Ultrasonic guided wave imaging of a composite plate with air-coupled transducers

In recent years, air-coupled transducers have been widely used for bulk wave C-scan imaging of materials with low acoustic impedances. In this paper, a long range ultrasonic guided wave imaging method using air-coupled transducers is presented to identify impact delaminations in a carbon-epoxy composite plate. Two air-coupled transducers were used to generate and receive Lamb waves in the composite plate using a through transmission setup. The Lamb wave mode was controlled by tuning the angle of the incident wave. In the scanning processes, the two transducers were moved synchronously in the direction perpendicular to the Lamb wave path. The composite plate was scanned in 4 directions (0°, 45°, 90°, and -45° with respect to the fiber lay-up). The energy distribution of the Lamb wave ray in each scan direction was combined with a probabilistic damage detection concept for image reconstruction. The delaminations in the composite plate were detected and located in the reconstructed images, and the potential exists to size and determine the severity of these defects.