On the use of an array of ultrasonic immersion transducers for the nondestructive testing of immersed plates

Abstract

This paper presents the results of an experimental study in which guided ultrasonic waves were used for the nondestructive evaluation of an aluminium plate immersed in water. Leaky Lamb waves were generated using a spherical focused transducer, and detected by five immersion transducers arranged in a semi-circular array. The signals were processed to extract seven damage-sensitive features from the time, frequency and joint time–frequency domains. These features were then fed to an unsupervised learning algorithm based on the outlier analysis to identify the presence of defects artificially devised on the plate. We found that the array of immersion transducers and the signal processing technique enable the detection of the defects with a success rate close to 95%.