Nondestructive testing for identifying defects on the surface of metal materials is important for industries and infrastructures. The Rayleigh wave is widely used for detecting these surface defects. For replacing piezoelectric transducers with electromagnetic acoustic transducers (EMATs) for the surface inspection of metal materials, this article proposes a new magnet and coil combination consisting of a periodic-permanent-magnet (PPM) and a returned dislocation meander line coil. The returned dislocation meander line coil was developed using a traditional meander line coil, whose wires return from one side to another and shift for a certain distance. A 2-D finite-element simulation was conducted to analyze the performance of the proposed Rayleigh wave EMAT. The simulation results revealed that, compared with a large conventional magnet, the PPM increased the maximum magnetic flux density, and made the magnetic flux density distribution more concentrated on the specimen’s surface, particularly below the coil. In the middle part of the coil, the PPM greatly increased the intensity of the horizontal magnetic field. Additionally, the returned dislocation meander line coil made full use of the strong magnetic field below the center of each small magnet and at the adjacent magnets. The designed Rayleigh wave EMAT was fabricated, and the experimental results revealed that the new design of the Rayleigh wave EMAT increased the received signal by 57.9% compared with the conventional Rayleigh wave EMAT.

中文翻译：

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电磁声换能器的磁体和线圈的新组合，用于产生和检测瑞利波

用于识别金属材料表面缺陷的非破坏性测试对于工业和基础设施至关重要。瑞利波被广泛用于检测这些表面缺陷。为了用电磁声换能器（EMAT）代替压电换能器来进行金属材料的表面检查，本文提出了一种新的磁体和线圈组合，该磁体和线圈组合由周期性永磁体（PPM）和返回的位错曲折线线圈组成。返回的位错曲折线线圈是使用传统的曲折线线圈开发的，其导线从一侧返回到另一侧并偏移一定距离。进行了二维有限元仿真，以分析所提出的瑞利波EMAT的性能。仿真结果表明，与大型常规磁体相比，PPM增加了最大磁通密度，并使磁通密度分布更加集中在样品表面，尤其是在线圈下方。在线圈的中间部分，PPM大大增加了水平磁场的强度。另外，返回的位错曲折线线圈充分利用了每个小磁体中心下方和相邻磁体处的强磁场。制作了设计好的瑞利波EMAT，实验结果表明，与传统瑞利波EMAT相比，新设计的瑞利波EMAT使接收信号增加了57.9％。在线圈的中间部分，PPM大大增加了水平磁场的强度。另外，返回的错位曲折线线圈充分利用了每个小磁体的中心下方和相邻磁体处的强磁场。制作了设计好的瑞利波EMAT，实验结果表明，与传统瑞利波EMAT相比，新设计的瑞利波EMAT使接收信号增加了57.9％。在线圈的中间部分，PPM大大增加了水平磁场的强度。另外，返回的错位曲折线线圈充分利用了每个小磁体的中心下方和相邻磁体处的强磁场。制作了设计好的瑞利波EMAT，实验结果表明，与传统瑞利波EMAT相比，新设计的瑞利波EMAT使接收信号增加了57.9％。