A Faraday cage is a metallic enclosure that prevents entry or escape of electromagnetic fields, including electromagnetic pulses (EMP). Survivalists care about this because nuclear weapons detonated high in the atmosphere cause EMPs that can affect (destroy) modern electronics, but not older electronics using tubes. This includes everything from communication to the computers that have been in most cars since the mid-1980s. The book One Second After deals with the aftermath of an EMP attack on the U.S.
Storing electronic items you don’t use daily – hand held radios, energy radios, laptop computers, GPS, other spare electronic equipment, etc. – in a Faraday cage/box is probably a good idea. It’s one of those low probability/ high risk scenarios; if you store those items in a Faraday cage and nothing happens, no harm. If there is an EMP, you’ll have that critical gear.
If you believe the potential threat is overstated, you can read a report by a government commission charged with investigating the issue. If you distrust the government because they tend to treat us as sheeple, this is one time there is not sugar-coating; see the Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack, April 2008 (PDF, 7MB). An excerpt from the preface:
The electromagnetic pulse generated by a high altitude nuclear explosion is one of a small number of threats that can hold our society at risk of catastrophic consequences. The increasingly pervasive use of electronics of all forms represents the greatest source of vulnerability to attack by EMP. Electronics are used to control, communicate, compute, store, manage, and implement nearly every aspect of United States (U.S.) civilian systems. When a nuclear explosion occurs at high altitude, the EMP signal it produces will cover the wide geographic region within the line of sight of the detonation. This broad band, high amplitude EMP, when coupled into sensitive electronics, has the capability to produce widespread and long lasting disruption and damage to the critical infrastructures that underpin the fabric of U.S. society.
Because of the ubiquitous dependence of U.S. society on the electrical power system, its vulnerability to an EMP attack, coupled with the EMP’s particular damage mechanisms, creates the possibility of long-term, catastrophic consequences.
Building a Faraday cage: There is a lot of information on the net about Faraday cages, some of it conflicting, none seemingly very authoritative. For example:
An ideal Faraday cage consists of an unbroken, perfectly conducting shell. This ideal cannot be achieved in practice, but can be approached by using fine-mesh copper screening. For best performance, the cage should be directly connected to an earth ground. [bold mine]
Note this says for “best performance” and not that it is a requirement. Other sites note that grounding is needed only for static discharge and is not necessary to protect the electronics inside the cage. Also see here (comments #13 and #23) and here (comment at 11:11am). Again, none of it authoritative.
Erring on the side of caution, I suggest grounding Faraday cages – but am seeking advice on this and will update if I get an answer. If you life in an apartment, finding an appropriate ground might be an issue. Note that anything put inside the can must be inside a non-conductive container such as plastic, rubber, wood, or cardboard. For more on building your own Faraday cage, see this.
Update: Also, test your Faraday cage. I purchased a small galvanized can – enough for a laptop, GPS receivers, emergency and hand-held radios, power inverters, and a few other electronics – thinking I would be set. However, both cell phone and GMRS radio signals passed through the galvanized can, grounded or not, and after ensuring the lid had a tight seal. The same is true of metal ammo cans, perhaps due to the gap created by the rubber seals, (though others still refer to this as a viable solution – search on “Faraday”). My own testing shows both method do not work for radio signals.
What does work? Aluminum foil. I tested both a cell phone and GMRS radio wrapped in common aluminum foil, and the did not receive signals if tightly wrapped. If the foil was loose, signals did get through. The video below also demonstrates wire mesh will work (poor OPSEC with phone numbers, though). In the near term I plan on constructing a Faraday cage and will post photos and video, updates to follow.
Update 2, 25 April 2010: I finally have a combination that will at least block radio signals (cell phone and GMRS/FRS). A shoebox carefully wrapped in foil did not work. Then I tried a slightly larger box (that the shoebox could fit into) and wrapped it with aluminum screen. Neither box alone blocked the signals, but nesting the foil covered shoebox inside the screen covered box blocked most signals. Placing the two into steel filing cabinet drawer completely blocked all radio signals.
But the signals aren’t the same as an EMP so I don’t know if it will actually work for that. Still it seems that demonstrating the ability to block at last some signals is needed.
It shouldn’t be as hard as it is to find clear, and especially credible, information on creating Faraday cages. I’ve still not found anything conclusive on the need for grounding but will go with what I have. In the off chance there ever is an EMP and it does work, I’ll have a pleasant surprise.
A couple months back I read on a website (don’t remember which) that aluminum foil would work to block cell signals. However, the article specified that the foil shouldn’t touch the phone. It recommended putting the phone inside a plastic sandwich bag, and then wrapping the package inside the foil. The article also specified that you should err on the side of too much foil, so that the inner package could be completely wrapped, with extra folds in the foil to cover/conceal any possible gaps.
It worked – I called the phone and it didn’t receive the signal and I left a message. Once I unwrapped it, I had my message waiting.
The article also mentioned nesting as a safeguard. You’ve got some good advice here.
For a Faraday cage, you want to use the best conductor available to you, most likely copper, as using silver would get expensive. Aluminum would be a second choice. You also want to use a solid conductor, not a screen. A screen will let certain frequencies pass though unimpeded, while a solid conductor will block all frequencies.
There is zero charge everywhere inside a thin perfectly-conducting spherical shell. This is the environment you are trying to create when you build a Faraday cage. Know that a corner will hold a greater charge than a flat plate (spherical shells are flat plates at atomic distances). Know that the quality of the conductor is important.
All dielectric materials (air, rubber, non-ferrous metals, glass, etc) have a dielectric constant. With enough power/ proper frequency, charges can bridge the dielectric (think spark plug). The cage seams should be welded or soldered in continuous beads. Any opening for access to the inside of the cage must seal perfectly and conductively on all edges.
The purpose of grounding the cage is to allow enough charges to flow from the Earth to the cage to offset the charges the cage takes on due to EMP-related events. The key is that those charges balance each other before the charges jump from the cage to your protected electronics (because you cannot build a perfect cage in real life).
As for electronics, protecting a cell phone is worthless, as the cell system will be toast. The GPS system may survive, though I suspect the government will shut off civilian access in the event of a nuclear detonation. I would also protect my LED headlamp, batteries, emergency radios, and my TI-89 calculator.
HTH
Thank Jesus that our prayers to God can never be shut down!
I think Mark missed something. The reason that the author was using a cell phone was to check to see whether or not the Faraday cages he was trying to make were working. Obviously if he could successfully call his cell phone while it was in the cage, then the cage wasn’t having the desired effect.
Mike raises a good point, so long as the author realizes the contrapostive isn’t true, i.e. because the cage blocks the cell phone signal that it would stop an EMP is not proved by the cage blocking the cell signal.
There are two points that must be understood before moving on… 1) A nuclear event is NOT the only source of EMP, it can be generated by specifically designed explosions of a non-nuclear nature, 2) There are two methods of mitigating the surge of power, first there is the process of conducting the surge to a ground and second, there is the reflective value of shielding. power strips with with a surge protector is useless against EMP, the difference between lighting (for which surge protectors are designed) and EMP is an order of magnatude at least. If you want a Faraday cage, use something that was designed to be one. An old microwave oven shell is specifically designed to shield and ground. The door has an RF gasket, the outer metal shell is very effective against outside RF and the ground is designed to keep RF within the skin and conduct it to ground. Make sure the RF gasket makes contact with the door and the frame and closes tightly. There is a reason that old systems were less vulnerable to EMP and it’s not the presence of tubes as noted above. It’s the use of full 110V throughout the system, rather than the greatly reduced (and more efficient) use of tiny voltages. A component that is expecting a full 110/220 Volts is unlikely to be damaged by EMP, however a component expecting 1/2 Volt is easily damaged by a pulse. One last note on EMP, it’s not an effective weapon for great distances. In a battlefield application, it’s a good tool, but as a strategic weapon, it’s effective range is a great deal less than the combined impact of a high altitude detonation interrupting the entire RF spectrum and the EMP impact combined.
Careful with the aluminum foil bags. Shoplifters often use a similar construction to block the signal from RIFD security tags. The bags (sometimes referred to as “magic bags”) are therefore considered a burglary tool and possession of one in the wrong place could lead to some unwanted legal attention. If it stays in your home no problemo, just be careful not to stroll around WalMart with one.
A good inner “last line of defense” shell would be the anti-static bags that computer components are shipped in. They’re pretty common these days too.
What about using an old refrigerator as a faradays cage by running a ground wire to a grounding rod outside?
I have an old refrigerator that has quit working and I currently use the freezer portion to store an emergency radio, batteries, and flashlights.
I use the bottom portion to store Bulk Rice, Beans, and Sugar.
Curtis, even if not effective in the prevention of EMP damage, that is a great storage idea to prevent vermin and insects from getting into your emergency supplies.
New to this but am a ham operator and trying to protect my gear as I’ll be a lifeline if I can get on the air post EMP whether man made or natural. I’ve read if you plan to ground then make sure the ground is really short. This means you’ll block the low to HF but not VHF and UHF part of the emp. I tested a couple of radios at 146mhz and the one in the galvanized can picked me up on low power no problem. I have yet to try it nested without the antenna. But if the suits the power line guys wear is based on induction and faraday’s discovery we aren’t really worried about radio waves because if we are – then the simple grounds and things like that won’t work – you’ll need layers and the more the merrier. – Steve
Reply to Steve’s comment. The length of all wires leading to the Faraday cage defines the frequency that they will conduct best, it’s an antenna, whether it’s short or not. We found while doing a very large scale hardening test some years ago, that the bestcables are the old ones, that were wrapped with something that both reflects and conducts. The reflective nature is some help and that which is conducted can be carried to a ground. The project I mention was the hardening of a naval vessel and the best results were with older cables. Distance from the source is a good thing, as is shielding and grounding. Keep in mind that is the weapon is a non-nuclear device, you stand a chance, but if it’s nuclear, the rise time renders useless, any off the shelf power interruption tools. The disruption of the spectrum will also make communications difficult for days as well. The best solution is to isolate the equipment by cutting outside sources entirely if threat is expected or the gear is not in use.
The best way to build a faraday cage is to use copper, either mesh or foil/sheet. Aluminium is NOT a good material as it can very easily re-transmit the signal. I built a faraday cage as a grad student from come copper mesh and a wooden frame. The box had several openings in it to run wires and let the laser beam into the box. The openings were simple steel pipe about 10x longer than their inside diameter. They were secured to the mesh with hose clamps, I was able to block the RF discarge from my laser (20 MW, pulsed UV) at a distance of about 2 feet. To test if the box works, stick an am/fm radio in the box and see if recieves a signal from the local stations. (I am unsure if the box blocks am or fm signals, but it will only block one of them). Be sure to ground to an earth ground (I used ~75 feet of 1/4″ steel cable feed out the window to a metal ground stake). The box worked very well for my application. You can check the SCIENTIFIC literature (try google scholar) for how to really build a faraday cage.
what about solar flares, how do you protect solar panels, wind generators and other such items?
What if you buried it in the ground, for example, in a bucket that you’ve cached? And if that works, most importantly, does anyone know how deep it must be buried??
Would it be protected if you buried it??
I am really wanting to buy a faraday cage to store some of my supplies as well and everything I am reading is so confusing! I am hoping someone comes up with one that we can buy with or without grounding that has been tested to work and then I don’t have to worry about making sure the one I make at home works. Who ever can come up with a tested one will make some good money selling it as I know numerous people wanting to buy more than one. I found someone on EBay that is selling them, he apparently made them and sells various sizes. However, when I asked him if he has had them tested I never received a reply back. As much as I would love to buy them hoping they will work, I would hate to find out they didn’t when I needed them most to work.
Anyone who comes up with a tested faraday cage that will be selling them please let us all know!
Shelli, the answer to question is this: My wife is a EE major and we have talked extensively about this, get a metal trashcan with lid, coat it with foam so that no exposed metal parts are in contact with any electronics bury it in the ground to ground it. POOF – you have a faraday cage. This is the very simplist example I can offer. You can go further and ground the metal trash can to the ground with a ground strap etc. but according to my wife that is not necessary EXCEPT that you must have the lid on it with electronics intact before any EMP.
jwc