The novelty of this paper is that a spiral-coil EMAT (electromagnetic acoustic transducer) is applied to rail subsurface inspection. To study the spiral-coil EMAT for rail subsurface inspection, the dominant mechanism is investigated emphatically. The interaction between the Lorentz-force mechanism and the magnetostriction mechanism is analyzed corresponding to the magnetic flux density and the frequency which has a significant effect on the magnetostriction mechanism. The effect of frequency on beam divergence is further discussed about the rail subsurface inspection using spiral-coil EMAT as well. A 2D FEM (finite element model) of spiral-coil EMAT is established and the simulation is carried out to analyze these issues. Besides, the experiments to inspect the subsurface crack of steel plate are carried out at various frequencies to verify the feasibility of the application. The experimental results demonstrate that the rail subsurface inspection by using the spiral-coil EMAT is feasible and the high frequency can contribute to distinguish the echo signal from the rail subsurface crack.

中文翻译：

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用于钢轨地下检测的螺旋线圈 EMAT 研究

本文的新颖之处在于将螺旋线圈 EMAT（电磁声换能器）应用于轨道地下检测。为了研究用于轨道地下检测的螺旋线圈 EMAT，重点研究了主要机制。根据对磁致伸缩机制有显着影响的磁通密度和频率，分析了洛伦兹力机制与磁致伸缩机制之间的相互作用。频率对光束发散的影响也在使用螺旋线圈 EMAT 的钢轨地下检测中进一步讨论。建立了螺旋线圈EMAT的2D FEM（有限元模型）并进行仿真分析这些问题。除了，以不同频率进行了钢板亚表层裂纹检测实验，验证了应用的可行性。实验结果表明，利用螺旋线圈EMAT进行钢轨地下检测是可行的，高频有助于区分回波信号和钢轨地下裂纹。