Zhai Guofu, Li Yongqian, Qin Yiren, Liu Yueyi
IEEE Trans Ultrason Ferroelectr Freq Control. 2021 Jun;68(6):2259-2270. doi: 10.1109/TUFFC.2021.3055871. Epub 2021 May 25.
Conventional electromagnetic acoustic transducers (EMATs) are generally only used to generate and detect guided waves with a single wavelength, which increases their sensitivity at that particular wavelength but limits their application scenarios and the accuracy of defect assessment. This article proposes a design method for multiwavelength EMATs based on spatial-domain harmonic control. First, the EMAT model is analyzed, where it is then outlined that the eddy-current density distribution of the specimen is equivalent to the spatial low-pass filtering of the coil-current density distribution. This shows that the multiwavelength guided waves can be achieved as long as the spatial distribution of the coil-current density contains those multiple harmonics that are desired. It is then proposed that the structure of the EMAT coil is equivalent to the spatial sampled pulse sequences of a spatial signal. The coil parameter design based on pulse modulation technology is proposed. Taking a dual-wavelength EMAT design for Lamb waves as an example, details of the coil parameter design are presented. The simulation and experiment with the dual-wavelength EMAT proved the correctness of the proposed method. Finally, an experiment with a three-wavelength EMAT demonstrated the feasibility of the proposed method in designing multiwavelength EMATs.
传统电磁超声换能器（EMAT）通常仅用于产生和检测单一波长的导波，这提高了其在该特定波长下的灵敏度，但限制了其应用场景以及缺陷评估的准确性。本文提出了一种基于空间域谐波控制的多波长EMAT设计方法。首先，对EMAT模型进行分析，接着概述了试样的涡流密度分布等同于线圈电流密度分布的空间低通滤波。这表明，只要线圈电流密度的空间分布包含所需的多个谐波，就可以实现多波长导波。然后提出，EMAT线圈的结构等同于空间信号的空间采样脉冲序列。提出了基于脉冲调制技术的线圈参数设计方法。以用于兰姆波的双波长EMAT设计为例，给出了线圈参数设计的详细过程。双波长EMAT的仿真和实验证明了所提方法的正确性。最后，三波长EMAT的实验证明了所提方法在设计多波长EMAT方面的可行性。
