Study of a spiral-coil EMAT for rail subsurface inspection.

The novelty of this paper is that a spiral-coil EMAT (electromagnetic acoustic transducer) is applied to rail subsurface inspection. To study the spiral-coil EMAT for rail subsurface inspection, the dominant mechanism is investigated emphatically. The interaction between the Lorentz-force mechanism and the magnetostriction mechanism is analyzed corresponding to the magnetic flux density and the frequency which has a significant effect on the magnetostriction mechanism. The effect of frequency on beam divergence is further discussed about the rail subsurface inspection using spiral-coil EMAT as well. A 2D FEM (finite element model) of spiral-coil EMAT is established and the simulation is carried out to analyze these issues. Besides, the experiments to inspect the subsurface crack of steel plate are carried out at various frequencies to verify the feasibility of the application. The experimental results demonstrate that the rail subsurface inspection by using the spiral-coil EMAT is feasible and the high frequency can contribute to distinguish the echo signal from the rail subsurface crack.