Shearography Counter-Propagation Moving Platform Speckle Stability
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Solution Overview
Problem
Existing shearography techniques are unable to collect data from moving platforms such as aircraft, surface craft, or handheld devices due to changes in laser speckle patterns, which renders the data useless.
Innovation Solution
The implementation of counter propagation in a shearography system, where the laser illumination source moves in an equal and opposite direction to the receiver, allowing the system to collect data from a moving platform while preserving the speckle pattern, enabling coherent superposition of images and detection of surface deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the shearography system is mounted on a moving platform, then the system can collect data from remote or difficult-to-access targets, but the laser speckle pattern changes due to platform motion, rendering the data useless
Solution Approach 1:
The patent applies counter-propagation by moving the laser source in the opposite direction to the platform motion, effectively inverting the motion effect. This causes the speckle pattern to remain stationary relative to the target surface, preserving the interference fringes needed for shearography while allowing platform mobility
Solution Approach 2:
The patent changes the motion parameter of the laser source to be equal and opposite to the platform motion. By adjusting the laser source velocity to match and oppose the platform velocity, the relative motion between the illumination and target is compensated, maintaining speckle pattern stability
2Reliability
If the laser source and receiver are both stationary relative to the target, then the speckle pattern is preserved, but the system cannot move to different locations or perspectives
Solution Approach 1:
The patent uses counter-propagation where the laser source moves in the opposite direction to the platform motion, inverting the effect of platform movement on the speckle pattern. This allows the system to be mobile while maintaining speckle stability as if the source were stationary relative to the target
Solution Approach 2:
The patent transitions from a static to a dynamic system by allowing the laser source to move with controlled velocity. The source velocity is dynamically adjusted to match and oppose the platform motion, enabling mobility while preserving the optical measurement conditions
3Measurement precision
If image processing is applied to remove speckle noise, then the grainy structure is reduced, but the processing complexity and time increase
Solution Approach 1:
The patent converts the harmful effect of platform motion (which causes speckle pattern changes) into a beneficial counter-propagation motion of the laser source. This active compensation eliminates the need for post-processing speckle removal, as the speckle pattern is preserved in the first place
Solution Approach 2:
The patent applies preliminary action by compensating for platform motion through counter-propagation before the shearography measurement is taken. This prevents speckle pattern degradation at the source, eliminating the need for subsequent image processing to remove speckle noise
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 allows for effective detection of anomalies on a moving platform by preserving the speckle pattern, resulting in improved fringe contrast and signal-to-noise ratio, enabling accurate imaging of surface deformations even from a moving vehicle.
Implementation Method 1
a surface being observed is illuminated by an expanding laser beam
Implementation Method 2
The two images are each laterally displaced images taken of the surface of the part being observed and the two images are coherently superposed
Implementation Method 3
The two images taken are processed together to produce a third image showing a fringe pattern that depicts the gradient of the displacement of the surface
Implementation Method 4
shearography is an optical measuring technique using coherent light
Data Source
AI summary
A shearography system that operates while moving at significant speeds over a surface is disclosed. Two lasers are utilized and the distance between the two lasers is adjusted based on the altitude of the aircraft on which the shearography equipment is located, the speed of the aircraft, the distance between two lasers in the shearography equipment lasers, and the time difference between the laser pulses from each of the two lasers. The adjustment of the distance between the two lasers causes the angles of incidence and reflection to be the same for two sequential images and permits the moving shearography to work.