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Analysis of the influence of lift-off variation on Eddy-Current images
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2nd IEEE International Workshop on Metrology for Aerospace, MetroAeroSpace 2015 - Proceedings
5 August 2015, Article number 7180650, Pages 182-187
2nd IEEE International Workshop on Metrology for Aerospace, MetroAeroSpace 2015; Benevento; Italy; 3 June 2015 through 5 June 2015; Category numberCFP1532W-ART; Code 113895
Analysis of the influence of lift-off variation on Eddy-Current images (Conference Paper)
Ricci, M.a ,
Silipigni, G.a ,
Ferrigno, L.b ,
Laracca, M.b ,
Adewale, I.D.ac ,
Tian, G.Y.c
a Dipartimento di Ingegneria, Polo Scientifico Didattico di Terni, Università di Perugia, Strada di Pentima 4, Terni, Italy
b Dipartimento di Ingegneria Elettrica e dell'Informazione, Università Degli Studi di Cassino e Del Lazio Meridionale, Via G. Di Biasio 43, Cassino (FR), Italy
c School of Electrical and Electronic Engineering, Newcastle University, Newcastle-upon-Tyne, United Kingdom
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Abstract
The development of lift-off invariant strategies is one of the main goals in Eddy Current Non-Destructive Testing research. In this paper various imaging procedures for Eddy Current Testing are analyzed with respect to change of lift-off and tested by varying randomly the lift-off value at every point in a measurement grid. The experimental data, collected with both chirp and multi-frequency excitation, shows that imaging procedures relying on phase analysis are quite insensitive to liftoff variation and then more robust with respect to imaging procedures based on the visualization of amplitude-derived features
An experimental comparison of multi-frequency and chirp excitations for eddy current testing on thin defects
No full textNon-destructive evaluation of materials and structures is still a key issue in some industrial scenarios as the production process and the quality inspection. In the case of metallic materials, economic and implementation reasons push for the use of Eddy Current Testing techniques. In the last years, the effort of the research activity is been focused on the development of eddy current measurement procedures capable of providing as much information as possible about the presence, the location and the geometrical characteristics of defects. To this aim, newer signals characterized by a wide spectral content able to penetrate in the different layers of the material under test are substituting the older sinusoidal excitation. Among these, multi-frequency and chirp represent two optimal candidates within the class of frequency domain-based signals. The former is characterized by the simultaneous presence of many sinusoidal tones, while the latter exhibits a constant envelope and an instantaneous frequency that increases or decreases with time. In literature many interesting papers dealing with both excitation types are reported but an experimental performance comparison on a number of real defects is missing. Moreover the comparisons are usually executed on single measurements collected in presence of a defect in the location corresponding to the highest defect signal. Even if this strategy allows the analysis of the defect signature in time and in frequency domain, from both experimental and practical point of view, this approach is extremely sensitive to noise and it could be also difficult to be applied in on-line or in-situ inspections. In this paper, the poposed comparison aims at highlighting the suitability of each considered excitation method with respect to the extraction of defects geometrical features. It is proposed to combine the various excitation signals with image processing: indeed by developing a proper 2D image procedure from 1D eddy-current data it is possible to improve the defect detection capability when difficult cases are experienced (such as annealed and small cracks) and to extract more accurate information about the defect’s geometric characteristics. After the image processing application, the multi-tone and the chirp approaches are quantitatively compared by using an ad-hoc figure of merit
Notice of Removal: Reducing pulse compression sidelobes by means of a reactance transformation
No full textReactance transformation to improve range resolution in pulse-compression detection systems
No full textOn the Use of Complex Excitation Sequences for Eddy Current Testing
No full textEddy Current Testing (ECT) is a Non Destructive technique widely used in many industrial
application fields in which it is very important to detect the presence of thin defects ( generally called cracks) in
conductive materials. Features of this technique are the cost-effective implementation and the kind of retrieved
measured data that make possible estimating geometrical characteristics of a crack as position, length, width and
depth. The analysis of these characteristics allows the user to accept or discard realized components then
improving the production chain. To accomplish for this task some aspects have to be taken into account during
the measurement process. They mainly concern with the realization of suitable measurement setup and post
processing stages. As far as the measurement setup is concerned, crucial aspects are the choice of measurement
and excitation devices. As for the former, in the past years the literature deeply explored many types of
measurement probes highlighting advantages and disadvantages of different solutions. The choice of optimized
excitation devices and strategies is now interesting recent studies about Non Destructive ECT (ND-ECT):
together with common aspects as the amplitude and the frequency of the exciting signal, recently the attention
has been paid to issues as the type of signal to be adopted. In particular it has been found as the use of complex
excitation signals, meant as signals different from the sinusoidal ones and with wide frequency content, might
raise eddy current responses trying to support the measurement, detection and characterization stages when
“difficult cases” are explored (i.e. very short or annealed cracks). In this paper the authors propose an
experimental comparison of different excitation signal designed to improve the quality of experimental data
when difficult cases are experienced (such as annealed and small cracks) and consequently to obtain a more
reliable extraction of defects geometrical features
Evaluation of the lift-off robustness of eddy current imaging techniques
No full textThe 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
Analysis of the influence of lift-off variation on Eddy-Current images
No full textThe development of lift-off invariant strategies is one of the main goals in Eddy Current Non-Destructive Testing research. In this paper various imaging procedures for Eddy Current Testing are analyzed with respect to change of lift-off and tested by varying randomly the lift-off value at every point in a measurement grid. The experimental data, collected with both chirp and multi-frequency excitation, shows that imaging procedures relying on phase analysis are quite insensitive to liftoff variation and then more robust with respect to imaging procedures based on the visualization of amplitude-derived features
An experimental comparison of complex excitation sequences for eddy current testing
No full textEddy Current Testing (ECT) is a Non Destructive technique widely used in many industrial application fields in which it is very important to detect the presence of thin defects (generally called cracks) in conductive materials. Features of this technique are the cost-effective implementation and the kind of retrieved measured data that make possible to estimate the geometrical characteristics of a crack as position, length, width and depth. The analysis of these characteristics allows the user to accept or discard realized components then improving the production chain. To accomplish for this task some aspects have to be taken into account during the measurement process. They mainly concern the realization of suitable measurement setup and post processing stages. As far as the measurement setup is concerned, crucial aspects are the choice of measurement and excitation devices. The choice of optimized excitation devices and strategies is of interest for research on Non Destructive ECT (ND-ECT): together with common aspects as the amplitude and the frequency of the exciting signal, the attention has been paid to issues as the type of signal to be adopted. In particular it has been found as the use of complex excitation signals, meant as signals different from the sinusoidal ones and with wide frequency content, might raise eddy current responses trying to support the measurement, detection and characterization stages when "difficult cases" are explored (i.e. very small and/or annealed cracks). In this paper the authors propose an experimental comparison of different excitation signals designed to improve the quality of experimental data when difficult cases are experienced and, consequently, to obtain a more reliable extraction of defects geometrical features
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