Development of a GMI sensor for evaluating microstructural degradation in ferromagnetic materials

A Giant Magneto-Impedance (GMI) based electromagnetic sensing device has been designed and developed using a nanostructured CoFeSiB microwire as sensing core element. The sensor consists of three segments, (i) signal generation and amplification unit, (ii) transducer with the bridge circuit and (iii) the detection circuit. The sensor output voltage is directly correlated to hardness variation in heat-treated 9Cr-1Mo steel and martensite volume fraction in the deformed 304 SS austenitic stainless steel. The amplitude of GMI voltage in defective welded pipe has also been investigated. The present study indicated that the developed GMI sensor can be applicable for structural health monitoring of service exposed engineering components.