Method and device for non destructive evaluation of defects in a metallic object
First Claim
1. A method for non destructive evaluation of defects in a metallic object by eddy currents, the method comprising the steps of emitting at least one alternating electromagnetic field at at least one first frequency fi in the neighbourhood of the metallic object and detecting through at least one magnetoresistive sensor a response signal constituted by a return electromagnetic field which is re-emitted by eddy currents induced by the alternating electromagnetic field in said metallic object,characterized in that it comprises the further steps of driving said at least one magnetoresistive sensor by a current at a second frequency fc which is different from said first frequency fi, so that said at least one magnetoresistive sensor acts as an in situ modulator and filtering the response signal detected by said at least one magnetoresistive sensor to keep either the frequency sum (fi+fc) of said first and second frequencies or the frequency difference (fi−
- fc) of said first and second frequencies before processing said response signal to extract eddy current information on defects in said metallic object (2).
2 Assignments
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Accused Products
Abstract
A device for non destructive evaluation of defects in a metallic object (2) by eddy currents, comprises a field emitter (3) for emitting an alternating electromagnetic field at a first frequency fi in the neighbourhood of the metallic object (2), and a magnetoresistive sensor (1) for detecting a response signal constituted by a return electromagnetic field which is re-emitted by eddy currents induced by the alternating electromagnetic field in the metallic object (2). The device further comprises: a driving circuit (230) for driving the magnetoresistive sensor (1) by a current at a second frequency fc which is different from the first frequency fi, so that the magnetoresistive sensor (1) acts as an in situ modulator; a detector for detecting a response signal between the terminals of the magnetoresistive sensor (1); a filter for filtering the response signal detected by the magnetoresistive sensor (1) to keep either the frequency sum (fi+fc) of the first and second frequencies or the frequency difference (fi+fc) of the first and second frequencies, and a processor for processing the filtered response signal and extract eddy current information on defects in the metallic object (2).
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Citations
33 Claims
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1. A method for non destructive evaluation of defects in a metallic object by eddy currents, the method comprising the steps of emitting at least one alternating electromagnetic field at at least one first frequency fi in the neighbourhood of the metallic object and detecting through at least one magnetoresistive sensor a response signal constituted by a return electromagnetic field which is re-emitted by eddy currents induced by the alternating electromagnetic field in said metallic object,
characterized in that it comprises the further steps of driving said at least one magnetoresistive sensor by a current at a second frequency fc which is different from said first frequency fi, so that said at least one magnetoresistive sensor acts as an in situ modulator and filtering the response signal detected by said at least one magnetoresistive sensor to keep either the frequency sum (fi+fc) of said first and second frequencies or the frequency difference (fi− - fc) of said first and second frequencies before processing said response signal to extract eddy current information on defects in said metallic object (2).
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 22, 23, 24, 25)
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11. A device for non destructive evaluation of defects in a metallic object by eddy currents, comprising at least one field emitter for emitting at least one alternating electromagnetic field at at least one first frequency fi in the neighbourhood of the metallic object, and at least one magnetoresistive sensor for detecting a response signal constituted by a return electromagnetic field which is re-emitted by eddy currents induced by the alternating electromagnetic field in said metallic object, characterized in that it further comprises:
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driving means for driving said at least one magnetoresistive sensor by a current at a second frequency fc which is different from said first frequency fi, so that said at least one magnetoresistive sensor acts as an in situ modulator, detecting means for detecting between the terminals of the magnetoresistive sensor a response signal, filtering means for filtering the response signal detected by said at least one magnetoresistive sensor to keep either the frequency sum (fi+fc) of said first and second frequencies or the frequency difference (fi−
fc) of said first and second frequencies, andprocessing means for processing said filtered response signal and extract eddy current information on defects in said metallic object. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 26, 27, 28, 29, 30, 31, 32, 33)
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Specification