Author Topic: Question - Faraday Cage  (Read 50184 times)

Offline RushMan

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Question - Faraday Cage
« on: June 25, 2009, 04:46:45 AM »
Does anyone know of good reference source on building your own Faraday Cage?

At this point, I want something moderate in size to hold a back-up radio and perhaps a few other electronic items.

Also, I am interested in providing similar protection for the small weather radios I carry in my vehicles.

I was considering building some boxes out of plywood and then encasing them in rectangular cross-sectioned ductwork, but I seem to recall reading that copper is the optimal encasement material.  If this is so, a couple of questions come to mind.  First, if not optimal, is ducting metal adequate?  And second, is copper mesh (not copper sheeting) adequate.

I appreciate any links or personal knowledge that you are able to share.

Offline Morning Sunshine

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Re: Question - Faraday Cage
« Reply #1 on: June 25, 2009, 09:16:48 AM »
i read somewhere that microwaves make a good faraday cage.  they built to contain micro-waves, so they can block them the other direction too.  go to your local freecycle or school (they have big microwaves, and replace them occasionally) and ask for not-working microwaves.  they do not need to work, so get the garbage ones.  As long as the box is intact, you are good.  cut the cord off so small children don't try to plug them in with your electronics inside :)

might want to do some checking on this, cuz I am woefully ignorant of these kinds of things.  just passing on what I have read elsewhere

Offline RushMan

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Re: Question - Faraday Cage
« Reply #2 on: June 25, 2009, 11:15:55 AM »
Morning Sunshine -

Thanks for the information.

Your suggestion was one that I had never considered and it gives me a new avenue to explore and research.  For the items I have in mind (small weather/shortwave radios and the like), even a common household microwave would satisfy the space needs.

I love the sharing of ideas among an informed group of people that this forum provides.

Thank again.

Hare of Caerbannog

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Re: Question - Faraday Cage
« Reply #3 on: June 25, 2009, 11:34:25 AM »
This is a good topic and I hope more people add to it.
The microwave is a good idea. Not sure it works but it makes sense. I would assume it would work.
About once a month or so I back up my hard drives on a seperate external hard drive that hooks up with a USB. Then I put that HD in my fire proof box. But if an old microwave would work to prevent EMP damage I would use that.

Offline DeepSea1985

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Re: Question - Faraday Cage
« Reply #4 on: June 25, 2009, 11:50:47 AM »
The little bit that I've read I seem to recall that to be effective it needs to be grounded to bled off the radiation.....But like Jack, I reserve to right to be wrong..

Offline Roknrandy

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Re: Question - Faraday Cage
« Reply #5 on: June 25, 2009, 12:00:56 PM »
Cages are made from a mesh cloth (Very tight weave) to block signals or voltage from entering the cage. It's normally a structure of some type wrapped in a mesh screen.  DIY Cardboard/wood box with mesh outside and Grounded directly to ground.


Good example

Faraday Cage  

also

Faraday Cage
« Last Edit: June 25, 2009, 12:14:16 PM by Roknrandy »

Offline “Mark”

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Re: Question - Faraday Cage
« Reply #6 on: June 25, 2009, 01:42:01 PM »
I seem to recall reading that copper is the optimal encasement material.  If this is so, a couple of questions come to mind.  First, if not optimal, is ducting metal adequate?  And second, is copper mesh (not copper sheeting) adequate.

Anything that conducts electrical current will work. Obviously, the better of a conductor it is, the better the cage. So gold would be better than copper if you had the coin for it.

A mesh is okay in some cases. As long as the holes are smaller than the wavelength of the electromagnetic radition you want to stop, the EM radiation will be absorbed by the mesh. Remember that wavelength for EM radiation is roughly E/f, where E is roughly 3.0 x 108 m/s, and f is the frequency of the radiation. In the case of a microwave which operates at the resonate frequency of a water molecule (H2O), the frequency is 2.4 Ghz, or 2.4 x 109. Plug that into the formula and it works out to 0.125 m, or just under 5 inches. The most powerful rays (cosmic or from nuclear explosion) are gamma rays which have frequencies over 1019Hz. Plug that into the forumula, and you're looking at sizes of 3.3 x 10-12m or about 1/130 billionth of an inch. In that case solid metal is the way to go -- and it need to be thick enough that the rays actually interact with the electrons in the metal and don't just pass straight through.

</nerd>

Hare of Caerbannog

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Re: Question - Faraday Cage
« Reply #7 on: June 25, 2009, 01:54:32 PM »
Great
So to stop an EMP were back to a lead box.
 :(

And I'm fresh out of lead sheeting.

Offline “Mark”

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Re: Question - Faraday Cage
« Reply #8 on: June 25, 2009, 02:42:45 PM »
Great
So to stop an EMP were back to a lead box.
 :(

And I'm fresh out of lead sheeting.

There's a reason why NORAD bunkers are deep inside a mountain. :D

But remember that the strength of an electromagnetic wave decreases with the cube of the distance. If you're reasonably far away, a simple cage may prove very effective. The cosmic rays coming from space, even though they're very high energy, do little more to computers than possibly flip a bit in memory.

Fred_47460

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Re: Question - Faraday Cage
« Reply #9 on: June 25, 2009, 03:15:53 PM »
Anything that conducts electrical current will work. Obviously, the better of a conductor it is, the better the cage. So gold would be better than copper if you had the coin for it.

Actually, that is a common misunderstanding....Gold is NOT a better electrical conductor than copper....Gold IS used in certain strategic areas (normally inter-connections...be it board edge or cable connections) because Gold does not corrode. Copper is by far a better conductor than Gold but it corrodes very quickly thereby contaminating the electrical connection. Although Gold sucks as a conductor, it sucks at a steady rate....which makes it possible to design in countermeasures to correct for its use.

Here is a link to some info on electrical conductivity: http://en.wikipedia.org/wiki/Electrical_conductivity

Actually, most gun safes have a pretty thick wall thickness of good ole STEAL.....which isn't a "great" conductor....but it is definately better than nothing if you want a quick and dirty Faraday cage.

Here is a link to some info on a "Faraday Cage": http://en.wikipedia.org/wiki/Faraday_cage

Cheers............Fred

Fred_47460

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Re: Question - Faraday Cage
« Reply #10 on: June 25, 2009, 03:30:51 PM »
Actually, upon further reflection, what would be wrong with a regular old metal trashcan with a tight fitting metal lid (They usually come as a matched set when you buy them at your local Walmart or hardware store). The big trouble with a Farady Cage is that....it really doesn't matter which of your electronic gizmos "would" work if you had power....you won't have power from the grid because the grid electronic equipment will be destroyed. So if you want to try to protect some important equipment from EMP , then you really need to think about how you will power them. It may be that part of the stuff you want to throw into the Faraday Cage is a small solar battery charger and some rechargeable batteries to fit the gizmos you would like to power.

Offline “Mark”

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Re: Question - Faraday Cage
« Reply #11 on: June 25, 2009, 03:43:00 PM »
Actually, that is a common misunderstanding....Gold is NOT a better electrical conductor than copper....Gold IS used in certain strategic areas (normally inter-connections...be it board edge or cable connections) because Gold does not corrode. Copper is by far a better conductor than Gold but it corrodes very quickly thereby contaminating the electrical connection. Although Gold sucks as a conductor, it sucks at a steady rate....which makes it possible to design in countermeasures to correct for its use.

Thanks for that!

Proof again that you learn something new every day. :)

Offline RushMan

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Re: Question - Faraday Cage
« Reply #12 on: June 25, 2009, 04:40:45 PM »
Everyone - Thanks for the discussion; very helpful.

Question - Would a mountainous topography mitigate the strength of an EMP pulse?  Or, is distance from the burst the critical factor?  I live in Appalachia, so there may be some benefit from the topography itself in this instance.

Thanks.

Offline “Mark”

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Re: Question - Faraday Cage
« Reply #13 on: June 25, 2009, 06:02:21 PM »
Everyone - Thanks for the discussion; very helpful.

Question - Would a mountainous topography mitigate the strength of an EMP pulse?  Or, is distance from the burst the critical factor?  I live in Appalachia, so there may be some benefit from the topography itself in this instance.

Thanks.


A mountain could shield you somewhat, but distance is the prevailing factor.

Fred_47460

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Re: Question - Faraday Cage
« Reply #14 on: June 25, 2009, 06:12:55 PM »
A mountain could shield you somewhat, but distance is the prevailing factor.

Also...bear in mind that an EMP pulse would be initiated by a nuke detonated a couple hundred miles above the atmosphere AND the pulse would follow the power lines coming in to your house. They would basically act as an antenna. I would encourage you to read "One Second After". It is a novel about an EMP attack....it IS FICTION...but the guy did lots of research into the actual EMP effect.

Offline mash

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Re: Question - Faraday Cage
« Reply #15 on: June 25, 2009, 06:22:28 PM »
The big trouble with a Farady Cage is that....it really doesn't matter which of your electronic gizmos "would" work if you had power....you won't have power from the grid because the grid electronic equipment will be destroyed. So if you want to try to protect some important equipment from EMP , then you really need to think about how you will power them.


I was just thinking about that one - unless you have a solar powered / hand cranked laptop in there with your backup hard drive, you are still going to be out of luck.

Offline mash

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Re: Question - Faraday Cage
« Reply #16 on: June 25, 2009, 06:39:48 PM »
Here is a link to some info on a "Faraday Cage": http://en.wikipedia.org/wiki/Faraday_cage

Ha! they actually list a foil hat as one of the items that acts as a Faraday cage!  :D

Offline Cave Dweller

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Re: Question - Faraday Cage
« Reply #17 on: June 26, 2009, 02:34:01 AM »
In theory, you basically need something to conduct the electrical charge around a protected object. I've seen steel framed buildings "block" radio signals.
Ready reserve suggests wrapping whatever you want to protect in a heavy cotton blanket and placing it in a galvanized trash can with the lid securely in place.

Cave dweller's method is to wrap the objects in cellophane. then in aluminum foil, the cellophane, foil cello, foil, cello etc.
I have my old laptop and a dc-ac power inverter done up that way. I'll probably be wrapping up some PV cells soon.

And then stuffing them in a metal trashcan.

Offline DIM TIM

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Re: Question - Faraday Cage
« Reply #18 on: July 01, 2009, 12:44:28 AM »
I have come upon the idea for a good field expedient faraday cage set up that can be put together very inexpensively. and as far as I have been able to determine, ( without an actual way to induce a pulse to test it ) this should work. I Have a two year technical degree in industrial electronics, and started towards a degree in electronic engineering at the local community college, so I do know a thing or two about this subject.

All your electronics, should be left in their original boxes. To begin, take and go to your local grocery store, and buy a roll or two of the HEAVY DUTY aluminum foil. Wrap all of the boxes with a couple of layers of the foil, taking care not to tear or puncture the foil covering. The foil is just a back-up precaution, but the electronic package should be covered completely by a couple of layers of foil at the least.

The next things that you will look to purchase are, a grounding rod kit, a nut and bolt with a couple of fender washers, and a lock washer, a good length of 8 or 10 ga. stranded or solid wire, and a 20 gal. galvanized trash can with a good tight fitting lid.

You first take the trash can, and there is a lip of folded metal at the base of the can. You will drill a hole through this lip, and your nut and bolt will go through this hole with a fenderwasher on either side of the lip, and the lock washer on one or the other to keep the nut and bolt secure when you tighten it up.
You then take one end of the wire, and strip off a few inches of the insulation, and wrap it around the bolt, and under one of the fender washers, and then tighten the nut and bolt down so that the wire will not come loose. The thing here is to have a real good metal to metal connection.

Next, you will take your grounding rod kit, whiich should consist of a three foot metal rod, a wire clamp, and a length of ground wire. Check to see if the other end of your larger ground wire that is fastened to the trash can will fit in the clamp. If it does not fit, you can get a hose clamp from any automotive section of any department store or auto parts store, and secure your beefed up ground wire to the rod using it instead. And as with the end of the wire where you attached it to the can, you strip off a few inches of the insulation to make sure you have a good metal to metal connection with the wire and the rod as well.

SO, if you have your can ready, and your wire and clamps ready to go, then you are ready to put your faraday cage together.

I plan to put mine in my shed, just because the door has a gap that will allow me to run the wire outside, without having to drill a hole in the wall and pass the ground wire through the hole, and then apply a small bit of caulking to seal the hole against the rain. You can do it that way, but I'll just pass it through the gap at the door that is already there.

First, you take a large hammer, and drive the ground stake into the earth, till only about 6-8in. of the stake is showing above the ground. Then clamp the end of your beefed up ground rod wire to the rod, and make sure that both the ends of your wire are secured to the rod and the trash can really well.

Now you can take your foil wrapped electronics, and place them inside your trash can faraday cage, and after you place them inside, place the lid securely back on the can, and you are good to go.

The Microwave oven sounds like a good one, but it is limited in the fact that the inside cavity is the limiting factor to the size and amount of electronics that you can place inside of it. The 20 gal. galvanized trash can could quite possibly contain one of the smaller microwave ovens, so you can see where this set up would be  able to handle larger electronic packages, or many more smaller ones.

I plan to make a few of these, to contain all of my  electronics, and a few small solar panels as well.  The can, with a good tight fitting lid, should shield the electronic packages inside, and the foil is just like I said earlier, a back up, and the ground wire and rod will conduct the electrical pulse to earth, and therefor should shield your gear from the effects of EMP waves.   ;D

CAVE DWELLER'S post was right about the theory of how they work, and Ready Reserve had the right idea with the can, but for the thing to work best, you need to attach the ground wire to conduct the electrical potential to the Earth's ground to be as sure as you can.

Offline ejsandstrom

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Re: Question - Faraday Cage
« Reply #19 on: July 01, 2009, 11:00:00 AM »
I have seen ammo cans lined with cardboard used. I dont worry to much about my pc and such things. I worry about the coil, ecm, alternator, and starter on my bov.

The trash can is a great idea. +1

Offline ozarked

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Re: Question - Faraday Cage
« Reply #20 on: July 01, 2009, 10:03:44 PM »
I've read on other boards that Faraday Cages do not need to be grounded.  This always seemed counterintuitive to me, but not being grounded (pun intended) in electronics, I couldn't debate the issue.  Thanks to you all for the info.

I plan to install a diesel powered generator sited in an outbuilding.  How would you recommend I protect it from EMP?  I've read that all six sides of the Faraday Box (the outbuilding) must be metal, while others say only the four sides must be metal (so long as the floor is non-conductive).  What are your opinions?

Also, how could I EMP-harden the transmission lines from the generator to my home's electrical panel?

Offline Cave Dweller

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Re: Question - Faraday Cage
« Reply #21 on: July 01, 2009, 11:55:49 PM »
Also don't underestimate the value of paying a voodoo witch to give it a little blessing. Or do they only curse things.
Anyway, the ammo can is a good idea, except the lip under the lid often has a strip of rubber to keep the can sealed from moisture n stuff.

Offline mash

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Re: Question - Faraday Cage
« Reply #22 on: July 02, 2009, 03:54:53 AM »
Also don't underestimate the value of paying a voodoo witch to give it a little blessing. Or do they only curse things.

May your every wish be granted.

-ancient Chinese curse

Thrivalist

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Re: Question - Faraday Cage
« Reply #23 on: July 02, 2009, 06:50:30 AM »
Here try this link for info on shielding equipment.I plan to build a room into our house when we build in a year or two and I probably will order their materials to do it with.

http://www.faradaycages.com/

Thrivalist

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Re: Question - Faraday Cage
« Reply #24 on: July 02, 2009, 06:52:48 AM »

Angie

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Re: Question - Faraday Cage
« Reply #25 on: July 02, 2009, 07:02:10 AM »
I heard you could take an aluminum backyard shed, ground it and cover the floor and have a large faraday cage.  Anyone know how true this is.  I have a large outdoor shed, I'd like to use it for that purpose. 

Fred_47460

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Re: Question - Faraday Cage
« Reply #26 on: July 02, 2009, 03:19:23 PM »
I heard you could take an aluminum backyard shed, ground it and cover the floor and have a large faraday cage.  Anyone know how true this is.  I have a large outdoor shed, I'd like to use it for that purpose. 

Angie...I don't know why that wouldn't work just fine. If there is any doubt you could always store some stuff inside metal trash cans....INSIDE your metal shed, for another layer of protection. The one thing I would caution against is having any electricity coming into the shed for lighting or outlets.....EMP can follow wiring right into the shed via the wiring for the lights/outlets otherwise.

Offline ozarked

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Re: Question - Faraday Cage
« Reply #27 on: July 02, 2009, 04:37:31 PM »
Thrivalist -
                    Thanks for the links.  Interesting stuff.  I couldn't get their price quote email to work.  Do you have any idea what it would cost to line an 8X10 room with this stuff?  I suspect its waaaaay out of my league!

I'm thinking more along the lines of what Angie suggested: a grounded metal shed with a metal floor, then lined with wood to protect the contents.  How "tight" would this structure have to be to protect against EMP entering through cracks?  A poster on another thread cited a formula which seemed to indicate electromagnetism could not penetrate an opening <5.3 inches.  Anyone know if this is accurate?

Thrivalist

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Re: Question - Faraday Cage
« Reply #28 on: July 02, 2009, 08:21:52 PM »
I had them send me their catalog. It was here in 2 days from over seas no less!!! They also include a small sampler package to go with the catalog. I may have a price list around here somewhere. I believe they sell the copper on a roll and in snap in panels too. I will dig it up and get back to you. I'm trying to come up with all the nifty ideas I can before i build my new house.

Offline LGM30

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Re: Question - Faraday Cage
« Reply #29 on: July 03, 2009, 02:53:53 PM »
Thrivalist -
                    Thanks for the links.  Interesting stuff.  I couldn't get their price quote email to work.  Do you have any idea what it would cost to line an 8X10 room with this stuff?  I suspect its waaaaay out of my league!

I'm thinking more along the lines of what Angie suggested: a grounded metal shed with a metal floor, then lined with wood to protect the contents.  How "tight" would this structure have to be to protect against EMP entering through cracks?  A poster on another thread cited a formula which seemed to indicate electromagnetism could not penetrate an opening <5.3 inches.  Anyone know if this is accurate?
I've been involved with EM propagation for 20+ years.  In the AF I was responsible for maintaining EMP hardness of ICBM Weapon Systems.  I have a degree in electrical engineering, and have designed several EMP resistant pieces of equipment for different contracts over the years.  I've been working on an EMP primer, but it is difficult to do it justice and maintain accuracy without resorting to a lot of "its the way it is because I said so." because of the math and nature of the documentation.
HEMP (High Altitude Electromagnetic Pulse) entry is through at least three different means.  Only one of which is leakage through an aperture.  The Shielding Effectiveness is a function of wavelength, and because it is a periodic wave form there are resonant regions where things get nasty at one aperture size but not necessarily a bigger one.  So as far as not penetrating an opening smaller than 5.3 inches, that isn't very accurate.  One factor complicating the SE is the incident angle of the waveform to the aperture.  The electric field is more likely to penetrate the cage at certain angles.
One thing I can safely say is that openings much smaller than 5.3 inches are cause for critical rejection of a design.

Another point to consider is that the zinc oxide that forms on a galvanized surface is a poor conductor.  A trashcan lid fitting tight is not an optimum design, but it may be satisfactory.  If you have the time and means, you would be better served maintaining a steel to steel contact, but periodic inspection to prevent iron oxide from forming is a must.

Even re-bar in the walls will protect you some, but consider that even a solid metal shield will allow a low frequency magnetic field to penetrate to the center.  I'll try to post part one of a blog entry I am working on here in the next day.
« Last Edit: July 03, 2009, 02:55:58 PM by LGM30 »