Noncontact measurement of bending stress using a magnetic anisotropy sensor

The magnetic anisotropy sensor (MAS) is based on the phenomenon that steel materials, when brought under application of stress, changes their magnetic anisotropy. The MAS has a small, light probe and is capable of noncontact stress measurement. In this paper, the magnetic anisotropy existing in steel materials is related to directional permeability, and on the assumption of elliptical distribution of directional permeability, a conversion theory is derived. It is derived from the theory that, in the range where directional permeability changes linearly with stress, the MAS output voltage changes linearly with stress. Experimental results disclosed good linearity between MAS output voltage and stress over the range of stress measurement -200 ∼ +200 [MPa], verifying the validity of the theory.