Building Your Own Faraday Cage

Written by Clayton Krebs

A Faraday cage is an enclosed space with an outer layer that conducts electricity. The physical shape of the Faraday cage does not matter: it can be spherical, cylindrical, or a box. Either the cage itself can be made of a conductive material, or the cage can be built of a non-conductive material such as wood and then covered in a conductive material.

The conductive material can be as simple as several layers of aluminum foil, which makes constructing your own Faraday cage a fairly simple and inexpensive affair.

What are Faraday Cages Used For?
Faraday cages are designed to guard whatever is inside of it from excessive levels of static and non-static electricity. This can be accomplished either by reflecting incoming electric fields, absorbing incoming fields, or creating opposing electrical fields.

The Faraday cage can help to protect whatever electrical equipment is contained within it from the kind of electromagnetic pulse (EMP), it’s a good practice to keep your emergency electronics such as radios and GPS devices stored in a Faraday cage so they are not incapacitated in the event of an EMP.

How Does a Faraday Cage Work?
Incoming fields are cancelled when the free electrons in the conductive material on the Faraday cage instantaneously realign themselves and block the incident electric field.

For this to work, the cage has to be made from a conductive material; otherwise, the free electrons are not sufficiently mobile to realign themselves. The layer of conductive material can itself be quite thin. This is thanks to the “skin effect,” which is a term that describes the inclination of electrical currents to move mainly on the outer layer of a conductor. Provided that the conductive layer is more than the skin depth of the material, the electrical shielding of the Faraday cage will be outstanding because there will be very high levels of absorption loss.

The skin depth is a function of the material the conductor is made of and the frequency of the incoming wave. Typically, wrapping your Faraday cage in several layers of heavy-duty aluminum foil will give you the needed skin depth to protect your electronics from high-frequency radiated fields like the kind generated by a EMP.

Building a Faraday Cage
The material you use for your Faraday cage does not have much influence on how effective the cage will be at protecting your electronics from high-frequency fields. Virtually any metal has the necessary conductivity to allow free electrons to realign and cancel out incoming electric fields.

Certain metals, are more conductive than others, which gives them a reduced skin depth – for example, at 200 MHz, silver has a skin depth of less than five microns, as compared to aluminum, which has a skin depth of 24 microns at the same frequency. But on a macro scale, that difference is negligible, which is why you can use heavy-duty aluminum foil, instead of far more expensive materials.

Your Faraday cage can have small holes in it, provided they are not too large with respect to the wavelength of the incoming electromagnetic wave. This is why you can also use fine aluminum mesh to build a larger Faraday cage. For example, a 1 GHz wave has a wavelength of 0.3 meters in space.

Generally with these kinds of mesh cages, the cage door is typically the part that causes the most leakage, but this can be fixed by taping the seams with conductive tape.

You can also use existing metal containers as Faraday cages, including metal ammunition boxes, metal garbage bins, anti-static bags, and even unused microwave ovens. Each of these has its own level of effectiveness: the main concern is that gaps and seams are minimized to reduce leakage.

You do not have to ground your Faraday cage in order to protect the electronics contained within, although doing so will help to keep the cage from becoming charged and possibly re-radiating charge, which could be dangerous if you touch it.

Large Faraday Cages
If you want to build a larger “shield room,” as engineers refer to rooms that are essentially large Faraday cages for storing electronics, you can do so by covering the inside of a small room or closet with several layers of heavy-duty aluminum foil.

Overlap all of the seams and tape them with regular cellophane tape. Cover all outlets, light switches, and other conductive breaches with aluminum foil, and do not plug anything into any outlets. Once the floor is covered in foil, place a piece of plywood over it so you do not damage it by walking on it. Such a room can store all of your emergency electronics and protect them from incoming high-frequency radiated fields.

Have You Made a Faraday Cage?
Have you made a faraday cage or room? Have you ever had to use it? How did it turn out?

Updated May 15, 2014

24 Comments

  1. Interesting wrote:

    Good basic article. You didn’t include the easiest and most practical cage for most people to make…the metal garbage can lined with cardboard and the lid seam taped with metal tape.

    May 18th, 2014 at 5:30 am
  2. NameSteve wrote:

    Will an EMP destroy common batteries that are used to power all small electronic devices?

    May 18th, 2014 at 6:22 am
  3. Jeanette wrote:

    If you line a room with foil, can you safely ground it through the grounding part of an electrical outlet (leaving the two current parts empty)?

    May 18th, 2014 at 6:53 am
  4. EDWARD EMORY wrote:

    Loved the Article. Thanks

    May 18th, 2014 at 6:57 am
  5. Brenda wrote:

    Building on Steve’s question…would it be advised to enclosed the room containing your battery storage for Solar Power/Wind generators?
    How would an EMP effect the diodes in your Solar panels?

    May 18th, 2014 at 8:53 am
  6. Madelaine wrote:

    Is aluminum the only conductive metal feasible for this use or are there other materials which can be used as well? Good article. Hope we get some good answers from other readers who are knowledgable on this subject.

    May 18th, 2014 at 8:56 am
  7. Brian Talarczyk wrote:

    @Madelaine,

    No, you can use any metal that is conductive. Aluminum works better than steel as it is more conductive but even better would be copper screen or copper foil. The best conductive metal would be gold, but that’s way too expensive (and overkill) for this purpose

    May 18th, 2014 at 9:10 am
  8. Grant wrote:

    @Brian,

    Point of order: Silver and copper are both better conductors of electricity than gold is.

    May 18th, 2014 at 9:38 am
  9. Jerry wrote:

    Grant is correct; silver conducts better than gold. Gold is a preferred connection matrial because it doesn’t oxidize, where silver and copper do, eventually creating poor electrical connections..

    May 18th, 2014 at 10:30 am
  10. NameCheryl Abdelnour wrote:

    I have had deep brain stimulation with a battery pack implanted in my chest. Do you have any idea what an EMP blast would do to me?? I have tried to research it but can’t find much.

    May 18th, 2014 at 1:25 pm
  11. mike wrote:

    A small or medium safe or gun safe, with your appliances wrapped in non-conductive material will also fill the bill.

    May 18th, 2014 at 3:42 pm
  12. Mike K wrote:

    First, EMP is a real threat to something like our national power grid – lots of very long conductors to capture the EMP and send the resulting current pulse into the computers controlling the power grid. The grid will probably fail. At home, typical power surge protectors will help protect electronics plugged into regular power outlets, not 100% but it will help. Items not plugged in will probably be unaffected, i.e. a laptop not connected to anything (example headphones)will likely not be harmed by a nuclear EMP. I know this is blasphemy but I did EMP testing for many years – small items (talkie-talkie)not connected to cables, especially power outlets, were not harmed. Any small item inside a metal box (old bread box)will not be harmed! Forget the tape. Batteries of any kind will not be harmed sitting outside on a picnic table! EMP can, maybe, damage microelectronic devices if they are connected to wires that direct the EMP to the device. Simple solution – keep your survival electronics unplugged. Don’t keep them on a charger. I’m sure other experts will disagree but they are over cautious in terms of preppy needs. The greatest, simple idea I read was a galvanized trash can with a lid (no tape needed)and I consider that overkill!

    May 18th, 2014 at 6:11 pm
  13. NSA bot 77,837 wrote:

    One thing I can’t wrap my brain around in all of this is what good are extra electronics after an EMP?
    An extra phone would have to already be activated and paid for monthly. Would there be any service, any towers? Would internet be working?
    Things like this leave me wondering, lots of unanswered questions.
    Maybe buy a cheap disposable phone for this purpose, not use it and just store it … is that the answer for the phone? Just in case there’s service.

    May 18th, 2014 at 8:07 pm
  14. David L wrote:

    Question – based on what I read, a motor home or even many mobile homes might be inherently Faraday Cages?

    May 18th, 2014 at 8:40 pm
  15. NameJerry"G" wrote:

    I have a ham radio (2 Meter ) can I have a antenna hooked to my radio while my radio is in the cage ?

    May 19th, 2014 at 12:40 pm
  16. Mike K wrote:

    Regarding motor home/mobile home – Most mobile homes are made of wood and will not provide much/any protection. Older ones had metal “siding” and might provide shielding. Motor homes these days are mostly made of “fiberglass” or something similar and don’t provide much protection. Jerry G – disconnect the antenna. It will “channel” the EMP right into the faraday cage.

    May 20th, 2014 at 10:19 am
  17. Bill wrote:

    I have a GE 3 watt “smart meter” outside my home office wall (that I didn’t even know FPL was going to install), and I’ve been having sleep issues and mental lapses lately. I suspect it’s related to the constant RF pulses from the smart meter.
    How would I go about shielding the smart meter so it doesn’t broadcast into my house? Do I need to completely enclose it?
    Thanks.

    May 21st, 2014 at 10:05 pm
  18. NameGeorge wrote:

    Bill:
    I have issues too with these too “Smart Meters”
    The RF I was subjected to has affected my sleep and caused me to suffer equilibrium issues until I stopped sleeping in my bed room that as far in line of sight , so to speak, was about 7-8 ft from the meter to where my head was. I corrected that problem with a parabolic dish ( discard Satellite dish network) It worked but appeared to screw with the transmission abilities from the meter to the Electric company…Boo Hoo …tough crap…Told them their meter was causing health issues and they can either put it on the pole where the power first comes into my property until the wires are underground or put up with the dish or I would sue them as I did have testing done to back me up…they moved the meter!

    May 23rd, 2014 at 10:51 am
  19. Denver F wrote:

    Lot of fear mongering about EMP. What I see left out of MOST equations here (as we struggle to micromanage the small stuff), is similar to questions with large food storage quantities: You can have an entire home Faradayed down, EMP proof to the MAX, and all your electronics protected. But the obvious target of ANY significant EMP attack will certainly be the main Electrical Grid. What good is a home full of like-new electronics with no power? What good is your emergency radio or your smart phone, with no transmission? Your generator might be able to run for a couple days, but THEN what? And MORE IMPORTANT: Who will be the first joker in the hood to run a LOUD, attention grabbing generator while gun toting neighborhood looters are scrambling for food & luxuries? Better have a large crew of very well trained shooters that you trust with your life, as well as a stocked arsonal for that one Chief.

    May 26th, 2014 at 3:46 pm
  20. John wrote:

    Solar Panels can be stored inside a large Faraday Cage, unconnected, and brought out after the attack and hooked up to storage batteries to buffer the energy stored. They would likely be destroyed in any EMP strong enough to damage other electronics equipment if they were outside a cage in use or not.
    Since a cage can have a lot of very small holes a panel inside could develop electricity, at a much lower power rate, but the wires connecting the panel to equipment outside the cage would likely nullify the effectiveness of the cage.

    Batteries only supply power a short time till they run out, generators only supply electricity until the fuel runs out, Solar panels while the Sun shines, wind power while the wind blows, water power only as long as you have a flowing stream nearby.
    Unless you are already set up to supply all the electricity you use, all by yourself, don’t expect to be able to rig up some equipment during the emergency to do it, if most of it is subject to the EMP. I suggest you read the book about the Triffids as to conditions you could expect.

    June 3rd, 2014 at 4:50 pm
  21. Frank wrote:

    Just an observation and my own thoughts: Whatever the situation, I believe that there will be generators, fuels, batteries, radios, etc., that people have stored safely and will be active again. We may not have cable or the internet and 24 hour a day power, but hand cracked (manually) powered devices will be put to use. Some will have solar panels, gasifiers, windmills, etc. So until the batteries die and the motors or electronic devices burn out, we might as well protect those gadgets and not assume we’ll all be living in a world without electronics.

    June 17th, 2014 at 6:58 pm
  22. Edna wrote:

    I built a couple of faraday cages using the cheap gift popcorn tins that are in abundance around Christmas. I put plastic buckets inside of them and then got some 14g copper wire and grounded them outside my garage attached to a rebar pole I sunk down about 2.5 feet. I put a radio inside them that was on and it went silent so I know it works.

    June 19th, 2014 at 2:28 pm
  23. Kathleen wrote:

    Could someone please tell me if I can use staples to when attaching the aluminum foil and/or aluminum screen to my walls? I’m wondering if the magnetic function of steel affects the performance of the faraday cage.

    June 29th, 2014 at 9:40 pm
  24. Sonya wrote:

    I am thinking of faraday proofing my shed. Can I use my solar generator to power my fridge in there. If an EMP happens and the fridge is on will that affect it? or am I okay to keep it running?

    August 13th, 2014 at 1:34 pm

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