Super-tiny ferrite rods anywhere?

Well, not exactly, but we had Coors (yes, the water-ey-beer company) make us a batch of tiny (40 mil dia, 0.5" long) ceramic rods as coil forms, for one of our magnetic field mapper systems.

But 4 mils sounds (how can I express this politely?) wildly ludicrously totally insane. Wouldn't they break if you tried to wind wire on them?

The Piconics inductors are something crazy like 40 gage wire, filled with ferrous-loaded epoxy. No self-resonance to 40 GHz.

damn how are you going to wind them? can't use standard smd?

doubt you can machine something that small and brittle I think they would have to be cast like that

-Lasse

Metglas! Or maybe steel or permalloy wire? Plated ceramic?

de

...

extruded and fired/baked like how they make pencil lead

-Lasse

And just as fragile.

Food for thought... how do they make hearing-aid telecoils? ...Jim Thompson

Just checking... you sure that's not a typo?

That's like... superconductor wire: a brittle ceramic, very fine, but made out of ferrimagnetic material rather than type II superconductor in this case.

Best thing I can suggest is, hope you're doing something in the billions units/year range and can get them made monolithically like ferrite beads. Or even thick film if it's really truely that tiny. Heck, if it's in the billions, maybe you can get a whole coil-on-chip monolithic process developed that puts ferrite and copper on top of silicon. Analog Devices would love that, I bet -- they already have their line of monolithic transformers, but those are air cored...

As I'm sure you already know, powdered iron is more common for inductors (as opposed to RFCs and transformers) at those frequencies. #61 and #67 are kind of on-par I'd say, of course you get more inductivity out of the ferrites.

Not sure how you might make a microscopic powdered iron choke anyway; I wonder if carbonyl iron can be deposited in a useful form directly?

Tim

Sounds microwaveish. Have you looked into the guys that do the micowave coils?

Cheers

Maybe you can wind the coil and dip it is a Fe loaded epoxy.

Nope. Make your own. Grind up some of your favorite ferrite shapes with a grinder or buy powder from some ferrite vendor. Find some tubing that's tiny enough. Pack the tubing with the powder, seal, and you're done. Just think of it as a ferrite bead with the hole and wire on the outside instead of down the middle.

If the increased diameter of the tubing is a problem, just mold your own from powder. Almost any thin glue should hold it together. Don't forget the mold release (grease). You're on your own for handling the very fragile result.

I think you may want to look for "CoorsTek" or something like that (I never heard it spelled -- just spoken). Born of the beer company, but does all sorts of fancy ceramic stuff. If you need it done and you have a great big pile of money, they'd like to hear from you.

The last I heard about them it was in a conversation about making a frame for some optics out of silicon carbide -- and it was a conversation with a guy who you can never tell if he's talking sensible mechanical engineering, or if he's strayed off into zap-ray science fiction, so I couldn't even tell you if what he was trying was sensible (well, other than the fact that Coors Tek was willing to take money to try it).

I believe these are the same guys who make ceramic nose cones for missiles and such like-- very capable company.. not sure if they do ferrites though. AFAIK ferrites require somewhat different processing.

Best regards, Spehro Pefhany

Hi, Joerg -

I seem to vaguely recall some conversation on this group a few years ago about "atomic" wristwatches and the ferrite rod antenna they used.

Maybe that will lead you somewhere.

Cheers, John

Coors has been in the commercial ceramics business for a very long time... I was buying Alumina "boards" for my hybrid circuits from Coors, 1970-73.

Coors uses ceramic for beer filtering. When their vendor quit the business they started making their own, and soon started selling on the side. ...Jim Thompson

Ouch, that sounds really hard. (I know that might just spur you on.) Have you contacted Fair-rite (or others)? Is there some other way to 'skin that cat'? JL suggested an iron or nickel (alloy) wire would that work? It'd be easy to try.

George H.

Did they send a six-pack along? :-)

You'd need other tricks, for example winding on a mandrel, torque coil open (in the direction where diameter increases), scoot over to the ferrite, gently release torque.

This is almost MEMS stuff and I may need to talk to MEMS folks about this.

Thanks, John, I'll talk to them. Iron-powder and ferrite-loaded epoxy are also an option. But it would need to be super-runny for this.

SMT won't work here. Unless there was stuff a lot smaller than 01005.

You probably can machine it. For example, leave the sides thick, machine down only a few millimeters in the center, break thick ends off. Of course this requires super-balanced machinery and nobody is allowed to sneeze with 10ft.

T-coils are much larger.

In our case it's all meggeehoitzish :-)

Do you have any company names that come to mind besides Piconics?

That's what I wanted to avoid if possible. Dissolved ferrite never reaches the performance of sintered ferrite. But if push comes to shove we may have to do it. I am a bit used to this process because in ultrasound we have to make acoustic backing material starting with a magic potion.

Thanks, Jeff, I have stored this document on my server. Just in case they ever pull it.