Measurement of underwater vibration by ultrasonic speckle stroboscopic technique

Abstract

Ultrasonic speckles are widely used in medical imaging, but are not commonly accepted in industry. An ultrasonic speckle stroboscopic technique for industrial applications is introduced in this manuscript. In this technique, a whole field ultrasonic speckle image converter is no longer needed as in B-mode scanning, and neither is the process of searching for the maximum correlation coefficient among sub-sets in the ultrasonic speckle field. In pulse-echo working mode, by the modulation of sweeping frequency and trigger delay and performing a digital speckle correlation calculation, it can be obtained point-to-point the vibration frequency, amplitude and phase difference of underwater solid surfaces. Compared with traditional vibration measurement techniques, ultrasonic speckle stroboscopic technique can perform on-line, underwater, noncontact experiments, and is insensitive to the environment and the sample surface roughness. In this manuscript this technique was applied to a vibrating cantilever underwater. The experimental results were in good agreement with other testing methods. Therefore, the noncontact testing technique for vibration coefficient, especially the vibration phase difference, provides an alternative method for the mode analysis of industrial constructions, which is a piece of very important work for industrial underwater structure design.