Method and device for non destructive evaluation of defects in a metallic object

摘要

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).