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The Comparison of Several Filtering Methods for ESPI and Research on Speckle Information Extraction Based on RBF

Author: WangLinLin
Tutor: TangChen
School: Tianjin University
Course: Detection Technology and Automation
Keywords: electronic speckle pattern interferometry digital specklecorrelation method information extraction partial differential equations radial basisfunction
CLC: TB302.5
Type: PhD thesis
Year: 2012
Downloads: 13
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Abstract

Optical measurement technology as a kind of whole-field, non-contactnondestructive measurement technique, has permeated into many fields of scientificand engineering. Electronic speckle pattern interferometry (ESPI) technology anddigital speckle correlation method (DSCM) are two kinds of commonly used opticalmeasurement technology. Information extraction with high accuracy is of fundamentalto optical measurement technology. In this paper some key problems to these twotechniques in information extraction are studied. ESPI measurement delive themeasurement results in the form of fringe patterns or phase patterns, both fringepatterns and phase patterns contain heavy speckle noise, which hampers the extractionof phase information seriously. Therefore, how to reduce the influence of specklenoise effectively, and improve the contrast of the fringe has become one key issue toESPI measurement technology. DSCM acquires the displacements of the testspecimen by use of correlation algorithm. The performance of the correlationalgorithm makes influence on the measurement accuracy and real-timing directly.Improving computing efficiency and accuracy is the key problem in this technique.The work in this dissertation is as follows:(1) The filtering model based on partial differential equation is an effective toolin ESPI filtering. Six non-orientation and two orientation partial differentialequation filtering models are analyzed and compared, and the feature of eachpartial differential equation filtering model and their respective flexibility aresummarized.(2) By use of the analyzing and comparing the eight PDE filtering model, theresult indicates that the second-order oriented PDE model is the mosteffective model. This PDE model is analyzed and compared with severalother representative and recent ESPI filtering methods, mainly including thewindowed Fourier transform method (WFF), the oriented, regularizedquadratic cost function (ORQCF) method, the oriented spatial filter masks(OSFM) and the localized Fourier transform filter (LFF). The summary ofthe performance for these filtering methods are presented.(3) Introducing the Radial basis function(RBF) to ESPI information extraction, mainly including: the new filtering method based on radial basis function forESPI fringe patterns with wide density; introducing the radial basis functionto interpolate the number of fringe in the fringe skeleton method; smoothingthe phase acquired by phase unwrapping algorithm by use of the radial basisfunction. By use of the information extraction method based on RBF, thethermal deformation of the Al2O3ceramic substrate at different moment ismeasured on the circumstance of laser radiation.(4) A new method for displacement field analysis based on the combination ofDSCM with RBF interpolation is proposed. The ability to approximatescattered data make this method has the advantage with better accuracy andless computational time. Another advantage is that this method does notrequire any smoothing algorithm to process the discrete displacement fielddata obtained. Using this method, the displacement fields for rigid bodytranslation and three-point bending are analyzed, the accurate displacementfields are acquired.

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