Optimization algorithms for ultrasonic array Imaging in homogeneous anisotropic steel components with unknown properties

Abstract : In this paper, we investigate the ability of an adaptive ultrasonic method to image point-like reflectors inside anisotropic and homogeneous nuclear steels with unknown properties, such as V-shape welds or cladded components. The optimization scheme combines the Total Focusing Method (TFM) imaging algorithm with a customized gradient ascent method to improve both the quality and the reliability of ultrasound images. A statistical analysis of its robustness is performed with simulated echoes and using a surrogate model to speed up the computation times of the TFM images. Then, the optimization procedure is evaluated with several experimental cases and provides highly enhanced images with a 5 MHz array. The positioning of the artificial defects of 2.0 mm diameter is estimated with less than 1 mm error with respect to their actual position, and the signal-to-noise ratio is increased by up to 10 dB. The elastic properties are also estimated with less than 10% error when compared to their actual values.