Patent ID: 8063631

Claim:
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 reemitted 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.