Step dB/dt switching characteristics of square loop, strip wound Ni-Fe toroids

Experimental step dB/dt magnetization characteristics are presented for toroidal cores prepared from 12 μm and 25 μm thick, heavily cold reduced, Ni50Fe50polycrystalline strip. The results relate to reversal rates (dB/dt) over the range 0.05 T/μs to 5 T/μs when cores are driven from remanence to saturation in an opposite sense. Two core geometries are considered; one in which the diameter ratios are essentially unity and one of more practical importance in which the ratio of outside to inside diameters is 1.5. The measurements demonstrate the effects of the increasingly non-uniform magnetization reversal with decreasing reversal rate and with decreasing material thickness in the practical toroids. These effects lead to extra losses not easily quantifiable from theory. The features of step dB/dt magnetization reversal in the radially thin toroids are discussed with reference to previous investigations.