"Fred Abse" wrote in message
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Secondly, permeability may not be independent of frequency, in some
ferrites. A glance at published data will illustrate this.

Even just playing with an iron-cored transformer can give one an interesting
perspective. Apply square wave, variable frequency; measure current. At
low frequencies, the current waveform is a sloping triangle, due to
inductive integration. Fine and dandy. Increase the frequency: the slope
gets less and less (as a percentage of amplitude), and the resistive (eddy
current) component dominates. Now increase the frequency still further.
Instead of falling or remaining constant, the current amplitude will
actually increase, because less and less core is being used (the skin depth
is significantly thinner than the laminations) and the effective
permeability (which at this point is almost entirely imaginary, mu'') is
falling.

Hard to see the same in ferrite, but the same effects apply. Different
mechanisms, same effects.

Tim

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