This work is mainly to describe the phenomenon at low frequency in my
previous publication. In this paper, the impact of the magnetostriction
mechanism is taken into consideration for the main idea. The
axisymmetric FEM model of the spiral-coil EMAT is established to
implement the simulation. With the help of the simulation, it is
demonstrated that the directivity of ultrasonic wave can be manipulated
by frequency. And it is found that the direction of Lorentz force that
dominates in the rail varies with time, but the magnetostrictive force
compels the ultrasonic wave mainly generated by the Lorentz force to the
axis. This describes well that the power of two combined mechanisms is
greater than that of only the Lorentz-force mechanism at low frequency.