Guest post by JMD – What is a faraday cage?
While I am not an expert in the field of EMP, I am an engineer and I work on military systems that are required to have EMP protection, so I have some exposure to the field and some knowledge of the theory.
I hope to gain substantially more knowledge and experience in the future. I will try to shed some light on the situation without spreading too much disinformation.
The idea of building a metal box completely surrounding whatever you want to protect is well-known and is a theoretically sound concept.
This box is called a Faraday cage and every sophomore engineering student should be able to tell you something about them (most freshmen too). What happens is that electric fields follow the metal cage around whatever object is inside the cage, rather than touching the actual object.
The key is that the Faraday cage must be electrically continuous all the way around. All sides must be connected to each other and there can’t be any large windows. I don’t know how small openings need to be for the cage to be effective. It probably has to do with the electromagnetic wavelength that you are trying to protect against.
What this means is that if you want to make your house into a Faraday cage, the metal portions on all walls, the roof and the floor must all be connected such that electricity can freely travel across the entire seam.
Likewise, you would need screens in your windows that are electrically connected to the walls surrounding them, and exterior doors would need to be metal and electrically connected to the surrounding (metal) door frame. This means no standard rubber weather seals. In military applications, we use special electrically conductive gaskets. Doors would also need to be closed in order for the Faraday cage to be effective.
Another important component to the Faraday cage is that the objects inside must be electrically isolated from the cage walls and from the outside. Don’t let your electronics touch the cage directly. Furthermore, any electric signal coming from the outside world would need to be run through an EM filter as it passes through the Faraday cage.
The filter removes voltage spikes that would otherwise come into the house through your power lines, phone lines or TV and internet cables. Exterior power lines will act as huge antennas, picking up the voltage spikes from an EMP source.
You may have the perfect Faraday cage, but if you have power lines coming through it directly into your home, the cage won’t do a bit of good. It would be like building a roof to keep out the rain and then cutting a big hole in it.
This is only a quick overview of EMP protection. Like I say, I don’t know everything about it. Theoretically, if your home is properly protected, you wouldn’t be able to use your cell phone in the house as the Faraday cage would block all electromagnetic signals. It will take a lot of research and work to reach this point.
Faraday Cage
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Will an EMP detonation ruin my electric toothbrush? Sheesh, that’s a lot to consider.
Let’s hope some over tanned towlhead or Asian wacko does not get ahold of the ability to launch an EMP assault on us…
The cage the professor stepped into in the YouTube reminded me of a scene from the Woody Allen movie Sleeper!
Hmmmm … I am wondering if they sell a PVC pipe big enough for my family to fit into and we can bury it in the ground somewhere out of harms way or, at least away from a metal detector….
Well, I feel better about my home now! The cell phones dont work for poo in here! grins……(Half the time the land line and TV doesnt either!) :-\
Now can concentrate more on my preps……Km
Interesting – have you constructed and tested a Faraday cage? I did, with poor results. Using my cell phone and a GMRS/FRS radio to test with, I wrapped them in aluminum foil, which successfully blocked radio waves to them. I also tried placing them in a small galvanized trash can with snug lid, which did not work (the radios were insulated). Having established that aluminum foil would work (and having read it would on the net), I carefully wrapped a shoebox and lid in the foil and looked it over to ensure all areas covered and not damaged. Added extra foil to the area where the lid went over the box to ensure a snug fit – but it didn’t’ work, both the cell phone and radio could rx in the cage. I’ve been meaning to try an extra layer of foil and to try screen, but haven’t gotten around to it. The devices I plan on protecting; laptop, GPS, shortwave radio, camera, etc.
I believe that I read somewhere (either on JWR web page or maybe in one of his books) that if you store your electronic gear in a galvanized metal trash can or an surplus military metal ammo box that it would prevent EMP damge to those devices stored in them. Anyone else hear about this? Any comments or better info? Thanks folks.
Patton,
Yes, JWR has written that a few times. I probably got the galvanized trash can idea from his blog. Forgot to mention – tried an ammo can and it didn’t work either. Actually tried two ammo cans (.30 cal and 40 mm). Also, ammo cans have rubber seal that mean they are not a continuous metal enclosure so theoretically shouldn’t work. Like I said, tried them both and could call the cell phone and tx to the hand held radio, meaning those radio waves could get through. I don’t know if EMP waves are different enough that they would be stopped, and it seems impossible to find solid info on this on the net that’s not in engineer speak. In the remote event an EMP does occur, a working GPS, shortwave radio, and hand helds would be priceless.
I wonder if you’re getting signal because the antenna on the device is so close to the wall of the faraday cage? It would seem like even with a faraday cage if you touched the antenna to the cage wall you could rx/tx?
JMD will probably have to correct me on this but if you had some sort of antenna/conductor and it’s collecting RF from the environment, an antenna on the inside could read the signal as it’s being passed over the conductor? The insulator on the inside wouldn’t stop the device antenna from seeing any signal on the faraday cage itself.
You could try to ground it to a known solid ground like the one outside your house and see what happens when the TX from your other devices are sent to ground instead?
Thanks!! The Galvanized trash can sounds as if it is a better idea. God forbid we get hit with an EMP. All bets are off after that.
Wouldn’t the whole thing work better if it was grounded? You can buy a ground post at a hardware store – a thick copper rod you hammer (not dig a hole and bury) into the ground about three to four feet, then connect by THICK copper wire to any Faraday cage. Same idea as a lightning rod – the EMP that builds up in your Faraday cage is directed into the ground.
I believe old fashioned vacuum tube equipment will work after an EMP. You can find vacuum tube radios at yard sales, swap meets and ebay. Take them to a musical instrument amplifier repair shop to get them fixed (many musicians still prefer tube amps).
Last but not least is the old fashioned crystal radio. No batteries required! You could put the components in a box, unassembled, then put them together after the EMP.
I’ve read conflicting information on the need to ground a Faraday cage. While I don’t see why it would harm it, I’m fairly certain that grounding is not required to achieve the desired result. Think of the Faraday cage as a submarine hull. The surrounding wateris the electromagnetic field. The hull merely channels the surrounding water around the ship, keeping the environment contained inside safe from the surrounding water.
I have also heard that vacuum tubes are safe from EMP effects. Knowing little about vacuum tubes, I can’t confirm or deny this.
In the video, he says that your car is a faraday cage already, does this mean that the electronics in your car are safe? The windows on a car are many and large. I am a bit confused.
Also in response to the can issues. I read that no part of the protected item can be in contact with the cage. Would Styrofoam work as an insulator? The surplus store near my house is selling steel boxes that were used to house NVG and they have foam already in them. Ideas?
I have heard that using copper mesh you can make a faraday cage. I would think that if you did use one you should put a few extra sets of whatever you want to protect, ie 2 way radios, SW radio equipment, NVGs,etc. You don’t want to be the only one with working electronic comm gear….who would you talk to?
Another concern would be solar/wind setup. I imagine that it would all be fried, so keeping back a small amount in your faraday cage would be helpful so that when the whole grid gets toasted you would be able to be up shortly afterwards.
And YET another concern would be Nuclear Power Plants, what would happen to them? I believe the safety overrides are all controlled by electronics, so after an EMP would they be in danger of a meltdown?
I think Nuclear plants would simply shutdown as long as there isn’t any mechanical problems with the control rods.
http://en.wikipedia.org/wiki/Scram
Wishful thinking, but I would hope there would be a manual way of shutting down a reactor. From the article above, it sounds like it would shut down in an EMP if the circuits failed.
Prepared N.D.;
In all cases the phone/radio was in an insulated container and not touching the side of the container. You’re right that if a conducting material of the device being shielded touches the metal, there is no protection, but an antenna close to the metal but not touching should not be affected.
John;
I did try it with the galvanized trash can grounded to a copper water pipe and it made no difference. I selected a pipe in the pantry that was already being used as a ground (the owner knows his stuff, so I don’t doubt the copper is in the ground).
JMD;
I’ve read some claiming grounding is absolutely necessary and others say it is not – confusion on the internet, who knew. In my view it seems ground should not be needed, and that when the container is touched it should discharge anything it’s holding. But I’m no engineer.
Nate;
I’ve read that copper mesh or metal meshes in general can be used to construct a Faraday cage. As aluminum mesh for windows is cheap and available, I picked up some but have yet to build a cage with it to test with. As for the radios, I have a pair and my brothers and parents all have identical pairs. If I had to bug out with only the pair I have, they would potentially be very useful for my wife and I on the long trip.
AsC;
I’ve also read some claim cars can act as Faraday cages, while other point out the car is not a continuous metal enclosure so won’t work. That they would not be seems consistent with most of what I’ve read.
What about burying stuff underground – would that help?
What about using galvanized steel pipe, sealing both ends and burying it underground? Or using a waterproof steel ammo can and burying it?
Awhile back the show FUTURE WEAPONS did a segment on emp. The host drove a vehicle under a huge emp simulator. The vehicle immediately stopped working and wouldn’t restart. However the radio and lights still worked. That seems to be the closest to real world testing /results that I’ve seen. I believe the video is on youtube.
Suburban Survivalist: Yeah the engine is open in the bottom part, i wonder if an engine skid like those used by off roaders would be enough protection.
Homer: thanks for the tip.
My older model car does have a computer in it on the firewall. I am forced to wonder if i kept a spare computer, radio and CB in a steel box in the car then i could recover after an EMP, right? What other items could be disabled after an EMP? I figure the lights still work because they are not electronic, they simply react to electricity coming from the battery.
Suddenly a stick shift is looking real attractive.
“In the video, he says that your car is a faraday cage already, does this mean that the electronics in your car are safe? The windows on a car are many and large. I am a bit confused.”
Yes. Vehicles and aircraft are Faraday cages. Many of each are struck by lightning each year, experiencing far greater charges than an EMP attack. Planes don’t shut down and fall from the sky. People get out of their cars and look dumbfounded at the hole in the pavement where the massive bolt of electricity left their vehicle. Most of the time you can drive away, thanking your Creator you were in a car and not standing exposed to that lightning.
Even though cars and trucks have large windows, there is still plenty of conductive metal surrounding the glass and weather stripping. Google the BBC show “Top Gear,” specifically the episode where one of the hosts sits in a brand new VW directly under a lightning simulator. He is struck repeatedly, yet the video camera used to film inside the car still works as does the vehicle itself. Lights worked, radio worked, engine started up first try and he drove away. And he received exponentially more charge than someone who was driving to work when an intentional EMP attack occurred.
Do NOT be fooled by the so-called emp videos and survival gurus!
EMP is A varied, powerful, and certainly not a joke!
You will read what “others” may say and supposedly have experience in…Yeah, well go and research it for yourselves first!
“Starfish Prime” is a good place to begin your searches!
1) in the video mentioned above, that is NOT, and I repeat: NOT a faraday cage!
2) Emp is an electromagnetic pulse, NOT, again I repeat: NOT just a static charge made by the Van De Graf machine!
3) the smallest opening-dimension allowed in any faraday cage is 1mm in size.
4) Screen works! Trash cans do NOT! Ammo cans will not!
5) ALL faraday cages MUST be grounded!
Not to your homes
water pipes either!
6) Cars and aircraft are NOT and again I will repeat: NOT a faraday cage!
7) the best is a gold mesh, second is silver, then copper, then aluminum for building a faraday cage. NOT aluminum foils, or metal cans, regardless of what you think or have been told, or read for that matter!
8) the ground rods available today are in fact: just copper clad/coated steel rods in 8 ft lengths.( Copper is far too soft to drive into the ground without bending!) They must be used in their full 8ft lengths, more research will show a different configuration also. An “L” design.
9) EMP does not dissipate in 1/100,000 of a second, despite what you hear, read and have been told! It all depends on: size of detonation , distance from detonation, atmospheric ( ionospheric) conditions…
Again, research for yourself what the HAM radio operators discovered following the “starfish prime” detonation!
10) the reasoning about using a metal building for emp shielding is fictictious! DO NOT EVEN buy into that one!
A large area of metal mass is a great conductor for EMP’s and will actually concentrate the charge, to a point that it may be detrimental to your health! READ and study people! Don’t believe everything you hear!
Honestly now, you REALLY believe that you are safe from lightning in your cars? Uh, sure…lightning is again a static charge NOT an EMP! 2ndly you think that a bolt of several thousands of volts that can travel for hundreds of miles, will be stopped by your cars tires as insulation? Ok, so what if they are wet assuming you are driving in the rain! NO! Do not buy into that theory either! It’s quite laughable at best! Aircraft are safer as they do NOT touch the ground or are grounded! See the differences? I hope so!!! For your sakes!
EMP= electromagnetic pulse. PERIOD. (study word that alone!)
Lightning and static are just that, and nothing more. They are NOT at all comparable by any means! It’s like comparing gasoline to water, yeah, both are liquids! That’s all!
Lightning will kill you! That is a well known fact!
EMP will not kill humans: (unless, you have some sort of electronic device like a pace maker keeping you alive) Then in that case, yes, EMP will certainly kill you!
The 2 are NOT at all similar and have little in common…
READ and research it, not taking anyone’s word that “KNOWS” all about it!
Copyright (C) Duncan Long 1989. All rights reserved.
PROTECTING YOURSELF FROM EMP by DUNCAN LONG
Read this for yourselves, PLEASE!
It is long, BUT it is important and VERY informative!
In Duncan Long’s report, he says that:
-metal boxes are Faraday cages
-boxes covered in aluminum foil are Faraday cages
-cars are EMP-resistant
-grounding a Faraday cage is NOT necessary
Why are you recommending his report when you disagree with all of his Faraday cage analysis?
In “PROTECTING YOURSELF FROM EMP” by DUNCAN LONG, he states that:
-metal boxes are Faraday cages
-boxes covered in aluminum foil are Faraday cages
-cars are EMP resistant
-Faraday cages do NOT have to be grounded
Why are you citing his report if you disagree with all of his Faraday cage advice?
A faraday cage MUST be grounded PERIOD! (I am an Electronics Engineer who has worked inside cages extensively) If you do not ground them they simply act as a passive antenna just as a car body does. the ground is necessary to bleed off the charge that develops on the cage itself. There are several videos on youtube that show a Ford Taurus being hit by an EMP and being killed. Bare in mind that the ecm in the car is completely shielded and bypassed to avoid being affected by RF (radio frequency) Emissions, but is still burned out by the emp pulse. This is because it is not grounded to the earth. Also keep in mind, the electrical ground in your home wont work as a ground for a faraday cage. It’s too large of a web of wire and can act as an antenna ( to prove this hook an ungrounded oscilliscope input of an ungrounded scope to the ground of an electrical outlet and look at all the noise on it), which can actually charge the cage. It needs a totally independent earth ground to funtion properly, and not a light duty gound cable going to it either, it has to be substantial. This is why these small cages often fail, insufficient grounding.
How do you ground a Faraday cage if you live in an apartment without direct access to an earth ground?
I totally agree with Dragon5126!
The entire home would only “appear” to be a “long wire” to an EMP. The absolute worst case scenario!
Too many do not quite unbderstand the EMP and how it operates and why. It consists of not just one single wavelength of energy, but a multitude of wavelengths. That is why people should avoid such enclosure’s as Conex boxes, even, ( dare I say it? ), Mobile homes, that are encased literally in an aluminum SKIN! Now, from having resided in a mobile home since the late 80′s to present, I can say that “IF” you remember the old “pagers”, I could NOT get a signal in from the outside world, even though living in the city…UNLESS I connected it to a coax, which was again connected to an outside multi- frequency antenna.
But then also take into consideration that was 1 single wavelength that could not penetrate…Today, there are thousands of wavelengths! From: 900 Mhz phones, 5.8 Ghz phones, etc.
It takes precautions to protect electronics from being “fried” by an EMP!
Okay, a perfect example of the conflicting information I referred to;
- Dragon5126 above claims to be an Electronics Engineer and that Faraday cages must be grounded.
- Wikipedia user Omegatron also claims to be an Electronics Engineer and says Faraday cages do not need to be grounded (and explains why some grounds are used within the cages).
I’m not doubting the credentials of either, but clearly the advice is opposite. If anyone can post some links with authoritative or well referenced research pointing to one or the other – rather than saying to search on an event – it would be welcomed.
I am NOT an electronic engineer!
Period.
I do NOT have an engineering degree….!
But, I do have AEC and NRC security clearances and I have worked at a nuclear generating station…
I also was involved in military training re: sadm’s.
Good enough?
Besides, what would the harm be in spending a few more minutes and dollars to properly “ground” your equipment’s faraday cages?
None.
Just do what you feel is correct!
Worse case scenario, if you fail to ground and the electronics get fried, NEXT time you’ll know better won’t you?
Simple.
Survivor,
I don’t think anyone said you were an engineer.
I’ll quote us both and leave it at that.
Survivor; “READ and research it, not taking anyone’s word that “KNOWS” all about it!”
SS; “If anyone can post some links with authoritative or well referenced research pointing to one or the other… it would be welcomed.”
http://en.wikipedia.org/wiki/Electromagnetic_pulse
If terrorists have access to nuclear based EMP’s AND the rocket/missiles to get them high enough to be effective then I think we have more to worry about than EMP. And from what I’ve seen the non-nuclear are a few hundred yards in power so they can do some damage but not citykiller style. Plenty of easier ways to bring a city to its knees.
And faraday cages don’t have to be grounded, it’s just advisable so the charge has somewhere to travel. Electricity takes the path of least resistance, and if the Cage itself is that path with no where else to go then it’ll get quite hot if the current is large enough and long enough…AKA Oven. Lightning will arc and find ground most likely anywhere that you’re in a faraday cage that could get hit anyway. (EG. Aircraft aren’t grounded…survive lightning strikes all the time. the aircraft is an ungrounded faraday cage and the air continues the conductivity towards the ground, tower, whatever)
I’ve got this one covered. I have my motorcycle sitting in the center of my enclosed aluminum and stainless steel trailer. Yes, aluminum is a conductor although it isn’t as good a conductor as silver or copper it is used for high voltage power lines because of its weight. I have it more or less grounded with the steel chain on the trailer tongue by laying it on the concrete floor. If a threat were imminent I’d put my atv in there with my generator and other electronics that I’d want to spare too. You could make a gun safe into a Faraday cage fairly easily.
JMD mentioned the wavelength of the EMP pulse. The screen in the door of your microwave oven is a perfect example of the validity of this assumtion. I would like to know, if anyone has researched this, just what wavelength(s) we are dealing with in the event of a nuclear EMP. I think this knowledge would be very important. I’d also like to comment on Suburban Survivalists experimentation. Were the devices insulated from the conductive containers with some material that is a proven effective electromagnetic insulator? Were the containers effectively grounded?
theantidrone,
To answer your questions, all the devices were well insulated (rubber in a few cases) from the conductive surfaces of the materials being used as Faraday cages. I used a galvanized trash can with a tightly seated lid in one case, and it was well grounded (also tried without grounding). That trash can would not block cell phone calls or GRMS radios, though that may or may not be a good test for EMPs. Credible, authoritative material is very scarce on this.
Cell phones are usually 2ghz and up, some dinosaur phones are 900 mhz, your gmrs or frs radios are 462mhz, which penetrates concrete, and some metal (if not grounded) pretty well and your handheld will have an output of .5 to 5w max. If you are using vhf its a bit harder
to escape even a car body with a rubber duck antenna on let alone any signal 54 mhz or lower getting thru your car (6 meter wavelength). Try the small galvanized trash can, a small oily rag sized one should do the trick for most hand held or mobile radio applications. If the radio still recieves well with the lid on, try a ground rod to wet dirt making sure to use a flat tape, and not a round wire that may be resonant length. Im fairly sure you will get the results your looking for. The water pipes in your house, although connected to ground ARE RESONANT. I think the ground rod, to ground strap to trash can should be as short as possible, with no resonant lengths past the can.
After reading some of this I decided to go poke around on the net. Try googling electromagnetic pulse protection. I found a few things that were interesting. Some were pages of what appear to be military (army in particular is what I found) testing, results, etc. I’ll see about posting links later as time is short.
What I found. Faraday cages do not need to be ground to work, however, grounding is advisable to mitigate other problems associated with electrical effects. Means it may help make the problem substantially less. Vacuum tubes are less susceptible to problems, however, components of the vacuum tubes can be affected. There is an idea of “nested” Faraday cages. Try phone, radio, etc., wrapped in plastic, then foil, then more plastic, and more foil. Same idea with trash can. Try plastic bucket inside metal can inside plastic bucket inside metal can. I will come back and post links to where I found some of this material.
@Suburban Survivalist:
There is a big difference in radio waves and (or cell phone waves) and an electrical charge. An E.M.P. is electricity in a way that we can’t feel, but can still be conducted through metal. You can’t conduct a radio wave through metal, which is actually what you were testing, not the effectiveness of the cage itself. The point of the Faraday cage is to conduct electricity. This absorbs the entire blast of an E.M.P. wave, while the non conductive rubber or other substance that you are supposed to line the inside of the cage with keeps your valuable electronics off of the conductive metal absorber. The type of electricity that is conducted through an E.M.P. wave is different than what we think of as electricity, we can’t feel, see, or hear it, even if we were touching something conductive at the time. That type of electricity just doesn’t effect us, and even if it did, it’s only there for the smallest fraction of a second, not long enough to effect anything except sensitive electronics. That’s why an E.M.P. is so dangerous.
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