Research And Application Of Phase Extraction From A Single Electronic Speckle Pattern Interferometry Fringe Pattern

The method of electronic speckle pattern interferometry (ESPI) is one of the modern optical measurement techniques. Compared with traditional methods, it has the merits of non-contact, high measurement accuracy and no special process of the surface, so it is widely applied to deformation measurement and non-destructive test of optical rough surface.Accurate extraction of phase information is fundamental importance for the successful application of ESPI in obtaining phase information of object deformation. This paper mainly studies the methods of phase extraction from a single ESPI fringe pattern.This paper proposes an ESPI phase extraction method based on BP neural network. To test the validity of this method in ESPI phase extraction, the method is applied to the patterns generated by computer simulation and patterns obtained by experiment. After the process of filtering, binarization, Hilditch thinning, The phase values are successfully extracted by using the neural network method, the neural network method has three advantages: First, the precision of this method is higher than that of the traditional interpolation. Second, the method is not only applied to the open-fringe patterns but also to the closed-fringe patterns. Third, the full-field phase can be obtained from the broken skeletons. The method is an effective ESPI phase extraction method and it is valuable in application.The Fourier-transform method can extract the phase map from only a single fringe pattern.However, for the closed-fringe patterns, it has to estimate the phase by the conventional Fourier-transform method with the carrier. A modified Fourier- transform technique that is applied to the phase extraction from the closed-fringe pattern is proposed. It adopts the coordinate transform method. First, the closed-fringe pattern is converted to an open-fringe pattern by transformation of the Cartesian coordinate system to a polar coordinate system. Then the phase extraction from the open-fringe interferogram is achieved by the Fourier-transform method. The full-field phase of the original closed-fringe pattern is obtained by inverse coordinate transfor- mation. With the new method , the phase values can be extracted from a single fringe-pattern without the need of carrier. Through the process of a closed-fringe pattern obtained by Computer simulation, the results show that the proposed techni- que has very high accuracy and is valid in phase extraction.