静态偏置磁场强度对铁磁材料电磁超声换能机制的影响

Effect of Static Bias Magnetic Field on Electromagnetic Ultrasonic Transducer Mechanism in Ferromagnetic Materials

铁磁材料具有磁致伸缩效应,因其磁化具有非线性特性导致其电磁超声换能机制变得复杂。分析不同磁场强度下铁磁材料中电磁超声换能机制的主导因素有利于提高电磁超声换能器(EMAT)的换能效率及信噪比。该文建立了铁磁材料电磁超声Lamb换能器的仿真模型,研究了洛伦兹力、磁致伸缩力和磁化力随外加磁场的变化规律。通过对比洛伦兹力作用下位移、磁致伸缩效应作用下位移和综合作用下总位移来分析影响换能机制的主导因素,并进行了实验研究,实验测得的质点位移、波速与仿真结果一致。研究结果表明,在弱磁情况下,磁致伸缩效应占主导作用;当铁磁材料接近磁饱和时,洛伦兹力逐渐增大并起主要作用;铁磁材料在达到磁饱和后,磁致伸缩效应引起的应变很小且几乎不再改变。

The electromagnetic acoustic transduction mechanism of the Ferromagnetic material is complicated because of its magnetostrictive effect and nonlinear magnetization characteristic.It is helpful to improve the transduction efficiency and signal-to-noise ratio of electromagnetic acoustic transducer(EMAT)that analyzing the dominant factors of electromagnetic ultrasonic transducing mechanism in ferromagnetic materials under different magnetic field strength.In this paper,the simulation model of Lamb wave EMAT for ferromagnetic material was established.With the change of external magnetic field,the variation laws of Lorentz force,magnetostrictive force and magnetizing force were studied.The main factors influencing the transduction mechanism were analyzed by comparing the displacements under the Lorentz force,the magnetostrictive force and composition of the Lorentz force and the magnetostrictive force.The experimental results show that the displacement and velocity of Lamb wave are consistent with the simulation results.The study proves that:The magnetostrictive effect plays a dominant role in the field of weak magnetic,the Lorentz force increases and plays a major role when the ferromagnetic material is near magnetic saturation,the strain caused by the magnetostrictive effect is very small and barely changes at the magnetic saturation stage.