Defect detection is an important part of heritage conservation and speckle pattern interferometry is a common technique for inspecting surface and internal defects. A speckle pattern interferometry coupled with pulsed laser system for non-destructive detection and prediction of different size cracks is introduced and tested. According to photoacoustic effect, ultrasonic waves are generated by pumping a pulsed laser beam to the rear surface of the sample. The ultrasonic waves serve as carrier propagating from the rear surface to the front, thus conveying deformation and crack size information. For obtaining information about simulated crack size, the front surface is detected by a speckle pattern interferometry system. And simultaneously, the generated ultrasound waves are detected by air-coupled transducer. In this study, the introduced system and method were validated by detecting medium density fiberboards with simulated cracks of different width and depth. Differentiated speckle pattern and ultrasound signals are compared and combined to indicate crack presence and to figure out different crack size qualitatively.
Microelectromechanical systems (MEMS) are electronic devices with movable micromechanical structures, which possess morphology and deformation in scales difficult to observe by traditional microscopic methods. In this paper, the surface morphology and deformation value of MEMS with complex structure was recovered by digital holographic technology, and the high precision detection of MEMS was realized. The local magnification was carried out through the microscope objective lens, and the magnification was calibrated by the resolution test chart. Due to the introduction of spherical wave by the magnification of the objective lens, this paper carried out the elimination of the quadratic term error. The shape of the comb tooth was reconstructed by setting a mask in the phase disturbance area. The deformation of the surface before and after voltage applied was measured, and the actual displacement deformation value was solved.
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