Examination of Pole Structure for Static Magnetic Field Constituting Electromagnetic Acoustic Transducer (EMAT) for Lamb Wave Using Electromagnetic Induction Coil with Ferromagnetic Core

Abstract

To increase the mechanical and thermal strengths of the EMAT for Lamb waves, the air-core electromagnetic induction coil that constitutes the EMAT was changed to a structure in which a conductor is wound around a ferromagnetic material. Initially, the coils for the static and dynamic magnetic fields were vertically wound around low-carbon steel, a ferromagnetic material. As a result, a transmission signal was detected. To further improve the received signal strength, a structure separating the poles for the static and dynamic magnetic fields was evaluated. It was then confirmed that an improvement in the received signal strength was obtained. Conventionally, the magnetic poles for a static magnetic field and dynamic magnetic field were alternately arranged. In the present paper, the structure was changed to a two-pole structure for the static magnetic poles, and all the dynamic magnetic poles were sandwiched between the two poles. As a result, a dramatic improvement in the sensitivity was achieved.