Amorphous metal tape

I have a spool of the stuff. I could send you some.

The advantage is enormous permeability, the disadvantage is that it makes an inductor yet more labor intensive.

Have you tried Coilcraft? They are helpful. Newava does custom magnetics for us and is good.

Can you use a few small toroidal cores sort of bent around the available volume? Better yet, some standard parts?

I think you're talking about Metglas; some quick-quench alloys that have a non-crystalline amorphous microstructure, so cannot be usefully cold-worked or reheated without destroying its virtues.

It can be produced as a thin tape, suitable for winding into toroid shape, and a crimped spool can hold it there. Presumably, a shaped core and epoxy could make an oval, but applying a winding would be a challenge (just as with any toroid). It's springy stuff (remember, you cannot anneal it to make it soft) so there's some force required to keep it together. As for getting a sample, just buy a toroid and cut off the spool; it'll unwind into a long strip . There may be some glue, though; that's a chemistry problem.

Elna and Hitachi make such cores.

Roughly oval, tape wound core, sounds like R-core.

But for an inductor you want a gap, and R-core (or any tape-wound core) won't give much of that SFAIK.

John Larkin wrote: =================

** Should be smaller than a golf ball ( 42mm dia)

..... Phil

Yes, that's about the right volume. Normally we'd use two or three stacked toroid cores, but this customer doesn't have the form factor space for that.

Mike Coon wrote: ===============

** FYI :

any "gapless" magnetic core saturates very easily, losing its magnetic properties when used as an *inductor". Transformers are a different story, since primary off load currents are small.

For a compact inductor that passes significant AC or DC current, a carefully sized air gap is essential. This apples to laminated steel or solid ferrite cores - but not so much to powdered iron cores as the air gap is intrinsic.

Not a simple topic, bore your self to tears looking it all up.

..... Phil

Clive Arthur wrote: ===============

** IMO ought to be possible with a powdered iron bobbin and just the right turns.

Loudspeaker passive x-overs often have such inductors in them.

..... Phil

It saturates at lower ampere turns than a gaped core, and the permeability of an ungapped core tenbds to be a bit less predictable.

That does depend on the application.

It can useful, but "essential" depends on the details of the appllcation.

There 's a shortage of good texts, and a liberal supply of bad ones.

E.C.Snelling's "Soft Ferrite" is about a bad as they get. It's got all the information you could ever need presented in way that is particularly confusing and unhelpful.

The Siemen's Soft Ferrite data book and application notes was much less ambitious, and enormously more helpful. Siemens ferrites as now EPCOS parts, and it''s part of TDK. The late great Tony Williams e-mailed a couple of megabyte worth of most of them to his friends some time ago.

No need, that was sufficient unto the day, thanks!