material, or in the case of a Faraday cage, by a mesh of such materials. Faraday cages are named after the scientist Michael Faraday, who first constructed A Faraday cage or Faraday shield is an enclosure used to block some electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material, or in the case of a Faraday cage, by a mesh of such materials. Faraday cages are named after the scientist Michael Faraday, who first constructed one in 1836. Faraday cages work because an external electrical field will cause th A Faraday cage or Faraday shield is an enclosure used to block some electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material, or in the case of a Faraday cage, by a mesh of such materials. Faraday cages are named after the scientist Michael Faraday, who first constructed one in 1836. Faraday cages work because an external electrical field will cause the electric charges within the cage's conducting material to be distributed in a way that cancels out the field's effect inside the cage. This phenomenon can be used to protect sensitive electronic equipment (for example RF receivers) from external radio frequency interference (RFI), often during testing or alignment of the device. Faraday cages are also used to protect people and equipment against electric currents such as lightning strikes and electrostatic discharges, because the cage conducts electrical current around the outside of the enclosed space and none passes through to the interior. Faraday cages cannot block stable or slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside one). To a large degree, however, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any hole is significantly smaller than the wavelength of the radiation. For example, certain computer forensic electronic systems test procedures that require an ele A Faraday cage or Faraday shield is an enclosure used to block some electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material, or in the case of a Faraday cage, by a mesh of such materials. Faraday cages are named after the scientist Michael Faraday, who first constructed one in 1836. Faraday cages work because an external electrical field will cause the electric charges within the cage's conducting material to be distributed in a way that cancels out the field's effect inside the cage. The metal layers are grounded 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). They provide less attenuation of outgoing transmissions than incoming: they can block electromagnetic pulse (EMP) waves from natural phenomena very effectively, but especially in upper frequencies, a tracking device may be able to penetrate from within the cage (e.g., some cell phones operate at various radio frequencies, so while one frequency may not work, another one will). The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage is heavily attenuated or blocked by the cage; however, a Faraday cage has varied attenuation depending on wave form, frequency, or the distance from receiver or transmitter, and receiver or transmitter power. Near-field, high-powered frequency transmissions like HF RFID are more likely to penetrate. Solid cages generally attenuate fields over a broader frequency range than mesh cages. == History == In 1754, Jean-Antoine Nollet published an account of the cage effect in his Leçons de physique expérimentale. Because a Faraday shield has finite thickness, this determines how well the shield works; a thicker shield can attenuate electromagnetic fields better, and to a lower frequency. === Faraday cage === Faraday cages are Faraday shields that have holes in them and are therefore more complex to analyze. Whereas continuous shields essentially attenuate all wavelengths whose skin depth in the hull material is less than the thickness of the hull, the holes in a cage may permit shorter wavelengths to pass through or set up "evanescent fields" (oscillating fields that do not propagate as EM waves) just beyond the surface. The shorter the wavelength, the better it passes through a mesh of a given size. Faraday bags are shielded security bags fabricated with metallic materials that are used to contain devices to protect them from electromagnetic transmissions for a wide range of applications, from enhancing digital privacy of cell telephones to 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. Electronic components in some music instruments, such as in an electric guitar, are protected by Faraday cages made from copper or aluminum foils that protect the instrument's electromagnetic pickups from interference from speakers, amplifiers, stage lights, and other musical equipment. Some buildings, such as prisons, are constructed as a Faraday cage because they have reasons to block both incoming and outgoing cell phone calls by prisoners. The exhibit hall of the Green Bank Observatory is a Faraday cage to prevent interference with the operations of their radio telescopes. == See also == Lightning rod Anechoic chamber Anti-static bag Conductive textile Foil hat Gauss's law Mobile phone jammer Mu-metal Mylar blanket Tesla coil Van de Graaff generator == References == == External links == Faraday Cage Protects from 100,000 V:: Physikshow Uni Bonn Notes from physics lecture on Faraday cages from Michigan State University Make in India Faraday Cage Top Gear's Richard Hammond is protected from 600,000 V by a car (a Faraday Cage).