Development of a Longitudinal Wave EMAT With High Conversion Efficiency

Until now, most of the bulk-wave electromagnetic acoustic transducers (EMATs) are developed for shear wave (S-wave) testing. This article presents the development of new longitudinal wave (L-wave) EMATs with high conversion efficiency by using a new magnetic configuration and a meander-line coil. The new magnetic configuration consists of several rectangular magnets arranged face to face to generate a strong horizontal magnetic field in periodical distribution under the magnets. By using the meander-line coil under the magnets, a strong L-wave can be generated and detected. The new EMATs have been characterized and optimized using numerical simulation methods. Simulation results show that the flux density of the horizontal magnetic field of the new EMATs can be increased by a factor of ~4.7, compared with that of the conventional U-type magnet. So, the conversion efficiency for L-wave generation and detection can be significantly improved. Finally, experimental measurement and comparison with the current L-wave EMATs with the U-type magnet have also been carried out. The experimental results have confirmed that the signal amplitude of the new L-wave EMATs is increased by a factor of ~8.3.