A Compact Digital Phase-Stepping Shearography System

Electronic shearography has proven to be a valuable tool in nondestructive evaluation. With this technique, correlation fringes corresponding to a deformation or movement of an object are produced electronically. In general, these correlation fringes are composed of random intensity fluctuations due to speckle, making it difficult to analyze the fringes and calculate the phase distribution accurately. If such quantitative information regarding the object is desired, direct interpretation of the fringe pattern is often attempted. Although various methods have been devised to accomplish this task, manual fringe counting is still often performed—a tedious job requiring much operator experience, yielding sparse data, and usually producing inaccurate results