Why is there no signal in the elevator, and what is the principle of the mobile phone shielding device?

Why is there no signal in the elevator, and what is the principle of the mobile phone shielding device?

Do you know why the mobile phone has no signal after entering the elevator? What is the principle of the cell phone jammer device?

We know that after entering the elevator, we usually cannot make a call, and there is no signal on the mobile phone. Some people will know that the signal of your mobile phone is blocked. This is indeed a shielding effect. We learned in high school physics that when an object is covered by a "metal bird cage", external electronic signals cannot enter. The elevator is just such an iron cage.

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According to this theory, the examination room can also take the same countermeasures to achieve a shielding effect. However, this requires the classroom to be completely covered with metal materials, which is obviously impossible to do. Even if the classroom is really covered, although the two mobile phones in the same classroom are disconnected from the communication base station, they can still transmit information based on the Bluetooth connection.

Now that this method of disconnecting from the outside world cannot be used to shield the data signal, what can be done? People think of a way to influence it. For example, at a football match with a lot of people, your friend wants you to talk on the phone, so you can't hear anything.

So, can everyone create the same noise signal transmitter to affect the communication of others? The mobile phone shielding device in the examination room is just such a device.

We know that communication on mobile phones and the Internet use relative electromagnetic wave frequency bands. Just like a tape recorder, when the frequency is matched, the communication is connected. The mobile phone shielding device can continuously send electromagnetic waves from low frequency to high frequency, and the mobile phone shielding device affects the electromagnetic waves transmitted by the mobile phone communication base station and the wireless router, making it impossible to connect to each other. The main manifestations are the phenomenon of poor signal and no network.

The above is why the mobile phone has no signal after entering the elevator and the principle of the mobile phone shielding device.