Characteristic research and analysis of EMAT's transduction efficiency for surface detection of aluminum plate

Electromagnetic acoustic technique possesses many distinct advantages, such as being free of couplant, no requirement of test-piece preconditioning, and being able to excite pure surface acoustic wave, etc. It can effectively detect the surface and subsurface quality of aluminum plates, which is quite hard for the traditional piezoelectric technique. However, the deficiency of designing theories of electromagnetic acoustic transducers (EMATs) leads to poor transduction efficiency of the transducers. Combining the practical detection requirements of aluminum plates, this paper built mathematical model of EMATs. Based on simulation of the model, we analyzed the distribution regularity of the eddy current, magnetic field, and Lorentz force produced by a surface wave EMAT. By studying the influence of EMAT parameters on the energy of the excited surface wave, we obtained the relationship between main structural parameters of the EMAT and the transducer's transduction efficiency, which indicates that, the decrease of lift-off distance, coil conductor's width, magnet's length and width, and the increase of magnet's thickness could effectively improve the transduction efficiency of the EMAT. Ultimately, validity and accuracy of the model was verified by experiment.