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<p>Non-contact inspection of cylindrical conductors, such as pipes and rods, is crucial in industrial applications. While traditional Eddy Current Testing (ECT) theory predominantly relies on flat-plate models, the specific geometric effects inherent to cylindrical geometries remain underexplored. This study investigates the relationship between eddy current behavior and sensor sensitivity, specifically frequency shift, using the Finite Element Method (FEM) and theoretical analysis. We identify a "Sensitivity Crossover" phenomenon in the intermediate frequency range, where thin-walled pipes exhibit a stronger sensor response than solid rods, despite their smaller conductor volume. Detailed analysis of current density distributions reveals that this counterintuitive behavior stems from an "Interference Boost" caused by electromagnetic wave reflection at the pipe's inner wall, which suppresses energy diffusion into the depths and enhances the effective magnetic coupling through current confinement near the surface. Furthermore, we construct a "Generalized Sensitivity Curve" correlating resistivity with sensitivity, establishing design guidelines to exploit the "Transition Region" where this crossover occurs. Finally, deriving scaling rules based on electromagnetic similarity, we present theoretical engineering solutions applicable to the inspection of cylindrical components of arbitrary dimensions.</p>

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Sensitivity Crossover and Generalized Scaling Laws in Resonant Eddy Current Testing of Cylindrical Conductors

  • 期刊论文

  • 发表日期：

    2026年7月8日

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  • Yukinaga Shimoguchiya,
  • Shigeharu Sugawara

摘要

Non-contact inspection of cylindrical conductors, such as pipes and rods, is crucial in industrial applications. While traditional Eddy Current Testing (ECT) theory predominantly relies on flat-plate models, the specific geometric effects inherent to cylindrical geometries remain underexplored. This study investigates the relationship between eddy current behavior and sensor sensitivity, specifically frequency shift, using the Finite Element Method (FEM) and theoretical analysis. We identify a "Sensitivity Crossover" phenomenon in the intermediate frequency range, where thin-walled pipes exhibit a stronger sensor response than solid rods, despite their smaller conductor volume. Detailed analysis of current density distributions reveals that this counterintuitive behavior stems from an "Interference Boost" caused by electromagnetic wave reflection at the pipe's inner wall, which suppresses energy diffusion into the depths and enhances the effective magnetic coupling through current confinement near the surface. Furthermore, we construct a "Generalized Sensitivity Curve" correlating resistivity with sensitivity, establishing design guidelines to exploit the "Transition Region" where this crossover occurs. Finally, deriving scaling rules based on electromagnetic similarity, we present theoretical engineering solutions applicable to the inspection of cylindrical components of arbitrary dimensions.