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1.3 PHYSICAL SCIENCES
Electronic Speckle Pattern Interferometry (ESPI) is used to measure surface displacements. Phase shifting can be used to obtain a fringe pattern which depicts the phase at every point in an image. Previous studies have used algorithms such as the 4-bucket algorithm to obtain phase maps of objects. After the object is displaced a second phase map is obtained in the same way and by correlation the phase difference due to the displacement can be determined. When the object is in rapid continuous motion these algorithms cannot be used. Towards this end a 5-frame algorithm was written, in which the calibrated phase steps are obtained when the surface is at rest and an array of images are grabbed when the object is in motion at high speed. Any one of these images can then be used as the fifth image in the algorithm, thus allowing for calculation of phase change at any pixel at any instant of the motion of the surface The entire process is automated using labVIEW software, which was specifically designed for the task. Both in-plane and out-of-plane systems were developed and calibrated. The systems were used to generate phase maps of an object undergoing motions at relatively high speeds.
Armstrong, C. (2004). High-speed electronic speckle pattern interferometry. Masters dissertation. Technological University Dublin. doi:10.21427/D7MK79