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

Abstract

A device for non destructive evaluation of defects in a metallic object () by eddy currents, comprises a field emitter () for emitting an alternating electromagnetic field at a first frequency fi in the neighborhood of the metallic object (), and a 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 the metallic object (). The device further comprises: a driving circuit () for driving the magnetoresistive sensor () by a current at a second frequency fc which is different from the first frequency fi, so that the magnetoresistive sensor () acts as an in situ modulator; a detector for detecting a response signal between the terminals of the magnetoresistive sensor (); a filter for filtering the response signal detected by the magnetoresistive sensor () 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 ().