Answer: The Faraday Cage
Common in everything from research laboratories to television cables to server rooms in hardened government facilities, Faraday cages are a firmly enmeshed, yet seldom seen, part of our modern world.
A Faraday cage is simply an enclosure made of a conductive material that blocks out external static and non-static electrical fields. What does that mean in layman’s terms? Anything within a properly designed Faraday cage will be perfectly insulated from outside electromagnetic energy. You could, for a rather dramatic example, stand inside a Faraday cage at the top of the Empire State Building, and every lightning strike that hit the cage would cause the electrical charge within the cage’s conducting material to be distributed such that the lightning strike’s effect would be canceled in the cage’s interior, leaving you completely unharmed inside (see the photo here for a smaller scale, yet equally dramatic example of a Faraday cage in action).
As far back as 1755, Benjamin Franklin observed the phenomenon with experiments that suspended uncharged cork balls via silk threads within electrically charged metal containers—the containers effectively shielded the balls from the electrostatic charges applied to the outside of the containers. At the time, however, there appeared to be no practical application for the phenomenon and Franklin paid little attention to it beyond noting it for posterity. Nearly a century later in 1836, Michael Faraday extended Franklin’s research by building large enclosures and subjecting them to high voltage discharges from an electrostatic generator. It is largely due to the time of the revisited discovery and the first useful application of said discovery that we call the resulting construction a Faraday cage instead of a Franklin cage.
So where do we find these Faraday cages in daily use today? Faraday cages are incorporated into all manner of structures, cabling, and even clothing. MRI rooms in hospitals are built to function as Faraday cages to cut down on external interference and improve the quality of MRI scans. Coaxial cable is wrapped in a sheath-style Faraday cage to protect the core of the cable from external interference and to prevent RF signals from leaking out. Lineman who work on electrical lines wear entire suits made of conductive mesh which allows them to work on high voltage lines in complete safety—the current flows over their bodies like water flows over a fish. Those RFID-blocking wallets you see all over the place? You guessed it. Little Faraday cages tuned to block the frequencies used by RFID-readers.
Image by Antoine Taveneaux/Wikimedia.