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Ferrite impregnated Silicone?

  1. Sep 9, 2009 #1
    I have a PCB inside of a consumer product that our company does not make. It is emitting a great deal of RF noise in the 350MHz band. I am looking to find a silicone or epoxy with ferrite impregnated in it.

    Where can I get it?

    I won't be able to get the company that makes the board to change the design in the near future, they are too big and too slow to respond. I have reverse engineered the board and constructed a schematic. I have exhaustively tried various decoupling methods to kill the noise but have not found a solution that is suitable.

    Thanks
     
  2. jcsd
  3. Sep 9, 2009 #2

    negitron

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    You don't need ferrite, you need an electrically conductive material. Ferrite is great for magnetic shielding, but is terrible for RF EMI. Try something like this:

    http://www.mgchemicals.com/products/841.html?PHPSESSID=d41c883dc3548ebc1362bc3c166c5db7 [Broken]

    Be sure you ground all of the indvidual coated parts to the supply ground either with wires or spring-loaded grounding fingers.
     
    Last edited by a moderator: May 4, 2017
  4. Sep 9, 2009 #3
    Ferrite is used for their RF lossy energy absorbing properties.

    Check out - I didn't have to go very for for a good explaination
    https://www.physicsforums.com/showthread.php?t=183148

    If I put the EMI shielding on the board it will
    1 - require that I connect it to ground
    2 - short everything that I pour it on

    I know, I know, I can put silicone on and then paint the silicone with the EMI shielding. I fact, I have a can of it right next to me, I'll try it out

    But I still would like a source for ferrite silicone or ferrite powder
     
  5. Sep 10, 2009 #4

    MATLABdude

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    No, ferrite beads are meant to keep long cables from acting like antenna and radiating the RF noise. In a way, it's meant to plug the RF leaks (from the cables coming out of your shielded enclosure). The stuff Negitron linked to is meant to coat the inside of a plastic enclosure, thus leaving enough metal that there's RF suppression due to skin-depth effects. Or you could just use a metal enclosure.
     
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