Non linearity anomaly of power losses vs. frequency in various soft magnetic materials

The anomalous non-linear behavior of the power losses per cycle P/f vs. frequency f has been investigated in various materials: oriented and nonoriented FeSi 3%, FeSi 6%, mild steel, pure Fe, ultraperm, mumetal, FeNi 50-50 alloys, and FeCo 50-50. Measurements were performed down to very low frequencies, typically between 1 and 80 Hz, by means of a specially designed high precision wattmeter, under controlled sinusoidal flux conditions. The non-linearity anomaly is found to be a rather general phenomenon, not only limited to the well known case of Goss - texture FeSi, and to be particularly strong on transverse laminations of oriented FeSi 3%, on cubic texture FeSi and on FeNi 50-50. It further appears to be very pronounced at very low frequencies: in this region the models which relate the non-linearity to changes of stripe domain spacing with frequency seem somewhat inadequate, since they would require variations of domain spacings much too large than apparently observed so far. It is suggested that local flux distortions may qualitatively justify at least in part the strong non-linearity of P/f vs. f, in the very initial frequency range.