Faraday cage

A Faraday cage is an enclosure made of conductive materials, which can block electromagnetic fields.

The Drum contained a Faraday cage that was also lined with lead to shield against radiation. The crew of the base sheltered inside the cage when the ghosts appeared, as the ghosts could not penetrate it. Later, the Twelfth Doctor organised the crew to trap the ghosts inside the cage. (TV: ''Under The Lake)