Electromagnetic acoustic transducers for guided-wave based robotic inspection

Ultrasonic guided waves can be used to produce structural images using techniques such as the reconstruction algorithm for probabilistic inspection of damage (RAPID), which is currently deployed using fixed piezoelectric transducers. Robotic inspection is an alternative for fast screening of large areas, but requires transducers which can easily be scanned. Electromagnetic acoustic transducers (EMATs) are non-contact and offer the potential for robotic implementation. They can be used to produce multiple guided wave modes, and in particular shear horizontal waves, which have been shown to be suitable for inspection of wall thinning in plates and pipes. Traditionally, EMATs contain large magnets which can cause difficulties for automated inspection using crawler robots when inspecting ferritic steel. We have developed miniaturised EMATs which have the benefit of reduced magnetic forces, alongside offering improved spatial resolution. The first steps towards application of such transducers on 10 mm thick steel have shown the potential for fast robotic screening of thickness, with mapping performed using the waves generated.