Theoretical investigation of eddy-current induction for nondestructive evaluation by superconducting quantum interference devices

An analysis of eddy-current induction is presented for applications in low-frequency electromagnetic nondestructive evaluation (NDE) using superconducting quantum interference devices (SQUID's). Analytical expressions are developed for the induced eddy currents, as well as the resulting magneti...

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Bibliographic Details
Published in:IEEE transactions on magnetics 2000-01, Vol.36 (1), p.292-298
Main Authors: Claycomb, J.R., Tralshawala, N., Miller, J.H.
Format: Article
Language:English
Subjects:
Applied classical electromagnetism
Conducting materials
Conduction
Eddy current testing
Eddy currents
Electromagnetism
electron and ion optics
Exact sciences and technology
Excitation
Fundamental areas of phenomenology (including applications)
Interference
Magnetic analysis
Magnetic fields
Magnetic materials
Magnetism
Magnetostatics
magnetic shielding, magnetic induction, boundary-value problems
Mathematical analysis
Nondestructive testing
Physics
Quantum mechanics
SQUIDs
Superconducting coils
Superconducting devices
Superconducting quantum interference devices
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Summary:An analysis of eddy-current induction is presented for applications in low-frequency electromagnetic nondestructive evaluation (NDE) using superconducting quantum interference devices (SQUID's). Analytical expressions are developed for the induced eddy currents, as well as the resulting magnetic fields produced by circular excitation coil above conducting plates of infinite and finite thicknesses. The in-phase (0/spl deg/) and quadrature-phase (90/spl deg/) components of the eddy-current density are plotted for the low-frequency excitations characteristic of SQUID NDE. The quadrature-phase eddy current has a peak value at the surface of conducting plates, while the in-phase eddy current is maximal at a characteristic depth in the conducting material. Also, both the quadrature- and in-phase eddy currents change signs at characteristic depths that depend on the skin depth. These features can be exploited in determining the depth of material defects. The expression for the magnetic field produced by an excitation coil above a conducting plate of finite thickness is then used to estimate the SQUID's response due to corrosion or variation in material thickness. The expressions derived here can be used to model the magnetic signature of localized defects.
ISSN:0018-9464
1941-0069
DOI:10.1109/20.822539