VIBRATION MONITORING BY FIBER OPTIC FRINGE PROJECTION AND FOURIER-TRANSFORM ANALYSIS

A fiber optic fringe projection interferometer is proposed to obtain l ocal amplitude vibration of a diffuse surface. A sinusoidal fringe pat tern is projected onto the vibrating surface by an optical fiber versi on of Young's interferometer. An image of this surface is captured by a CCD camera and fed to a PC through a frame grabber and hence display ed onto a TV monitor. The visibility of the interference pattern is mo dulated by a function of the local amplitude of vibration. Thus loci o f constant vibrational amplitude can be directly observed as regions o f low fringe visibility in the image of the surface. A quantitative an alysis is performed by a Fast Fourier Transform (FFT) algorithm. Exper imental results in agreement with the theory are presented.