From Event: SPIE Optical Engineering + Applications, 2017
The increasing industry demand for specialized materials promotes a breakthrough in material engineering. In this context, composite materials have gained recognition and have been increasingly employed in the most diverse segments of the industry. When applied to equipment with structural requirements, it is fundamentally important to periodically inspect these materials to ensure their integrity and safety. Often inspections are performed in the field, under unstable conditions generated by operational and environmental factors. Shearography is a valuable method of nondestructive testing (NDT) for industrial applications. This optical technique is less sensitive to environmental disturbances when compared to other interferometric techniques. This paper presents a new shearography configuration based on Diffractive Optical Elements (DOE). In the proposed configuration, a diffraction grating is positioned between the camera sensor and the imaging lens. Therefore, a more compact and robust system is obtained. Another advantage of the proposed system is related to phase shifting, which is generated by the lateral movement of the diffraction grating. Thus, phase shifting is relative to the diffraction grating period and not the laser wavelength as in traditional interferometers. This feature makes the system insensitive to variations in laser wavelengths. Since the period of the diffraction grating used is about 60 times greater than the laser wavelength applied, the shearography system using diffraction grating becomes much more robust for external influences compared to other configurations based on the Michelson interferometer. This paper also presents the evaluation of the proposed shearography system as well as prospective steps.
Fabio A. A. da Silva, Daniel Willemann, Analucia V. Fantin, Mauro Benedet, Sérgio D. Soares, and Armando Albertazzi, "Robust shearography system for inspection of defects in composite material using diffractive optics," Proc. SPIE 10376, Novel Optical Systems Design and Optimization XX, 103760O (Presented at SPIE Optical Engineering + Applications: August 10, 2017; Published: 24 August 2017); https://doi.org/10.1117/12.2274138.
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