Vibration monitoring using 2D speckle pattern images

A high speed data acquisition system has been developed for monitoring the speckle pattern produced by a fibredyne interferometer. The system captures data from a 256 element, linear, CCD array with sample frequencies of up to 18.5 k.Hz. Data from the system is in the form of a two dimensional image showing the variation in pixel intensity as a function of time. The system is used to address the speckle pattern produced by a fibredyne interferometer which is used as a vibration sensor. Information taken using this system is compared with the predictions of an existing theoretical model which indicates that all speckles should be affected by a vibration signal but, that the amplitude and phase of the resulting variations will be speckle dependent. Data taken using this system agrees with these predictions. All of the pixels in the CCD array show some variation when subjected to a sinusoidal vibration signal. The amplitude and phase of the pixel signals show a considerable variation in both amplitude and phase, indicating that the model is valid. By averaging the spectra obtained by performing a Fourier transform on each pixel it is possible to substantially reduce noise effects making the system more sensitive to changes in the acoustic signal.