We explain what a Faraday cage is, its history, how it works and how it is built. In addition, examples of everyday life.
What is a Faraday cage?
A Faraday cage is a container covered by electrically conductive materials (such as irons or metal meshes). Its shape and size may vary, as well as the materials of which it is coated.
It works as a shield against the effects of an electric field coming from outside . Many elements that we use in everyday life apply the Faraday cage principle, for example: cables, microwave ovens, cars and airplanes.
History of the Faraday cage
Faraday’s cage is named after its inventor, British physicist Michael Faraday (1791-1867), who observed that a conductive material showed the effects of an electric shock only outside. This seemed to indicate that the external charges were distributed in such a way that they canceled the internal electric fields .
To prove it, in 1836, Faraday covered the walls of a room with aluminum sheets. Using an electrostatic generator, he applied high voltage discharges to the outside of said room. Using an electroscope (device that allows to detect the presence of electric charges in a body) he could verify that inside the room the electric field was null.
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.
How does a Faraday cage work?
When electrical energy is applied to a container that has been coated with aluminum or metal meshes, that container functions as an electrical conductor that polarizes .
When polarized, the conductor is positively charged in the direction in which the external electromagnetic field moves and, at the same time, is negatively charged in the reverse 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 Faraday container or cage, will be equal to zero.
How to make a Faraday cage?
Making a Faraday cage is simple: it only involves enclosing a certain space within a conductive material . The necessary materials are quite accessible: metal meshes, aluminum foil, boxes or even a steel trash can.
Before proceeding, we must consider the following:
- If metal meshes or gratings (such as those used for chicken coops) are to be used, the holes of that conductor must be smaller than the length of the signal to be blocked.
- The interior space must be completely isolated, without cracks.
- The thickness of the conductor to be used will depend on the frequency to be blocked.
There are many ways to make a Faraday cage, but with this simple experiment we can check its characteristic shielding effect:
- Make a cylinder with metal mesh and an aluminum platform.
- Place a radio on and tuned to the platform , and then mount the metal mesh cylinder on the platform. You will immediately notice how the radial transmission ceases. 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 making 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 of everyday life:
- When we notice that in an 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 are equipped with Faraday cages to prevent their waves from escaping outside and have some harmful effect on our health.
- The special suits of electrical technicians who repair power lines.
- When driving a car during a thunderstorm, it is recommended to remain inside the vehicle, as their bodies will function as a Faraday cage in the lightning.
- On the walls of the MRI laboratories where magnetic resonance images are made, metal sheets or meshes are also placed to prevent waves from escaping and protect the health of the operators.
- The cyber attacks have generated a large range of products to inhibit electromagnetic waves sent by possible hackers. Several 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 principle of the Faraday cage.