Modelling ultrasonic generation for Lorentz force EMATs

Abstract

A model for transient ultrasonic wave generation by Electromagnetic Acoustic Transducers (EMATs) is presented. Analytical solutions are currently available only for a few kinds of sources and the model combines these analytical solutions and numerical computation to predict the ultrasonic field generated by arbitrary sources. This model can be used to calculate bulk waves within samples as well as surface waves with the advantages of explicit physical meaning and quick processing speed over pure numerical calculations such as the Finite Element Method (FEM). The model is used to explain how static and dynamic magnetic fields generate ultrasonic waves in a sample. It is desirable to characterise the EMAT source in detail in order to tailor sources for optimal configuration for specific NDE applications. A Michelson laser interferometer is used to measure the out-of-plane surface displacement of a sample, and results agree well with the modelling simulation. The modelling can be used for sources with arbitrary shape and temporal profile, but works most efficiently for sources with circular symmetry or line shape forces.