Sensitive testing of small surface cracks with Rayleigh wave polarisation by a 2D EMAT

In this paper, a non-contact and highly sensitive ultrasonic testing method based on measuring Rayleigh wave polarisation (RWP) by a new two-dimensional electromagnetic acoustic transducer (EMAT), which refers to its ability to measure two displacement components, is developed for small surface crack inspection in metal structures. The specially designed two-dimensional EMAT with face-to-face magnet configuration and two signal receiving coils can measure the out-of-plane and in-plane components of the Rayleigh wave simultaneously. The change of the Rayleigh wave polarisation parameter caused by the small surface cracks is simulated and measured by the two-dimensional EMAT. The experiment results confirm that the proposed method can be used to inspect very small surface cracks with depth of approximately 0.1 mm, which cannot be detected by the conventional electromagnetic acoustic testing method.