A faraday cage is a grounded material screen that surrounds a part of equipment. It is sealed and has an electrically conductive outer layer. It serves the purpose of excluding electrostatic and electromagnetic influences. It can be in different shapes for example the shape of a sphere, box or a cylinder.
It is made of either conductive material or non-conductive material for example wood or cardboard. The material is then put in a conductive material like aluminum foil. It blocks external static by directing electricity along and around the mesh. It does not allow the electricity through and this provides a regular voltage on each side of the enclosure.
There is no flow of current through the space thus creating a difference in voltage. The faraday bag can shield a person from electricity. It does this because the electric charge on the conducting material of the cage is distributed in a way that cancels the effect of the field in the interior part of the cage. However, the cage does not protect from static magnetic fields for example the magnetic field of the earth.
This is evident because a compass still works even if it is inside the faraday bag. However, if the conductor is very thick and the holes made are tiny just like the wavelength of radiation, then the cage can protect from electromagnetic radiation. You can try this by placing an antenna within a faraday cage you will find that radiation to or from the antenna is blocked by the cage.
Why It Was Invented
The main reason why the faraday cage was created is for field cancellation. This is whereby the free carriers in the conductor realign in a very quick manner to cancel out incident electric field. If the faraday cage was made of non-conductive material, then the free carriers will not move fast enough to oppose the electric field.
It does not matter the thickness of the conductor. This is because of an effect known as the skin effect. Skin effect is the habit of current flowing mainly on the skin of the conductor. The conductivity levels of a conductor do not matter because either can work. The Faraday bags is named after the English scientist who invented them.
He is known as Michael Faraday. He invented the faraday cage in the year 1836. It was invented so as to offer protection to equipment from lighting strikes and electrostatic discharges. Michael Faraday made an observation that extra charge on an already charged conductor stayed only on the exterior and had no effect on anything enclosed within it.
The faraday bag uses three mechanisms to operate. First of all, the incoming fields are reflected by the conductor. Then, incoming energy is also absorbed by the conductor and finally opposing fields are created by the cage. All of these processes happen so that the contents inside the faraday cage are protected from excessive field levels. The faraday cage is useful when it comes to protection from EMP attacks.