Research On Electronic Speckle Interference Information Extraction Method Based On Partial Differential Equations

In recent years, electronic speckle pattern interferometry (ESPI) is widely used for deformation measurement and nondestructive testing of optical rough surface. The displacements and deformation of the specimen can be computed from the phase of the electronic speckle fringe patterns. This thesis emphasizes the methods of skeleton extraction and phase interpolation for single ESPI fringe patterns, which are the key steps in ESPI phase extraction. The validity of the proposed method is verified by computer-simulated and experimentally obtained poor-quality ESPI fringe patterns.The proposed skeleton extraction method is based on the partial differential equation (PDE) and the divergence of the gradient vector field (GVF). In this thesis, the fringe orientation is applied in the anisotropic partial differential equation, and the GVF of the initial fringe is adjusted by this equation. This method can reserve the topological characters of the initial fringe well. The fringe skeletons are obtained through divergence analysis on the updated GVF. The experiments illustrate that the proposed method can work on the fringe patterns with the poor quality, different closed state and different density degree. The phase interpolation method based on the PDE regards the phase values on the fringe skeletons as a source of heat. The heat conduct equation is used for phase interpolation to obtain the whole-field phase values of the fringe patterns. The proposed method is simple, rapid and accurate. This thesis studies on the phase extraction method in the application of ESPI and designs the fringe pattern acquisition device. Then the methods of skeleton extraction and phase interpolation are used to extract the phase information of the fringe pattern obtained by the device. The proposed method is verified by computer-simulated and experimentally ESPI fringe patterns.