Mechanisms of Elastic Wave Detection by EMAT in Ferromagnetic Media

Le résumé fourni par la source

The paper addresses the problem of elastic wave detection mechanisms (WDMs) by an electro-magnetic-acoustic transducer (EMAT) in ferromagnetic media. While various works have focused on elastic wave generation mechanisms (WGMs), WDMs in ferromagnetic materials have received little attention. This study derives a model of these detection mechanisms, by assuming the elastodynamic problem due to the wave passage as a linear perturbation of the initial static equilibrium. The passage of the wave is represented by the induction of three currents, whose origins are identical to those responsible for WGMs: eddy currents, magnetization, and magnetostriction. Maxwell’s equations are solved considering these currents, providing an expression for the induced electromotive force in the EMAT coil. The expression is subsequently reformulated using reciprocity arguments, leading to a result involving only the currents from both generation and detection problems. Numerical simulations are conducted to analyze WDMs in relation to various model parameters: 1) the material properties, by examining three ferromagnetic materials (Ni, 30MnB5 and Z20C13), 2) the polarization orientation and magnitude of the permanent magnet, and 3) the lift-off. Simulations reveal a strong dependency of WDMs on these parameters, mirroring the dependencies observed in WGMs.

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