Evaluation of the planar inductive magnetic field sensors for metallic crack detections

The planar inductive magnetic field sensors were fabricated by photolithography process. The sensor was composed of the planar coils (42 turns and 120 turns) with magnetic thin film as a core. To evaluate the sensor for crack detection, the nonmagnetic Al and magnetic FeC specimens were prepared with the circular and slit shaped artificial surface cracks. The alternative current (0.1 A to 1.4 A) with frequency range of 1.0–2.0 MHz was generated by the straight shaped driving Cu coil. In the case of 120 turns of planar inductive magnetic field sensor, the induced signals on crack positions exhibited the high intensities and stable signal to ratio as varying the driving current and frequency in comparison with those of 42 turns of planar inductive sensor. The measured output signals on FeC specimen with the micro-sized surface crack by the non-contacted scanning were converted to the image which was compared with that of the optical image, respectively.