From my relatively limited experience with them, laminated iron cores seem to give constant-loss results. Give or take. That is, at the eddy current cutoff frequency, real permeability goes from ~constant, to dropping
2nd-order like. Meanwhile, complex permeability goes up, peaks at cutoff, and comes back down, with linear slopes on either side.
That is to say: losses (parallel equivalent) increase linearly with frequency, until they become dominant, at which point impedance remains constant (permeability becomes imaginary, and drops linearly with frequency).
Physics tells us, it should be more of a f^0.5 (diffusion) slope. Depends on materials and construction. It could very well be that the exaggerated hysteresis loss of silicon steel (as compared to lower loss materials like Vitroperm or ferrite) contributes another f^0.5, more or less; or that the excitation B_pk is exploring an ever-smaller portion of the B-H curve, and thus permeability measures anomalously low (steel is particularly awful about initial permeability, that is, mu at very small B_pk).
At even higher frequencies, the capacitance between plates matters, and the permeability drops even faster (in the process, wrapping around the circle -- it goes from imaginary, to negative real: which is to say, the core looks capacitive).
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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"Tim Wescott" wrote in message
news:kv2dnXfFKcUMIkTKnZ2dnUU7-ePNnZ2d@giganews.com...
> Wanted to know the lead inductance of a motor. No RLC bridge, so I take
> my reliably-50-ohm output impedance generator, vary the frequency,
> measure the amplitude.
>
> One ought to be able to fit a model circuit to that pretty easily.
> Except that the voltage should be proportional to frequency at the bottom
> end. Instead, it's proportional to f^0.75.
>
> Grr. Off to do more testing.
>
> --
>
> Tim Wescott
> Wescott Design Services
> http://www.wescottdesign.com
>
> I'm looking for work -- see my website!