Method and apparatus for detecting flaws below the surface of an electrically conductive object
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United States of America Patent
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Mar 11, 1997
Grant Date -
N/A
app pub date -
Jun 7, 1995
filing date -
Jun 7, 1995
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A sheet inducer carrying a uniformly distributed ac current induces a sheet eddy current generally parallel to a generally smooth surface of an electrically conductive object. A magnetometer, preferably a superconducting quantum interference device (SQUID) magnetometer, detects the component of a magnetic field generally perpendicular to the generally smooth surface resulting from disturbances in the sheet eddy current caused by a flaw. Through appropriate selection of the phase angle between the detector signal and the applied current, the response can be adjusted to suppress surface flaws and enhance detection of flaws below the surface. The sheet eddy current is induced in multiple directions to detect flaws of all orientations and at multiple frequencies to refine determination of the size, shape, and depth of a flaw. An elongated solenoid is used to induce a circumferential sheet eddy current in elongated objects such as tubes and rods, and a current-carrying rod is used to induce a longitudinal sheet eddy current in an elongated tubular object.
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