Weird permeability curve

This thing:

I don't know that it's actually that exaggerated, but it's behavior that matches with rolled silicon steel: low initial permeability, higher dynamic permeability. Typical figures are, say, mu ~ 700 below, oh I don't know, a kG? Average mu ~ 20k up to 10kG, then saturation in the 10-20kG range.

Or 0.1, 1 and 1-2T in non-heathen units. :^)

This is a wide difference, which is mostly attenuated by the distributed air gap. Evidently, the exact figures for this material (that is, the B-H curve of a single grain) are enough to give this response.

Note that this is not a B-H curve, but the cycle averaged slope (magnitude).

I guess it's not obvious if the cycle being averaged over, is, say, a sine wave in B, H, or some distorted waveform inbetween (say that you'd get from an LC resonant tank in the presence of this nonlinearity). The ratio depends on how much time is spent in each region, so a cuspy waveform might show a larger ratio than a smooth one; it matters, but isn't documented.

This is pretty useless for most purposes, even for yours I suppose -- check the core loss at 60Hz and 1000s gauss, it's still dissipating something! These materials (40, 26 and 52) are gnarly beasts.

That said, you may well have even smaller size if you opt for a "Hi-Flux" core, or a laminated material. If you can handle even more losses, that is.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: https://www.seventransistorlabs.com/ 

"Piotr Wyderski"  wrote in message  
news:p0tkfb$i6$1@node2.news.atman.pl... 
> While experimenting with my inductors, the Micrometals design 
> software plotted the following graph (iron powder): 
> 
> https://s18.postimg.org/gyx3fi989/weird_core.png 
> 
> Why does the inductance rises about 3 times as H increases? 
> This looks very much like a lambda diode, may be useful. 
> 
> Best regards, Piotr

Thats a lot, but the behaviour is pretty normal. Most magnetic material BH curves start with a low slope ( hence permeability is low ) for H near zero, then rise rapidly over the 'mid range', falling off to 1 as saturation is reached.

So you see exactly that, for low excitation field, the inductance is low, rises to a max as the field increases, then falls off again.

--
Regards, 

Adrian Jansen

I've seen that in silicon-steel tape-wound current transformers. L goes down and phase shift goes up below roughly 1 or 2% of rated current.

The Micrometals things are often powdered iron and behave like cheap steel. But they do now have some cool-mu equivalents that behave better.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

But why the initial increase? A form of magnetostriction or what?

Best regards, Piotr

The physics of ferromagnetism is complicated.

I'd expect that the "exchange interaction" is going to be different in a higher magnetic field than in a lower one, but this isn't an expert opinion.

Maybe Phil Hobbs or George Herold will know ... they did physics to a higher level than I did.

--
Bill Sloman, Sydney

How should I understand it? Won't see the bump in the DC case at all?

You're right, their design software is in full agreement with the above statement. But I'm more concerned about its thermal aging than the dissipation itself. Sad, the inductance bump is just about there where it is needed most. The HiFlux cores seem more promising/forgiving. MPP is too pricey.

Best regards, Piotr

Hah, not me. I want my ferro magnets to be spherical and have a constant permeability. Anything beyond that and I have to call in an engineer. :^)

Tim, Joerg or some other 'magnetics' guy may know. (Does it have to do with getting more domains pointing in the 'right' direction? Or is that just the linear part of it?)

George H.

No, just 'remanent' magnetism. There are energy barriers, tiny ones, in moving magnetic domain walls through these materials. Every flaw in the crystal structure is another bump in the road...

That's why tape recorders needed an ultrasonic-frequency bias, to ensure that the tape's magnetisation doesn't remain stuck on zero when a small signal is imposed on it

The simple answer is that 'it just does'. Seems to apply across all magnetic materials I know of.

Probably a search in some reference work like the old Philips "Ferrites" by Smit and Wign would give you some clues. Magnetics is pretty complicated at the domain level. Nearly everything down there is non-linear in all sorts of ways.

By comparison, metallic electric conduction is a piece of cake !

--
Regards, 

Adrian Jansen

Thanks, an easy find.

12M pdf Woah! its a whole book. 387 pages. I'm not going to get through that tonight. :^)

George H. Magnetics is pretty

If you are collecting books on ferrites, here's another by Snelling a decade later. Full text search, about 15MB, 411 pages

If that doesn't work due to the wrap, here's the tinyurl

ade

I've read Snelling. It's horrible. It seems contains everything that anybod y had ever measured before Snelling started writing but it's a pedagogic di saster - there's no attempt to pull the data into any kind of coherent whol e, and Snelling is the last person to go to the trouble of explain why perm eability might increase with increasing magnetic field (up to a point).

He'd point out that it did, and how the effect varied between materials, bu t he seems to have seen his job as purely cataloguing what happens, with ma king any kind of sense of what he was reporting as above his pay grade.

This isn't the first time I've been rude about his contribution here.

--
Bill Sloman, Sydney

[about low-field magnetic susceptibility]

Cool book; page 70 is clue-ful.

Chap. 5 is an OK read. I didn't know of Weiss domains and Bloch walls. Back then those guys got to have all the fun.

George H.

Yeah, I only skimmed bits of it, Thanks Adrian.

(figure 16.3 Bulging Bloch walls. :^)

George H.