Guided Ultrasonic Wave Imaging for Immersed Plates Based on Wavelet Transform and Probabilistic Analysis

We propose a nondestructive evaluation method for immersed structures based on the propagation of ultrasonic waves induced by means of laser pulses and detected with an array of immersion transducers. In the study presented in this article, a laser operating at 532 nm is employed to excite leaky guided waves on an aluminum plate immersed in water. An array of immersion transducers is used to record the waves radiating from the laser-illuminated point. The detected signals are processed with an imaging algorithm based on continuous wavelet transform and probabilistic analysis to localize the presence of artificial defects machined in the plate. With respect to the existing imaging methods for plates, the proposed algorithm is pseudo baseline free, because it does not require data recorded from a pristine plate, but it requires that only a portion of the plate is free from defects. We find that the proposed algorithm enables the detection of surface cracks. Advantages and limitations of the algorithm for the nondestructive evaluation of underwater structures are discussed.