Wang Shen, Huang Songling, Wang Qing, Wang Zhe, Zhao Wei
State Key Lab. of Power System, Dept. of Electrical Engineering, Tsinghua University, Beijing 100084, China.
State Key Lab. of Power System, Dept. of Electrical Engineering, Tsinghua University, Beijing 100084, China.
Ultrasonics. 2019 Mar;93:71-80. doi: 10.1016/j.ultras.2018.10.013. Epub 2018 Oct 31.
Electromagnetic acoustic transducers (EMATs) are versatile non-contact ultrasonic transducers with relatively low transduction efficiency. A fundamental problem not answered completely yet is how the structure of an EMAT influences the generation of various Lamb wave modes. We tackle this problem with fully coupled frequency domain EMAT models where the underlying integro-differential equations are solved directly and the magnitudes of the phasors of the displacement components at a point in the middle plane of a plate are used to represent the strength of the S0 and A0 mode waves. Idealized single-wire, two-wire and wire bundle EMATs with uniform bias magnetic field and practical meander line and tightly wound EMATs with distributed bias field are studied. Polar plots of the idealized EMATs with swept angle of the bias field show that the vertical component of the bias field decides the strength of the S0 mode waves. Sweeping of the width of the magnet for the practical EMATs generates S0 mode curves that could be explained from the distribution of the vertical component of the bias field. This work represents the first attempt to solve the proposed problem of characterizing excitability of Lamb waves with EMATs quantitatively, via the model-based approach.
电磁超声换能器（EMATs）是一种多功能的非接触式超声换能器，但其转换效率相对较低。一个尚未完全解决的基本问题是EMAT的结构如何影响各种兰姆波模式的产生。我们通过完全耦合的频域EMAT模型来解决这个问题，在该模型中，直接求解基础的积分 - 微分方程，并使用板中平面上某一点处位移分量相量的大小来表示S0和A0模式波的强度。研究了具有均匀偏置磁场的理想化单线、双线和线束EMAT，以及具有分布偏置场的实际曲折线和紧密缠绕的EMAT。偏置场扫角的理想化EMAT的极坐标图表明，偏置场的垂直分量决定了S0模式波的强度。实际EMAT磁体宽度的扫描产生的S0模式曲线可以从偏置场垂直分量的分布来解释。这项工作是首次尝试通过基于模型的方法定量解决用EMAT表征兰姆波激发性这一提出的问题。
