Miniaturised SH EMATs for fast robotic screening of wall thinning in steel plates

Trushkevych, O and Tabatabaeipour, M and Dixon, S and Potter, MDG and Dobie, G and MacLeod, C and Edwards, RS (2020) Miniaturised SH EMATs for fast robotic screening of wall thinning in steel plates. IEEE Sensors Journal. ISSN 1530-437X

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    Electromagnetic acoustic transducers (EMATs) are well suited to generating and detecting a variety of different ultrasonic wavemodes, without the need for couplant, and they can be operated through some coatings. EMATs can be used to generate shear horizontal (SH) waves, which show promise for fast screening of wall thinning and other defects. However, commercial SH-wave EMATs are not suitable for robotic implementation on ferritic steel due to the large magnetic drag force from the magnets. This paper describes the design and characterisation of miniaturised SH-wave EMATs, which significantly reduce the magnetic drag and enable mounting onto a small crawler robot for sample scanning. The performance of the miniaturised EMATs is characterised and compared to a commercial EMAT. It is shown that signal to noise ratio is reduced, but remains within a suitable range. The bandwidth and directivity are increased, depending on the exact design used. Their ability to detect flat bottomed holes mimicking wall thinning is also tested.