Flux focusing eddy current probe
First Claim
1. A flux-focusing eddy current probe for non-destructive evaluation of an electrically conductive material comprising:
- (a) an excitation coil for inducing eddy currents within the electrically conductive material, the excitation coil having windings wherein the excitation coil'"'"'s longitudinal axis is perpendicular to the surface of the electrically conductive material;
(b) a pick-up coil having an outer edge and having windings which are surrounded by the windings of the excitation coil; and
(c) a tubular flux focusing lens disposed between the excitation coil and the pick-up coil, composed of a conductive material having a high magnetic permeability, having a first opening opposite the surface of the electrically conductive material and having a second opening adjacent to the surface of the electrically conductive material and which prevents magnetic coupling between the excitation coil and the pick-up coil when said probe is placed above an unflawed electrically conductive material and which produces high flux density at the outer edge of the pick-up coil.
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Accused Products
Abstract
A flux-focusing electromagnetic sensor which uses a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks and material loss in high conductivity material. The unique feature of the device is the ferrous shield isolating a high-turn pick-up coil from an excitation coil. The use of the magnetic shield is shown to produce a null voltage output across the receiving coil in the presence of an unflawed sample. A redistribution of the current flow in the sample caused by the presence of flaws, however, eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal.
The maximum sensor output is obtained when positioned symmetrically above the crack. Hence, by obtaining the position of the maximum sensor output, it is possible to track the fault and locate the area surrounding its tip. The accuracy of tip location is enhanced by two unique features of the sensor; a very high signal-to-noise ratio of the probe'"'"'s output which results in an extremely smooth signal peak across the fault, and a rapidly decaying sensor output outside a small area surrounding the crack tip which enables the region for searching to be clearly defined. Under low frequency operation, material thinning due to corrosion damage causes an incomplete shielding of the pick-up coil. The low frequency output voltage of the probe is therefore a direct indicator of the thickness of the test sample.
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Citations
17 Claims
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1. A flux-focusing eddy current probe for non-destructive evaluation of an electrically conductive material comprising:
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(a) an excitation coil for inducing eddy currents within the electrically conductive material, the excitation coil having windings wherein the excitation coil'"'"'s longitudinal axis is perpendicular to the surface of the electrically conductive material; (b) a pick-up coil having an outer edge and having windings which are surrounded by the windings of the excitation coil; and (c) a tubular flux focusing lens disposed between the excitation coil and the pick-up coil, composed of a conductive material having a high magnetic permeability, having a first opening opposite the surface of the electrically conductive material and having a second opening adjacent to the surface of the electrically conductive material and which prevents magnetic coupling between the excitation coil and the pick-up coil when said probe is placed above an unflawed electrically conductive material and which produces high flux density at the outer edge of the pick-up coil. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A flux-focusing eddy current probe resistant to conductive material edge effects for non-destructive evaluation of an electrically conductive material comprising:
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(a) an excitation coil for inducing eddy currents within a conducting material, the excitation coil having windings wherein the excitation coil'"'"'s longitudinal axis is perpendicular to the conducting material; (b) a pick-up coil having an outer edge and having windings which are surrounded by the windings of the excitation coil; (c) a tubular flux focusing lens disposed between the exciation coil and the pick-up coil, composed of a conductive material having a high magnetic permeability, having an opening at opposite ends of its longitudinal axis and which prevents magnetic coupling between the excitation coil and the pick-up coil when said probe is placed above an unflawed electrically conductive material and which produces high flux density at the outer edge of the pick-up coil; and (d) a flux focusing shield which surrounds the excitation coil.
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17. A flux-focusing eddy current probe highly resistant to lift off conditions for non-destructive evaluation of electrically conductive material comprising:
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(a) an excitation coil for inducing eddy currents within a conducting material, the excitation coil having windings wherein the excitation coil'"'"'s longitudinal axis is perpendicular to the conducting material; (b) a plurality of pick-up coils each having windings which are surrounded by the windings of the excitation coil; and (c) a tubular flux focusing lens disposed between the excitation coil and the plurality of pick-up coils, composed of a conductive material having a high magnetic permeability, having an opening at opposite ends of its longitudinal axis, which prevents magnetic coupling between the excitation coil and the pick-up coils when said probe is placed above an unflawed electrically conductive material and which produces high flux density.
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Specification