Therefore, I'm seeing it from a permeability point of view. It's already given that as the frequency increases, the permeability of the core decreases:
http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29#Complex_permeability
... shows a curve illustrating this.
The effect would also be present in an air core system, but since air already has such a low permeability, the effect is less noticed.
Not saying you're wrong, by any means, because I'm not exactly a physicist, but that's where it points, to me.Steve
It appears that the "complex permiability" is just another way of looking at hysteresis loss.
but i have not read the referance recently M. Getzlaff, "Fundamentals of magnetism" to see how they are applying it.
as far as air is concerned...at Ghz perhaps, or perhaps a few thousand teslas before its sigificant.
as far as iron transformer cores, generators and such, the permiability of the steel is not a significant factor in the operation of the machine.
losses are dominated by eddy current which follows Hz^2 and hysteresis loss, which is linear with Hz and the old books say follows flux to the 1.6 power, but that's for old silicon iron from 1940.
today's iron losses follow the charts provided by the manufacturer.
the most sensitive part of any machine is the teeth, here a decrese in permiability would serve to reduce hysteresis losses, as regions of high flux around the edges and tips would be averaged out, and hysteresis losses would then decrease.
in a stepper motor there isn't much eddy current from spinning it, at least when compared to the eddy current
generated from running it.
I've got a 5 volt 4 amp 6 wire stepper motor (4 inch diameter, about 6 inches long). When you short all the coils and spin it, you'll find the torque and rpm linear to a point, (perhaps a hundred rpm) at which point it will let go and you can spin it at hundreds of rpm with a drill or even your fingers and there is relativly no torque whatsoever.
I suspect it is due to the hysteresis losses in the teeth, and teeth alone. keep in mind that although the stepper motor acts as a permanent magnet generator, you'll find that down the center of the shaft
(this particular motor had 7 magnets with 8 sets of disks with teeth) is a steel shaft.
when you run the stepper as a stepper motor, you can generate much higher torque than you can shorting the coils, because it stops acting like a stepper motor and more like a switched reluctance motor.