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Thread: Faraday Cage Issues

  1. #1
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    Question Faraday Cage Issues

    Hello,

    I am currently building a faraday cage to keep WiFi out - for a science experiment. However, the phone still detects WiFi when inside the cage.

    It is essentially a 40x40x40cm cardboard box wrapped in Aluminium foil, with one side being conductive mesh with more than small enough-sized gaps. There is an opening at the back which is covered in foil and secured with metal drawing pins when the cage is in use.

    The foil covers the box entirely (outside only), and in some places is double or triple-layered. It is fixed with regular transparent tape or duct tape, which covers the foil where placed. There are also staples on the corners.

    The mesh and foil overlap, and this overlap is covered in duct tape.

    We have tried earthing the cage but the effects are negligible.

    Any ideas on how we could improve the cage and solve the problem?

    Many thanks,

    Dorfkrug

    TL;DR: Our faraday cage isn't working. Why?
    P.S. I hope this is the right forum section. Please let me know if it's not.
    Last edited by Dorfkrug; 11-18-2013 at 12:11 AM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    Welcome to EE!

    Quote Originally Posted by Dorfkrug View Post
    It is essentially a 40x40x40cm cardboard box wrapped in Aluminium foil, with one side being conductive mesh with more than small enough-sized gaps. There is an opening at the back which is covered in foil and secured with metal drawing pins when the cage is in use.
    You need copper or iron - aluminum doesn't work that well...

  3. #3
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    Thanks a lot Kelly!

    We will see if our school can get one of these materials for us. Which one is better or doesn't it matter?

  4. #4
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    I’ve had good luck using copper window screen and soldering all the joints to make faraday cages. Do you have any wiring penetrating the cage? They take special precautions. If you are stuck with aluminum foil; put it together with aluminum foil tape, available at any building supply store, not duct tape. Conductivity across the joints in the cage is necessary.

    Timelord



  5. #5
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    Quote Originally Posted by Timelord View Post
    Iíve had good luck using copper window screen and soldering all the joints to make faraday cages. Do you have any wiring penetrating the cage? They take special precautions. If you are stuck with aluminum foil; put it together with aluminum foil tape, available at any building supply store, not duct tape. Conductivity across the joints in the cage is necessary.

    Timelord

    We did not have any wiring penetrating the cage, but will do soon, going through the mesh. Is that OK considering the wire is insulated with plastic/rubber?

    We are now trying to make a cage using only mesh, as we have found that to work better than aluminium foil. One of the reasons why it didn't work before was that, as you say, there was duct tape between the layers of foil.

    Thanks.

  6. #6
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    You may find that a wire penetrating the cage will act like an antenna and conduct the Wi-Fi inside where it is reradiated. The solution is as simple winding your wiring thru a ring core just outside the cage which will reject any common mode signal.

    Timelord

  7. #7
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    We have not succeeded in making a Faraday cage that works 100%, but more like 70 or 80. Unfortunately we are running out of time and have to move on to the experiment the cage was originally intended for.

    But thanks a lot for your help.

  8. #8
    Lead Engineer Cake of Doom's Avatar
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    What size grid did you use to make the mesh?

  9. #9
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    The squares are 65mm wide, which is much more than enough for WiFi. Using the wave equation we determined the wavelength was 12.5cm.

  10. #10
    Lead Engineer Cake of Doom's Avatar
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    Academic now it's built, but perhaps the Wi Fi was running more towards the higher ranges (say between 3 to 5 GHz) which is why the cage didn't 100% work.

  11. #11
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    Could be. Thanks for your ideas. We will certainly add this to the report.

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