Vibration Measurement with Electrical Speckle Shearing Pattern Interferometry

Electrical speckle shearing pattern interferometry (ESSPI), being a kind of high-precision noncontact real-time measurement method in the whole field, has been used in the field of deformation measurement and harmonic vibration measurement deviating from rough object plane in the optical scale. The method can also be used in the field of nondestructive test (NDT). Two general methods, time-average methods and stroboscopic method, are studied to measure harmonic vibration deviating from object plane and corresponding mathematical models of electrical speckle shearing interfering stripes distribution are set up based on the theory of statistical optics. The vibration measuring system based on ESSPI is designed and the experiments are done to verify measurement availability of the above two methods. The experiment results with time-average method and those with stroboscopic method are compared to prove the following conclusions. The contrast of speckle stripes in electrical speckle shearing interfering stripe images with time-average method is decreased obviously with increase of the stripes level and therefore the time-average method is generally used in qualitative analysis of vibration. The speckle stripes quality in the electrical speckle shearing interfering stripe images with stroboscopic method is better than that with time-average method and the instant vibration distribution can be analyzed quantitatively with stroboscopic method too.