It often happens that when you enter the lift your phone moves out of range of the cellular network. In other cases, only the signal level drops. Variuos factors may be responsible for the occurrence of both phenomena.
The total lack of coverage in cases where before entering the elevator all of the signal bars on your mobile are displayed can be caused by Faraday cage effect. After closing the door completely, the metal construction of the elevator creates a screen that does not allow penetration of radio waves inside or outside the cabin.
|Before closing||Unsealed closing||Sealed closing|
A very simple experiment can be carried out at your home to get a similar effect. Just prepare two phones (at least one mobile) and aluminum foil. Wrap turned on mobile phone in aluminum foil so as not to leave any gaps. In order to verify whether the aluminum foil really acts as a Faraday cage try to call the mobile phone that you have just wrapped. The result should be the same regardless of the previous signal level, which is the inability to make a call.
Below is a simple Faraday cage made of a packaging box wrapped in aluminum foil.
The lower level of the signal inside the elevator without complete loss of coverage may be caused by a totally different reason. Even in the case of the metal structure it may turn out that the door is not closed tightly enough. Longitudinal, even very narrow gap at the junction of the elevator door wings makes it possible for radio waves to penetrate inside. Then, the above-described effect of the Faraday cage is not applicable. Similarly in the case when the elevator is not made entirely of metal and, for example, it has a single glass wall.
Then the attenuation of signal by the structure of the lift shaft is responsible for the decline in number of signal bars. The walls made of concrete and metal reinforcement significantly impede penetration of radio waves to the interior. That is why the signal level decreases.
Travelling in the elevator is usually very short, so making a call or using the Internet is not a priority. However, in case of failure of the lift cellular network coverage may be necessary to call for help.