Vibration analysis with pinhole confocal technique

A pinhole confocal imaging system is developed to measure both frequency and amplitude of harmonic vibrations. The optical depth discrimination capability of confocal imaging is utilized to detect and measure vibrations. The beam is focused on to the vibrating surface and the change in intensity resulting from defocusing due to vibration is used to determine the vibration amplitude. The frequency is determined from temporal change in intensity. The instrument could be extended to measure nonharmonic vibrations by incorporating Fourier analysis algorithm. A vibrating speaker was used as the object and tests were carried out with the present setup and vibration amplitudes were measured with an accuracy of 0.014 mm .