Based on the proper assumptions and approximations, the coupling mechanism of the electromagnetic acoustic transducer (EMAT) for ultrasonic generation within ferromagnetic material was studied by analyzing the eddy current distribution, Lorentz force, magnetostriction force and magnetization force. Some useful numerical calculations are presented to explain the EMAT behavior with general geometric arrangements. It is indicated that for the ferromagnetic material the magnetostriction effect dominates the EMAT phenomenon for ultrasonic wave generation in low magnetic field intensity, while the material does not reach its magnetizing saturation. But, with the increase of the bias magnetic field and saturation, the magnetostrictive terms will make no contributions to the ultrasonic generation and the Lorentz force becomes the only exciting mechanism. It is important to determine both the Lorentz and magnetostriction forces and select the appropriate working manner for achieving an optimized design.
