Microscopic Modelling for EMAT in Ferromagnetic Materials

There are three main mechanisms in the transduction process of ferromagnetic material electromagnetic acoustic transducers (EMAT), Lorentz force, magnetization force, and magnetostriction, among which the modeling of magnetostriction is insufficient. Since the change of the magnetic flux density always lags behind the change of the magnetic field, and the magnetization process is nonlinear, the electromagnetic acoustic transducer cannot be well described. Moreover, the use of high-frequency excitation in the electromagnetic acoustic transducer causes the magnetization process to be dynamic magnetization process, and it cannot be simply approximated via a hysteresis loop. The main work of this paper is to establish an electromagnetic acoustic transducer model suitable for ferromagnetic materials, and to dedicate to describe the nonlinear process of the magnetostriction from a microscopic point of view. On top of this, the dynamic magnetization process is considered under certain conditions. The model was validated by finite element simulations, and the results agreed well with the model.