An Innovative Phase Shifting System for Non-Destructive Testing

ABSTRACTPhase shifting technique is one of the most important technologies in the metrology field. Simply by performing an interferogram measurement, and then adopting the phase shifting technique to unwrap the interferogram into a phase map, tasks such as object surface profile reconstruction, holographic interferometry, electronic speckle pattern interferometry, etc., can all be easily accomplished. An innovative phase shifting system, which uses piezoelectric actuators to execute phase shifting first and then implementing a cellular automata algorithm to unwrap phase data, was designed, built, and tested. Since cellular automata is a true parallel process, and noise appearing within the interferogram will not get propagated, this novel system is far more robust than the systems based on the traditional path following phase-unwrapping algorithm. In addition, this new algorithm also provides us with a way to adopt phase-masks within the cellular automata implementations of the phase unwrap operations. All these newly developed techniques make this newly developed system adaptable to many metrology applications, even when high noise is present or when lateral shear exists within the image field. The successful incorporation of the phase-mask approach into the cellular automata phase unwrapping algorithm essentially makes this newly developed system adaptable to take phase map measurements in many practical applications.