A study of magnetostriction mechanism of EMAT on low-carbon steel at high temperature

The Electromagnetic acoustic transducer (EMAT) is used in a number of non-destructive testing applications [1-5]. The EMAT's operation is principally based on one of two mechanisms; the Lorenz force and magnetostriction mechanism [6-9]. The magnetostriction mechanism of an EMAT at elevated temperatures is reported in this paper. An optimized model is developed to describe the magnetostriction of polycrystalline iron, which is based on Brown's magnetic domain wall movement model [10] and Lee's magnetic domain rotation model [11]. The magnetostriction curves of polycrystalline iron for the temperature range 300 K-900 K are predicted, which reveal that the saturated magnetostriction coefficient changes from −4×10−6 to approximately 12×10−6. A non-linear, isotropic magnetostriction, finite element model is developed to simulate the Lamb waves generated in 4 mm thick steel plate by an EMAT, and the results show that the amplitude of S0 Lamb wave is greatly enhanced with an increase of temperature. In the experiments, a magnetostriction-based EMAT is used to generate Lamb waves in 4 mm thick steel plate. Experimental measurements verify that the contribution of the magnetostriction mechanism on steel rises as temperature increases in the range 298 K-873 K, while the contribution to ultrasonic generation from the Lorenz force mechanism decreases, as expected.