Saturation and engineering magnetostriction of an iron-base amorphous alloy for power applications

The saturation magnetostriction λs of a ferromagnetic material is measured by determining the strain that occurs when the saturation magnetization vector is rotated through 90°. However, the magnetostrictive strain responsible for transformer noise is the net strain measured parallel to the applied field when the material is magnetized from the demagnetized state. Because of its engineering significance, we propose to call this net strain measured parallel to the applied field the engineering magnetostriction λe. The value of λe depends on the domain structure both in the demagnetized and magnetized states whereas λs is an intrinsic property of the material. In the present study, λe for an iron-base amorphous alloy, Metglas 2605S2, is measured as a function of the direction of the field induced anisotropy using a piezoelectric transducer. Although Metglas 2605S2 has a high value of λs (∼27×10−6), the value of λe in the longitudinal field annealed condition is found to be nearly zero. The magnitude of λe measured on a prototype transformer core is also discussed.