(s)