Low Frequency Eddy Current Testing of Insulators and Composites

  • Lee Hamill
  • Jane Emerson
  • Kevin McGushion
  • Steven NuttEmail author


Eddy current testing (ECT), a non-destructive testing method widely used to evaluate defects within conductive materials, is explored in this study as it applies to insulators and non-uniformly conductive materials. Previous work has shown that at high frequencies, differences in electric permittivity can be detected with ECT. In this study, a new design of an ECT sensor that employs two resonance-tuned coils is evaluated. Results show that material inconsistencies in insulators are detectable due to spatial variations in permittivity and magnetic permeability, and that detection is possible at lower frequencies than previously demonstrated. In addition to determining signal dependence on individual electromagnetic parameters, sensitivity for defect detection in a carbon fiber-reinforced polymer (CFRP) composite is qualitatively determined. Although low signal-to-noise ratio is observed with a small-diameter coil, by increasing the coil diameter, the signal to noise ratio is increased while preserving adequate spatial resolution to detect defects in the sample. This study expands on previous studies of the application of ECT to insulators, and demonstrates that defect detection is possible in CFRPs.


Composite materials Defects Eddy currents Material properties Magnetic materials 



This research was supported by Northrop–Grumman Corporation. The sensors were designed and supplied by Exel Orbital Systems Inc. Solvay Inc. and Airtech International donated prepreg and consumable materials, respectively. Experimental assistance on the project was provided by Ellen Emerson. David B. Chang, PhD, provided assistance in the discussion of physical concepts.


  1. 1.
    Sophian, A., Tian, G.Y.: Electromagnetic and eddy current NDT: a review electromagnetic and eddy current NDT: a review. Insight 43, 302–306 (2001)Google Scholar
  2. 2.
    Auld, B.A., Moulder, J.C.: Review of advances in quantitative eddy current nondestructive evaluation. J. Nondestruct. Eval. 18, 3–36 (1999)CrossRefGoogle Scholar
  3. 3.
    Garcia-Martin, J., Gomez-Gil, J., Vazquez-Sanchez, E.: Non-destructive techniques based on eddy current testing. Sensors 11, 2525–2565 (2011). CrossRefGoogle Scholar
  4. 4.
    Yi, J., Lee, S.: Analytical solution for impedance change due to flaws in eddy current testing. J. Nondestruct. Eval. 4, 197–202 (1984)CrossRefGoogle Scholar
  5. 5.
    Gäbler, S., Heuer, H., Heinrich, G.: Measuring and imaging permittivity of insulators using high-frequency eddy-current devices. IEEE Trans. Instrum. Meas. 64, 2227–2238 (2015)CrossRefGoogle Scholar
  6. 6.
    Mizukami, K., Mizutani, Y., Todoroki, A., Suzuki, Y.: Design of eddy current-based dielectric constant meter for defect detection in glass fiber reinforced plastics. NDT E Int. 74, 24–32 (2015). CrossRefGoogle Scholar
  7. 7.
    Goeje, M.P.D.E., Wapenaar, K.E.D.: Non-destructive inspection of carbon fibre-reinforced plastics using eddy current methods. Composites 23, 147–157 (1992)CrossRefGoogle Scholar
  8. 8.
    Lange, R., Mook, G.: Structural analysis of CFRP using eddy current methods. NDT E Int. 27, 241–248 (1994)CrossRefGoogle Scholar
  9. 9.
    Schulze, M.H., Heuer, H., Ku, M.: High-resolution eddy current sensor system for quality assessment of carbon fiber materials. Microsyst. Technol. 16, 791–797 (2010). CrossRefGoogle Scholar
  10. 10.
    Heuer, H., Schulze, M.H., Meyendorf, N.: Non-destructive evaluation (NDE) of composites: eddy current techniques. In: Karbhari, V.M. (ed.) Non-Destructive Evaluation (NDE) of Polymer Matrix Composites, pp. 33–55. Woodhead publishing, Cambridge (2013)CrossRefGoogle Scholar
  11. 11.
    Cheng, J., Ji, H., Qiu, J., Takagi, T., Uchimoto, T., Hu, N.: Role of interlaminar interface on bulk conductivity and electrical anisotropy of CFRP laminates measured by eddy current method. NDT E Int. 68, 1–12 (2014)CrossRefGoogle Scholar
  12. 12.
    Mizukami, K., Mizutani, Y., Todoroki, A., Suzuki, Y.: Detection of delamination in thermoplastic CFRP welded zones using induction heating assisted eddy current testing. NDT E Int. 74, 106–111 (2015)CrossRefGoogle Scholar
  13. 13.
    Cherry, M.R., Welterr, S.S., Blodgett, R.P.: Development of high resolution eddy current imaging using an electro-mechanical sensor. In: AIP Conference Proceedings. pp. 324–331 (2012)Google Scholar
  14. 14.
    Nalladega, V., Sathish, S., Jata, K., Blodgett, M., Knopp, J.: high resolution eddy current atomic force microscopy: development, theoretical modeling and application. Electromagnetic Nondestructive Evaluation (XII). pp. 115–122 (2009)Google Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Chemical Engineering and Materials ScienceUniversity of Southern CaliforniaLos AngelesUSA
  2. 2.Department of PathologyUniversity of Southern CaliforniaLos AngelesUSA
  3. 3.Exel Orbital Systems, IncSanta MonicaUSA

Personalised recommendations