A novel apparatus for measuring permeability of weak magnetic materials

Weak magnetic materials are widely used for electric and electronic devices. In this paper, a novel apparatus is described for measuring the dc permeability μ_r of this material more precisely and easily. From the variation of a mutual inductance value in two different conditions, i.e., with and without the specimen situated in the gaps formed by a pair of cores, the permeability of the specimen can be obtained with a simple calculation. The advantage of this method is that only the ratio of two mutual inductance values is needed and the knowledge about exact mutual inductance values is not necessary. To eliminate the influence of distorted field distribution at the edges of the gaps, some corrections are derived from electromagnetic field calculation. The measurement uncertainty of (μ_r-1) is about 8.7% for a specimen with μ_r=1.0013. This apparatus can be directly used for specimens in large plate shape so that the tedious preparation of specimens of special shape is unnecessary. Therefore, it may be used for industrial procedures where the dc permeability of the weak material is important.