Abstract
In this paper an eddy current imaging method for nondestructive testing purposes is presented which utilizes the concept of broadband holography. An eddy current coil which is used simultaneously as an antenna for eddy current generation and as a probe for detection of response of interaction between eddy currents and flaws, respectively, is moved along a synthetic aperture during the imaging procedure generating synthetic eddy current pulses by scanning a certain frequency range. In terms of wave propagation phenomena the penetration depth (range) of eddy currents in conducting media is small compared to the equivalent wavelength of this type of fields. Therefore, adequate resolution can only be obtained in the reconstructed cross-sectional images by phase multiplication of received multifrequency signals, which is equivalent to a fictitious reduction of wavelengths. Experimental results verify the imaging capability of this method with improved resolution compared to conventional eddy current testing methods.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
O. Zinke and H. Brunswig,Lehrbuch der Hochfrequenztechnik. Band 1 Springer-Verlag, (Berlin, 1973).
B. P. Hildebrand, A. J. Boland, and T. J. Davis, Holographic Principles Applied to Low Frequency Electromagnetic Imaging in Conductors, Proc. IEEE Int. Optical Computing Conf., 1983, pp. 59–66.
H. D. Collins, T. J. Davis, and L. J. Busse, Eddy current phasography,Acoust. Imaging 11:37–43 (1982).
J. H. Hippler, H. Ermert and L. v. Bernus, Über die Nutzung des Skin-Effekts für holographische Abbildungsverfahren zur zerstörungsfreien Prüfung metallischer,Materialien und Bauteile. AEÜ 4 (44):257–264 (1990).
J. H. Hippler, Möglichkeiten Holographischer Abbildung bei der Zerstörungsfreien Werkstoffprüfung Mittels Multifrequenter Wirbelstromfelder, Dissertation, Universität Bochum, 1991.
H. Ermert and R. Karg, Multifrequency acoustical holography,IEEE Trans SU-26 279–286 (1979).
R. Karg, Multifrequency microwave holography,AEÜ 31:150–156 (1977).
M. Riaziat and B. A. Auld,Eddy Current Probe Design and Matched Filtering for Optimum Flaw Detection.Review of Progress in Quantitative Nondestructive Evaluation, Vol. 2 (Plenum Press, New York, 1983), pp. 189–204.
A. Papoulis,Signal Analysis (McGraw-Hill, New York, 1977).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Hippler, J.H., Ermert, H. & von Bernus, L. Broadband holography applied to eddy current imaging by using signals with multiplied phases. J Nondestruct Eval 12, 153–162 (1993). https://doi.org/10.1007/BF00567083
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00567083