Super-tiny ferrite rods anywhere?

You might talk to shops- we have had some custom cores made (very expensive in small quantities), but nothing really small- this was for an application that was very, very special.

A note on communication terminology with shops- you'll most likely be talking about "centerless grinding" rather than "machining" per se. Maybe try All Diameter Grinding in Orange, CA 714-744-1200 .. if they can't do it, they ought be able to point you to someone who can. Grinding diamters down to a couple of thou (half of what you're asking for) is not unusual. Maybe start with the minimum Fair-Rite can do-

0.5 or 0.75mm, IIRC).

BTW, Tim W., I now have a 0.394" dia x 0.394" diamond grinding bit in hand (literally) and will hopfully try gapping an E-core over the holidays. They recommend mist or flood. It would be nice to get close to the 30K RPM limit, but I don't have a TP grinder . There's a 0.256" one that's rated at 60K RPM (4000+ SFM), 10-20x what I can get with the 0.394 bit and the spindle of either of my mills. I suppose I could try and clamp an air die grinder (noisy..).

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward" 
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There are spin coated ferrites (binder plus nanoparticles).. if you search for chips with integrated ferrite inductors you'll find some, but they're talking pH or likely nH at best, and probably a science project to boot.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
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Is it commercially available? I know some guys who have been following metglas developments (afaik it's sort of a subset of nanomaterials), but last I looked the research guys were mostly making their own in the lab.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
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you

Flat stuff, tape, is available. I bought a spool of it on ebay. The tape is wound on bobbins to make toroids. It's great for wideband CTs and DCCTs and stuff.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

you

So, useful at 10's or 100's of MHz?

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
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I've spoken with a coil winding company (in New England, IIRC) that can do microscopic coils- they seem to target biomedical anyhow.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

[about very-small-diameter ferrite rods]

Ferrite is an aggregate of carefully sized grains; the ferrite manufactories DON'T generally sell the powder, because that would give away their technology. And, grinding a built ferrite object into powder changes those grain sizes, so there's no hope of replicating the original material specifications.

That's ok. Even if we only get a 1.5x in inductance increase it'll sure be worth it. Also, sometimes you can line up deals with NDAs or by lining up a custom deal. For example, where a ferrite manufacturer has an in-house department or a trusted companion enterprise provide epoxy-ferrite mixes to us.

--
Regards, Joerg 

http://www.analogconsultants.com/

I was wondering that, too, but am too reserved to ask. ;-)

Essentially it's measuring minute changes of a variable capacitor. It's only 6pF and the variation is +/-0.5pF full scale. The capacitor is going to be 0.008" width and height. This is wired up as a super-tiny resonant circuit and, after 5ft of not very ideal cable we'll have to detect the resonance and track it. IOW, the system has to extract the FM-modulation and quiescent bias in this signal. In order for this job not to become too simple or boring, this is all going to be immersed in fairly conductive fluids.

Sounds all simple but when you have to do all this (less the electronics) in a metal cylinder of under 0.015" O.D. it becomes non-trivial. The challenge is that the coil can't be too close to metal or fluids or the Q and thus the resonance would almost collapse.

--
Regards, Joerg 

http://www.analogconsultants.com/

Thanks! Duly noted and will call them. Theye even have a web site:

That's one thing I was planning to do.

I hope your shop is heated :-)

Yesterday we had a guide dog meeting in an unheated warehouse. It was a great event but chilly.

--
Regards, Joerg 

http://www.analogconsultants.com/

I really enjoy meeting that kind of "almost-impossible" set of requirements.. good luck with it.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Germany.

wafers

Whether this particular venture will be profitable isn't sure, of course. That's what we engineers are for, to push the envelope and try to make the impossible not just possible but turn it into a product.

you

I only found links like this:

125um sounds just right, about 0.005" would be ok. Got to call Metglas after New Year.

--
Regards, Joerg 

http://www.analogconsultants.com/

Why resonate? Why not measure the 3T capacitance directly? fF resolution isn't hard, aF has been done with some accuracy.

My old Boonton 72 would measure 6+-0.5 pF easily at the end of some long cables.

I'd be concerned about variation in cable capacitance changing the resonant frequency. A 3T cap measurement doesn't much care about cable capacitance.

Or use one of Phil's fiberoptic interferance things. Presumably capacitance is just a surrogate for displacement.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

If the name of it jumps at you please let me know. I only know New England Wire but they don't do inductors and are in New Hampshire.

--
Regards, Joerg 

http://www.analogconsultants.com/

That's because there's roughly 5ft of cable between the place of measurement and the system. It moves around a lot. The unintended variations in the capacitance would suffocate any measured information unless we make sure there is a distinct local resonance that can be seen from afar.

cables.

In a not too noisy environment. We have to put this into a fairly quiet frequency band and remain very selective in the system filters.

It works, I've tried it on the bench here. But with slightly larger inductors of about 0.060" O.D., that's the smallest I have right now.

Can't use that for various reasons, one of them being IP.

--
Regards, Joerg 

http://www.analogconsultants.com/

Yes.

Still well above freezing.. I suppose we'll get some cold days soon and the rain will turn into something more inconvenient.

I've got a bunch of hard cider sitting in the garage- it's about at the perfect drinking temperature. Saves room in the dual-zone wine fridge for better stuff. ;-) The cold cellar is about right for reds.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

We've got some "La Fin du Monde" in the fridge, from your neck of the woods. Very good stuff. It seems it should be on sale now, considering that the world did not end on Dec-21.

Oh, and we also have "Delirium Noel" from Belgium. Can't wait.

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Regards, Joerg 

http://www.analogconsultants.com/

It's not NE wire... we do deal with them regularly.

A quick look, can't find them (they showed up at a trade show and I talked with them a couple of times, but we ended up designing our own coil winding machine). 8-(

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com