Frequency spectra of magnetostrictive and Lorentz forces generated in ferromagnetic materials by a CW excited EMAT

12th Anglo-French Physical Acoustics Conference

Rouge, C.^1,2 ; Lhémery, A.^1 ; Aristégui, C.^2

CEA, LIST, F-91191 Gif-sur-Yvette cedex, France^1

Université de Bordeaux, UMR CNRS 5295, I2M/Acoustique Physique, 33405 Talence cedex, France^2

关键词: Discrete frequencies;    Dynamic magnetic fields;    Electromagnetic acoustic transducers;    Excitation frequency;    Magnetostrictive forces;    Magnetostrictive strain;    Static magnetic fields;    Transduction process;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/498/1/012014/pdf
DOI  :  10.1088/1742-6596/498/1/012014

来源: IOP

【 摘 要 】

Magnetostriction arises in ferromagnetic materials subjected to magnetization, e.g., when an EMAT (Electro-Magnetic Acoustic Transducer) is used to generate ultrasonic waves. In such a case, the magnetostriction force must be taken into account as a transduction process that adds up to the Lorentz force. When the static magnetic field is high compared to the dynamic field, both forces are driven by the excitation frequency. For lower static relative values of the magnetic fields, the Lorentz force comprises both the excitation frequency and its first harmonic. In this work, a model is derived to predict the frequency content of the magnetostrictive force that comprises several harmonics. The discrete frequency spectrum strongly depends on both the static field and the relative amplitude of the dynamic field. The only material input data needed to predict it is the curve of macroscopic magnetostrictive strain that can be measured in the direction of an imposed magnetic field. Then, the various frequency-dependent distributions of Lorentz and magnetostriction body forces can be transformed into equivalent surface stresses. Examples of computation are given for different static and dynamic magnetic fields to study their influence on the frequency content of waves generated in ferromagnetic materials.