A new omni-directional EMAT for ultrasonic Lamb wave tomography imaging of metallic plate defects.
A new omni-directional EMAT for ultrasonic Lamb wave tomography imaging of metallic plate defects.
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一种用于金属板缺陷超声兰姆波断层扫描成像的新型全向 EMAT
DOI：
10.3390/s140203458
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发表时间：
2014-02-20
期刊：
影响因子：
--
通讯作者：
Wang S
中科院分区：
文献类型：
--
作者：
Huang S;Wei Z;Zhao W;Wang S
本文提出了一种新型全方位电磁声换能器（EMAT），用于金属板缺陷的超声兰姆波（ULW）层析成像（TI）。该电磁超声换能器由永磁体和具有反弯曲结构的线圈组成。这种新的电磁超声线圈结构首次用于全向超声波发射和接收以及超声波TI。介绍和分析了这种电磁超声换能器的理论背景和工作原理。在3mm厚铝板上的实验结果表明，采用反弯曲线圈（CFC）的EMAT能够发射和接收高信噪比的纯A0单模超声波。因此，可以准确地执行用于ULW TI的投影数据的提取。投影数据的周向一致性仅受到由具有不规则形状的新CFC引起的涡流场的畸变的轻微影响。将该电磁超声阵列应用于超声波探伤中，采用跨孔法和SIRT算法，可以获得满意的成像质量，对人工腐蚀缺陷的尺寸估计与实际值吻合较好。分析了重建分辨率与所用新EMAT数目之间的关系。为了进一步研究新型电磁超声换能器的性能，本文还对铝板缺陷相对于电磁超声阵列的两种不同位置进行了TI实验。
This paper proposes a new omni-directional electromagnetic acoustic transducer (EMAT) for the ultrasonic Lamb wave (ULW) tomography imaging (TI) of defects in metallic plates. The proposed EMAT is composed of a permanent magnet and a coil with a contra-flexure structure. This new EMAT coil structure is used for omni-directional ULW transmission and reception and ULW TI for the first time. The theoretical background and the working principles of this EMAT are presented and analyzed. The experimental results of its use on a 3 mm thick aluminum plate indicate that the EMAT with a contra-flexure coil (CFC) can transmit and receive a pure single A0 mode ULW with a high signal-to-noise ratio (SNR). Thus, the extraction of the projection data used for ULW TI may be performed accurately. The circumferential consistency of the projection data is only slightly influenced by the distortion of the eddy current field that is induced by the new CFC with an irregular shape. When the new EMAT array is used for ULW TI using the cross-hole method and SIRT arithmetic, a desirable imaging quality can be achieved, and the estimated size of an artificial corrosion defect agreed well with its actual value. The relation between the reconstruction resolution and the number of the new EMATs used is analyzed. More TI experiments are carried out when the aluminum plate defect is in two different locations relative to the EMAT array, for the further investigation of the performances of the new EMATs.
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