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How do you build an inexpensive faraday cage?

topic posted Tue, March 10, 2009 - 10:57 AM by  Unsubscribed
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I've been looking to build a faraday cage but the cost of copper foil from Holland is outrageous for my budget. Anyone have any suggestions?
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  • i've read that any metal box, grounded, will do the job. i've even seen pictures of one of those steel garden sheds, with a good ground pole and cable used as a large faraday cage. the key is that the device to be protected is well insulated from the inside of the box. i've also read that those mylarr 'space blankets will work..
    • I concure with Patrick
      • Jon
        Jon
        offline 2

        Re: How do you build an inexpensive faraday cage?

        Wed, March 11, 2009 - 10:20 AM
        Iam electrical engineer by no means so I went to the old referance library,according to Nuclear War Survival Skills by Cresson H.Kearny,p.#22it says to keep antennas short 10 inches or less and to disconnedt if EMP is expected,2 keep radio/electronics away from(6 ft)from any long metal conductors,3 electronics can be sheilded by placing inside a metal box 0r completely surrounding with aluminum foil (??? ) or metallic window screen..If it was me I would probably use military ammo cans and make sure they were well grounded.Hope that helps !
  • Unsu...
     
    I've researched this extensively in the past.

    ANY metal, properly grounded, will do, provided that the metal surface area is proportionally supported by sufficient thickness to safely conduct the ammount of electromagnetic energy it will attract.

    There is a mathematical algorithm to work it out, if you were engineering specific sizes of faraday cages and wanted to get the exact appropriate thickness of material needed. This is useful where weight is a factor, like in an aircraft or on a space station (launching metal into space is expensive)

    BUT for the layperson like you and me, the simple addage 'Overkill Never Fails' is good enough.

    To protect something that would fit in a shoebox (palm pilot, cellphone, hand crank radio, etc) You could simply wrap a shoebox in aluminium foil. Be sure to overlap the seams. Taping them wouldn't hurt, as it would ensure conductivity between pieces, and help resist snagging and tearing. It is doubtful whether such a small faraday need be grounded, but it can easily be done.

    For medium items, like a laptop, you could get by with the same approach and doubled aluminium layers, and this MUST be grounded.

    Larger items, like HAM radio components, desktop computers, etc, a frame of angle iron can be made, and then attach the thinnest gauge sheet metal you can find, to create the enclosure, fastened with bolts or ideally blind rivets (pop rivets)

    Large items can also be 'mothballed' in a grounded metal trash-can with the lid on. Problem solved.

    If you need visual access to a part, like a monitor display, you CAN use screen portions for your faraday without compromising much integrity. The trick is to make sure the mesh of the screen is smaller than the wavelength of the radiation you plan to intercept. In this case, simple 1/4'' square mesh screen like what's used for rat-cages is fine. This must be securely mounted and grounded to the rest of the faraday.

    TO GROUND a faraday box, the easiest way is to use your house's ground circuit, which is usually anchored to your metal water pipes going into the ground around your home. The way to tap into this system is through the little 'third hole' in your wall sockets. you know the one. you've got the positive and negative slits, and the little 'mouth' below those two 'eyes'... that third, mailbox-door-shaped hole is where you want to go.

    Get yourself to a hardware store. Find where they have extension-cord ends. Get the male end. The kind that comes apart, and you attach wires to the different screws inside, and voila, you have a new 'plug' on the end of your cord.

    Attach your ground wire to your faraday box. Attach the other end to the screw in the male-end-plug that corresponds to that ground-hole on your outlet. Voila. grounded faraday.

    If your house was wired correctly, there will NEVER be ANY current in that grounding hole. It's just there because some appliances with spinning parts, like motors, can develop a static charge which will build and build, leading to an internal arc which can serve as an instant conduit for the alternating current to get out of the parts it's supposed to be in. Having the chasis of your large appliances grounded to that third hole allows for instant dissipation of static charge, and no risk of sparking.
    • Unsu...
       
      Oh yea.... don't have the items touching the faraday box itself. ideally they need to be insulated... like in their own cardboard box, or somehow suspended away from touching the faraday box. The shoebox wrapped in foil is it's own insulation as long as there's no foil on the inside of the box.
      • Unsu...
         

        Re: How do you build an inexpensive faraday cage?

        Thu, March 12, 2009 - 10:13 AM
        Thousand, my idea was/is to build a cage for my F-150. So I am thinking that with the info you all have given me that a sheet metal barn properly grounded might make the faraday cage. As I understand it you're really creating a very large Gaussian surface and that seems as if it might work. My electricity and magnetism class in college was at 8:00 am, therefore I am not particularly well versed on this subject. I did manage to salvage a C however.

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