Evaluation of the lift-off robustness of eddy current imaging techniques

Abstract The development of lift-off invariant strategies is one of the main goals in Eddy Current Non-Destructive Testing research. In the present work, from the analysis of amplitude and phase signals of magnetic field sensors under Multi-Frequency Eddy Current excitation, two imaging procedures are analyzed and compared with respect to their ability to retrieve reliable results even in presence of huge changes of lift-off. A figure of merit based on the Signal to Noise Ratio evaluated on the 2D reconstructed images allows the comparison of the different strategies in terms of the quality of the image to show the defect. The numerical and the experimental tests realized show that the imaging procedure relying on the analysis of the phase-lag is quite insensitive to changes in the lift-off with respect to that based on the amplitude analysis. In detail the former guarantees good results even when the probe lift-off is randomly changed during the test with variations up to 3 mm, while the latter is able to tolerate only lift-off fluctuation lower than 1 mm.

[1]  Kai Xu,et al.  A Novel Triple-Coil Electromagnetic Sensor for Thickness Measurement Immune to Lift-Off Variations , 2016, IEEE Transactions on Instrumentation and Measurement.

[2]  Zsolt Badics,et al.  Fast flaw reconstruction from 3D eddy current data , 1998 .

[3]  Tomasz Chady,et al.  Eddy Current Testing of Thick Aluminum Plates with Hidden Cracks , 2003 .

[4]  Yves Jayet,et al.  NUMERICAL AND EXPERIMENTAL-STUDY OF EDDY-CURRENT PROBES IN NDT OF STRUCTURES WITH DEEP FLAWS , 1995 .

[5]  Luigi Ferrigno,et al.  An experimental comparison of multi-frequency and chirp excitations for eddy current testing on thin defects , 2015 .

[6]  Philip J. Withers,et al.  Noncontact Characterization of Carbon-Fiber-Reinforced Plastics Using Multifrequency Eddy Current Sensors , 2009, IEEE Transactions on Instrumentation and Measurement.

[7]  Tapan Kumar Saha,et al.  Diffusion of current into conductors , 2001 .

[8]  C. Mandache,et al.  Study of Lift-Off Invariance for Pulsed Eddy-Current Signals , 2009, IEEE Transactions on Magnetics.

[9]  Yann Le Bihan,et al.  Study on the transformer equivalent circuit of eddy current nondestructive evaluation , 2003 .

[10]  Luigi Ferrigno,et al.  Analysis of the influence of lift-off variation on Eddy-Current images , 2015, 2015 IEEE Metrology for Aerospace (MetroAeroSpace).

[11]  Satish S. Udpa,et al.  Rotating Field EC-GMR Sensor for Crack Detection at Fastener Site in Layered Structures , 2015, IEEE Sensors Journal.

[12]  Pietro Burrascano,et al.  Exploiting Pseudorandom Sequences to Enhance Noise Immunity for Air-Coupled Ultrasonic Nondestructive Testing , 2012, IEEE Transactions on Instrumentation and Measurement.

[13]  Gui Yun Tian,et al.  Design of a pulsed eddy current sensor for detection of defects in aircraft lap-joints , 2002 .

[14]  Y. Le Bihan,et al.  Lift-off and tilt effects on eddy current sensor measurements: a 3-D finite element study , 2002 .

[15]  J. Takatsubo,et al.  Multi-frequency ECT with AMR sensor , 2011 .

[16]  Young-Kil Shin,et al.  Signal characteristics of differential-pulsed eddy current sensors in the evaluation of plate thickness , 2009 .

[17]  Dominique Placko,et al.  Characterization of subsurface defects in aeronautical riveted lap-joints using multi-frequency eddy current imaging , 2009 .

[18]  Octavian Postolache,et al.  GMR array uniform eddy current probe for defect detection in conductive specimens , 2013 .

[19]  Yu-hua Zhang,et al.  Impedance Evaluation of a Probe-Coil's Lift-off and Tilt Effe ct in Eddy-Current Nondestructive Inspection by 3D Finite Element Modeling , 2008 .

[20]  Huang Songling,et al.  Development of differential probes in pulsed eddy current testing for noise suppression , 2007 .

[21]  Marc Kreutzbruck,et al.  Defect detection and classification using a SQUID based multiple frequency eddy current NDE system , 2001 .

[22]  Gui Yun Tian,et al.  Reduction of lift-off effects for pulsed eddy current NDT , 2005 .

[23]  Javier García-Martín,et al.  Non-Destructive Techniques Based on Eddy Current Testing , 2011, Sensors.

[24]  H. Geirinhas Ramos,et al.  Liftoff insensitive thickness measurement of aluminum plates using harmonic eddy current excitation and a GMR sensor , 2012 .

[25]  Luigi Ferrigno,et al.  Multifrequency Excitation and Support Vector Machine Regressor for ECT Defect Characterization , 2014, IEEE Transactions on Instrumentation and Measurement.

[26]  J. C. Baboux,et al.  Pulsed eddy current signal analysis: application to the experimental detection and characterization of deep flaws in highly conductive materials , 1997 .

[27]  Masato Enokizono,et al.  Crack detection and recognition using an eddy current differential probe , 1999 .

[28]  Li Shu,et al.  Study of pulse eddy current probes detecting cracks extending in all directions , 2008 .

[29]  S. A. Jenkins,et al.  Eddy‐current probe impedance due to a volumetric flaw , 1991 .

[30]  Zhiwei Zeng,et al.  Pulsed Eddy-Current Based Giant Magnetoresistive System for the Inspection of Aircraft Structures , 2010, IEEE Transactions on Magnetics.

[31]  Manfred R. Schroeder,et al.  Synthesis of low-peak-factor signals and binary sequences with low autocorrelation (Corresp.) , 1970, IEEE Trans. Inf. Theory.

[32]  Gerhard Mook,et al.  Non-destructive characterisation of carbon-fibre-reinforced plastics by means of eddy-currents , 2001 .

[33]  Richard Binns,et al.  Analysis of the Liftoff Effect of Phase Spectra for Eddy Current Sensors , 2007, IEEE Transactions on Instrumentation and Measurement.