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What is a Faraday Cage and Will It Really Protect Against EMP?

faraday cage

We can’t see it, but there is electromagnetic radiation all around us. It is in the light we see, it is in our microwaves, it is in our radio waves when we listen to music, and it is in many products that we use. This electromagnetic radiation generally isn’t harmful. However, a huge blast of electromagnetic radiation – or Electromagnetic Pulse – could have devastating effects on the electric grid. To keep your electronics safe from EMP, you need to put them in a Faraday cage.

What is a Faraday Cage?

The science behind the Faraday cage begins with Benjamin Franklin in the 1700s. When he wasn’t busy flying kites with keys on them, Franklin was doing all sorts of other experiments with electricity. In one experiment, he electrified a silver can. Then he put a cork ball on a silk thread (both non-conductive). When he dangled the ball outside of the can, the ball was drawn towards the walls of the can. But, when he lowered the ball inside of the electrified can, the ball wasn’t drawn towards the sides. Franklin was at a loss to explain why this happened.

Many years later, an English scientist named Michael Faraday took Franklin’s discovery a step further. He found that, when you charge a conductive material, the charge is only present on the surface and not on the interior of the conductor. To test this, he lined an entire room with foil and then used a generator to charge the foil. He then put an electroscope (which detects electrical charges) in the interior of the room and found that there was no charge going through.

This led to the invention of the Faraday cage in 1836. A Faraday cage can be any sealed enclosure which has is an outer layer made from a conductive material and an inner layer made from a non-conductive material. For example, a simple Faraday cage could be a filing cabinet lined with Styrofoam.  The non-conductive lining prevents the charge from getting to the contents inside.

foil room faraday cage

Here is one way to protect your home from EMP 😉

How Faraday Cages Work

The Faraday cage protects against electromagnetic radiation and pulses in 2 ways:

  1. The conductive outer layer reflects incoming pulses
  2. The conductive outer layer absorbs incoming pulses

Wait, the Faraday cage absorbs pulses?!?

To someone without a physics background, this would seem to go against logic. Wouldn’t absorbing pulses cause anything inside the Faraday cage to get fried? This isn’t the case because of something known as “field cancellation.”

As EMF Services explains:

“A magnetic field can be thought of as a force that has both strength and direction. If it is met with an equal force of exactly opposite direction, the forces will cancel and the net force will be zero.”

In layman’s terms, the pulse travels all around the conductive outer layer of the Faraday cage. It meets with other pulses and they cancel each other out.

Why does this only work with conductive materials? As Lew Rockwell explains:

“Field cancelation occurs when the free carriers in the conductive material rapidly realign to oppose the incident electric field. If the cage is made from something non-conductive, the free carriers are not mobile enough to realign and cancel the incident field.”

Examples of Faraday Cages in Everyday Life

You might think that Faraday cages are only found in the movies and in the homes of smart preppers. But there are actually Faraday cages all around us. You might even be sitting in one now.

Have you ever thought about why it isn’t dangerous to be in an airplane during a lightning storm? After all, a plane is a giant piece of metal flying in the sky and it is going to draw lightning to it. Well, it turns out that airplanes do get hit by lightning all of the time – but that the plane acts as a giant Faraday cage to protect the people inside of it.

The same goes for your car. If your car gets struck by lightning, it is the Faraday cage effect which protects you – not the rubber tires.

Lineman working on power lines may wear special suits called “barehanded suits” (or conductive suits) which use the Faraday principle. This lets them work on live wires with their bare hands!

And the Faraday principle can even be used to prevent spying. Just have the discussion in a Faraday cage and eavesdropping equipment won’t be able to hear anything.

barehand suit faraday principle

A barehand conductive suit made by Hubbell Power Systems


But Will a Faraday Cage Really Protect Against EMP?

If you aren’t familiar with EMP, I suggest you read this article about EMP and its effects first. According to theories, an EMP blast would knock out our electrical grid and electronics. Peter Vincent Pry, who heads the EMP Task Force on National and Homeland Security believes that an EMP blast would kill 9 out of 10 Americans.

The truth is that we don’t really know what would happen in the aftermath of an EMP attack, what the pulse would do to our electronics, and whether a Faraday cage would really protect our electronics.

As EMF Services points out, Faraday cages might not be 100% effective because “the strength of a magnetic field often varies greatly across a given area, and the invisible lines of magnetic flux that constitute a magnetic field are often at inconvenient angles relative to the earth plane.”   Since Faraday cages only work because pulses of equal strength cancel each other out, then the cage might fail if the pulse isn’t radiating over the cage equally.

So, while it might be fun to make a DIY Faraday cage out of a metal trashcan, you might want to stick to a metal container which is more evenly constructed!

Testing Your Faraday Cage

Since you are relying on your Faraday cage to keep all your vital survival electronics (HAM radio, flashlights, phones…) safe from EMP, you better make sure your Faraday cage works!

One way to test a Faraday cage is to simply put an FM radio inside of it while it is tuned to a strong station. Once inside of the cage, the FM signal should stop. If you can still hear the radio, then the Faraday cage isn’t working.

 Are you using a Faraday cage to protect your electronics?  Did you make it yourself? We’d love to hear from you in the comments section or join the conversation on our Facebook page.