Prepping

How to Make a Faraday Cage for less than $5

faraday cage pinterest

Hey everyone,

With all this talk about EMPs and how some or all electronics can be fried in an instant when it happens, it’s time to see what we can actually do to protect our devices. The most popular solution you will find to survive an EMP (apart from learning to actually live without electricity) is to make a Faraday cage, that is to say an enclosure that would protect your devices from this electromagnetic pulse.

Although the EMP literature is scarce, and often contradictory, I found a “recipe” for a Faraday cage that should withhold both types of EMPs, whether natural or man-made. Based on my own research, I’m pretty sure this will work better than a microwave, a galvanized trash can, or some of the other solutions you can find online.

The idea is simple: wrap your devices inside a thick layer of aluminum foil, the thicker the better, after they’ve been covered by a layer of insulating material to avoid your devices from touching the conductive material.

Aluminum foil is cheap, you can find cardboard around the house for free, duct tape and packaging tape are also dirt-cheap, so you can make a cheap Faraday cage for less than $5. Now you will spend more than $5 for these supplies, but keep in mind you’ll be able to make several cages for this amount of money.

The idea behind a Faraday cage is that right before this electric surge reaches your devices, it will hit the conductive material box instead (made in our case of aluminum foil), flow around it and leave the contents of the cage intact.

The electric current always takes the path of least resistance, so it will go through the conductive layer and not inside it, so long as inside you have an insulating layer that will ensure your phone or flashlight is NOT in direct contact with the conductive layer.

Depending on the intensity of the EMP and the frequency spectrum, the first conductive layer might not be strong enough to absorb the whole pulse, which is why we need a conductive layer that’s as thick as possible.

The conductive layer should NOT have any holes in it. Fully enclosed Faraday cages generally do a better job at dissipating electric current than mesh cages (source).

How to make Faraday  Box Step-by-step

So step one, get some heavy-duty EMP, preferably one that’s as thick as possible.

step 1 aluminum foil

 

Step 2, get a cardboard box. You will need several of different sizes, actually. Keep in mind you won’t be using these items until after the EMP, you can’t take them out and put them back in, as it will compromise the integrity of the layers.

step 2 cardboard box

 

Step 3: Feel free to add additional insulation inside the box, such as bubble wrap. This will ensure the items are shock-proof.

step 3 bubble wrap

 

Step 4: wrap your device with the bubble wrap, then put it into the cardboard box and seal it with duct tape or something similar.

step 4 sealing cardboard box

Make sure you don’t leave any open spaces in your box, the cardboard should overlap in all the places it can be open and, needless to say, it shouldn’t have any holes in it.

 

Step 5 is to wrap the cardboard box in aluminum foil. Feel free to wrap it several times, to make the layer thicker more effective. The box should look like this:

step 5 aluminum foil

 

That’s about it. A cheap an easy way of making a Faraday cage that should keep your devices safe from an EMP blast. The more layers you add, the safer it will be, but then you sacrifice portability. You may want to make one for your bug out bag and one to keep inside your safe room or your black out box.

Are there any Faraday cage variations you think will make it even safer? Let us know in the comments below.

Dan Sullivan

About Dan Sullivan

Dan has come into contact with homesteading when he was 4 years old, and would spend summers in the countryside with his grandparents. The skills and the mindset that he's learned now allow him in his mid 30s to better prepare for whatever may come.
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24 thoughts on “How to Make a Faraday Cage for less than $5

    1. BLACK,
      Articles like this one bring up a good point. Assuming the equipment in your Faraday enclosure are things you need to use, getting them in and out of the enclosure while still providing protection is an issue not often thought about. What happens if you’re putting items in or taking items out of a cage when the event occurs.

  1. Sometimes your just burned. A interview where temp were his specialty. You don’t want to open your box for 2 or 3 days. Where you could get another. Blast. A few times, like stronger echoes.

    1. Black,

      Sometimes your just burned. A interview where temp were his specialty. You don’t want to open your box for 2 or 3 days. Where you could get another. Blast. A few times, like stronger echoes.

      While you do need to be aware of another EMP; it would require another “Blast”. There are no echoes or aftershocks from a single EMP, so it would take another detonation or CME to produce the effect. The CME is predictable while another HEMP might not be.

        1. BLACK,
          I snagged a copy of the interview and listened to it; but, the guy being interviewed gets more than a few things wrong. He mentions hard gamma rays; but, never mentions the atmospheric effect interacting with the magnetic field of the earth or the Compton Effect
          It sounds like he is basically trying to sell his equipment.
          When discussing the 1859 Carrington event, he says that the long copper wires of the telegraph system acted as capacitors, which is completely incorrect. The long conductors acted as inductors AKA antennas, and the EM field passing them generated induced currents in them.
          When he says to not open his protective cases for 36 hours, that would depend on what you are storing in them. Taking items that connect to the power grid (if it’s still up and running) or connected to an antenna, could be an issue until the geomagnetic activity calms down; but, that activity is unlikely to harm equipment not connected to an outside long wire (AKA antenna)
          The EMP basically comes in three phases; but, they are all over within a few minutes, as detailed below.
          E1; Fast and immediate in the 5 ns range reduced by 3 dB within 200ns and is gone in 1000 ns range. A TVS (Transient Voltage Suppression) diode can act fast enough to block this pulse, and most modern electronics use these on their connections.
          E2: This pulse is similar to Lighting; but, less powerful and last from 1 ms to 1 second
          E3: Like a geomagnetic storm, this can introduce energy into long conductors and last tens to hundreds of seconds.
          When we talk about the Solar CME induced EMP, it is only this E3 component and does not include the E1 or the E2.
          In short, if you and your equipment survive the initial EMP, then you are probably OK, unless a second detonation occurs.

  2. While a Faraday Enclosure is the popular method of protection, there are other practices one can do to mitigate the effects of an EMP, and practicing these perhaps along with multiple Faraday enclosures would be the best practice.
    The mention of both types of EMP is a bit misleading, since there is only one type with different sources. A transmitter using tubes and one using transistors are two types of transmitters; but, the resulting transmitted radio signals are the same. The EMP and mitigation are similar to this.
    There is BTW no need for the ammunition box other than to carry the equipment inside it, if you need to move it. Taking a new electronic device and wrapping the cardboard box in which it came, a few layers of aluminum foil will do the trick. The key is to make sure there is a contiguous layer of foil, with no cracks that would allow emissions to “leak” through.
    The phrase:

    The idea behind a Faraday cage is that right before this electric surge reaches your devices, it will hit the conductive material box (made in our case of aluminum foil), move through it, and then past it, leaving its contents intact.

    Comes close; but, is a little incorrect. The energy pulse is basically a high power, short duration, wide spectrum radio wave, not unlike the energy generated from a local AM or FM station or your microwave oven. When this Electromagnetic energy impinges on a conductor, it creates currents that flow through the conductor. A power generator works based on the same physics, where a magnet moved past a conductor or the conductor is spun (moved) past the magnet, a current is produced in the conductor. In this case, if the conductor is contiguous with no holes into the inside of the enclosure, the currents that are produced simply flow around the conductor and the EM pulse doesn’t impinge on any of the conductors on the inside of the enclosure, causing currents in those devices that can damage them.
    The statement:

    Depending on the intensity of the EMP and the frequency spectrum, the first conductive layer might not be strong enough to absorb the whole pulse, which is why we need several alternating layers of conductive and insulating material; the more the better. If one layer won’t stop it, the next one might.

    Is a bit misleading, since if the conductive layer of the enclosure is contiguous, it stops all of the energy. Multiple layers without the insulation in between will give the conductor more current carrying capability and provide overall better shielding; but, the insulating layer between the conducting layers are not required, and could actually be detrimental. A layer of thick copper foil would be even better, since copper is a better conductor than aluminum; but, that would defeat the $5.00 article theme.

    Step 7 (optional): put everything inside one or more cardboard boxes, then put those in a thick ammo box. You don’t want the aluminum foil to touch the ammo box because they’re both conductive

    If the conductors touch it’s really not a problem. I store my mini enclosures in the drawers of a large old metal desk or a metal filing cabinet; but, even if you use a meatal ammunition box, unless the paint has all been stripped to bare metal, the conductive path is broken by the paint, not that it matters.

    The more layers you add, the safer it will be

    Once again, this is not true. One thick, contiguous conductive layer is all that is needed, the thicker and more conductive the better.
    On additional comment on this method in general, is similar to how onw might store whoel grains like where. If you store a lot of #10 cans of wheat and have a failure, you lose a can of wheat. If you store you wheat in 5 or 6 gallon buckets and have a failure, you can lose a lot more wheat in one event.. A failure in a single small enclosure and you lose one device, where a failure in your Faraday cage room, and you could lose a lot more. In short, redundancy is good.

    1. Thanks for your feedback. Do you have any links to research that compares a one layered faraday cage to one that has several? I’d be interested in reading that.

      1. Dan,

        Thanks for your feedback. Do you have any links to research that compares a one layered faraday cage to one that has several? I’d be interested in reading that.

        I don’t have any links handy; but, my comments were based on 40+ years of engineering, that included compliance testing both inside and outside of both solid and screened (fine mesh copper) Faraday rooms. The screened rooms are great because they allow outside light into the room without running any outside power that could introduce a conductive path (leak) into the system. I’ve also designed RF systems (radios) that have segments of the circuits inside small metal shields (Faraday cages) to isolate radio signals from one section in close proximity to another. If you pop the case on many electronics items and look, you’ll see these little metal boxes numerous places on the circuit boards.
        If you look at your linked Wikipedia article, even it mentions the key thing about the conductor thickness to the wave length of the incoming energy.

        A good idea of the effectiveness of a Faraday shield can be obtained from considerations of skin depth. With skin depth, the current flowing is mostly in the surface, and decays exponentially with depth through the material. Because a Faraday shield has finite thickness, this determines how well the shield works; a thicker shield can attenuate electromagnetic fields better, and to a lower frequency.

        In this case thicker shield is the thickness of the metal conductor, so adding layers with insulation in between actually creates a capacitor that can pass AC energy.
        As for the size of a leak, we once were testing where we beamed energy at the screened room from outside the room, and listened for the signal inside. While it was weak, we could detect , it and numerous engineers and technicians look for hours, to find a small 1.5 inch overlapping area of the copper mesh that was not properly connected. We pushed some silver solder into the tiny gap, hit it with a heat gun, and pressed it flat until it cooled. The signal inside then completely disappeared.
        As I mentioned, layers of conductive and non-conductive material are capacitors that can pass energy through them. For more details than I should put here, see: https://en.wikipedia.org/wiki/Capacitor
        I hope this helps.

  3. microwave ovens make good fariday cages, find them on the curb all the time. i don’t bother with them though, the only things i have that would be damaged by an emp are my winvista ancient laptop, a prepaid cell that expires in 4 days (which i am not renewing, i only keep them in the fall to sell firewood and farm products), a radio i never listen to, and lights, but i also got gallons of tallow and candles and my solar array has not been all that reliable so i am used to turning the power off and using candles. an emp would be a minor inconvinience at best, booring at worst. i suppose i could toss another old laptop in a microwave with a spare 200 watt inverter and a solar charge regulator, but i don’t see enough risk to bother. and all i would really loose is my ability to play dvds at night

  4. I have a couple of questions. I plan to make a Faraday box out of steel sheets, cover the inside of the cage with fiberglass, which is insulating and so I don’t have to worry about the walls of the cage touching the electronics. My question is, do I have to put a grounding wire attached to the cage?
    My other question is. To make a cage that prevents a cell phone or computer from receiving or emitting radio signals, such as wifi, bluetooth or cell network, is it necessary that the cage has a continuous walls or a metallic mesh is enough, if a metallic mesh is enough, what size do the holes have to be to be effective?
    Thank you very much for reading!

  5. James,

    I plan to make a Faraday box out of steel sheets, cover the inside of the cage with fiberglass, which is insulating and so I don’t have to worry about the walls of the cage touching the electronics. My question is, do I have to put a grounding wire attached to the cage?

    No, grounding it is not required and can actually add an external antenna to bring energy to or into the container. The only thing that can happen to an ungrounded unit is that anyone touching it during the event could get a nasty shock.

    My other question is. To make a cage that prevents a cell phone or computer from receiving or emitting radio signals, such as wifi, bluetooth or cell network, is it necessary that the cage has a continuous walls or a metallic mesh is enough, if a metallic mesh is enough, what size do the holes have to be to be effective?

    A solid continuous metal enclosure is best; but, mesh may be used to block radio signals, in and out, with the mesh size based on the frequencies you need to block.

    • The Cellular bands 1850-1990 824-894 range.
    • WiFi (Wireless Fidelity) 900 MHz 2.4, 3.6, 4.9 GHz, 5-5.9 and 60 GHz ranges.
    • 2.4 GHz = 12.5 cm so holes < 1.25 cm = 2 inches
    • Blue Tooth @ 2.45 GHz
    The holes need to be somewhere between .5 and .1 wavelength with the wavelength in meters calculated as 300 / (frequency in MHz)
    Thus WiFi @ 2,4 GHz or 2400 MHz would be 300/2400 or 0.125 meters, 125 mm and the maximum hole size and spacing would be .5 or .1 times that or 0.05 to 0.24 inches; but, even smaller would be better.

    Grounding in this case will help; but, that is not the same as protecting from EMP, because of the voltage reference.

  6. Regarding the use of aluminum foil: There is a big difference between relatively low-power radio frequencies and high-power high-frequency EMPs. Foil may be enough to stop radio frequencies from getting through, but it is not substantial enough to handle the current generated by an EMP. Using foil to guard against an EMP would be similar to using 24 gauge wire for a car battery; it is likely to burn through. The Carrington Event of 1859 proved this point when it caused telegraph wires much thicker than foil to catch fire.
    Read more at http://www.preparednesspro.com/many-myths-emps-and-faraday-cages#VEWMOjRvRb158WQB.99

    1. Debra Bacon,

      Regarding the use of aluminum foil: There is a big difference between relatively low-power radio frequencies and high-power high-frequency EMPs. Foil may be enough to stop radio frequencies from getting through, but it is not substantial enough to handle the current generated by an EMP.

      How is this current magically generated. The amount of current is related to the colleting surface (e.g. the antenna) and while covering my 2 ½ story 1600 square foot barn with aluminum foil would pose a problem, several overlapping layers of aluminum foil wrapped around a small cardboard box containing your electronics works just fine. You don’t seem to understand the physics involved and the fact that the Electric and Magnetic fields interacting with a conductor, generate currents in proportion to the size / length of the conductor.

      Using foil to guard against an EMP would be similar to using 24 gauge wire for a car battery; it is likely to burn through. The Carrington Event of 1859 proved this point when it caused telegraph wires much thicker than foil to catch fire.

      Once again you don’t seem to have a grasp on the physics. Artificially forcing high current through a too small wire from a car battery is rather contrived and not even related to The Carrington Event. In that event, hundreds of miles of antenna (telegraph wire) collected enough energy to create a voltage at the endpoints and the grounded poles to cause arcing at the pols and shorts at the sending and receiving apparatus in the offices.
      Do you even understand how the old style basic telegraphs system worked, with nothing but coils of wire, switches, and batteries?
      Does the equation M=N*I, mean anything to you? For a hint look up ”Ampere-turns”

      Read more at

      I read the article and the guy gets a lot of it wrong. He talks about surges jumping gaps and grounding the enclosure, all of which show another with a lack of understanding the physics.
      I don’t know the authors credentials,; but, I hold two engineering degrees and have worked doing compliance testing working inside of commercial Faraday cages. I am now retired; but, still have quite a lot of that test equipment on hand.

      Too many people who don’t understand the math or physics, continue to pass on the myths.

      1. You stated: “Do you even understand how the old style basic telegraphs system worked, with nothing but coils of wire, switches, and batteries?
        Does the equation M=N*I, mean anything to you? For a hint look up ”Ampere-turns””

        My suggestion: Lighten up on snippy, condescending remarks.

        1. Jeff,

          My suggestion: Lighten up on snippy, condescending remarks.

          My remark was not meant to be either snippy or condescending; but, as I stated above: ” Too many people who don’t understand the math or physics, continue to pass on the myths.”
          There are just too many self appointed “experts” discussing things and events they don’t really understand that can lead people astray who are simply trying to mitigate the issue as best they can.

          1. I was trying to help by quoting someone I thought knew what they were talking about. The tone of your comment felt demeaning to me. No I don’t understand physics – however, I do hold 2 degree in (software) engineering so I am open to light and knowledge. I did cite my source for you and others to analyze. The unique situation here is that I don’t have any way to validate that any of the DIY faraday cages “recipes” will work in a true EMP situation so it’s a “bet your life” situation. In a perfect world, someone would post a DIY faraday cage recipe that has been validated in an environment the replicates the applicable electromagnetic signals.

          2. Debra Bacon,

            I was trying to help by quoting someone I thought knew what they were talking about. The tone of your comment felt demeaning to me. No I don’t understand physics – however, I do hold 2 degree in (software) engineering so I am open to light and knowledge. I did cite my source for you and others to analyze.

            I’be been working with electronics for nearly 60 years and writing software (professionally) for nearly 50) so I understand your ability to understand logic and basic scientific methods; but, you have to realize that your analogy of power wiring and the Carrington event strayed very far from the physics and elements of a Faraday enclosure. Connecting that too small wire from the battery to your vehicle starter and drawing too much current would indeed be a problem; however, the power from an EMP is not connected directly; but, induced into the wire as it acts as an antenna, and the induced current is spread rather equally along the length of the conductor. The components at the time of the Carrington event in 1859 consisted of nothing more than wires, coils of wire and batteries and even then lightning was a serious problem at the time that often destroyed components of the system. Wires were either steel or copper and the batteries were simple lead acid types, so a voltage induced into the line in the hundreds or thousands of volt range would often arc over the glass, stone, or wooden insulators or go directly to ground through one of the sounding coils with very low resistant that was designed for only a few volts to operate. A description of the system can be found here: http://www.w1tp.com/pertel.htm

            A physical analogy could be a barrier to stop an incoming projectile like a bullet or a rock delivering a lot of energy to a single point like the battery connection in your vehicle example. Firing a shotgun or throwing a handful of small pebbles would require less protection, since the energy is spread over a larger area and more easily dissipated.
            From a software perspective, you can write a large piece of unorganized code that can be logically correct and perform the proper processing on the incoming data; but, take too long to be effective for the application. Much of my software career was spent developing real time systems, where the logic must be correct; but, timing is also critical. A spreadsheet or business program cranking out tax returns or processing payroll can take minutes to hours to perform the job with no ill effects; but, when the software is reading the accelerator pedal or information from the cruise control module in a vehicle and running the fuel injection system to accelerate the vehicle you have a different design, often an order of magnitude in different complexity. This is the difference I am talking about.

            The unique situation here is that I don’t have any way to validate that any of the DIY faraday cages “recipes” will work in a true EMP situation so it’s a “bet your life” situation.

            You are correct and it’s the same for all of us who are trying to roll our own. This is why I always recommend distributed protection for DIY systems. Take your electronic gadgets and individually wrap them in their boxes using overlapping layers of aluminum foil, and then place those individually wrapped boxes in metal containers, like desk drawers, filing cabinets, old cookie and candy tins, etc. Each contiguous metal layer provides added protection, and distributing the items in different places with different shielding and orientation helps ensure that one failure doesn’t affect all devices.

            In a perfect world, someone would post a DIY faraday cage recipe that has been validated in an environment the replicates the applicable electromagnetic signals.

            I have worked with “real” proven faraday enclosures for FCC compliance testing and in secure EOC & ECC facilities and unless you are very wealthy, none of these is possible as a DIY recipe for any of us. The equipment used to generate the EM fields and measure them is also very expensive and if you could replicate it to test your own equipment, I suspect your neighbors would all be very unhappy, LOL.
            I’m sorry for any misunderstanding as I was not trying to be condescending; but, this is an area where there are often too many “experts” who read something on the internet and continue to pass on myths that could well turn out to be deadly.
            If I shoot you with a firearm and damage you, you would have legal recourse; but, in an EMP event, recourse for potentially horrible damage is unlikely to be available, so we each do the best we can do with the resources we have on hand from devices wrapped in their boxes with layers of aluminum foil, to a sophisticated solid or screen copper mesh enclosed room if you can afford it.

  7. Just something I have been thinking about, if you make a shed out of metal roofing would that be adequate for protection?

  8. Hi Dan,

    Would you consider integrating the knowledge in your post and its comments to the Wikipedia page about the Faraday cage?
    I found both your article and the comments of the experienced people fascinating and it would be great to share this knowledge in wiki format as well (including the typical misconceptions the commenters talked about).
    My native language is not English, but I would be more than happy to help. I’ll build a small Faraday cage in the following weeks and I have a signal generator and oscilloscope to make some tests.
    We could publish the results, if you are interested.

  9. Ohio Prepper:
    I cannot thank you enough for your efforts here! I hae spent days on the net, trying to understand how the effects of the rays from EMP/CME could be mitigated by means of a Faraday Cage/Box. Yours is the only advice that I have so far found that made all the pseudo-expert bs I have seen elsewhere understandable. I now feel comfortable building a number of small containers (Faradays) instead of trying to effectively convert my large safe (with humidity holes in the bottom and doors that seal only in case of fire) into a working Faraday box. Thank you! Thank you! Thank you!

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