The multimode and dispersion characteristics of Lamb waves make them difficult to apply to nondestructive evaluation. This paper presents a paired configuration of a meander-line coil electromagnetic acoustic transducer (EMAT) to generate a single-mode symmetric and antisymmetric Lamb wave in aluminum plates. In the paired structure, the bias magnetic field of the EMAT that generates symmetric mode Lamb waves is perpendicular to the plate surface, while the bias magnetic field of the EMAT that generates antisymmetric Lamb waves is parallel to the plate surface. The symmetric and antisymmetric exciting forces generated by these two EMATs are consistent with the dispersion equations of single symmetric and antisymmetric Lamb wave modes, respectively. The numerical simulations and experiments verified that the presented paired configurations of meander-line coil EMATs can effectively control the generation of single-mode Lamb waves at low frequencies.

Mode analysis method based on finite element theory is proposed to plot dispersion curves in metal sheet. This method is implemented by adopting COMSOL software to numerically solve and plot the dispersion curves. Compared with results obtained by semi-analytical finite element method, the calculating results are basically consistent and the modal caused by mode blending is obtained, which proves the mode analysis method is effective. Finally, the wave structure characteristics of various models are analysed, this provides a basis for the application of ultrasonic guided wave testing.