Abstract
Properties of electromagnetic acoustic transducers (EMATs) for S0 mode Lamb wave are experimentally studied. The EMAT, which consists of a meander coil and an electromagnet, can transmit and receive the S0 wave in a thin metal plate effectively. When the EMAT is applied to nonmagnetic materials such as aluminum alloys, the excitation mechanism relies on the Lorentz force, which is a product of the interaction between the induced eddy current and the static magnetic field. The amplitude of the S0 wave is thus proportional to the static field strength. When used with ferromagnetic materials such as steel, the S0 wave is generated mainly by magnetostriction, while contribution of the Lorentz force is negligibly small, especially in the low-field region. In this study, two types of EMATs, one applying a horizontal magnetic field and the other a vertical field, are used for the aluminum sheet and the low-carbon steel sheet. The results turn out to be in good agreement with the above prediction. The horizontal field type EMAT is proved to be suitable for the ferromagnetic materials, while the vertical type for the nonmagnetic materials.
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