Comprehensive Study of the Transduction Mechanisms of Normally Biased EMAT Configuration Operating on Ferromagnetic Material

摘要

Normally Biased Electromagnetic Acoustic Transducer System (NB_EMAT) is one the most popular EMAT configurations for the generation of surface wave on conducting media. It require a static magnetic field normal to the surface of the test specimen for the magneto-elastic phenomenon (leading to wave generation) to take place. With the goal of improving the performance and better understanding of the transduction mechanisms involved in the generation of surface acoustic wave on ferro-magnetic material, a comprehensive modelling technique for NB-EMAT is proposed. The technique accounts for the static Lorentz force (SLF), dynamic Lorentz force (DLF) and the magnetostrictive force (MF). The study established that beyond certain excitation current of 190A, the NB-EMAT operating on CS70 grade of pipe steel generate surface acoustic waves more efficiently by employing the dynamic Lorentz force mechanism. This implies that beyond this current, the permanent or electromagnet (which is a major drawback for EMAT in high temperature measurements) can be effectively eliminated from its operation. The model used for this study has been experimentally validated and the model predictions shows good agreement with the experimental result.