Strain measurement by ultrasonic speckle technique based on adaptive genetic algorithm

Abstract

By comparing the unloaded and loaded ultrasonic speckle fields with cross-correlation, ultrasonic speckle technique can be applied to measure displacements and strains on the surface which is perpendicular to the propagation direction of ultrasound. Based on the adaptive genetic algorithm, the ultrasonic speckle measurement technique has higher efficiency and less measurement errors than the existing ultrasonic speckle correlation method. By adjusting genetic parameters through the adaptive mechanism, the adaptive genetic algorithm searches for the maximum value among the whole distribution of correlation coefficients efficiently. In this study on displacement measurements of an inner surface of an underwater object, the results obtained with different algorithms, including the adaptive genetic, coarse-fine interpolation and hill-climbing searching algorithms, were compared with each other. It was clear that the adaptive genetic algorithm outperformed other methods in computational time and accuracy. Considering above findings and the penetration of ultrasound, one can measure the strain of an inner surface of an underwater object using the ultrasonic speckle measurement technique based on adaptive genetic algorithm. This idea was proved by the good agreement of the measured strain with the corresponding simulation results from finite element analysis.