High frequency magnetic permeability of sendust ribbons made by a disk quenching method

Sendust ribbons, 18-26 μm thick, 5.5-6.5mm wide and several meters long, are made by a disk quenching method. Ribbons obtained are so mechanically ductile that it is easily possible to punch out ring cores with 3mm and 5mm inner and outer diameters, respectively. Roughness of ribbons is ±1 μm at disk surface and ±4 μm at free surface. The maximum value of the permeability at the frequency of 10kHz is 2.3 × 10⁴at the composition of 84.9Fe. 9.5Si. 5.6Al. The composition dependence of the permeability is found large below 100kHz, but becomes very small above 100kHz and the value decreases with frequency approximately as (f)^-0.9above 100kHz. The permeability decreases with thickness approximately as (t)^-1at frequencies above 200kHz. The permeabilities are within 1400-1700 and 400-500 at 1 and 4MHz respectively.