Improved Magnetic Tunnel Junctions Design for the Detection of Superficial Defects by Eddy Currents Testing

In the last decade, magnetoresistive sensors attracted great interest for integration in eddy current-based non-destructive testing due to their high sensitivity and signal to noise ratio in a large range of frequencies (from dc to hundreds of megahertz). In this paper, a sensor composed of several magnetic tunnel junction (MTJ) elements in series is optimized and included in a custom probe configuration for the detection of superficial defects. Since the signal magnetic fields are very low, a finite element modeling simulation was supporting the sensor design optimization. The MTJ chips were microfabricated, assembled with the excitation coils and used in experimental measurements of defects 400 μm wide and 500 μm deep. The experimental results obtained showed very good agreement with the simulations.