Study of magnetic pole materials for static magnetic field and dynamic magnetic field that compose an electromagnetic acoustic transducer for Lamb waves using the magnetostriction effect

Abstract

For the purpose of strengthening the mechanical and thermal properties of an electromagnetic acoustic transducer (EMAT) for a Lamb wave, we considered changing the air-core electromagnetic induction coil that composes an EMAT to a structure in which a conducting wire is wound around a ferromagnetic material. Initially, as a ferromagnetic material, the structure was constructed in which an electromagnetic induction coil for a static magnetic field and an electromagnetic induction coil for a dynamic magnetic field were wound up and down on the same pole made of low carbon steel. As a result, the transmitted signal could be confirmed. Furthermore, in order to improve the received signal amplitude, we evaluated a structure that separates the magnetic poles for the static magnetic field and the magnetic poles for the dynamic magnetic field, and confirmed that the received signal amplitude can be improved. The purpose of this study is to determine the best combination and the structure of the steel, pure iron, PB perm alloy, and PC perm alloy as magnetic pole materials based on the results of this research. In the steel, pure iron, PB perm alloy, and PC perm alloy, when the material itself is not magnetized, the relative permeability decreases in the order of the PC perm alloy, PB perm alloy, pure iron, and steel. However, when the material itself is magnetized, the relative permeability decreases, and the degree of the decrease is reduced in the order of the PC perm alloy, PB perm alloy, pure iron, and steel. As a result of the experiment, the static magnetic pole and the dynamic magnetic pole are separated, and steel is suitable as the static magnetic pole, pure iron is suitable for the dynamic magnetic pole for the EMAT for transmission, and the PB perm alloy is suitable for the EMAT for reception. It was also clarified that the performance of the PC perm-alloy magnetic pole is improved by magnetically shielding the magnetic pole.