Displacement measurement for ferromagnetic materials based on the double

This paper introduces a magnetic displacement sensor comprising of a double-layer parallel cables (PCs) magnetizer, tunnel magnetoresistance (TMR) sensors and magnetic flux concentrating plates (MFCPs). By uti-lizing a double-layer PCs magnetizer, the background magnetic field in the TMR sensor's location can be eliminated, while enhancing the magnetization field of the workpiece. This ensures that the highly sensitive TMR sensors operates within its measurement range. Additionally, the MFCPs concentrate the magnetic field at the TMR sensor location to further improve the displacement measurement sensitivity. After optimizing the geom-etry and excitation frequency of the probe with FEM, the probe can achieve displacement measurements with 0.1 mm accuracy in the range of 0.5-6.0 mm for ferromagnetic workpieces with linearity of 4.5 % and average relative error under 2.0 %.