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Super-tiny ferrite rods anywhere?

Discussion in 'Electronic Design' started by Joerg, Dec 21, 2012.

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  1. Joerg

    Joerg Guest


    Looking for a way to either buy very tiny ferrite rods or have them made
    somewhere. Like this:

    Except that we need to get the diameter down 0.004" (0.1mm). Length
    0.120" to 0.160" (3-4mm) but that's easy to cut. We need to make coils
    with these ferrites that will be used in the >10MHz range, so 43, 61 or
    67 material would be ok.

    Do you guys know any sources or shops that can machine ferrite to such a
    small size?
  2. Guest

    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

  3. Guest

    extruded and fired/baked like how they make pencil lead

  4. Tim Williams

    Tim Williams Guest

    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

    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

    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?

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

  6. tm

    tm Guest

    Maybe you can wind the coil and dip it is a Fe loaded epoxy.
  7. 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
  8. John S

    John S Guest

    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.

  9. Ouch, that sounds really hard. (I know that might just spur you
    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.
  10. Joerg

    Joerg Guest

    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.
  11. Joerg

    Joerg Guest

    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.
  12. Joerg

    Joerg Guest

    T-coils are much larger.
  13. Joerg

    Joerg Guest

    In our case it's all meggeehoitzish :)

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

    Joerg Guest

    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.
  15. Joerg

    Joerg Guest

    Their ferrite antennas are huge monsters compared to ours :)
  16. Joerg

    Joerg Guest

    It sure does :)

    Not yet. My experience with large companies is that they wave off the
    minute you want baked potatoes instead of fries with that.

    Yeah, we can use other materials but they all come with a penalty.
    Generally in the form or less or much less inductance for the max number
    of turns we can get on there. We need all the inductance we can get.
  17. Guest

    How much inductance?? And what frequency range? ">10Mhz" isn't a range; it's a lower limit.
  18. Joerg

    Joerg Guest

    The goal is to get above 5uH. Frequency will be determined by how much
    inductance we get because the capacitance will be fixed (most likely
    around 5pF). That's why I wrote >10MHz, because it is unlikely we can
    get below that. Worst case we'll end up at up to 80MHz. Of course, for
    obvious reasons we want to really avoid the FM band and also the
    aircraft band above that. So 80MHz is a hard limit for this case. Lower
    = better.
  19. Am 21.12.2012 18:05, schrieb Joerg:
    Piconics prices are breathtaking.

    Mini Circuits comes to mind.

    When I was with Infineon Fiber Optics, I said to a MCL sales man
    that they could sell a bias tee for every ERA-8 or so if the
    price was right. Seems they listen. :)
    Ok, at least the price is better.

    BTW a colleague of mine decided not to wait until the Piconics
    samples were here, put ferrite into a mortar, added
    epoxy glue and formed some ferrite cores. They were ugly,
    but his conical coils where surprisingly good.

    regards, Gerhard
  20. Am 21.12.2012 18:15, schrieb Joerg:
    HAve you contacted Fair-rite (or others)?
    You might try Würth, also. They have been quite flexible for
    a friend, even for small runs.

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