Faraday Cage

What You Should Know About Faraday Cages

Faraday cages are a tool used to block electromagnetic radiation, whether in the form of microwaves, radio waves, or otherwise. They’re used in a wide range of applications to keep sensitive equipment safe from interference or to prevent devices from generating interference.

The Faraday Cage takes its name from Michael Faraday, a 19th century English physicist. The protection that the enclosure provides relies on principles that Faraday discovered through his experiments with electricity.

He noticed that excess charge only affects the outside of a charged container. This eventually culminated in an experiment where he lined an entire room with metal foil to demonstrate that high-voltage electricity outside the room could not generate a charge inside the room.

How Does a Faraday Cage Work?

Today, Faraday cages don’t necessarily have to be made with foil. Instead, they’re more often built with a metal mesh or wiring similar to a chain-link fence. The mesh that you see in the window of your microwave oven is one example, preventing microwaves from escaping.

When electromagnetic waves pass through a wire or other long and thin piece of metal, they generate a current. That’s how the radio in your car works, with the radio waves sent out from the radio station hitting your antenna and generating the electrical signal that is then turned into sound by your speakers.

The problem is that we don’t always want wires to spontaneously have currents generated whenever an electromagnetic wave passes by. This can be destructive to some electronics, and even minor electromagnetic radiation can affect sensitive detection and measurement equipment. A Faraday cage prevents this from happening.

An object inside the cage is protected from outside electromagnetic waves and also isolated from putting any out. That’s because as the waves reach the enclosure, they generate a current in the network of thin metal mesh or wire. This current is then safely discharged to the ground by the Faraday cage.

Why Does a Faraday Cage Only Affect Some Waves?

Any particular Faraday cage only affects certain types of electromagnetic waves. Visible light is made up of electromagnetic waves, but you can still see inside your microwave or through a chain-link fence. The reason behind this is the frequency of the waves.

Electromagnetic waves all have distinct frequencies, ranging from the highest frequency gamma radiation to the lowest frequency radio waves. The lower a wave’s frequency, the longer its wavelength. A Faraday cage blocks any waves that have wavelengths greater than the size of the holes in the mesh.

Radio waves can range from hundreds of meters to as small as 30cm, meaning almost any mesh will keep them out. Visible light has wavelengths from 400 to 700 billionths of a meter, so any mesh that blocks visible light in this way is essentially a solid object.

How Are Faraday Cages Used Today?

Faraday cages provide effective shielding for a wide range of uses today, from medical equipment to telecommunications. As our reliance on increasingly sophisticated electronics continues to increase, more and more applications need protection from electromagnetic interference.