Design of A Rayleigh wave EMAT by using Racetrack Coil and Periodic Permanent Magnets

Rayleigh waves are widely used for the detection and characterization of defects nearby the surface in the modern industries. Electromagnetic acoustic transducers (EMATs) have received extensive attention because of the lack of physical coupling. However, the main drawback of the inefficiency in generating and receiving ultrasonic waves restricts the extension and application of Rayleigh wave EMAT. This article proposes a type of Rayleigh wave electromagnetic acoustic transducer, which is consisted of a racetrack coil and a group of periodic permanent magnet array with a special configuration. The configuration of PPMs in the proposed EMAT is different from that in the common sheared-horizontal wave EMATs. The magnet units are magnetization along the width direction. The racetrack coil generates eddy current, and the periodic permanent magnet array provides bias static magnetic fields. The directions of generated Lorentz forces depend on the relative position between the magnet units and the conductors. The center frequency of the generated guided waves depends on the distance between the adjacent magnet units. In 2D FE simulations, different models were established, and the generation efficiencies for Rayleigh wave of vertical and horizontal Lorentz forces were compared. In the experiments, the guided wave EMAT, generating both horizontal and vertical Lorentz forces, was fabricated and used in the experiment system. The results prove the performance of the proposed EMAT for the effective generation Rayleigh waves.