Shearography Interferometer Layout for Variable Shear Control
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Solution Overview
Problem
Conventional shearography systems struggle with adaptability to parts having different surface variations, as they are not readily adjustable to maintain a constant fringe frequency during shear adjustments.
Innovation Solution
The placement of an interferometer at or near the pupil plane of an imaging optical system allows for varying shear while keeping the fringe frequency substantially constant, using components like a Wollaston prism or polarization grating to adjust shear without significantly changing the fringe frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If shear magnitude is adjusted in conventional shearography systems, then adaptability to different surface variations is improved, but fringe frequency changes significantly requiring reconfiguration
Solution Approach 1:
The system separates the control of shear magnitude and fringe frequency into independent components. The Wollaston prism controls shear magnitude through translation, while the diffraction grating maintains fixed fringe frequency through angular diffraction. This segmentation allows independent adjustment of shear without affecting fringe frequency, resolving the contradiction between adaptability and reconfiguration complexity.
Solution Approach 2:
The system introduces dynamic adjustability of shear magnitude through translation of the Wollaston prism while maintaining static fringe frequency. The translation distance of the Wollaston prism directly controls the shear magnitude, enabling real-time adaptation to different surface variations without requiring system reconfiguration, thus improving adaptability while reducing complexity.
2Measurement precision
If shear is introduced at a particular carrier frequency in conventional systems, then measurement capability is achieved, but the system is not readily adaptable to parts having different kinds of surface variations
Solution Approach 1:
The system achieves multi-functionality by enabling the same optical configuration to measure different types of surface variations (out-of-plane displacement, in-plane displacement, curvature) through adjustable shear magnitude. The Wollaston prism translation mechanism allows the system to adapt to various measurement requirements while maintaining the same carrier frequency, thus improving versatility without sacrificing measurement precision.
Solution Approach 2:
The system changes the shear magnitude parameter through Wollaston prism translation while keeping the carrier frequency parameter constant. This parameter change approach allows adaptation to different surface variations by adjusting only the shear magnitude, maintaining measurement precision across different application types without requiring system reconfiguration.
3Length of moving object
If an interferometer is placed away from the pupil plane to adjust shear, then shear magnitude can be varied, but fringe frequency changes significantly
Solution Approach 1:
The Wollaston prism acts as an intermediary element that introduces shear magnitude through translation while the diffraction grating serves as another intermediary that maintains fixed fringe frequency through angular diffraction. This intermediary approach allows independent control of shear magnitude without affecting fringe frequency stability, resolving the contradiction between shear adjustment and frequency stability.
Solution Approach 2:
The system controls shear magnitude through translation in one dimension (prism position) while fringe frequency is determined by diffraction angle in another dimension. This dimensional separation allows independent adjustment of shear magnitude without affecting fringe frequency, achieving both variable shear and stable frequency simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables shearography systems to maintain a fixed fringe frequency while allowing for variable shear magnitude, enhancing their adaptability to different surface variations and reducing the need for reconfiguration when adjusting shear for different applications.
Implementation Method 1
a Wollaston prism or a polarization grating (PG) are configured to be translated with respect to a fringe sensor to adjust shear while angular deviations produced by the Wollaston or diffraction angles of the PG determine fringe frequency
Implementation Method 2
a Wollaston prism or a polarization grating (PG) are configured to be translated with respect to a fringe sensor to adjust shear while angular deviations produced by the Wollaston or diffraction angles of the PG determine fringe frequency
Implementation Method 3
an interferometer placed at or near a pupil plane of an imaging optical system is used to vary shear. Placement at or near the pupil plane substantially reduces or eliminates changes in fringe frequency
Data Source
AI summary
Shearography systems provide independent setting of fringe frequency and shear magnitude by situating an interferometer with a tiltable reflector proximate a pupil plane of an imaging optical system. Fringe frequency can be selected based on a modified Savart plate. In other examples, a Wollaston prism or a polarization grating is translated with respect to an image sensor to vary shear magnitude while maintaining a substantially fixed fringe frequency.