# A good faraday cage?



## budgetprepp-n (Apr 7, 2013)

I have a aluminum tool box that's suppose to fit in the back of a truck. 
Would that make a good faraday cage?


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## HuntingHawk (Dec 16, 2012)

Yes as long as the inside is lined that nothing is touching the outside of the box.


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## stillacitizen2 (Jan 30, 2015)

Paint Cans work too.


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## HuntingHawk (Dec 16, 2012)

I like lining with thin Styrofoam so square or rectangular cages work for me better then round objects.


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## Big Country1 (Feb 10, 2014)

Here's a couple articles worth reading:
Electromagnetic Pulse Protection - EMP - Futurescience.com

AusSurvivalist - EMP Protection

Yes, it will work. The inside will need to be insulated, I use peices of old conveyor belt that i have laying around. Anything can be used really, wadded up papper, styrofoam, rubber, plastic etc. You just want a "space" between the metal and your objects. While i havent, Ive heard that "big" faraday cages should be grounded and it isnt as easy as you'd think.


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## Kauboy (May 12, 2014)

Any metal container, that is completely encased, can make a decent cage. If there are seams, they need to be sealed. Most people use a covering of foil, but don't trust just one sheet.
The principle behind a Faraday cage is to give electromagnetic energy a path of least resistance that causes it to avoid contact with your items inside. Thus, you want to make sure you have sealed insulation on the interior to keep all items away from the metal walls.


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## SOCOM42 (Nov 9, 2012)

I have US GI com shelters that are made of aluminum.
They are EMP proof, they even have stainless steel screening seals on the doors to keep out a pulse.
ALL are grounded into the water table, a must to work right.
ANY metal container will work.


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## Big Country1 (Feb 10, 2014)

A Faraday box is simply a metal box designed to divert and soak up the EMP. If the object placed in the box is insulated from the inside surface of the box, it will not be effected by the EMP travelling around the outside metal surface of the box. The Faraday box simple and cheap and often provides more protection to electrical components than "hardening" through circuit designs
which can't be (or haven't been) adequately tested.

Many containers are suitable for make-shift Faraday boxes: cake boxes, ammunition containers, metal filing cabinets, etc., etc., can all be used. Despite what you may have read or heard, these boxes do NOT have to be airtight due to the long wave length of EMP; boxes can be made of wire screen or other porous metal.

The only two requirements for protection with a Faraday box 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) and (2) the metal shield is continuous without any gaps between pieces or extra-large holes in it.

Grounding a Faraday box is NOT necessary and in some cases actually may be less than ideal. While EMP and lightning aren't the "same animal", a good example of how lack of grounding is a plus can be seen with some types of lightning strikes. Take, for example, a lightning strike on a flying airplane. The strike doesn't fry the plane's occupants because the metal shell of the plane is a Faraday box of sorts. Even though the plane, high over the earth, isn't grounded it will sustain little damage.

From one of the articles ive already linked.
AusSurvivalist - EMP Protection


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## SOCOM42 (Nov 9, 2012)

An old microwave will do quite well. 
Designed to keep RF in, works great in reverse.
As mentioned in last post, my shelters are grounded, if by chance someone was standing next to them ungrounded, they could get fried.
The FM's specify the grounding for EMP protection.
IF no chance of arcing then ungrounded is ok.


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## paraquack (Mar 1, 2013)

Everything I ead says there must be metal to metal contact between cover and container or you need to put a metal (preferably copper with conductive glue) over the gap.

SOCOM42, take a portable radio and find a good and strong AM or FM station and put it in your microwave oven. It WILL keep working. It is designed for a specific frequency. An HEMP is so much stronger it's like putting a fire cracker in a paper bag and expecting the bag to stop the explosion.
Yah, I know, heard the stories on the internet and tried it with my cell phone and I could not ring my cell phone. Cell Phones are only 1/4 watt of RF and the microwave will block it effectively. But and HEMP is so powerful and cover such a wide range of frequencies, it won't work. Try the AM-FM radio.

edit:

Stolen from: https://www.physicsforums.com/threads/microwave-faraday-cage.650830/
First, there is a common misconception that a microwave oven is a Faraday cage. It is not. Not even a close approximation. Go in your kitchen and open the door of your microwave. Look at the mating surfaces between the door and oven. There is no bare conductive metal at all, usually power coated sheet metal or plastic on both surfaces. It is essentially *wide open* from an RF perspective except right at 2.4GHz. Attenuation at 2.4GHz is achieved through the use of metal features inside the door that make the slot between the door and the oven look like a quarter wave reactive choke. 2.4GHz is essentially reflected back into the oven from the door/oven seam. This is why the door is so thick. The amount of attenuation at 2.4GHz is chosen to address human safety limits for RF exposure, with no consideration for RF communications. It is generally 30-40dB, At 30dB, 600W on the inside, enough to cook your chicken, becomes 600mW on the outside, about the same amount your cell phone radiates. This is a *lot* of attenuation when viewed from a human safety perspective, but only a modest amount of loss from an RF communications perspective. RF link budgets for WiFi can be > 100dB.


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## paraquack (Mar 1, 2013)

Here's some light reading about HEMP (EMP) and what is needed to protect electronics.

Protecting Your Electrical Equipment from Solar Flares

Electromagnetic Pulse - EMP Myths - futurescience.com

http://science.howstuffworks.com/faraday-cage.htm

http://www.futurescience.com/emp/super-EMP.html

http://www.futurescience.com/emp/vehicles.html

http://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-320.pdf

http://www.futurescience.com/emp/ferc_meta-r-321.pdf

http://www.futurescience.com/emp/emp-protection.html

http://www.dtic.mil/dtic/tr/fulltext/u2/771997.pdf

http://www.eei.org/about/meetings/meeting_documents/t-eternod.pdf

http://www.sunshineworks.com/faraday-cage-building-material.htm

http://boards.straightdope.com/sdmb/showthread.php?t=540036

http://www.findtape.com/product329/JVCC-CFL-5CA-Copper-Foil-Tape.aspx?idx=1&tid=25&info=copper%2bconductive


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## PaulS (Mar 11, 2013)

Any gap bigger than 0.1mm can allow enough of the E1 pulse into the container to damage the contents.
You need to have an overlapping contact between the lid and the box.
To be most efficient the box should be made of on of the four best conductors: Silver, copper, gold or aluminum. The least expensive and most available of these conductors is aluminum. The heavy duty foil that is used to wrap turkeys to bake is as good as you need - for the same cost as a galvanized can you can get enough foil to cover a room.


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