Wednesday, April 27, 2016

How to Build A Faraday Cage

Faraday Cages are fairly easy to build and do not require a lot of material. Most people probably have most of the items lying around the garage or can obtain them at the surplus or hardware store. The idea of a faraday cage is relatively simple. Shield the object from electromagnetic energy with a metal cage or mesh. There should be minimal or no gaps and the object cannot touch the shielding that surrounds it. (continued below...)

Different items can be used for the metal shield. Some people have had success un using an ammo can while others have taken a cardboard box and lined it with multiple layers of heavy duty aluminum foil. Depending on what is used aluminized duct tape may also be needed. The following are only a few of may ways to build a faraday cage.

Metal Trash Can
Metal trash cans with metal lids are one option. The solid metal container not only provides a weather shield but also does well in protecting against a strong electromagnetic pulse. There are a couple of items to consider. First make sure the lid seals completely against the can itself. The better can and lid combos are the ones where the old overlaps the can. The concern is not air-tightness but rather to eliminate any major gaps in the container.  Second, make sure you line the interior with something like cardboard to create a gap between the metal and the items in the can. If the can is large enough you can put the items inside a cardboard box and set the box inside the can. Remember the protected items cannot touch the metal of the can.

Metal Lined Cardboard Box
Obtain a cardboard box the size necessary to store the items you wish to be protected. Any cardboard box can be used, but thick cardboard would be preferred. NOTE: The thickness of the cardboard does nothing to shield electromagnetic signals but rather offers a greater gap between the shield and the items you wish to protect. Remember the items inside the cage cannot make contact with the shield. Next, obtain a metal shielding material. The following are adequate items for the shield (pick one):

  • Heavy duty aluminum foil (need enough for three or more layers around the box)
  • Fine wire mesh
  • Reflective mylar from a cheap space blanket
If using aluminum foil, then wrap the outside of the cardboard box with three layers of the heavy duty material. Otherwise using the wire mesh or reflective mylar, completely enclose the outside of the box with the selected material. Make sure there are no gaps where the materials connect against each other. Also make sure the material holds to the cardboard. Insert any items into the box that needs protection. 

Ammo Can
Find an ammo can at a surplus store, gun show, or sporting goods store. Make sure the ammo can is metal. A plastic ammo can will do no good. Line the inside of the can with cardboard to insulate any device from touching the outside of the can. Place items that need protection inside the can. Obtain aluminized duct tape (or any conductive tape) and tape around the lid to conductively seal the can. 

Some people have said that a microwave oven can also make a good faraday cage. In theory this should work because the lining of the microwave is designed to keep harmful radio waves from exiting the unit when it is in operation. The same lining should help protect sensitive equipment from outside electromagnetic energy. However some have reported their testing of microwave ovens did not perform as expected. Note that the microwave oven is designed to shield the energy produced by the magnetron at its frequency of operation. Also assume the quality of some ovens may be in question. Therefore don't stand too close when nuking your leftovers.

If possible, ground your faraday cage by attaching a conductive wire from the box/cage/can to a ground rod in the ground. This does not aid in shielding your equipment but it does help in making the box safe. If an EMP occurred and the box was not grounded it is possible that the box become energized with no way of escape. This energy could be transferred to you by making contact with the cage soon after the event. 

The success of the faraday cage depends on a number of things. The following checklist of questions is important: 
  • Is the cage well sealed with little or no metal gaps? 
  • If using aluminum foil, are there sufficient layers of foil on the box?
  • Is the equipment to be protected isolated from touching the metal of the cage? 
  • Is the box grounded for safety?
If you have assembled your box you can test basic functionality by putting a small radio inside the box. Make sure the radio is on and the volume turned up. Sealing it inside the box should cause the radio lose signal. This is a basic test and not all inclusive. Keep in mind that a faraday cage will not remove all frequencies and therefore is not the perfect solution in all applications. But it can help protect against certain wavelengths of electromagnetic energy. 

Another factor that would determine success of the faraday box is the power of the EMP and the distance from detonation to the faraday cage. Too close and you won't have to worry about it. 

Have fun!

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