Demagnetizing Effects and Correction in Permeameter Measurements of Soft Magnetic Cylinders

摘要

The demagnetizing field H-d produced by local magnetic poles around the ends of soft magnetic cylinders magnetized in International Electrotechnical Commission type-B permeameter is studied experimentally along the major hysteresis loop M(H). The usual relation of H-d = -NpM is shown to be valid with a positive demagnetizing factor N-p < 0.0003, but at H similar to +/- H-cJ, the intrinsic coercivity, the action of H-d is anomalously characterized by an oscillation of N-p from -infinity to at H = +/- H-cJ with increasing vertical bar H vertical bar, owing to a local decrease of differential reluctance in the cylinder around where the maximum differential susceptibility occurs. These unusual demagnetizing effects make the M(H) measured at high vertical bar H vertical bar be rather accurate with often presented significant error at H similar to +/- H-cJ. Having an over-large measured HcJ, this error is systematic, and it may be corrected with a shift in H-cJ and a residual demagnetizing factor Delta N-p < 0.0001, if compared to demagnetizing corrected solenoid measurements of the same cylinders of large length-to-diameter ratio.