Use of GMR-Sensors for Eddy Current Testing

The conventional eddy-current testing is based on an induction pick-up coil as signal receiver. The measuring effect is proportional to the time-derivative of the magnetic flux. Therefore the sensitivity of the coils is reduced with lower working frequencies. A number of the applications, e.g. detection of subsurface defects in the inspection specimen, requires the use of low inspection frequencies because of the electromagnetic skin effect. Use of the sensitive magnetic field sensors such as SQUID's or magnetoresistive sensors can increase the efficiency of the measurement, since this type of the sensors compared with coils indicates frequency-independent sensitivity beginning with 0 Hz. The present paper reports to the application of a so-called GMR-sensor (GMR from giant magnetoresistance) as an EC receiver.