Faraday cages

I must have missed that episode as I haven't seen any cages on Doomsday Preppers. I have them all saved so I'll go through them again and see if I can find that one. The cage must keep electromagnetic radiation out. The way that it works is that when placed in a field one side becomes positive and the other negative with a null field and no charge on the inside. Faraday cages do not need to be grounded unless you are operating equipment inside them that requires an external source. Not quite sure what the sparkplug test was for.

it just proves the stuff inside is isolated from the charge on the outside. (but that's all i understand about it, i'm a nurse, i know electricity shocks me when i screw with it. . . lol)

On the ammo boxes, take out the rubber gasket, remove paint from contact area and put in some fine steel wool in place of place of the gasket.

just did a lil experiment, and a couple of biscuit tins i have blocked the signal to my phone. with it in it's leather case, means i can potenially protect my small electronics like ipod, media player and a crank torch, radio, usb charger type things.

Cookie tins work great. I use them. You can insulate the interior, just remember not to insulate the container/lid interface. Very secure, very simple and you can hide them in plain sight!

Doomsday Preppers had an episode where a guy used a metal trash can for his bigger electronics ( Ham Radio etc) he tested it by hooking it up with jumper cables to a car battery, seemed to work fine...pretty expensive test though if it failed - lol

A metal trash can will work well too. However it has to be the type that has continuous contact around the lid. I also needs to be insulated on the inside. Connecting a car battery is not a good test. You would need a burst of electromagnetic energy to test it

Put your cell phone inside and call it. If it rings you do not have a good "seal".

If you want a good seal in the garbage can, use fine steel wool along the inside of the lid. If done right you can tape it in place, just make sure that the wool is twisted lightly to maintain shape.

Are Galvanized trash cans ok to use as Farraday cages?

Yes, as long as you get good contact all the way around the lid.

For those of you worried about good contacts around the lid of whatever metal container you are using for your cage you can easily solve conductivity problems with 3M® Copper Conducting Tapes. The tape AND the adhesive are conducting. It is a cheap and simple solution.

Thank you!

A few thoughts on this ...

1) Electromagnetic waves can appear anywhere from ELF (Extremely Low Frequencies) to beyond the visible light spectrum, and the properties of the wave varies with the wavelength. For instance, the military uses VLF (Very Low Frequency) transmitters to communicate with submerged submarines because VLF frequencies pass right through water while higher frequencies will reflect off water like light hitting a mirror. Very high frequency waves act like light in a straight line while lower frequencies will bend along the earth's surface.

2) Putting a cell phone in a faraday cage only proves that you can block electromagnetic waves at the 900 mHz range, not the full spectrum.

3) A microwave oven is designed to block microwaves, not lower frequency cell phone waves. Old C-band satellite dishes could use chicken wire as a reflector but the later K-band satellite signals would pass through which meant the use of a smaller mesh in dish construction.

4) If the container being used as a cage happens to be resonant (at the vibrational frequency) of the wave approaching it, that container could actually conduct the wave rather than block it.

Sorry to say I don't have any solutions at hand to the problem, but I hate for anyone to have a false sense of security without researching the matter further.

A metal container will work as long as it is sealed and the whole thing is electrically conductive. Depending on its intended use a Faraday cage cane be made of mesh. A simple formula dictates the size of the hole mesh depending on the frequency to be blocked. Generally to prevent transmission the holes need to be no larger than 1/10 of the wavelength of the signal. Therefore for a 3G cell phone that operates at a frequency of 2.1 GHz the holes in the cage should be smaller than 1.4 cm. That is why the front of a microwave oven is made of metallic mesh.

For our purposes, EMP protection a metal container with all solid sides is the best. Some metals conduct electricity better than others. Silver is the best, then copper followed by aluminum. For most of us cages made from these materials are out of reach but luckily any conducing metal will do. A galvanized trash can or a large cookie tin will work just fine. No false sense of security, it will work.

A cardboard box, severly wraped with aluminum foil will work.