Tin-foil hat
From Wikipedia, the free encyclopedia
A tin-foil hat is a piece of headgear made from one or more sheets of aluminium foil or similar material. Some people wear the hats in the belief that they act to shield the brain from such influences as electromagnetic fields, or against mind control and/or mind reading.
The concept of wearing a tinfoil hat for protection from such threats has become a popular stereotype and term of derision; the phrase serves as a byword for paranoia and is associated with conspiracy theorists.
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[edit] Tin-foil hats and paranoia
There have been some people who believe in the efficacy of tin-foil hats and similar devices. Reasons for use include preventing perceived harassment from paranormal beings or stopping the experience of hearing voices in one's head. These draw on the stereotypical images of mind control operating by ESP or technological means, like microwave radiation. Belief in the effectiveness of tin-foil hats is popularly linked to mental illnesses such as paranoid schizophrenia.[1]
The delusion of "mind control rays" or other invasive mental activity may seem very real to those afflicted with severe paranoid delusions, and such persons have been known to make and wear improvised defences against the imagined invasion.
[edit] Scientific basis
The belief that a tin-foil hat can significantly reduce the intensity of incident RF radiation on the wearer's brain is not completely without a basis in scientific fact. A well constructed tin-foil enclosure would approximate a Faraday cage, reducing the amount of (notionally harmless) radiofrequency electromagnetic radiation inside. A common high school physics demonstration involves placing an AM radio on tinfoil, and then covering the radio with a metal bucket. This leads to a noticeable reduction in signal strength. The efficiency of such an enclosure in blocking such radiation depends on the thickness of the tin-foil, as dictated by the skin depth, the distance the radiation can propagate in a particular non-ideal conductor. For half-millimeter-thick tin-foil, radiation above about 20 kHz (i.e., including both AM and FM bands) would be partially blocked.[2]
The effectiveness of the tin-foil hat as electromagnetic shielding for stopping radio waves is greatly reduced by the fact that it is not a complete enclosure. Placing an AM radio under a metal bucket without a conductive layer underneath demonstrates the relative ineffectiveness of such a setup. Indeed, because the effect of an ungrounded Faraday cage is to partially reflect the incident radiation, a radio wave that is incident on the inner surface of the hat (i.e., coming from underneath the hat-wearer) would be reflected and partially 'focused' towards the user's brain. While tin-foil hats may have originated in some understanding of the Faraday cage effect, the use of such a hat to attenuate radio waves belongs properly to the realm of pseudoscience.
A study by graduate students at MIT determined that a tin-foil hat could either amplify or attenuate incoming radiation depending on frequency; the effect was observed to be roughly independent of the relative placement of the wearer and radiation source.[3] At GHz wavelengths, the skin depth is less than the thickness of even the thinnest foil.
Tin foil hats are seen by some as a protective measure against the effects of electromagnetic radiation (EMR). Despite some allegations that EMR exposure has negative health consequences,[4] at this time, no link has been verifiably proven between the radio-frequency EMR that tin-foil hats are meant to protect against and subsequent ill health.[5]
[edit] References
- ^ Hey Crazy--Get a New Hat. Bostonist (15 November 2005). Retrieved on April 5, 2007.
- ^ Jackson, John David (1998). Classical Electrodynamics. Wiley Press.
- ^ Rahimi, Ali; Ben Recht, Jason Taylor, Noah Vawter (17 February 2005). On the Effectiveness of Aluminium Foil Helmets. Ali Rahimi. Retrieved on April 5, 2007.
- ^ Story on EMR radiation and health in The Independent..
- ^ Office of Safety and Health page on Radio Frequency Emissions and Health.
