A spiral electromagnetic acoustic transducer (EMAT) is efficient in eddy current generation and has been used for surface defect inspection using Rayleigh waves or thickness gauging based on plane waves in echo mode. Measured and calculated particle velocities and directivities are presented. It is found that the shear wave is not predominantly a plane wave. It has zero amplitude on the axis of the generation EMAT and has maximum amplitude at the critical angle. The shear wave could be used in the steel industry for both internal and surface defect inspections together with Rayleigh wave.

A pulsed laser to generate ultrasound has been used with an electromagnetic acoustic transducer (EMAT) to successfully detect ultrasonic waves for the fast online inspection of steel billets. Simulations of the ultrasonic signals have been performed by the finite element method to explain the laser-generated ultrasonic field and to compare it favourably with the signals detected by a water-cooled EMAT. With an understanding of the nature of the generated ultrasonic field, the separation between the laser and EMAT can be optimized for internal defect inspection using bulk waves and surface defect inspection, using Rayleigh waves, as the pulsed laser source can generate both these wave modes simultaneously.

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