A modified WFT for shape and deformation measurement

Abstract

Time-frequency analysis is widely applied to the optical measurement for phase retrieval from fringe patterns. Windowed Fourier transform (WFT) is one of the time-frequency analysis methods and has recently received extensive study on phase retrieval from fringe patterns generated by the optical interferometry or structured light illumination. WFT has been applied for shape and deformation measurement in dynamic nondestructive testing. However, the computation time of WFT is longer than that of conventional Fourier transform method for fringe demodulation. This has restricted the WFT in the application for dynamic measurement. Therefore, a modified WFT is introduced to reduce the computation time. In this approach, the fast Fourier transform is implemented in the WFT algorithm to improve the computational efficiency and border effect of the proposed method for fringe analysis is discussed. The phase retrieval of the proposed method is simulated and the simulation results are compared with conventional Fourier transform method and convolution method of WFT in terms of noise reduction. The experimental work on shape and deformation measurement is conducted to verify the effectiveness and validity of the proposed method.