Integrated giant magnetoresistive transducer for eddy current testing

摘要

Among electromagnetic methods for detecting cracks in conductive materialsusing eddy currents, that based on the giant magnetoresistance (GMR) effectoffers promising characteristics. Besides high sensitivity to low magneticfield (comparable to anisotropic magnetoresistive sensors), GMR sensorspresent some distinct advantages versus other technologies when applied toeddy current testing (ECT). The unipolarity of the magnetoresistancecharacteristic eliminates the need for synchronous detection, leading to asimplified signal conditioning circuitry. Compatibility between GMR filmtechnology and the standard CMOS planar manufacture enables the integrationof the GMR sensor together with signal conditioning circuitry on the samesilicon chip. This paper reports the full-custom design of the CMOS signalconditioning circuit to be used in the integrated GMR transducer for ECT. Aneddy current probe comprising a GMR sensor and a pancake-type excitationcoil placed on the top of the sensor is presented and experimental resultsfrom scanning calibrated cracks using this probe are included within thepaper. Surface cracks as small as 2 mm in length were reliably detected.