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Faraday cage

Entrance to a Faraday room

Faraday shield at Art Nouveau power plant in Heimbach, Germany

A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.^[1]

A Faraday cage's operation depends on the fact that an external static electrical field will cause the electrical charges within the cage's conducting material to redistribute themselves so as to cancel the field's effects in the cage's interior. This phenomenon is used, for example, to protect electronic equipment from lightning strikes and electrostatic discharges.

Faraday cages cannot block static and slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside). To a large degree, though, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation. For example, certain computer forensic test procedures of electronic systems that require an environment free of electromagnetic interference can be carried out within a screen room. These rooms are spaces that are completely enclosed by one or more layers of a fine metal mesh or perforated sheet metal. The metal layers are grounded in order to dissipate any electric currents generated from external or internal electromagnetic fields, and thus they block a large amount of the electromagnetic interference. See also electromagnetic shielding.

The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage are heavily attenuated or blocked by a Faraday cage.

History[link]

In 1836, Michael Faraday observed that the charge on a charged conductor resided only on its exterior and had no influence on anything enclosed within it. To demonstrate this fact, he built a room coated with metal foil and allowed high-voltage discharges from an electrostatic generator to strike the outside of the room. He used an electroscope to show that there was no electric charge present on the inside of the room's walls.

Although this cage effect has been attributed to Michael Faraday, it was Benjamin Franklin in 1755 who observed the effect by lowering an uncharged cork ball suspended on a silk thread through an opening in an electrically charged metal can. In his words, "the cork was not attracted to the inside of the can as it would have been to the outside, and though it touched the bottom, yet when drawn out it was not found to be electrified (charged) by that touch, as it would have been by touching the outside. The fact is singular." Franklin had discovered the behavior of what we now refer to as a Faraday cage or shield (based on one of Faraday's famous ice pail experiments which duplicated Franklin's cork and can).^[2]

Operation[link]

An external electrical field causes the charges to rearrange, which cancels the field inside.

A Faraday cage is best understood as an approximation to an ideal hollow conductor. Externally or internally applied electromagnetic fields produce forces on the charge carriers (usually electrons) within the conductor, generating electric currents that rearranges the charges. Once the charges have rearranged so as to cancel the applied field inside, the currents stops.

If a charge is placed inside an ungrounded Faraday cage, the internal face of the cage will be charged (in the same manner described for an external charge) to prevent the existence of a field inside the body of the cage. However, this charging of the inner face would re-distribute the charges in the body of the cage. This charges the outer face of the cage with a charge equal in sign and magnitude to the one placed inside the cage. Since the internal charge and the inner face cancel each other out, the spread of charges on the outer face is not affected by the position of the internal charge inside the cage. So for all intents and purposes, the cage will generate the same DC electric field that it would generate if it was simply affected by the charge placed inside. The same is not true for electromagnetic waves.

If the cage is grounded, the excess charges will go to the ground instead of the outer face, so the inner face and the inner charge will cancel each other out and the rest of the cage will retain a neutral charge.

Effectiveness of shielding of a static electric field depends upon the geometry of the conductive material. In the case of a nonlinear varying electric field, and hence an accompanying varying magnetic field, the faster the variations are (i.e., the higher the frequencies), the better the material resists penetration, but on the other hand, the better it passes through a mesh of given size. In this case the shielding also depends on the electrical conductivity of the conductive materials used in the cages, as well as their thicknesses.

Examples[link]

• A microwave oven is an example of an inside out Faraday cage, keeping the RF energy within the cage rather than keeping it out.^[3]
• The shield of a screened cable, such as USB cables or the coaxial cable used for cable television, protects the internal conductors from external electrical noise and prevents the RF signals from leaking out.
• A booster bag (shopping bag lined with aluminum foil) acts as a Faraday cage. It is often used by shoplifters to steal RFID-tagged items.^[4]

A home-made Faraday cage at the University of Arizona in Dr. Michael Heien's Lab

• Plastic bags are included with electronic toll collection devices which are impregnated with metal to allow motorists to place them in the bag so that a toll charge is not registered or a device will not register a charge while being shipped to a customer's home after ordering in a delivery truck.
• Some linemen wear Faraday suits, which allow them to work on live, high voltage power lines without risk of electrocution. The suit prevents electrical current from flowing through the body, and has no theoretical voltage limit. Linemen have successfully worked even the highest voltage (Kazakhstan's Ekibastuz–Kokshetau line 1150 kV) lines safely.
• The scan room of a Magnetic Resonance Imaging (MRI) machine is designed as a Faraday cage. This prevents external RF (radio frequency) signals from being added to data collected from the patient, which would affect the resulting image. Radiographers are trained to identify the characteristic artifacts created on images should the Faraday cage be damaged.
• Faraday cages are routinely used in analytical chemistry to reduce noise while making sensitive measurements. A home-made Faraday cage used for simultaneous microscopy and electrochemistry is shown to the right.

See also[link]

• Frieder Kempe
• Anechoic chamber
• Conductive textile
• Electromagnetic field
• Electromagnetic interference
• Mu-metal

References[link]

External links[link]

• Faraday Cage Protects from 100,000 V :: Physikshow Uni Bonn
• Notes from physics lecture on Faraday cages from Michigan State University
• Make a Faraday Cage Wallet
• Michael Faraday: The Invention of Faraday Cage background and related experiment
• Top Gear's Richard Hammond is protected from 600,000 V by a car (a Faraday Cage).
• Top Gear's Richard Hammond as a human lightning rod - protected by a Voltrex Suit

Adam Savage
Savage in July 2011
Born	Adam Whitney Savage[1] (1967-07-15) July 15, 1967 (age 44) New York City, U.S.
Nationality	American
Education	Tisch School of the Arts
Occupation	MythBusters co-host, designer/fabricator, actor, educator
Height	6'0"
Religion	None (Atheist)
Spouse	Julia Savage (2002-present)
Children	Two
Website
adamsavage.com

Adam Whitney Savage (born July 15, 1967)^[2] is an American industrial design and special effects designer/fabricator, actor, educator, and co-host of the Discovery Channel television series MythBusters.^[1] His model work has appeared in major films, including Star Wars: Episode II - Attack of the Clones and The Matrix Reloaded. He is a prominent member of the skeptic community. He lives in San Francisco with his twin sons and wife, Julia.

Early life and education[link]

Born in New York City, Savage was raised in Sleepy Hollow in Westchester County New York.^[3] He graduated from Sleepy Hollow High School in 1985.^[4] His father, Whitney Lee Savage (1928-1998), was a painter, filmmaker and animator known for his work on Sesame Street, and has a permanent exhibit in the Avampato Discovery Museum.^[5] His mother is a psychotherapist. His sister Kate Savage is also an artist. As a teenager in Sleepy Hollow, he routinely visited the local bike shop to have flat tires fixed. The shop showed him how to do the repairs himself. From this experience, Savage said, "I realized you could take a bike apart and put it back together and it wasn't that hard...I've been building and putting bicycles together since then."^[4]

Adam Savage began acting as a child, and has had five years of acting school.^[1] His early credits include voicing animated characters that his father produced for Sesame Street, Mr. Whipple's stock boy "Jimmy" in a Charmin commercial, a helper in the special effects of Star Wars, and a drowning young man saved by a lifeguard in the 1985 Billy Joel music video "You're Only Human (Second Wind)."^[6] He attended New York University's Tisch School of the Arts for acting for six months before dropping out.^[7]

Describing the early abandonment of his acting career, Savage said "...by the time I was, I guess probably nineteen, I had passed on that in favor of doing stuff with my hands – graphic design, assistant animation in New York, and then eventually working in theater in San Francisco, and film special effects. Then MythBusters came along and it was the perfect marriage of two things, performance and special effects."^[8] On November 25, 2011, Savage received an honorary doctorate from the University of Twente (Enschede, Netherlands) for his role in the popularization of science and technology.^[9][10]

Career[link]

Savage in July 2008

Savage has worked as an animator, graphic designer, carpenter, projectionist, film developer, television presenter, set designer, toy designer, and gallery owner. He worked as a model maker on the films Galaxy Quest, Bicentennial Man, Star Wars: Episode II - Attack of the Clones, The Matrix Reloaded, and Space Cowboys, among others.

Savage played the role of a helpful engineer in the 2001 film Ever Since the World Ended^[11] and the role of an army surplus store owner who sells a man a rocket engine for his pickup truck in 2006 in The Darwin Awards, which also featured MythBusters co-star Jamie Hyneman.^[12] He made a cameo appearance along with Jamie Hyneman on CSI: Crime Scene Investigation on the May 1, 2008, episode "The Theory of Everything." In the "making of" material for The Matrix Revolutions, he appears in his role as a special effects artist and discusses some of the miniature effects used and the difficulties involved.

He previously taught advanced model making in the department of Industrial Design at the Academy of Art University in San Francisco.^[1]

Savage has become a regular presenter at magician James Randi's annual skeptics' conference, The Amaz!ng Meeting, since first appearing in January 2006.^[13] He also appeared in the UK, giving a talk at the first Amazing Meeting London from October 3–4, 2009, hosted at the Mermaid Conference Centre, Blackfriars.^[14]

Savage was a featured performer at the three w00tstock v1.x shows in 2009, and appeared in four w00tstock v2.x shows in 2010. He also appeared as a guest on Diggnation's 220th show.^[15]

Savage has also been a regular guest speaker at the annual Maker Faire since 2008, speaking on different topics such as his obsession with the dodo bird and problem solving, and also taking questions from the audience members about the Mythbusters and other things.

Savage hosted an episode of the Discovery Channel series Curiosity, in which he speculated as to whether or not it is possible for humans to live forever. During the program various topics such as limb regeneration, organ printers, and even age reversal are discussed.

Savage and Hyneman are judges on the game show Unchained Reaction which premiered in March 2012.^[16]

[edit] MythBusters

Savage has been involved in MythBusters since its creation. His role in the show (that he shares with all the other talent) is to either disprove ("bust") myths or confirm them through testing and experiments done at different scales. If the myth is about a one-time occurrence and not about whether or not something can happen at all, it is often deemed "plausible" instead.

Savage's demeanour on MythBusters is animated and energetic, providing a foil to Jamie Hyneman's more reserved straight man persona.^[17]

Savage and Hyneman were the only hosts of the show for the first season of MythBusters, but starting with the second season, members of Hyneman's staff were introduced and began to appear regularly in episodes; Kari Byron, Tory Belleci and welder Scottie Chapman appeared in the second season. In the third season, Chapman was replaced by Grant Imahara, a robot builder and model maker. In an interview Savage gave during The Amaz!ng Meeting 5, he expressed an interest in proving natural selection over creationism on MythBusters.

Savage also stated that such an episode is unlikely because MythBusters has a policy against trying to disprove supernatural phenomena.^[19]

Personal life[link]

At Reason Rally Washington D.C. March 23, 2012

Savage and his wife Julia were married in 2002. He has twin sons from a previous relationship.^[20] He wears a hearing aid on his left ear due to a congenital condition.^[21] He is a practiced juggler, as seen on Mythbusters. He is also an atheist.^[22] He has a lifelong interest in costume making. He said, "I remember my mom getting me a 'Jaws' costume when 'Jaws' came out...and wearing a Batman costume. Back then, everyone dressed up as hobos." He strives for authenticity with his costumes. While in high school, he and his father made a suit of armor out of aluminum roof flashing that had 700 rivets. He said, "I wore it to school and passed out from heat exhaustion in math class. I woke up in the nurse's office and the first thing I said was 'Where's my armor'?" In 2011, he built a costume based on the character No-Face from the film Spirited Away.^[4] In early 2012, it was announced that he would be the commencement speaker at Sarah Lawrence College.^[23]

References[link]

External links[link]

Wikimedia Commons has media related to: Adam Savage

• Adam Savage's personal website
• Adam Savage at the Internet Movie Database
• Adam Savage on Twitter
• Adam Savage's biography from the Discovery Channel
• Interview with The Sneeze
• Interview with Reddit.com
• Adam Savage interviewed on Penn Radio
• Discovery
• Savage Presentation at The Entertainment Gathering (December 2008)
• Adam Savage on Diggnation (September 2009)
• Adam Savage interviewed on Geek a Week