強磁性体内での電磁気力による体積波発生のメカニズム

抄録

Bulk-wave generation in plates of aluminum, stainless steel, and carbon steel by a spiral elongated coil and a static magnetic field is analyzed experimentally and numerically. First, the field dependences of the wave amplitudes are investigated using the electromagnetic acoustic resonance (EMAR). The magnetic field is applied parallel to the sample surface. A theoretical model developed to explain the considerable difference in the field dependence between nonmagnetic and ferromagnetic metals is presented, which shows the dominant contribution of the magnetostrictive forces to bulk wave generation in ferromagnetic metal rather than the Lorentz force and the magnetization force, especially in the shear wave generation. The model is further developed by the FEM simulation of the two-dimensional body force profile within the metal. The simulation is Performed for a practical bulk-wave electromagnetic acoustic transducer (BW-EMAT), which has an elongated coil and a pair of permanent magnets of the coil. The calculation strictly predicts several important features of the BW-EMAT, and has significant implications for the practical use of the EMAT.