Analytical Model and Analysis of Spiral-Coil EMAT Above a Ferromagnetic Plate

To further study the dominant mechanism, this article utilizes the analytical model to analyze the spiral-coil electromagnetic acoustic transducer (EMAT) above a ferromagnetic plate. The analytical model includes the spiral coil as well as the sintered NdFeB (S-NdFeB) permanent magnet (PM) whose analytical solutions inside the ferromagnetic material are rarely presented relative to the coil. Because of this point, this article presents the analytical model for S-NdFeB PM by the equivalent ampere current to compute the magnetic-flux density and compare the computational results with that by finite-element method (FEM) and measurement. The comparison shows that the analytical model is valid to analyze the spiral-coil EMATs. Based on the analytical model, both Lorentz force and magnetostrictive force are computed and compared, as well. Finally, it is found that the Lorentz force is a dominant mechanism in spiral-coil EMATs, which is verified by the experimental result.