A METHOD AND DEVICE FOR PHASE SHIFTED SHEAROGRAPHY
Outside the optics laboratory, shearography measurements in the field or under harsh industrial conditions require both an enhanced system and a reliable phase shift to reduce the environmental influences, so that a desired measurement can be carried out to analyze the surface of the target, locate flaws, and/or map the strain distribution etc. The common-path phase-shifting shearography system is promising for field measurements, because the two interfering beams propagate along es- sentially the same optical path, so the environmental influences are cancelled. However, this feature also makes it more difficult to introduce a varying phase shift in the system.
Generally, the piezoelectric transducer, Pockels cell, and liquid crystal modulator are commonly used to get a phase shifted shearogram. But the piezoelectric transducer involve mechanical movement and the Pockels cell, as well as the liquid crystal, are sensitive to the orientations of the optical com- ponents. Therefore, the proposed system is designed to address the concerns above.
The invention is a method and a system for obtaining a phase shifted shearogram. The captured she- arograms can be further turned into phase distribution by applying a conventional phase retrieval al- gorithms. There is no reference beam in the proposed system. The two object beams with orthogonal polarizations propagate along the same light path and interfere with each other at the image plane. The phases of the two object beams are phase shifted simultaneously inside the phase-shifting unit of the system. No moving parts are involved in the system and the amount of the phase shift between the two object beams is only determined by the phase-shifting unit, which means the phase shift is insen- sitive to the orientations of the optical components in the system. Hence, the invention provides an enhanced system with a reliable phase shift for field measurements. The invention is low-cost, robust, and easy to be implemented without much efforts to adjusting the optical components. The output speed of the invention could be at least video frame rate (≥24 fps), outperforming all state of the art shearographs.
- The novel shearograph allows for yet unreached full field measurements at video rate speed.
- The invention has superior anti-noise ability and requires less efforts to adjustment and main- tenance
- Shearography is widely used by leading manufacturers within Aerospace, Automotive, Wind Power, Marine, Aviation, Textile and similar composite related industries.
- Shearography technique provides a powerful tool for locating and quantifying flaws, such as Wrinkles, Disbonds, Delaminations, Cracks, Crushed core, Fluid ingress, Cracked cores, Repair defects, Voids, Foreign Objects, Impact damage and many more.
The technique has already been prototyped and a phase change map of a deformed target is recovered by using the phase shifted shearograms and Fourier transform.