Synchronized reference updating technique for electronic speckle interferometry

In this paper, a video-based speckle interferometric method using a continuous reference updating technique is presented. Unlike conventional ESPI techniques, this method synchronizes the optical interferometric detection system with the acoustic stressing of the test object, and includes continuous renewal of the reference image. It is shown that the susceptibility of the method to environmental noise caused by vibration, temperature gradients, or thermal currents is substantially lower than that of conventional techniques. The application of this technique to the detection of defects in adhesively bonded structures is demonstrated.