(a) The coil with no debris
(b) The coil with nonferromagnetic debris
(c) The coil with ferromagnetic debris
Figure 1: The schematic drawing of the microinductance sensor. The black arrow lines indicate the magnetic lines generated by the coil, the orange arrow lines indicate the magnetic lines of force generated by eddy current, the blue arrow lines indicate the increasing magnetic lines by the ferromagnetic debris, and the white arrow lines indicate the direction of the eddy current, the irregular geometry indicates the metal debris, and the circular arrangement indicates the coil.