Faraday Cages - FAQs

A Faraday cage (sometimes called a Faraday shield, RF cage or EMF cage) is a RF shielded enclosure formed by conducting material or by a mesh of such material. The enclosure is like a sealed tin can; it keeps the electromagnetic fields inside, and blocks the entry of external electric fields and radiofrequency waves. Faraday cages are named after an English scientist Michael Faraday, who is credited with their invention in 1836.

Typical LBA EMFaracages® currently in use

Although the development of the cage effect has been attributed to Michael Faraday, it was actually Benjamin Franklin in 1755 who observed the effect by lowering an uncharged cork ball suspended on a silk thread through an opening.  He noted that the cork was not attracted to the inside of the can as it would have been to the outside and although it touched the bottom, when pulled out it was not found to be “charged” by the touch. Thus, Franklin actually discovered the behavior of what we now refer to as a Faraday cage or shield.  Faraday’s famous ice pail experiments duplicated Franklin’s cork and can trial.

A Faraday cage was first built in 1836 by Michael Faraday who observed that the charge on a charged conductor remained only on its exterior with no influence on the interior.  He built a room coated with metal foil and aimed high voltage discharges from an electrostatic generator to strike the outside of the room.  Using an electroscope he demonstrated the absence of an electric charge on the inside of the walls.

The operation of the Faraday is best understood as a hollow conductor. Externally applied electric fields produce forces on the charge carriers (usually electrons) within the conductor, generating a current that rearranges the charges. The rearranged charges cancel the applied field within and the current stops. However, they shield the interior from external electromagnetic radiation if the walls are thick enough and any holes are much smaller than the radiation’s wavelength.

The usefulness of the RF Faraday Cage is its ability to protect sensitive test equipment from radio frequency waves.  In the hospital environment, sensitive operating room tools are protected from the bombardment of radiofrequency.  In research and test labs and industrial shops similar protection is afforded by a faraday cage.  The security of wireless communication can also be protected using the Faraday principle by shielding building areas and forensic test facilities.  The shield of a screened cable, such as a coaxial cable used for cable television, protects the internal conductors from electrical noise and external radiation of the enclosed RF. Finally, the military uses this technology for protection of defense equipment for both RF protection, and protection from electromagnetic pulse attacks.  

Ironically, the technology can also be used for illicit purposes.  A shopping bag lined with aluminum foil acts as a faraday cage assisting shoplifters to steal RFID tagged merchandise. Hackers can set up faraday cage test cells for “black” development of wireless LAN intrusion tools, for instance.  See our technical note about black hat use of a faraday cage in security applications.

EMFaraCage Faraday Cage in use in University lab environment.

The EMFaraCage® faraday cage shown above is one of a line of innovative portable desktop RF shielded chambers developed by LBA for production testing, laboratories, and other applications. Many other RF shielding requirements may be accomplished through building RF shielding. We design and furnish rf cages integrated into room or building construction using the most effective RF fabrics and RF conductive paints. We can also furnish architectural shielding solutions against EMF effects of nearby power lines, such as encountered in utility telecommunications sites.