Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Faraday cage, lower frequencies

  1. Feb 21, 2016 #1
    Faraday cages of the conducting type are not effective for lower frequencies; https://en.wikipedia.org/wiki/Electromagnetic_shielding#Magnetic_shielding mentions a frequency of 100 kHz. The electromagnetic spectrum is composed of both an electrical, and a perpendicular magnetic field. If a faraday cage works by 'earthing' the electrical field, would the cages effectiveness depend on its size? For lower frequencies the wave length is longer, so does the electrical field 'dodge' the cage? hence the need to saturate the magnetic field with Mu-metal.
     
  2. jcsd
  3. Feb 21, 2016 #2

    berkeman

    User Avatar

    Staff: Mentor

    You are confusing a Faraday cage with Magnetic Shielding. A Faraday Cage is not meant to shield Magnetic fields -- it is generally just for Electric field shielding and shielding RF EM..
     
  4. Feb 21, 2016 #3

    davenn

    User Avatar
    Science Advisor
    Gold Member

    and it also doesn't work by earthing the electric field ... a Faraday shield can be completely isolated from earth/ground
    and will still shield the inside from the outside fields or visa versa


    Dave
     
  5. Feb 21, 2016 #4

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Right. It just reduces the PD across the cage by conduction. The more conductive the surface (including seams, doors and signal connectors), the better the screening. There will be currents flowing over the outer surface and these can end up flowing on the inner surface if there is finite resistance across any gaps. It is possible to treat the gaps round doors (as in microwave ovens) over a small range of wavelengths by including a system of quarter wave slots which, cleverly, present a short circuit across the finite door gap.
     
  6. Feb 23, 2016 #5
    Are there any other references as to at what (low) frequency faraday cages become ineffective?
     
  7. Feb 23, 2016 #6

    berkeman

    User Avatar

    Staff: Mentor

    Faraday cages work down to DC for electric fields.

    Can you say what your application is? Maybe we can help you figure out your optimum shielding solution... :smile:
     
  8. Feb 23, 2016 #7

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    If your knowledge (like mine) is not sufficient to make a good engineering choice of design then you should read as much stuff as you can find. This link seems well informed but there is a lot to read and there is no 'single figure' answer to your question.
     
  9. Feb 24, 2016 #8

    tech99

    User Avatar
    Gold Member

    But magnetic shielding can be obtained using a non magnetic conducting shield, provided the fields are alternating and the frequency is high enough. For example, radio frequency inductors can be shielded magnetically when placed in an aluminium can. The action is caused by the eddy currents induced in the shielding conductor.
     
  10. Feb 24, 2016 #9

    berkeman

    User Avatar

    Staff: Mentor

    Sure, I use that all the time. That's why I asked the OP to tell us more about their application. It's hard to know what they really want, and so far their posts haven't really helped us to figure it out... :smile:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Faraday cage, lower frequencies
  1. Faraday cage (Replies: 3)

  2. Faraday cage ? (Replies: 5)

  3. Faraday cage (Replies: 10)

  4. Faraday Cage (Replies: 1)

Loading...