Abstract
Although superconducting quantum interference devices (SQUIDs) provide an exquisitively sensitive means for measuring magnetic fields, their usage in the past has been limited chiefly to biomagnetic research. However, over the past few years interest in applying SQUID techniques to the field of nondestructive evaluation (NDE) has blossomed [1]. Many experiments have exploited the sensitivity of SQUIDs for diverse NDE applications, especially those requiring large separation distances between the sensor and the item to be inspected. Our work instead has focused on the potential to detect very small defects with SQUIDs, specifically in thin-walled tubes. In this paper, we discuss three different methods for creating magnetic fields in tubes. The methods comprise (a) directly injecting a current through the tube, (b) using a separate induction coil to create induced currents in the tube, and (c) utilizing a ferromagnetic tracer technique. To illustrate the capabilities of each method, we present two-dimensional maps of the spatial distribution of the magnetic field as measured by a SQUID magnetometer — that is, SQUID images. The images will also be used to compare the sensing methods with respect to such practical considerations as relative sensitivity and signal-to-noise ratio.
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References
H. Weinstock, IEEE Trans. Magn. 27, 3231 (1991).
J.P. Wikswo, Jr., J.M. van Egeraat, Y.P. Ma, N.G. Sepulveda, D.J. Staton, S. Tan, and R.S. Wijesinghe, in Digital Image Synthesis and Inverse Optics, edited by A.F. Gmitro, P.S. Idell, and I.J. LaHaie (Society of Photo-Optical Instrumentation Engineering, Bellingham, WA, 1990), SPIE Proceedings Vol. 1351, p. 438.
D.C. Hurley, Y.P. Ma. S. Tan, and J.P. Wikswo, Jr., GE Corporate Research & Development report 92CRD072, 1992 (unpublished).
We used product #9C-M from Magnaflux (Chicago, IL), which consists of an iron oxide-based ferromagnetic powder in an oil-based aerosol.
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© 1993 Plenum Press, New York
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Hurley, D.C., Ma, Y.P., Tan, S., Wikswo, J.P. (1993). A Comparison of Squid Imaging Techniques for Small Defects in Nonmagnetic Tubes. In: Thompson, D.O., Chimenti, D.E. (eds) Review of Progress in Quantitative Nondestructive Evaluation. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-2848-7_80
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DOI: https://doi.org/10.1007/978-1-4615-2848-7_80
Publisher Name: Springer, Boston, MA
Print ISBN: 978-1-4613-6233-3
Online ISBN: 978-1-4615-2848-7
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