A Faraday cage is a metallic enclosure or cage used to isolate space from the influence of external electric fields. Inside the cage, the electric field is nil, even if there are electrical charges placed outside or if the cage is connected to an electrostatic generator.
Conversely, if charges are introduced inside an earthed Faraday cage, the electric field outside will not be perturbed.
A disadvantage: radio waves (electromagnetic waves) do not pass through Faraday cages, which can prevent receivers or transmitters (such as car radios and mobile telephones) from working properly. A roof aerial is then used.