We have all seen spy, action thriller movies like James Bond movies. One thing these movies have common, a critical condition. Where the protagonist gets struck, but couldn't contact anyone because of the signal blockers. This scene has something special and when I was a kid, I had always wondered how the hell these blockers work. So let's dig into it.
Signal Blockers are created on the principle of Faraday cage. Faraday cage is just a box which is completely made of a metal. Metals have unique properties that there can be no electric field inside them. Of course, you will argue that all of our electrical wirings is of metal, but in them charge flow on the surface of metal not inside. Now you will be wondering how this cage can work as signal blockers. All means of wireless communication uses Electromagnetic waves as a carrier. Electromagnetic waves consist of mutually perpendicular oscillating electric and magnetic fields. All the signal information is carried in electrical part of waves. When the wave hits the Faraday cage, it induces the charge on the surface of the cage. These charges are induced as such they produce an electric field inside the cage in the direction opposite to the waves electric field. The net result is that both fields cancel each other. In this way, there is no signal inside the cage.
We can see the use of Faraday cage in our daily life. The most unexpected example of Faraday cage is metal elevators. They are also used in cable wires. When you open a cable wire, you see a metal covering outside the copper wire. This covering act as a Faraday cage, so that no external signal can interfere your original signal. They are also used in Microwave oven so that you don't fry out.
They always don't work. If there is a hole in your cage, such that wavelength of the wave is smaller than the size of the hole then, waves can easily transmit through it. So if your considering making your own Faraday cage, keep it in mind. That's all about signal blockers. Now next time, you watch a movie, you can explain your friends about signal blockers.
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