Effect of Static Bias Magnetic Field on Electromagnetic Acoustic Transducer for Ferromagnetic Materials

The relative low signal to noise ratio (SNR) of Electromagnetic Acoustic Transducer (EMAT) limits its further application. To improve the SNR of EMAT, the effect of the static bias magnetic field has been studied in this paper. At first, an algorithm and numerical code for simulation EMAT signals of a ferromagnetic material have been developed based on the Maxwell-equations and the wave equation of continuum material. The effect of static bias magnetic field intensity on EMAT has been studied then based on the developed code. The numerical results show that the magnetostrictive force decreases with the increasing magnetic field intensity, while the Lorentz force gets bigger all the time. In addition, it is also found that the sensitivity of EMAT is affected by the thickness of permanent magnet, e.g., with the increment of thickness, the amplitude of first bottom surface echo signal decreases but the gradient gradually becomes smaller.