Abstract
An electromagnetic acoustic transducer (EMAT) is suitable for measuring the propagation time more accurately without causing abrasion to the transducer during testing due to the principle of its excitation. This work designs a flux-concentrating EMAT with a radial-flux-focusing permanent magnet to significantly enhance static magnetic field strength. Through theoretical analysis and finite element simulation, two kinds of coils are designed according to the concentration areas of the horizontal and vertical components of the magnetic field. One is used to generate pure longitudinal waves, and the other is used to generate both longitudinal waves and shear waves. The experimental comparison shows that the amplitudes of the pure longitudinal wave and the dual-mode wave excited by the two kinds of coils with the radial-flux-focusing magnet are more than two times higher than those with the ordinary magnet. Therefore, the flux-concentrating EMAT with the appropriate coil provides an insight into realizing more accurate detection where longitudinal wave detection is required.
Highlights
Electromagnetic acoustic transducers (EMATs) are widely used in the field of nondestructive testing (NDT), and have the superiority of non-contact and no couplant with the specimen [1]
The middle echo, which appears after the first longitudinal wave reaches the bottom at 7 μs, is the shear wave according to the snapshots and propagating time
We found a wave peak between two adjacent bottom echoes, which was concluded from the simulation, as the shear wave signal was generated by the wave mode transformation whenFlux-concentrating the longitudinal wave reflected through
Summary
Pure Longitudinal EMAT by Using a Keywords: electromagnetic acoustic transducer; longitudinal wave; flux-concentrating; transducer design.
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