A Faraday cage is a metallic enclosure that prevents the entry or escape of an electromagnetic field (EM field). An ideal Faraday cage consists of an unbroken, perfectly conducting shell. This ideal cannot be achieved in practice, but can be approached by using fine-mesh copper screening. For best performance, the cage should be directly connected to an earth ground.

Faraday cages are used in electronic labs where stray EM fields must be kept out. This is important in the testing of sensitive wireless receiving equipment. In addition, a Faraday cage can prevent the escape of the EM fields emitted by a cathode-ray-tube (CRT) computer monitor. Such fields can be intercepted and translated to allow hackers to remotely view on-screen data in real time without the need for wires, cables, or cameras. This practice, known as van Eck phreaking, can also be used by government officials to view the computer activities of known criminals and certain criminal suspects.

A heavy-duty Faraday cage can protect against direct lightning strikes. When properly connected to an earth ground, the cage conducts the high current harmlessly to ground, and keeps the EM pulse from affecting personnel or hardware inside.

How Faraday Cages Work

Electricity is the lifeblood of many aspects of our world. Without volts and amps, many of our technological innovations would cease to exist. Even our bodies wouldn't function without an electrical charge zipping through our cells. But what electricity gives, electricity can take away.
Although this form of energy is vital to so much of our lives, it's one of those things that are only good in the right amounts. Too much electricity can electrocute people. Likewise, it can kill our modern electronics and machines.

But thanks to Michael Faraday, the brilliant 19th-century scientist, and one of his namesake inventions, the Faraday cage, we humans have developed plenty of ways to control electricity and make it safer for our computers, cars and other inventions -- and for us, too.
Faraday cages shield their contents from static electric fields. An electric field is a force field surrounding a charged particle, such as an electron or proton.

These cages often look distinctly, well, cagelike. Some are as simple as chain-link fences or ice pails. Others use a fine metallic mesh. Regardless of their exact appearance, all Faraday cages take electrostatic charges, or even certain types of electromagnetic radiation, and distribute them around the exterior of the cage.

Electromagnetic radiation is all around us. It's in visible and ultraviolet light, in the microwaves that cook our food and even in the FM and AM radio waves that pump music through our radios. But sometimes, this radiation is undesirable and downright disruptive. That's where Faraday cages come in.

As a Faraday cage distributes that charge or radiation around the cage's exterior, it cancels out electric charges or radiation within the cage's interior. In short, a Faraday cage is a hollow conductor, in which the charge remains on the external surface of the cage.
That basic function has plenty of fascinating uses in our electrically cluttered and technology-packed world. And although Faraday would eventually have his day, the backdrop for his invention actually has its roots in earlier times. So, where did the idea for these ultra-useful cages come from?

How to build a Faraday cage wallet

With more and more access and transaction cards going contactless, it's OK to be a little paranoid and invest in a Faraday cage wallet.

A Faraday cage wallet serves to disperse electromagnetic fields across a metal surface to stop them from interacting with cards. A good one can cost anywhere between $30 and $200, which isn't so bad when you think about the retail cost of a standard folding leather wallet. But here at Nerdcam, we like to do things on the cheap, so today we'll look at how to make one for less than $10.

To build this Faraday wallet, we tried a modified version of a method developed by the geniuses over at Wired. The base of the wallet follows the Wired design, but our method splits off when we go on to create the card pouch.
You'll need:

• Duct tape
• Sticky tape
• Aluminium foil
Scissors (ask your parents before using them, kids).

From there, cut or fold two pieces of aluminium foil to stick to the duct-tape panels you've created. You'll want the aluminium foil to be about a centimetre smaller in area than the duct-tape panel. Place the aluminium foil onto the duct-tape panels, and secure the edges in place with sticky tape.
From there, sandwich the two pieces of duct tape together to create the wallet, and fold it in half.

Set your sandwich aside for a moment, and cut two more pieces of duct tape approximately 8 centimetres in length. This will be for the card pouch.

Line the card pouch with a strip of aluminium foil, using the same method we did to create the wallet section, and stick it onto one of the wallet's inside halves to create the card pouch.
Gently lift the top of the pouch you just stuck down to place your card into it.
From there, you can touch up the corners of the wallet, or apply your own designs to make it look a little nicer, and you're done.

Head to your nearest contactless swipe point to test your work. If the card is still able to be used, you haven't covered it completely with aluminium foil.

Alternatively, if you don't want to make your own wallet, you can always just line one particular card pouch in your existing wallet with a bi-fold strip of aluminium foil.

This method, however, requires a little more finesse than merely creating a foil-lined wallet, as the card needs to be completely covered, but still be easily accessible.