Non-destructive evaluation of magnetic metallic materials using Hall sensors

In this paper we present a laboratory developed Hall sensor for non-destructive testing of ferromagnetic surfaces, based on magnetic anomaly detection phenomena. The principle of operation is based on the detection of the magnetic flux leakage in the dimensional boundaries of a gap, mainly of the vertical component Bz referring to the surface plane. Hall sensor is set parallel and very close to the magnetized surface, so as to increase the sensitivity, since the present fields are relatively weak. Small changes in its direction and lift-off movements result in decreasing and noisy output signal. Sensor properties in combination with an appropriate signal processing unit and an effective and fully controlled inspection technique can be used to applications where a rapid and qualitative inspection is needed.