Mechanisms of elastic wave generation by EMAT in ferromagnetic media

The present paper deals with the problem of elastic wave generation mechanisms (WGMs) by an electromagnetic-acoustic transducer (EMAT) in ferromagnetic materials. The paper seeks to prove that taking into account all the WGMs must be a general rule to quantitatively predict the elastic waves generated by an EMAT in such materials. Existing models of the various physical phenomena involved, namely magnetic and magnetostrictive, electromagnetic, and ultrasonic, are combined to solve the multiphysics wave generation problem. The resulting model shows that WGMs (i.e., electromagnetic force, magnetostrictive strain, and magnetic traction) strongly depend on material properties and EMAT design and excitation. To illustrate this, four magnetic materials (nickel, AISI410, Z20C13, and low carbon steel) with similar elastic but contrasting electromagnetic properties are studied. A given EMAT of fixed excitation and geometry yields WGMs with highly different amplitudes in these materials, with a WGM dominant in one material being negligible in another. Experimental results make it possible to validate the accuracy of certain predictions of the model developed. In summary, the present work shows that considering all WGMs is the general rule when working with ferromagnetic materials. Furthermore, it offers a generic model that can be integrated into various numerical tools to help optimize EMAT design and give reliable data interpretation.