Abstract
Permanent magnet is widely used as one of the three elements of electromagnetic acoustic transducer (magnet, coil, tested specimen). However, due to the immutability and non-uniformity of the permanent magnet magnetic field, the electromagnetic acoustic transducer (EMAT) will produce other unwanted modes, which will affect the purity of the targeted mode in signals. Therefore, the multi-mode problem of EMAT is still an important issue to be solved. In order to solve this problem, a new type of directional magnetic-concentrator-type electromagnetic acoustic transducer (D-MC-EMAT) is proposed to generate a single S0 mode in plates. The magnetic concentrator is added to the traditional EMAT to guide and concentrate the magnetic field generated by the magnet and remove the unwanted A0 mode. Both finite element simulation and experiments proved that the mode selectivity of proposed D-MC-EMAT improved by adding the magnetic concentrator, and transducer characteristics and defect inspection experiments were carried out. Finally, the structure of D-MC-EMAT was optimized by an orthogonal experiment and the optimal parameter combination was confirmed.
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