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Buying or making an electret

  1. Apr 26, 2009 #1
    I am interested in buying or making an electret - preferably the oriented dipole version - not the probably more common real or surface charge version. I have read about the old procedure of making an electret from a mixture of beeswax, carnuba wax and rosin, but I think that by now there must be newer materials and procedures that produce better and longer-lasting electrets. Any thoughts? Thanks
     
  2. jcsd
  3. Apr 28, 2009 #2

    vk6kro

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    You can buy them at Radio Shack. Price $3.79.


    Electret Microphone Element with Leads
    Model: 270-092 | Catalog #: 270-092

    This omnidirectional microphone element has a wide 30-15,000Hz frequency response. Requires 4-10VDC.

    Probably cheaper ones around if you go hunting.

    These have an amplifier built into them and you need to add a load resistor of about 4.7K.
     
  4. May 3, 2009 #3
    Thanks for the tip on the Radio Shack electret microphones. So I bought two microphones and removed their electret diaphragms, but I was disappointed to find they did not exhibit any noticeable attraction or repulsion to each other or to anything. Perhaps because the opposite sides of the diaphragm might be charged to only a few hundred volts ( adequate for microphone operation but inadequate for electrostatic demonstrations, which usually involve thousands of volts). To measure such a static-charge voltage I would need a special meter, which I don't have.
    Since electrets are interesting, I thought I could easily buy them from science supply houses- but no such luck. I have read that electrets are used in microphones, air filters, copy machines and static cling films (for windows, stickers, etc.). Thus, I am thinking about buying some static cling stickers since they might be electrets. But I can't find any source that states definitely that static cling film is an electret, only that the film is made from PVC. And I would like to know which type of electret- ionic or oriented dipole. And what about the old child's toy, Colorforms (vinyl static cling stickers)? Are they electrets?
    Thoughts? Thanks
     
  5. May 3, 2009 #4

    vk6kro

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    Maybe we are talking about different things.

    Electret microphones only ever work on small voltages, up to 10 Volts, maybe.
    They are just condenser microphones with an amplifier attached.

    I don't see why they would attract each other. They are just microphones and have no magnets in them and not enough electric charge to attract anything.
     
  6. Sep 3, 2010 #5
    It appears you're not alone. I have searched for some time to find a supplier, and they simply do not exist on the web. As I mentioned to someone else on the forum, I think electric manufacturers are not interested in selling to individuals, but only to other manufacturers.
     
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