Optimum Yoke Shape Designs for Enhancing Flux Density in Dual-Halbach Arrayed Permanent Magnets

Dual-Halbach arrayed permanent magnets were produced with Dy-free Nd bonded permanent magnets whose external dimensions were 14×14×4 mm. The dual-Halbach magnets were arranged facing different poles with a 6-mm-distance air gap using the back yoke. The magnetic flux density at the center of the air gap was measured with a two-axis Hall prober and was also numerically calculated with the three-dimensional finite-element method. The flux density was enhanced with the front yoke by 9% compared to that without the front yoke. The front yoke also improved the irreversible flux loss after high temperature annealing. Furthermore, a 2.2% increase was successfully achieved with fragmentation of the back yoke. The calculated three-dimensional flux structure indicated that the efficient magnetic circuits with less stray flux to the outside enabled further enhancement of the flux density even in magnet arrays that involved complex multi-poles.