Cage the Faraday

A Faraday cage, also known as a Faraday shield, which doesn’t sound nearly as good, is any kind of special enclosure used to block electric fields. Built with conductive materials, often in mesh form, a Faraday cage causes the electric field picked up by that material from outside sources to be distributed such that the field is canceled out inside the cage.

Neither A Franklin Nor A Beccaria Cage

The Faraday cage gets its name from English scientist Michael “Big Mike” Faraday, who observed the phenomenon described above when working with charged conductors in 1836. By way of demonstration, Faraday constructed a metal foil-coated room and hung out inside it with an electroscope (a device that can measure electrical charges) whilst high-voltage discharges from an electrostatic generator blasted the walls of the room. His electroscope showed no electric charge present within the cage’s walls.

Big Mike explaining his namesake cage to the dummies of his day.

In fact, the “Faraday cage effect” was first observed by Benjamin “Big Ben” Franklin nearly a century earlier, in 1755. Franklin used a ball of cork, silk thread, and an electrically-charged metal can to conduct a similar, if smaller-scale, experiment. (Faraday’s experiment was consciously designed as a modified version of Franklin’s.)

Historians have pointed out that the Faraday cage may have been invented even earlier than that, by Italian physicist Giovanni Battista “Big Johnny” Beccaria in 1753. However, as the device is called neither a Franklin nor a Beccaria cage, this writer is still going to give all credit to Faraday.

Faraday Cages Today-ges

Though the name and the explanation may make them seem like quaint, old-timey devices that have fallen out of use as technology has improved, Faraday cages are still used to this day, for a variety of purposes.

Faraday cages are frequently used to guard sensitive electronic equipment against RFI and other interference. Faraday bags—essentially portable Faraday cages made of fine metal mesh and fabric—can be used to shield smartphones and other gizmos against tampering and interference.

Elevators, by the nature of their construction, usually act as Faraday cages automatically. This explains why your cell phone coverage disappears when you step into an elevator. The wire on the inside of the window on your microwave door creates a low-key Faraday cage that protects you from radiation leakage.

In 1997, American physicist Austin “Big Austin” Richards created a wearable metal “Faraday suit” that protects the wearer against discharges from Tesla coils. Richards has “performed” in the suit as Doctor MegaVolt at various festivals throughout the United States.

Certain highly specialized painting processes—rack-spray coating, etc.—require Faraday cages to prevent paint particles from becoming electrostatically charged, which can affect their flow and adhesion rate.

Photo credit: okfn via / CC BY