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Old 03-03-2009, 12:57 PM
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Default Faraday Cages

With all of this Talk about EMP, I thought something should be said about Faraday Cages.

A Faraday cage is an enclosure formed by conducting material; or by a mesh of such material; to block out external static electrical fields. Faraday cages are named after physicist Michael Faraday. For more information on how Faraday cages work you can go to http://en.wikipedia.org/wiki/Faraday_cage. Below are just a few examples of Faraday cages:

Faraday Boxes: A Faraday boxes are a metal box designed to divert and soak up the EMP, by having the object inside the box is insulated from the inside surface of the box.

Homemade Faraday Boxes
The only two requirements for Homemade Faraday Boxes are:
1. The equipment inside the box does not touch the metal container (plastic, wadded paper, or cardboard can all be used to insulate it from the metal)
2. The metal shield is continuous without any gaps between pieces or extra-large holes in it.
Many containers are suitable for make-shift Faraday boxes: cake boxes, ammunition containers, metal filing cabinets, etc., etc., can all be used. Faraday Boxes can also be made of wire screen, any porous metal or by simply using the cardboard packing box lined aluminium foil.

Faraday Blankets: The Faraday Blanket are for larger items which cannot be boxed, such as living room TV sets, etc. The Blanket is basicly a Mylar space blanket with a piece of 6mm black plastic sheet, leaving a 2” edge of black plastic showing all around the blanket. The blanket can be draped over any object.

Faraday Cage: A Faraday Cage is a room lined with copper or aluminium foil, with the floor covered with a false floor of wood or with heavy carpeting to insulate everything and everyone inside from the shield (and EMP). The door is also covered with foil and electrically connected to the shield with a wire and screws or some similar set up.
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Old 03-03-2009, 01:39 PM
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Thank you for the explanation.
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Old 03-03-2009, 04:48 PM
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In other words, any gap bigger than say your fingernail is going to make it virtually worthless.

Therefore, car windows are definately going to render the metal body useless as protection for the electrics...

I believe the thickness of the metal has a lot to do with it too. Foil and thinner materials are fine for everyday protection, but you need something thick and solid to have a chance of standing up the the EMP produced by a nuke.
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Old 03-03-2009, 10:00 PM
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http://en.wikipedia.org/wiki/Faraday_cage
From that, it's about negating the charge rather than blocking it so you can have holes in metal as long as they are too small to allow the EMF wavelengths through. Most car electronics are in the boot or the enginebay, both of which would form some sort of shield.
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Old 03-03-2009, 10:56 PM
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However, wiring is usually throughout the vehicle and would act like an antenna, channelling the EMP waves right into the heart of things...
Yes, wiring is insulated, but not against EMP.

How long is an EMP wavelength?
Well, it appears to actually vary over a very wide range. While close mesh will help, it's not going to stop everything. The most common advice I've found is to make sure all holes are closed ie use solid sheeting in preference to anything else otherwise you're running a significant risk of at least partial EMP exposure (which if you're at 40,000 feet could be just enough to really ruin your day).

The quote below (from wiki) I think is rather telling.
Quote:
Misconception:Nuclear EMP is not a problem because there are ways to protect against it.
The fact: Although there are ways to protect against nuclear EMP (or to quickly begin repairs where protection is not practical), the United States EMP Commission determined that such protections are almost completely absent in the civilian infrastructure of the United States, and that even large sectors of the United States military services were no longer protected against EMP to the level that they were during the Cold War.
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Old 03-04-2009, 01:35 AM
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Quote:
Originally Posted by Legbreaker
However, wiring is usually throughout the vehicle and would act like an antenna, channelling the EMP waves right into the heart of things...
Yes, wiring is insulated, but not against EMP.
Yep, all too true
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