A novel method for reducing the lift-off effect in coercivity measurement through auxiliary inductance data

Abstract

Coercivity is the strength of the reverse magnetic field required to demagnetize a material after saturation, and it is an indication of the hardness of the magnetic materials. Airgaps causes errors in coercivity measurement referred to as the lift-off effect. This paper proposes a new method to address this issue by incorporating additional inductance measurements and formulating a calibration method. The calibration principle is based on the fact that both the coercivity and the inductances measurements change with the variation of airgaps. This paper starts from finding how the coercivity changes with airgaps between the sensor and the sample, then derives the coefficients for coercivity-inductance relationship for different samples. A correction method is then proposed to predict the base coercivity (i.e., the coercivity when airgap = 0) using the inductance and coercivity measurement results at an unknown lift-off. The measurement system was implemented and experimental results suggest the error caused by airgaps can be reduced from 40% to less than 10%.