Flexible Sensors for NDI of Curved Surfaces on Turbofan Components

The inspection of turbofan components is becoming increasingly complex as new designs contain more curved surfaces requiring periodic non-destructive evaluation. These technical advances complicate the need to efficiently perform rapid inspections and provide reliable indications of threshold sized cracks in low conductivity metals such as titanium or nickel alloys. RMD has developed a membrane style coil sensor array that conforms to complex surfaces and has enough sensitivity to reliably detect 250 micron flaws at high speed. This sensor technology is widely applicable to surface inspections of small flaws on complex contours. The microFlex ribbon sensor is an array of reflective coil based eddy current elements that have predictable flaw signatures and can be arranged to be less sensitive to edges. This is possible because of the non-concentric, orthogonally oriented sense coils, which give the sensors a uniquely directional response to flaws. We have shown that the sensors can be formed to tight curvatures, with radii down to 2mm, and will still perform well. This is because the sensor elements are small and do not begin to fold back onto themselves until they are curved very tightly. Arrangements of sensors can be in series for high speed single channel applications, and in parallel for wide swath, low noise scans, and they can be printed in any orientation. The sensors are currently being integrated into US Air Force propulsion maintenance inspections as replacements for traditional wound-coil based ECT sensors.



  • T. Tiernan, N. M. Rensing, M. Steinback and E. Weststrate, "Eddy Current Detection". United States of America Patent 9,678,175, 13 June 2017.
  • T. Tiernan, N. M. Rensing, M. Steinback and E. Weststrate, "Eddy Current Detection". United States of America Patent Application Pending 15/620756, 1 February 2018.
  • E. R. Weststrate, M. S. Squillante, M. Steinback, S. Chekanov and M. R. Squillante, "Hybrid NDI Technology for Rapid Inspection of Large Aircraft," in ASNT Annual Conference, Long Beach, CA, 2016.
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