Faraday Cage

What is a Faraday cage and can you make one yourself? A Faraday cage is a container that is made to protect the contents from an electromagnetic pulse, or better known as an EMP. 

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The Faraday cage is named after the creator, Michael Faraday (1791-1857) who was an English physicist and chemist. 

The idea behind the Faraday cage is to house and protect your most important electronic devices to keep them functional after the power grid is taken down. Think of it as an electronic isolation chamber. It prevents electrical waves from passing through it. Much the same way a grounding wire for a battery would work. 

What to keep in a Faraday cage

  • Medical devices such as a CPAP machine
  • Communication devices such as a 2 way or ham radio or a cell phone 
  • Laptop computer or Kindle
  • Solar battery chargers
  • LED flashlights 
  • Computer hard drives or portable hard drives
  • Night Vision goggles 

Modern Faraday cage uses 

There are many modern applications of the Faraday cage, and are more common than most people realize! 

Microwave Ovens

The mesh screen in the window of a microwave is part of a Faraday cage. This is what keeps the radiation inside to heat up leftovers efficiently, and not leaking outside into the kitchen. 

Elevators

How many times have you entered an elevator and had absolutely no cell phone service? The elevator essentially being a dead zone. The metal doors act as an unintentional Faraday cage by blocking cell signals. 

Vehicles

The metal body of a vehicle acts as a Faraday cage when a power line is down. This is why you should never exit a vehicle near a down power line. The metal body will direct dangerous electricity around the vehicle, allowing it to pass harmlessly into the ground, because it isolates and protects the passengers inside. 

What to use to build a Faraday cage

  • Ammo cans 
  • Trash cans
  • Metal cabinets
  • Steel lockers 

Using an ammo can

If you know me, you know I am a huge fan of ammo cans for a lot more than simply storing ammunition. Ammo cans have a million different uses. The reason I’m such a fan is they are small, very portable, lightweight, waterproof and can keep things very organized. Perfect for a home office or garage. One of my favorite ammo can uses are for blackout boxes for the exact reasons I just listed. 

How to make a Faraday cage using an ammo can

Select the container for your Faraday cage

In this case, I’m using an ammo can. But you can use any of the containers I mentioned above. The size of the container will really depend on what you want to store in it. If storing something like a CPAP machine or a full size laptop, I recommend something bigger than an ammo can. 

For smaller things like communication devices and portable hard drives, an ammo can is perfect. Think about what you plan to store in your personal Faraday cage. 

Line the container

I used 1/8th inch reinforced cardboard. Other items that will work are thick fabric or styrofoam. Make sure that all the pieces of styrofoam or cardboard fit snugly together. 

The goal here is that nothing is touching the metal walls of the ammo can. It is another layer of protection. 

Wrap the contents

Note that you will want to wrap and protect each item individually. 

Remove the batteries from each item, if possible. Batteries corrode over time and destroy items. 

Wrap each item in a layer of newspaper, then a layer of foil. Follow this with another layer of newspaper and then place inside a Ziploc bag. If you want an added layer of protection, these EMP bags are a great way to go. 

It is also important to label each bag for organizational purposes. Once they are wrapped up, it is impossible to tell what is what. 

Seal the ammo can

Make sure the ammo can has a layer of cardboard on top that fits the top of the can, not the lid. It should be exactly the same size as the bottom layer of cardboard. 

Close the lid on the ammo can and then seal it with aluminum foil tape around the lid. Also be sure to tape up the hinge. The more layers, the more protection. Don’t be afraid to use the tape! 

Testing

You can easily test the functionality of your Faraday cage. Place a functioning cell phone inside the Faraday cage, and follow the above directions. If you can call the cell phone and it receives a signal and rings, the cage isn’t working correctly. The signal should be blocked and prevent the phone from receiving the call. 

Do you have a Faraday cage?

Have you made a Faraday cage? If not, why? If so, what have you chosen to keep in it? What is an absolute necessity to keep in your Faraday cage? Let’s discuss this in the comments! 

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13 thoughts on “Faraday Cage”

  1. Wow, really interesting article about a Faraday cage. Thank you for sharing your DIY tips and all info.

  2. Kelly Martin

    I’ve heard of faraday cages before but I didn’t know what they were or what they were used for so this was interesting. I have an old steel locker that I could turn into a faraday cage.

  3. Melanie williams

    We do not have a Faraday cage and in fact this is the first time that I have ever heard of this. Very interesting and a good item to have.

  4. Interesting, I never even knew what a Faraday cage is. I don’t have one, but it’s interesting to know that you can make your own and also that this technology is used in so many different everyday applications. It always astounds me how little we actually know about the way our gadgets function.

  5. Subhashish Roy

    This was a completely new learning for me. And thoroughly loved understanding what a Faraday Cage is and the utilities. That we all can make it ourselves is amazing.

    1. The Prepping Wife

      I’ve often found that making things like this is a million times better than simply buying it. The best piece of advice I’ve always been given and give out too is to know your gear. By knowing your gear and practicing with it, you get comfortable using it and can respond much better in an emergency. Or if a part of something breaks, it is easy to fix because you put it together originally. Plus it is far cheaper to make it yourself, and that means that money can be saved or used in other areas of preparing.

  6. This was really interesting. I’ve never heard of creating and using a faraday cage at home, but it makes sense in the event that something were to happen. Especially when it comes to electronics that you highly depend on, like a cpap machine. I know that there are people who would be in a REALLY bad place without the option to use their cap machine… There are a few different people that I’m going to pass this on to. Better to be informed and prepared than left unaware, right?

    1. The Prepping Wife

      I hope your friends and family who use a CPAP machine find this useful! In their case, I would recommend a metal trash can, just because of the size of a CPAP machine. It won’t exactly fit into an ammo can. Spare parts for them would also be really important. Hoses and masks wear out fairly easily. Having those at home to replace if supplies were limited would be absolutely vital as well.

  7. I learned so much in this post! I never heard of a faraday cage before, but now I know. Thank you! I think it’s cool you are able to make your own.

  8. I have heard of Faraday in my physics classes but that is pretty much all I remembered. This was well summarized in practical uses and while we all know we use a cell connection in an elevator – how many of us wondered why? I think I assumed it is something to do with us being in a metal box, lol. I love that this article explains the practical and not abstract use. And that we can make it ourselves, wow! Good to know at least theoretically for now.

  9. Wow…what an interesting article. I have never heard of a Faraday cage in the real world. I recently learned about it from one of my students who is taking Physics.

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