Positive Faraday Cage

Discussion in 'General Electronics Chat' started by Atenuator, Oct 6, 2016.

  1. Atenuator

    Thread Starter New Member

    Jun 22, 2012
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    Hello, I am trying to block or redirect a strong magnetic field. I was successful for a while with building a makeshift faraday cage and grounding it. Now it appears the ground I was using has been biased, so the cage no longer functions. I was wondering if I could positive bias the cage by connecting to the positive post of a car battery to make the cage effective against the magnetic field.

    Thanks
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
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    Magnetic fields require hi μ materials to block. Biasing your cage won't do anything except possibly make it dangerous.
     
    Aleph(0) likes this.
  3. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Faraday cages are good for electric fields, not magnetic fields.
     
  4. Atenuator

    Thread Starter New Member

    Jun 22, 2012
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    the cage worked perfectly while I had a source of true or pure ground, with just aluminum and copper for the cage. I was thinking that because the ground attracted the electrons from the mag' field, that a positive potentialed cage might do the same.
     
  5. Atenuator

    Thread Starter New Member

    Jun 22, 2012
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    I am dealing with a field generated by equipment similar to a hospital MRI machine.
     
  6. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Is this a static magnetic field or if it's not, what frequency?

    Typical Faraday shielding requirements.
    [​IMG]
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    MRI uses a static magnetic field for the main coil.
    Inside the main coil there are gradient coils wich are pulsed to make the image.
    The Z-gradient is is line with the main coil.
    You will likely not notice the gradient pulses outside of the MRI magnet.
    You can hear the gradient pulses as ticking and buzzing, so they must be in the audible range.

    Bertus
     
  8. Atenuator

    Thread Starter New Member

    Jun 22, 2012
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    Yes it is static.
     
  9. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If the field is static then coils can counteract it.
     
  11. Atenuator

    Thread Starter New Member

    Jun 22, 2012
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    Any idea what that cost, or how I can build a simpler home version.
     
  12. sailorjoe

    Member

    Jun 4, 2013
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    You can get an explanation of Helmholtz coils on Wikipedia. In that article there is also a photo of a three axis Helmholtz coil arrangement around an electron microscope. After that, just google "Helmholtz coil" and you'll see things you can buy.
     
  13. Atenuator

    Thread Starter New Member

    Jun 22, 2012
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    Thank you.
     
  14. Aleph(0)

    Member

    Mar 14, 2015
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    @Atenuator Based on other post and now this I say you need to ground your al foil hat too:rolleyes:
     
  15. Atenuator

    Thread Starter New Member

    Jun 22, 2012
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    May God bless you.
     
  16. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Building the small coil structures and getting the power supplies to energize them is not the problem. Getting good reliable readings of the magnetic field inside and periodic calibration to maintain field cancellation settings
    Doing it is easy, doing it right is the hard part
     
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