A model to predict the elastic field radiated by a magnetostrictive patch transducer into an omnidirectional waveguide

Abstract

Magnetostrictive patch transducers (MPT) can be used as sources or sensors of elastic guided waves in non-destructive testing and structural health monitoring methods. A tool for simulating them is under development to help designing optimal MPT for a given application. It requires the prior accurate modelling of transduction phenomena involved in such patches and of the GW fields they generate. A MPT is made of a thin magnetostrictive strip under a static magnetic field, glued to the waveguide under examination and excited by an alternative current circulating in a coil. In the strip where they take place, transduction phenomena are similar to those generated by an electro-magnetic acoustic transducer (EMAT) in a ferromagnetic medium. They involve magnetostrictive strain, magnetization force and surface traction and Lorentz force (Clausse et al. 2017 J. Phys.: Conf. Ser. 797 102004), which can be transformed into equivalent surface stresses at the outer surface of the strip. A matrix model is developed to propagate the equivalent stresses from this outer surface to that of the waveguide. Once equivalent stress distributions are computed at this latter surface, a model (Barras et al. 2020 Ultrasonics 103 1060782) is used to predict the MPT radiation into the waveguide. Overall, the chaining of these models constitutes a semi-analytical multi-physics model for GW radiation by MPT of high computing efficiency.