Development of magneto-impedance microsensors for the detection of deep-lying defects using eddy current testing

The detection of deep-lying small defects using eddy current non-destructive testing (NDT) involves high spatial resolution and AC field measurement capability. For this purpose multilayered Finemet®/Copper/Finemet magneto-impedance microsensors were elaborated by microfabrication process. The films were deposited separately by sputtering using bi-layers lift-off method. A post-annealing step was achieved under magnetic field, which led to induce a transversal anisotropy in the magnetic films. A method based on double amplitude demodulation was proposed for the AC sensitivity characterization. A sensitivity of 2100 V/T/A has been measured and the sensors presented no hysteresis since a DC bias field larger than anisotropy field is applied. In addition, the sensors sensitivity remains constant up to 1 kHz.