Development of a new EMAT for multi-helical SH guided waves based on magnetostrictive effect

Electromagnetic acoustic transducers (EMATs) have the advantage of non-contact and have been widely used in nondestructive testing (NDT). However, the propagation of the guided wave generated by present transducers is either concentrated with narrow beam directivity or omni-directional with disperse energy. To overcome these disadvantages, a new EMAT is proposed to generate multi-helical shear horizontal (MHSH) guided waves. The waves can propagate in multiple helical angles within a certain range while the energy is still concentrated. In this paper, the excitation and reception process of the guided wave are modeled based on the magnetostrictive effect, and then Finite Element Method (FEM) is applied to confirm the models and to further study the wave radiation pattern. Series of experiment are carried out to evaluate the performance of the proposed EMAT. Finally, the influences of two key design parameters on the beam divergence angle are discussed.