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Tin foil hat

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Title: Tin foil hat  
Author: World Heritage Encyclopedia
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Subject: Reference desk/Archives/Miscellaneous/2008 July 13, Electronic harassment, Paranoia, Mind control, Denpa Onna to Seishun Otoko
Collection: Hats, Mind Control, Paranoia, Pejoratives, Protective Gear, Pseudoscience
Publisher: World Heritage Encyclopedia

Tin foil hat

Man wearing a tin foil hat

A tin foil hat is a hat made from one or more sheets of aluminium foil, or a piece of conventional headgear lined with foil, worn in the belief it shields the brain from threats such as electromagnetic fields, mind control, and mind reading.

The notion of wearing homemade headgear for protection has become a popular stereotype and byword for paranoia, persecutory delusions, and belief in pseudo science and conspiracy theories. Tin foil hats have appeared in movies such as Signs and Futurama: Into the Wild Green Yonder.


  • Origin 1
  • Scientific basis 2
    • Electromagnetic radiation 2.1
  • See also 3
  • References 4
  • External links 5


The concept of a tin foil hat for protection against interference of the mind was mentioned in a science fiction short story by Julian Huxley, "The Tissue-Culture King", first published in 1927, in which the protagonist discovers that "caps of metal foil" can block the effects of telepathy.[1]

Over time the term has been associated with paranoia and conspiracy theories.[2] It is often associated with beliefs that tin foil hats prevent mind control by governments, spies, or paranormal beings that employ ESP or the microwave auditory effect.

Scientific basis

Electromagnetic radiation

The notion that a tin foil hat can significantly reduce the intensity of incident radio frequency radiation on the wearer's brain has some scientific validity, as the effect of strong radio waves has been documented for quite some time.[3] A well-constructed tin foil enclosure would approximate a Faraday cage, reducing the amount of (typically harmless) radiofrequency electromagnetic radiation passing through to the interior of the structure. A common high school physics demonstration involves placing an AM radio on tin foil, 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-millimetre-thick tin foil, radiation above about 20 kHz (i.e., including both AM and FM bands) would be partially blocked, although tin foil is not sold in this thickness, so numerous layers of tin foil would be required to achieve this effect.[4]

The effectiveness of the tin foil hat as electromagnetic shielding for stopping radio waves is greatly reduced by it not being 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. However the hat may be partially grounded by the conductive properties of the skin with which it contacts.

A study by graduate students at MIT determined that a tin foil hat could attenuate incoming radiation depending on frequency. At WIFI frequencies - 2.4 GHz is attenuated by up to 90 dB; the effect was observed to be roughly independent of the relative placement of the wearer and radiation source.[5] At some microwave wavelengths, the skin depth is less than the thickness of even the thinnest foil.[6]

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,[7] at this time no link has been established between the radio-frequency EMR tin foil hats are meant to protect against and subsequent ill health.[8]

In 1962, Allan H. Frey discovered that reception of the induced sounds by radio-frequency electromagnetic signals heard as clicks and buzzes can be blocked by a patch of wire mesh (rather than foil) placed above the temporal lobe.[9]

See also


  1. ^ Huxley, Julian (1927). The Tissue-Culture King. Well, we had discovered that metal was relatively impervious to the telepathic effect, and had prepared for ourselves a sort of tin pulpit, behind which we could stand while conducting experiments. This, combined with caps of metal foil, enormously reduced the effects on ourselves. 
  2. ^ "Hey Crazy--Get a New Hat". Bostonist. 15 November 2005. Retrieved 2007-04-05. 
  3. ^ Adey, W. R. (December 1979). Neurophysiologic effects of Radiofrequency and Microwave Radiation, Bulletin of New York Academy of Medicine, vol. 55, no. 11,. pp. 1079–1093. 
  4. ^ Jackson, John David (1998). Classical Electrodynamics. Wiley Press.  
  5. ^ Rahimi, Ali; Ben Recht; Jason Taylor; Noah Vawter (17 February 2005). "On the Effectiveness of Aluminium Foil Helmets: An Empirical Study". Ali Rahimi. Archived from the original on 2010-07-08. 
  6. ^ Skin Depth - Microwave Encyclopedia -
  7. ^ Lean, Geoffrey (2006-05-07). "Electronic smog - Environment - The Independent". London:  
  8. ^ "Safety and Health Topics: Radiofrequency and Microwave Radiation - Health Effects". Retrieved 2009-06-09. 
  9. ^ Elder, Joe A.; Chou, C.K. (2003). "Auditory response to pulsed radiofrequency energy". Bioelectromagnetics (Wiley-Liss) 24 (S6): S162–73.  

External links

  • Do tinfoil helmets provide adequate protection against mind control rays? – from The Straight Dope
  • Tinfoil hats attract mind-control signals, boffins learn
  • Mind Games -Washington Post
  • On the Effectiveness of Aluminium Foil Helmets: An Empirical Study, Electrical Engineering and Computer Science department, MIT
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