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Faraday Cages - Your trashcan might not work

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  • Faraday Cages - Your trashcan might not work

    I decided to start a thread on Faraday Cages because I think they are an important part to any prepping for SHTF. As most folks already know what a Faraday cage is, I'm just going to cover some of the mathematics involved so folks can make informed design choices.

    Obviously Faraday cages are used to protect electronics in the case of an EMP... But that's kind of like saying body armor protects you from bullets.. the real question is how big is the bullet and how good is the body armor?

    I have done a lot of research on this and have read the data reports from the Star Fish Prime testing as well as what I could gather from the Russian tests. I've also spoke to Arthur T. Bradley of NASA (who specializes in this stuff), read government and Homeland Security reports, and have run my own calculations (I am an electrical engineer after all).

    So here is what I've found.. some very basic stuff to help in your cage design.

    First, I suggest reading this report:
    https://www.gao.gov/assets/680/676361.pdf

    There are two types of High Altitude EMP to be worried about. The first is a run-of-the-mill bomb being detonated ~300 miles up, the second is what is known as a Super EMP weapon. Without getting into a bunch of technical babble, the only difference between a normal bomb and a Super EMP bomb is that everything that is done to a normal bomb to increase its explosive yield is NOT done to an EMP bomb. Instead of adding globs of shielding and reflectors to redirect the gamma rays back into the core to increase the nuclear reactions, those reflectors and shielding are removed to allow as many gamma rays to escape as possible. It is the gamma rays that interact with our atmosphere, strip away electrons from their atoms and create the EMP pulse, not the actual bomb itself. The effect is a chain reaction which uses Earth's own atmosphere as a sort of amplifier.

    A normal high altitude electromagnetic pulse created from a regular nuclear bomb will create an EMP that will induce about 50,000 volts PER meter (at ground level) into all conductive surfaces.. A super EMP, depending on its size, could induce 100,000 to 200,000 volts per meter. Gamma flux on a bomb without a neutron reflector is far higher.

    A trash can Faraday cage will not be enough to protect electronics from an EMP.. it will protect some, but the more sensitive stuff like laptops will get fried. Modern ham radios, calculators, computers, and pretty much anything with a microprocessor integrated "IC" chip, will be fried if your location gets the full EMP effect.

    So here's some numbers: db (or -db) is a mathematical ratio of power and it is logarithmic. Every increase of 10db means 10 times the power, or in our case, every -10db decrease means
    ten times the attenuation of power.

    Regular EMP:
    Assuming a 50,000 volt per meter pulse, we know that a properly sealed galvanized trashcan will provide about -40db of attenuation. Knowing that, a 50,000 volt per meter pulse will attenuate to about 500 volts per meter inside the trashcan. So lets say you have a diode that measures 1 cm long.. (that's a big diode!), 500 volts per meter divided by 100 centimeters = 5 volts. That's 5 volts across the diode.. Probably not a problem for a diode of that size, but now imagine that's a computer processor integrated chip.. that 5 volts is likely to fry that chip.. and that's just the chip sitting in a package! Imagine that chip being attached to a motherboard that is 8 inches x 8 inches! 8 inches x 2.54 cm per inch x 5 volts per cm = 101.6 volts! WOW! That EMP pulse just induced 101.6 volts into your computer's motherboard.. Unfortunately, your computer is now a paperweight.

    Lets improve our Farday cage a bit. Lets add a second layer of protection to our items. While we could put a trashcan inside a trashcan (must be totally insulated from each other!), doing so gets kind of cumbersome and problematic. So instead of adding another piece of steel, lets put our items in special aluminum foil bags or just wrap them in aluminum foil and then put them in the trashcan. (Note: Mylar bags will not work!) A good aluminum foil shield will provide about -45db of protection. Aluminum conducts current better than steel does so even though the aluminum bag is thinner, we get an extra 5db of protection out of it. Both layers of protection must be perfectly sealed..

    So now we have the trashcan ( -40db of protection) added to our individual item wrapped in aluminum (-45db).. so we have -85db of protection. Lets run those numbers again.
    50,000 volts per meter attenuated by -85db = 2.8 volts per meter! WOW! That extra 40 to 45 db of protection makes all the difference in the world! At 2.8 volts per meter, even the most sensitive electronics would survive unscathed in the slightest. I won't even bother breaking down 2.8 volts per meter into centimeters because its obvious it doesn't amount to anything.

    Super EMP:
    Lets up the power.. what kind of moron dictator / terrorist would waste a perfectly good nuclear bomb to create a 50kv pulse when they can redesign it and make the pulse up to 200,000 volts right?
    200,000 volts attenuated by -40db of trashcan shielding works out to 2000 volts per meter or 20 volts per centimeter.. At 20 volts per centimeter, everything you own just got fried.

    200,000 volts attenuated by -85db of shielding (trashcan + aluminum foil), works out to 11.2 volts per meter. Once again, I won't bother to break that down into centimeters because there's nothing there that's going to damage anything.

    So the moral of this all? Use 2 layers of shielding and make sure they are perfectly sealed. One layer of steel, one layer of aluminum, and make sure an insulating material separates them by at least 1/4 inch.

    You can purchase aluminum foil bags at Digikey for less than $1.00 each for small bags or $3 -$4 for very large (almost trashcan sized) bags. Look for Dri-Shield 3400.

    When it comes to really important things, laptop, ham radio, medical equipment, and things which can be considered critical, I suggest using 3 layers. Put your device in a aluminum bag, then a plastic bag, then another aluminum bag, and then into the trashcan. The third layer will add some extra attenuation in case one of the other layers is not perfectly sealed.

    So lets ask another question: What are the chances you will get a direct hit and be subject to the full power of an EMP bomb? Well, if a single EMP is detonated over Kansas, the full radiated power only extends out to around a 500 mile radius, after that, the power gets cut to around 50% and folks on the coastal areas will have less damage. But if we get hit with multiple devices, then the entire country, with the exception of places like Southern Florida, Maine, etc, would be hit with the full force.

  • #2
    Murphy, I tend to go to my kids for engineering help (daughters, one is a aerospace engineer and the other is a biomedical engineer) so I tend to get conflicting answers. Since your a electrical engineer I'll ask you. I have a building that I built specifically for storing off road vehicles and backup comms. The building has a steel roof, wood walls & floor (Plywood) and lined with aluminum wire screening, The building is completely off the ground and has a 1/2 inch barrier of live rubber separating the building from the foundation. I have #4 copper wire running from the roof, walls and foundation bolts to a copper grounding rod drove to bedrock (5 feet here in WV). How safe will this keep the equipment stored inside? Thanks

    Dale

    Comment


    • #3
      Originally posted by dalewick View Post
      Murphy, I tend to go to my kids for engineering help (daughters, one is a aerospace engineer and the other is a biomedical engineer) so I tend to get conflicting answers. Since your a electrical engineer I'll ask you. I have a building that I built specifically for storing off road vehicles and backup comms. The building has a steel roof, wood walls & floor (Plywood) and lined with aluminum wire screening, The building is completely off the ground and has a 1/2 inch barrier of live rubber separating the building from the foundation. I have #4 copper wire running from the roof, walls and foundation bolts to a copper grounding rod drove to bedrock (5 feet here in WV). How safe will this keep the equipment stored inside? Thanks

      Dale
      I'm an electrical engineer, and not even a very good one since I do very little of that type of work.. and I'm certainly NOT an RF guy.. that a whole different thing and a very specialized one at that.

      However, I do know a few things and one of them is that in order to know how effective your aluminum wire screen is, we'd need to know the size of the holes in the screen.

      The frequency (wavelength) of the RF energy and the dimensions of the holes in the screen are critical variables. The problem here is that an EMP pulse, at least the part we're worried about, has a very fast rise time (called Slew Rate).. its on the order of 10 to 100 Ghz which basically means wavelengths as short at 3mm.. 3 millimeters is a pretty small hole.. of course, the entire EM energy spread of the pulse isn't going to all be at 100Ghz, but it gives us a point of reference.

      For delicate electronics, I think the basic rule is that nothing short of a solid barrier of metal is going to provide adequate protection.. even a solid barrier will allow some energy to pass through.

      If the detonation takes place over your head, your steel roof will provide some attenuation but it probably won't be enough to make any significant difference. Like someone shooting you through a couple sheets of plywood, the bullet will slow down, but it won't make any difference as it will still pass through you..

      Depending on the type of bomb, your location (distance or geological formations) may have a significant effect on its power. Someone living in a deep valley with a mountain between them and the point of detonation may not experience any effects at all as the higher frequencies are very much "line of sight" in their effectiveness.

      I've been trying to figure out what the effects would be of someone living at a location near an Iron Mine.. what would be the effect of the high iron content of the ground?

      My best guess is that unless your aluminum screen has very small holes like window screen, and unless those individual sections are well bonded electrically to each other, it won't provide much protection. It may attenuate some of the longer wavelengths, but the high frequency stuff is going to zip right through like it wasn't even there.

      Its like trying to use chicken wire to hold back pea gravel.. if the holes are too big, it won't work.

      Comment


      • #4
        Originally posted by Murphy View Post

        I'm an electrical engineer, and not even a very good one since I do very little of that type of work.. and I'm certainly NOT an RF guy.. that a whole different thing and a very specialized one at that.

        However, I do know a few things and one of them is that in order to know how effective your aluminum wire screen is, we'd need to know the size of the holes in the screen.

        The frequency (wavelength) of the RF energy and the dimensions of the holes in the screen are critical variables. The problem here is that an EMP pulse, at least the part we're worried about, has a very fast rise time (called Slew Rate).. its on the order of 10 to 100 Ghz which basically means wavelengths as short at 3mm.. 3 millimeters is a pretty small hole.. of course, the entire EM energy spread of the pulse isn't going to all be at 100Ghz, but it gives us a point of reference.

        For delicate electronics, I think the basic rule is that nothing short of a solid barrier of metal is going to provide adequate protection.. even a solid barrier will allow some energy to pass through.

        If the detonation takes place over your head, your steel roof will provide some attenuation but it probably won't be enough to make any significant difference. Like someone shooting you through a couple sheets of plywood, the bullet will slow down, but it won't make any difference as it will still pass through you..

        Depending on the type of bomb, your location (distance or geological formations) may have a significant effect on its power. Someone living in a deep valley with a mountain between them and the point of detonation may not experience any effects at all as the higher frequencies are very much "line of sight" in their effectiveness.

        I've been trying to figure out what the effects would be of someone living at a location near an Iron Mine.. what would be the effect of the high iron content of the ground?

        My best guess is that unless your aluminum screen has very small holes like window screen, and unless those individual sections are well bonded electrically to each other, it won't provide much protection. It may attenuate some of the longer wavelengths, but the high frequency stuff is going to zip right through like it wasn't even there.

        Its like trying to use chicken wire to hold back pea gravel.. if the holes are too big, it won't work.
        Actually, it is window screening with about a 2mm space. I grounded each panel by soldering the #4 gauge copper wire to it and ran the wire to the grounding rod. My area of WV "shouldn't" be a primary target zone but I won't bet on anything the enemy willing to start a nuclear war is going to do.

        I have a Can Am Commander SXS that I store in the building that is my primary concern. Plan on using the vehicle for foraging, personnel collection and recon if the worst would happen. I'm planning on buying and storing the few comprisable electronic components that are on the vehicle but until then the storage shed will have to do.

        Thanks,

        Dale

        Comment


        • #5
          Originally posted by dalewick View Post

          Actually, it is window screening with about a 2mm space. I grounded each panel by soldering the #4 gauge copper wire to it and ran the wire to the grounding rod. My area of WV "shouldn't" be a primary target zone but I won't bet on anything the enemy willing to start a nuclear war is going to do.
          Well you've certainly gone further than most others have! Sounds like you've done a lot to mitigate RF propagation. Can you get a cell phone signal when you're inside the building? Will an FM radio pickup your local radio station? If either of these answers are yes, then your shielding is ineffective.

          Here's an experiment you can try that will give you some kind of reference point to work with. Have someone stand inside with a two way radio and then someone stand a couple feet outside and try to transmit.. If the two way radios will not signal each other, then your attenuation is above -95 to -100 db.. (that's good) If they do pick up the signal from the other radio, then the attenuation is somewhere below. Most walmart type two way radios are sensitive to around -95db.. some go to around -110db.

          If you do get a two way radio signal through, its not the end of the world... Take the radio that is inside the building and wrap it in tinfoil and then try to call it again. If the call fails, then your building's protection falls somewhere around -40db to -90db.. But if the signal still makes it through the aluminum foil, then the building's protection is less than -40db.

          This works because we know what the signal sensitivity is on the radio and we know what the approximate signal sensitivity is on aluminum foil... so long as its properly sealed.

          If the test fails and the radio inside can pick up the signal from outside, put the wrapped up radio in a plastic bag and add a 2nd layer of foil.. If it still fails, your building's protection doesn't work at all.

          I have a Can Am Commander SXS that I store in the building that is my primary concern. Plan on using the vehicle for foraging, personnel collection and recon if the worst would happen. I'm planning on buying and storing the few comprisable electronic components that are on the vehicle but until then the storage shed will have to do.

          Thanks,

          Dale
          Depending on what you're testing above shows, you could just build a second room inside the shed.. Line it with radiant barrier foil and you'd have a 2 layer Faraday cage that would most likely protect it. You could also just create a conductive blanket to throw over it... Even if it only gives you -20 db, that's still something.

          I was worried about our cars as well and was just going to get on Ebay and purchase a backup computer for my truck.. problem is I can't seem to figure out if a computer is all I would need or if an EMP would burn out sensors as well.

          Comment


          • #6
            Originally posted by Murphy View Post
            Well you've certainly gone further than most others have! Sounds like you've done a lot to mitigate RF propagation. Can you get a cell phone signal when you're inside the building? Will an FM radio pickup your local radio station? If either of these answers are yes, then your shielding is ineffective.

            Here's an experiment you can try that will give you some kind of reference point to work with. Have someone stand inside with a two way radio and then someone stand a couple feet outside and try to transmit.. If the two way radios will not signal each other, then your attenuation is above -95 to -100 db.. (that's good) If they do pick up the signal from the other radio, then the attenuation is somewhere below. Most walmart type two way radios are sensitive to around -95db.. some go to around -110db.

            If you do get a two way radio signal through, its not the end of the world... Take the radio that is inside the building and wrap it in tinfoil and then try to call it again. If the call fails, then your building's protection falls somewhere around -40db to -90db.. But if the signal still makes it through the aluminum foil, then the building's protection is less than -40db.

            This works because we know what the signal sensitivity is on the radio and we know what the approximate signal sensitivity is on aluminum foil... so long as its properly sealed.

            If the test fails and the radio inside can pick up the signal from outside, put the wrapped up radio in a plastic bag and add a 2nd layer of foil.. If it still fails, your building's protection doesn't work at all.


            Depending on what you're testing above shows, you could just build a second room inside the shed.. Line it with radiant barrier foil and you'd have a 2 layer Faraday cage that would most likely protect it. You could also just create a conductive blanket to throw over it... Even if it only gives you -20 db, that's still something.

            I was worried about our cars as well and was just going to get on Ebay and purchase a backup computer for my truck.. problem is I can't seem to figure out if a computer is all I would need or if an EMP would burn out sensors as well.
            Murphy, I get zero cell phone reception and my wife can't get through to me on either my mobile or hand held walkie talkies from 25 feet away. I also get no FM, AM or sirrus radio reception. I do really like your suggestion of lining the building with the radiant barrier foil. Insulation in the building would be great for working in it anyway.

            One of the reasons I like the SXS is that it's a simpler system to work with and it gets great mileage, can traverse rough terrain and actually makes a great weapons and observation platfoem.

            Thanks for your help.

            Dale

            Comment


            • #7
              Originally posted by dalewick View Post

              Murphy, I get zero cell phone reception and my wife can't get through to me on either my mobile or hand held walkie talkies from 25 feet away. I also get no FM, AM or sirrus radio reception. I do really like your suggestion of lining the building with the radiant barrier foil. Insulation in the building would be great for working in it anyway.

              One of the reasons I like the SXS is that it's a simpler system to work with and it gets great mileage, can traverse rough terrain and actually makes a great weapons and observation platfoem.

              Thanks for your help.

              Dale
              Check the specs on the walkie talkies and see how sensitive they are.. Try it again but this time, make it so there's only a couple feet between you and the other radio.. 25 feet is a very long distance for a 1/2 watt radio. Why? Because of the inverse square law of RF propagation power. The radio you're using is already VERY VERY low power.. at 25 feet away, its power output is cut by something like 40 db already.

              Just stand next to the inside wall of your shed and have the other radio right on the other side of the wall within a foot or two.. Try it again.

              I'll be quite surprised if a single layer screen can stop that transmission. Also, don't try speaking into the radio, try pressing the CALL button that makes the other radio sequel with the alert tone.

              Comment


              • #8
                Originally posted by Murphy View Post


                I was worried about our cars as well and was just going to get on Ebay and purchase a backup computer for my truck.. problem is I can't seem to figure out if a computer is all I would need or if an EMP would burn out sensors as well.
                I would stock critical sensors. I am thinking an EMP would fry them because they are so electrically sensitive. For example, car repair manuals instruct us to disconnect the battery before attempting to replace any sensor...
                Genius is making a way out of no way.

                Comment


                • #9
                  Your electronics that are not plugged into the grid are not in danger of being damaged by the EMP

                  Comment


                  • #10
                    Originally posted by Snyper708 View Post
                    Your electronics that are not plugged into the grid are not in danger of being damaged by the EMP
                    That applies to a solar EMP which is also called a Coronal Mass Ejection or CME.

                    A HEMP (High Altitude Electromagnetic Pulse) nuclear detonation in space will fry everything that isn't protected, plugged in or not.

                    The difference is that Solar CME's are mostly conductive.. they are low frequency and need a conductive path to follow like a wire.

                    Nuclear EMP is very high frequency and travels like any other radio wave.. The HEMP is has both a conductive component and a electromagnetic radiation component.. Its far worse than a CME.

                    Here's a great document to read:
                    www.dtic.mil/dtic/tr/fulltext/u2/a554607.pdf
                    Here's a great video to watch:
                    https://www.youtube.com/watch?v=PUZZ3XflO-M

                    And keep in mind, mankind can't generate near the types of energies nature can... and a nuclear weapon goes right to the heart of nature.

                    The EMP generator in the youtube video is a narrow bandwidth (under 1 Ghz) whereas a real bomb would be a very wide bandwidth and stretch all the way up into the 100 Ghz range.

                    Comment


                    • #11
                      Dale........empty your Private Mail. It is over full
                      One day you eat the chicken.....next day the left-over chicken.....next five days you eat chicken feathers, head and feet.

                      Comment


                      • #12
                        A HEMP (High Altitude Electromagnetic Pulse) nuclear detonation in space will fry everything that isn't protected, plugged in or not.
                        That's mostly science fiction.

                        This guy does this stuff for a living:

                        http://www.timebomb2000.com/vb/showt...63#post5910763
                        Originally Posted by LoupGarou View Post
                        "Super EMP" (enhanced gamma yield) nuclear devices do exist, but still will not cause enough of a heave to cause anywhere near the damage that they are hyped about. The soviet union quickly caught up, and passed us in HEMP testing, and had created several devices that they were trying to enhance the gamma yields on. They had some limited success on the last four, which all were over 250KT yield devices, but nothing that caused widespread damage (and nothing that could not be quickly repaired).

                        Most of the damage that any HEMP could cause will be in the blowout of protection circuits (both the US, and the soviets found this out), and not by actual damage to the parts of the system. This is why the streetlights went out in Hawaii during starfish on a few streetlight runs that were parallel to the test (the fuse disks shunted). Actual hard damage to the larger active devices on the grid will not come from HEMP (not talking about the fuses and safety parts, but the transformers and other larger parts). HEMP is too quick of a pulse and heave. GICs from solar bursts on the other hand are long enough in duration to actually damage the larger system components.
                        .
                        Here's a great document to read:
                        www.dtic.mil/dtic/tr/fulltext/u2/a554607.pdf
                        You link goes nowhere:

                        "This is Essentially a missing page or bad url Error"

                        Comment


                        • #13
                          Originally posted by Snyper708 View Post
                          That's mostly science fiction.

                          This guy does this stuff for a living:

                          http://www.timebomb2000.com/vb/showt...63#post5910763
                          I'm an electrical engineer by education and my hobbies include astrophysics among other things. I've read the congressional reports, the homeland security reports, and have one-on-one conversations with Dr. Arthur T. Bradley who actually works for NASA.

                          You posted a link to a post in a forum by some obscure guy in a forum named LoupGarou who posted a couple of links to opinion articles.. HUH??? What was the point of that?

                          Lets fire up the Horse Crap detector and see what it says:
                          1st Warning - These articles label themselves as "Gingrich's ideas".. or variations of that.. EMP is not Gingrich's idea by a long shot, but we do know that it helps to manipulate people by throwing in a name that can generate the most desirable returns.. Perhaps they should have called it "Obama's idea".. or they could have gotten a lot more traction calling it "Diane Feinstein's" idea..

                          That's the first warning sign.

                          The second, as I've said before, is the talent of some of these people to take truths, half-truths, and quasi-half truths, and mix them with pure horse crap to make a statement look true or legitimate. Lets face it, you could get a turd to taste good if you throw in enough sugar and deep fry it.

                          Nuclear EMP isn't any politician's "idea" anymore than Cancer is... EMP is a fact of science and we have scientific data to back up the results of what would happen. Starfish Prime blew out street lights 800 miles away and saturated the scientific sensor platforms, and the Russian tests did far more damage. And that was back in the mid 1900's when vacuum tubes were the mainstay of the day and the transistor was still the size of a green pea.

                          Here's a manmade EMP taking out a vehicle at the White Sands testing facility...
                          https://www.youtube.com/watch?v=PUZZ3XflO-M

                          After viewing that video and seeing the test, only one of two responses can be made.. 1) Wow, EMP is a threat, or 2) That was fake.

                          There's a reason the Military's equipment is hardened against EMP.. and its not because EMP isn't real. Words are cheap and meaningless, as are most of these bloggers and authors who have a talent for mixing truths with horse crap.. The only thing that counts is science and real actions... and I don't think our Military hardens their important equipment because of some obscure forum blogger.

                          You link goes nowhere:
                          "This is Essentially a missing page or bad url Error"
                          The link's address works fine, you need to copy and paste it into your address bar as this forum isn't recognizing it for some reason.


                          My attitude to all this as far as others are concerned is: If you don't believe what I say then that's your prerogative, good luck. I am a man of science and only science.. Science is where I turn when I want answers or solutions, its where I turn for entertainment, and if someone's claim doesn't hold up to scientific scrutiny then I label it as pure horse crap.

                          If you don't prep for an EMP, that's probably fine as it will probably never happen anyhow. The governments of the various nations do a pretty good job of keeping nuclear material away from terrorists and a nation like North Korea isn't likely to start a fight they can't win.


                          Comment


                          • #14
                            Originally posted by Sourdough View Post
                            Dale........empty your Private Mail. It is over full
                            Sourdough, The site is telling me my inbox is empty. I have no idea what's wrong with it.

                            Dale

                            Comment


                            • #15
                              You posted a link to a post in a forum by some obscure guy in a forum named LoupGarou who posted a couple of links to opinion articles.. HUH??? What was the point of that?
                              He's an engineer too.
                              He specializes in this sort of physics,
                              He's done actual EMP testing..


                              Lets fire up the Horse Crap detector and see what it says:
                              Mine says there's plenty to go around.,

                              My attitude to all this as far as others are concerned is: If you don't believe what I say then that's your prerogative,
                              I've seen too many "internet experts" to believe every claim made,.
                              I've heard it stated that one can be anything they want on the internet as long as they have Google.

                              No one said EMP isn't real,
                              It's just not the threat it's hyped up to be.

                              Comment

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