[3A3] Focused Lamb waves for sub-wavelength defect detection using EMATs
J Cregeen and R S Edwards
University of Warwick, UK
Ultrasonic inspection is routinely used to detect defects in a broad range of materials, including conductive materials such as aluminium, which offer the opportunity to use electromagnetic acoustic transducers (EMATs). EMATs can easily generate Lamb waves, which are useful for inspection over long distances. Larger wavelengths are advantageous as they are less attenuated, but are also less sensitive to small defects. Defects smaller than the incident wavelength can be challenging to resolve. This work presents an improvement to the wavelength limitation by demonstrating the detection of defects in 1 mm-thick aluminium sheets using geometrically focused EMATs. A single EMAT is used to generate and focus Lamb waves to a focal spot of approximately 2 × 3 mm. An array of focused and linear receiver EMATs allow for the detection of transmitted and reflected waves. The array is arranged such that transmission and reflection in the forward, reverse and perpendicular directions to the direction of wave propagation can be observed. B-scans of 0.5 mm-deep square defects of 30 mm and 5 mm width are presented and show good agreement with the actual defect size and position. Post-processing methods to improve the detection capabilities of this array are also presented.
