Digital Speckle Pattern Interferometer for Measuring Micro Deformation Area

Nondestructive testing(NDT) and inspection of structural materials are becoming increasingly important to assure the safety level in the present industries. Nondestructive measuring techniques using an optical interferometer have emerged as a valuable tool for many industrial applications. This non-contact optical method is a full-field measurement technique with high speed. Recently, by virtue of the development of electronic technologies, a digital speckle pattern interferometer (DSPI) has been highly developed and widely used in many engineering applications to measure the deformation area of objects. The great advantage of this system is that the data processing can be done easily in real time and can provide highly accurate deformation data by using phase-analyzing techniques. In this paper, a DSPI based on remote communication is developed on a movable table for measuring 3D deformation of an object. Wrapped phase data of the deformed area can be measured by acquiring phase shifted fringe images. The 3D deformation phase image can be extracted by applying an unwrapping algorithm to the wrapped phase data. Usually, many impulse pattern noises are included in the acquired wrapped phase image because these are produced from the interfered speckle pattern fringes. We developed an efficient phase unwrapping algorithm by developing an efficient removing filter. This filter is designed and applied to a phase map image that efficiently removes impulse noises. The filter improves the extracting efficiency of the phase information around the wrapping area. A fast unwrapping algorithm based on the discrete cosine transform (DCT) is adopted. The hardware and software configurations of the developed DSPI are described in this paper