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Lorentz Force Eddy Current Testing: a Prototype Model

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Abstract

We report an investigation of the motion of a free-falling permanent magnet in an electrically conducting pipe containing an idealized defect. This problem represents a highly simplified yet enlightening version of a method called Lorentz force eddy current testing which is a modification of the traditional eddy current testing technique. Our investigation is a combination of analytical theory, numerical simulation and experimental validation. The analytical theory allows a rigorous prediction about the relation between the size of the defect and the change in falling time which represents the central result of the present work. The numerical simulation allows to overcome limitations inherent in the analytical theory. We test our predictions by performing a series of experiments. We conclude that our theory properly captures the essence of Lorentz force eddy current testing although a refinement of the experiment is necessary to reduce the discrepancy to the predictions. In spite of its apparent simplicity the present system can serve as a prototype and benchmark for future research on Lorentz force eddy current testing.

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Notes

  1. Using an electrical conductivity of \({20}~\mathrm{MS/m}\) we obtain at a measurement frequency (AC-field) of 1 kHz an skin depth of 3.56 mm whereas the DC-field at a velocity of \({8}~\mathrm{cm/s}\) provides 89.21 mm for an inner radius of the pipe of 8 mm.

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Acknowledgements

The present work is supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the Research Training Group “Lorentz force velocimetry and Lorentz force eddy current testing” (GK 1567) at the Ilmenau University of Technology. The authors thank the reviewers for their careful and insightful reviews which have significantly improved the quality of this paper.

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Authors and Affiliations

  1. Department of Advanced Electromagnetics, Ilmenau University of Technology, P.O. Box 100565, 98684, Ilmenau, Germany

    Robert P. Uhlig, Mladen Zec & Hartmut Brauer

  2. Institute of Thermodynamics and Fluid Mechanics, Ilmenau University of Technology, P.O. Box 100565, 98684, Ilmenau, Germany

    André Thess

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  1. Robert P. Uhlig
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  2. Mladen Zec
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  3. Hartmut Brauer
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  4. André Thess
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Correspondence to Robert P. Uhlig.

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Uhlig, R.P., Zec, M., Brauer, H. et al. Lorentz Force Eddy Current Testing: a Prototype Model. J Nondestruct Eval 31, 357–372 (2012). https://doi.org/10.1007/s10921-012-0147-7

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