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Alternative Faraday cage
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  1. #1
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    Alternative Faraday cage

    I had a thought last night, and sought advice from one of my professors here at the school. He is a geophysicist by training, and as such knows far, far more than I about such things.
    The thought was this:
    Would a microwave oven make a rough-and-ready Faraday cage? The thinking is, if it is designed to contain high-frequency energy, then surely it will repel the same, which includes EMP from tactical nuclear explosions.
    I asked Grant, my professor, and he said yes. It would repel the higher-freq stuff, which is what does the damage to electronics, but not the low-freq, which is irrelevant. He then wondered why he hadn't thought of that.

    Opinions?

    Bailey

  2. #2
    Put a cellphone into your microwave oven and try to call it.

  3. #3
    Sounds like a great idea! Kinda small but for smaller gear will work...I think.
    Thanks

  4. #4
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    put a small radio inside turned on. as soon as you shut the door the signal should be interrupted.
    "Peace is that brief, glorious moment in history when everybody stands around reloading."-Thomas Jefferson



  5. #5
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    Quote Originally Posted by Kar98
    Put a cellphone into your microwave oven and try to call it.
    I tried it and the phone didn't ring, the voice mail answered! Then I tried it ouside the microwave, right next to it and it rang! Cool, thanks for the info!
    "If anyone shall be outside the ark of Noe he shall perish when the flood prevails." St Jerome
    Extra Ecclesiam Nulla Salus

    Truth

    The ONLY way out of the mess this world has become is for the Pope and the Bishops of the world to Consecrate Russia to the Immaculate Heart of Mary.
    Pray for the Consecration of Russia.

    Peace

    Tulmeadow Farm Grass Fed Beef
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  6. #6
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    Just don't turn it on!

    You can wrap stuff in foil to get the same effect!
    "We have blown our chance: Instead of going into outerspace we have ventured into cyberspace" (c)2000 Ofuzzy1
    The fine print: Quoted items are used under the Fair Use Act for educational purposes. In other words: In accordance with Title 17 U.S.C. Section 107, this material is distributed without profit to those who have expressed a prior interest in receiving the included information for research and educational purposes.

  7. #7
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    ofuzzy1
    You can wrap stuff in foil to get the same effect!
    Are you saying wrapping sensetive equiptmant in FOIL would do the same thing as a faraday cage??? Go ahead....laugh....I know NOTHING...I tell you!!! NOTHING about these kinds of things!!
    There can be no divided allegiance here. Any man who says he is an American, but something else also, isn't an American at all. We have room for but one flag, the American flag... We have room for but one language here, and that is the English language... and we have room for but one sole loyalty and that is a loyalty to the American people."Theodore Roosevelt-1907.

  8. #8
    If you wrap it in foil, that _is_ a Faraday cage. A Faraday cage is simply conductive material completely surrounding a certain volume. As lond as it's continuous, in theory, the aluminum foil ought to work fine.

    Testing it by using a cel phone is a very good idea. Wrap it up, dial the number, and see if it rings. (I would first wrap it in something non-conductive such as paper or cloth, to prevent the battery connection from shorting out on the foil.)

    Personally, I think that any electronic device that is not connected to an antenna would be very unlikely to be damaged by EMP. ("An antenna" would include connection to the power source or phone lines.) But foil is cheap, and it certainly won't do any harm. So if it makes you feel better to wrap your spare electronic devices in foil, I don't see why not. IMHO, it would improve the chances of EMP survival from about 99% to about 99.9%.

  9. #9
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    Hmmm, I gotta stop at the supermarket on my way home to pick up enough aluminum foil to wrap my Ford F250 in!!!!

  10. #10
    Actually, if you haven't noticed, most of the truck is already covered--not with aluminum foil, but with a bunch of sheet metal.

    And the electronics under the hood are generally shielded. Granted, there are some antennas attached to them (spark plug wires and other wiring), so there's a possibility of EMP damage. But even those antennas are fairly well shielded by the truck's body.

    So, IMHO, the risk of EMP damage to automotive electronics are greatly overrated. But on the other hand, foil is cheap.

  11. #11
    Does this mean I should use more layers of foil around my head to keep "them" from reading my thoughts? Or just stick my head in the microwave when I have a particularly deep thought? Gotta run - I think I see a crop circle in my tomato plants...

    Kidding, Bailey 1. That's the kind of "out of the box (or cage)" thinking that makes this board such a draw. What is the shielding material used in microwaves?

  12. #12
    well, the brain is a very sensitive electro-chemical computer...

    you mean there is really something to "tin foil hats"???



    -t

  13. #13
    Keep the shiny side out for EMP protection. Keep the shiny side in to keep "them" from reading your mind.

  14. #14
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    Seriously......I thought a Faraday Cage had to be grounded to properly protect against EMP?????
    There can be no divided allegiance here. Any man who says he is an American, but something else also, isn't an American at all. We have room for but one flag, the American flag... We have room for but one language here, and that is the English language... and we have room for but one sole loyalty and that is a loyalty to the American people."Theodore Roosevelt-1907.

  15. #15
    No. It does _not_ need to be grounded. A faraday cage does not work because it sends the energy to ground. It works because the currents in the shield are such that any fields induced inside the shield are cancelled out.

    I suppose there could be situations where the earth itself formed one side of the faraday cage--for example, four wire mesh walls and one wire mesh ceiling, with the ground forming the floor of the cage. In that case, of course, the four walls would need to be bonded to the ground. But in the general case, no, a faraday cage does not need to be grounded.

  16. #16
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    Shiny side out, and a smaller one to fit your head, shiny side in ...tucking the last into the first...........Your good to go...no emp in, no loose change out!!

  17. #17
    Quote Originally Posted by aquadog
    Does this mean I should use more layers of foil around my head to keep "them" from reading my thoughts? Or just stick my head in the microwave when I have a particularly deep thought? Gotta run - I think I see a crop circle in my tomato plants...

    Kidding, Bailey 1. That's the kind of "out of the box (or cage)" thinking that makes this board such a draw. What is the shielding material used in microwaves?
    Well this man is ready for anything!

    Seriously, though, here is a very helpful site I recently found concerning EMP's..with a link with info about faraday cages.

    http://www.unitedstatesaction.com/electrical-threat.htm
    "One sees clearly only with the heart. Anything essential is invisible to the eyes." - Antoine de Saint-Exupéry

    "Never apologize for a dumb question. Dumb questions are better than dumb mistakes."-SmartAZ

    Inasmuch as ye have done it unto one of the least of these my brethren, ye have done it unto me.-Jesus Christ

    my faith? Look here: [url]http://www.uua.org/aboutuua/principles.html[/url]

  18. #18
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    I have a experiment going on that I hope I never find out the answer to. If it works, it'll be a 30' x 40' Faraday cage. Hopefully, the F-350 and the Gold Wing will be parked inside it if the experiment takes place.

  19. #19
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    Yes, that is what a microwave oven does; sort of a reverse faraday cage.

    But remember, there is nothing magic about either an EMP or a faraday cage. The cage doesn't keep radiation out, it only reduces it. The EMP works because it has a very large amount of power. If your cage reduces power by 100 db and the EMP has a gazillion db, your cage is not much better than no protection at all.

    A faraday cage only keeps out electrical fields, and the EMP is an electrical-magnetic pulse. You can only protect against the magnetic field by surrounding your little goodie with audio iron, also called transformer core material. Figure about one pound per watt. How many watts of EMP do you guess you will get?

  20. #20
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    RC....Thank you for that answer.
    Smart AZ.......
    You can only protect against the magnetic field by surrounding your little goodie with audio iron, also called transformer core material. Figure about one pound per watt. How many watts of EMP do you guess you will get?
    Translation PLEEEASE into language the electronically retarded can understand> DUH!!!!!
    What is audio iron? Are you saying it needs to be encased in one pound of this per watt of the EMP??
    There can be no divided allegiance here. Any man who says he is an American, but something else also, isn't an American at all. We have room for but one flag, the American flag... We have room for but one language here, and that is the English language... and we have room for but one sole loyalty and that is a loyalty to the American people."Theodore Roosevelt-1907.

  21. #21
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    A microwave oven will work great against a MHD bomb (E-Bomb), but unless you plate over the window and ground strap the door, I would not trust it with a HEMP blast. Microwave ovens are designed to shield RF in the 2-3GHz range, no the lower frequencies (<10MHz) that are generated in a HEMP event.

    The Aluminum foil would work better than the microwave oven. Faraday cages do not need to be grounded for the items inside to be saved, they just need to be a contiguous shield all the way around and the items can not touch the metal (insulated). Ammo boxes, all metal trash cans, file cabinets with spring fingers around the opening cracks, any fully enclosed metal box will do. Just insulate the insides with something to keep the contents from making contact with the shield. The only time you might want to ground it is if the enclosure is very large (like over 8'X8'X8' or so), and this is only to remove any stored charge after a blast (think Layden Jar). The charge will usually dissapate quick enough, but just in case you might be near or touching it, you will not get the zap of the century.

    If you had an old (dead) microwave and wanted to convert it to a Faraday cage, cut off the power cord, cover the front screen with a piece of sheet metal screwed into the front door on the inside, and then run jumper wires from the outside case to the front door and to the sheet metal. You might also want to take the case apart and sand down the paint at all of the screw holes to guarantee a good contact.

    And as far as the magnetic component, unless you are close enough to get burned by the blast, you are too far from the source to worry about the magnetic part. The damage from a HEMP blast is from a point source, and point source rules apply, like the inverse square law. The inverse square law basicaly states that for every doubling of the distance from the source, the power level decreases by a factor of four. Both the magnetic and electronic components of the blast drop in power this way. The main thing that you have to worry about with HEMP is the grid connections like the power grid, phone lines, or cable TV connections. This is the reason that a handheld radio with an antenna smaller than 19 inches or so would be ok outside of the cage as long as nothing is connected to it, while your VCR gets smoked with no antenna connected to it (just power).

    Loup Garou
    Last edited by LoupGarou; 09-19-2005 at 07:55 PM. Reason: magnetic comp...

  22. #22
    I think for EMP protection it would be a bad choice for many reasons but here is just one.

    Your microwave has an antenna inside it. Sure its inside the shielded area.

    BUT..............

    It is connected to a feeder wire that brings the signal into the shielded area to feed the antenna. So how much charge do you think will hit the cord and all the other wires and how much of that pulse will be fed to that antenna inside the microwave?

    I don't have the test equiptment to test every brand of microwave so I don't have a clue. My comms are/will be too important to me to take a chance.

    I like the option of the metal garbage can. Not only for the size but cost. If you want to multiple that protection even more use ammo cans INSIDE the garbage can.

    Opinions vary and thats mine for what its worth.

    RCSAR

  23. #23
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    What is audio iron? Are you saying it needs to be encased in one pound of this per watt of the EMP??
    Audio iron is an alloy with certain magnetic characteristics. It is used in sheets. If you look at any transformer you will see that it is made of stacked sheets of iron. Another material is ferrite, a black sort of ceramic, which may be made as transformer core or as noise suppressor, and you can't tell which by looking.

    The figure of "one pound per watt" was a guess. One tenth pound per watt might be a more accurate guess. Engineers assume a limit of 2,000 gauss for transformer cores, which is also a guess, and the power level of an EMP is also a guess except that you're likely to guess way too low on that one.

    With all this guessing, you might as well not bother. Rust is more of a threat.

  24. #24
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    With all this guessing, you might as well not bother. Rust is more of a threat

    OK....I understood that part!!
    So you are saying....maybe it will work....but probably it won't if it's a BIG'UN....Right?
    There can be no divided allegiance here. Any man who says he is an American, but something else also, isn't an American at all. We have room for but one flag, the American flag... We have room for but one language here, and that is the English language... and we have room for but one sole loyalty and that is a loyalty to the American people."Theodore Roosevelt-1907.

  25. #25
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    One continuous layer (no gaps) is all you need, insulated on the inside. The iron will work fine, but is not necessary, the magnetic part of the pulse has dropped way below the level of concern. The electronic part of the pulse is the massive part due to Compton scattering, where gamma radiation gets changed into a massive pulse of electrons over a wide area. Because of compton scattering, that part of the blast does not follow closely the inverse square law (it is not as much of a point source). This is why one or two HEMPs can take out most of the entire country's grid tied electronics.

    Most transformer cores will saturate in the 20-25KGauss, sheet metal can handle 5-6KGauss and even ceramic-metal alloys will hold a few thosuand Gauss. The remaining magnetic part of the pulse is so miniscule that you don't have to worry about it. More of a local magnetic pulse would be created by grid tied transformers inside the office or home.

    Look for average everyday things like the metal trash cans or ammo cans. Watch out for items like refrigerators since they look perfect for the job until you start the conversion and have to replace the plastic coated magnetic seal with several layers of spring fingers. A lot of the fridge doors are on plastic bushings and have little or no electrical contact with the rest of the unit, great for not getting shocked in the winter, but lousy for a Faraday cage.

    I have converted two 20' SeaPacs to Faraday cages for a friend of mine. It took almost 150 feet of sheet metal flashing, 12 sheets of galvanized sheet metal, steel screening, 46 sheets of 1/4" plywood to insulate the interior, and several grounding straps to link the doors in. A weekend of fun.

    Loup Garou

  26. #26
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    Only two things can ruin my communication systems...fire and water. Water because it would make wood too wet to burn, and fire because it would use up all the wood.

    My comm system? Why smoke signals, of course!
    You say "trigger-happy cowboy" as if it were a bad thing.

    "If they come a'huntin' me; they can consider themselves lucky if they*don't* find me!"

    No surrender; no retreat!

    If we fight, victory is not certain. If we do not fight, defeat surely is.

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