Faraday Cage (Meaning and Explanation)

We explain what a Faraday cage is, its history, how it works and how it is built. Also, examples from everyday life.

faraday cage roof insulation — Many roofs function like a Faraday cage to isolate the interior from electricity.

What is a Faraday cage?

A Faraday cage It is a container covered with electrically conductive materials (such as metal plates or mesh) that functions as a shield against the effects of an electric field coming from the outside.

Many items we use in everyday life apply the Faraday cage principle, for example: cables, microwave ovens, cars and airplanes. Its shape and size may vary, as well as the materials with which it is covered.

History of the Faraday cage

faraday cage creator michael faraday — In 1836 Michael Faraday carried out the experiments that allowed him to build the insulating cage.

Faraday cage It is named after its inventor, the British physicist Michael Faraday (1791-1867), who observed that a conductive material showed the effects of an electric discharge only on its exterior. This seemed to indicate that The charges of the conductor were distributed in such a way that they canceled the internal electric fields.

To prove this, in 1836, Faraday covered the walls of a room with aluminum sheets. Using an electrostatic generator, he applied high voltage shocks to the outside of said room. And with an electroscope (a device that allows detecting the presence of electric charges in a body) he was able to verify that inside the room the electric field was zero.

Thanks to this and many other experiments, Faraday occupies a prominent place among those scientists who made it possible for electricity to have the practical uses we know today.

You may be interested: Newton's First Law

How does a Faraday cage work?

When an electric field is applied to a container that has been covered with aluminum or metal mesh, said container works as an electrical conductor that polarizes.

When polarized, the conductor becomes positively charged in the direction in which the external electromagnetic field moves and, at the same time, it becomes negatively charged in the opposite direction, generating an electric field equal in magnitude but opposite to the electromagnetic field that has been applied.

The sum of both fields, inside said container or Faraday cage, will be equal to zero. That is, conductive materials, in the presence of external electric fields, always arrange their charges on their surface in such a way that the internal electric field is zero.

How to make a Faraday cage?

faraday cage telephone experiment — If you completely wrap a phone in aluminum, its signal will be blocked.

Making a Faraday cage is simple: it only involves enclosing a certain space within a conductive material. The necessary materials are quite accessible: metal mesh, aluminum foil, boxes or even a steel trash can.

Before proceeding, we must take into account the following:

If we are going to use metal mesh or grilles (such as those used for chicken coops), the holes in that conductor must be smaller than the length of the signal that you want to block.
The interior space must be completely isolated, without cracks.
The thickness of the conductor to be used will depend on the frequency that you want to block.

There are many ways to make a Faraday cage, but with this simple experiment we can check its characteristic shielding effect:

Prepare a cylinder with metal mesh and an aluminum platform.
Place on the platform a radio turned on and tuned and then mount the metal mesh cylinder on the platform. You will immediately notice how the radio transmission stops. The electromagnetic waves that the radio should receive are interrupted by the placement of the mesh.
Take two cell phones and verify that they can make and receive calls without difficulty. Then wrap one of the phones inside a sheet of aluminum foil. When you make a call to this phone you will notice that the signal is blocked.

Examples of the Faraday cage

The principle according to which Faraday cages work can be observed in multiple examples from everyday life:

When we notice that in a elevator or inside a building made of metal grilles our cell phones do not work, we are facing a manifestation of the Faraday cage principle.
Our microwave ovens They are equipped with Faraday cages to prevent their waves from escaping outside and having any harmful effect on our health.
The special suits of electrical technicians who repair high voltage lines.
When driving a automobile During a thunderstorm, it is recommended to stay inside the vehicle, since its bodies will function as a Faraday cage against lightning.
On the walls of the MRI laboratories Where magnetic resonance images are performed, metal sheets or meshes are also placed to prevent waves from escaping and protect the health of the operators.
The cyber attacks have generated an important offer of products to inhibit electromagnetic waves sent by potential hackers. Various companies offer accessories to make our devices invisible in the field of wireless connections: covers for car keys, backpacks, envelopes, wallets or briefcases manufactured under the Faraday cage principle.