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Extremely low frequency (ELF) is the ITU designation〔(【引用サイトリンク】url=http://www.itu.int/dms_pubrec/itu-r/rec/v/R-REC-V.431-7-200005-I!!PDF-E.pdf )〕 for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths from 100,000 to 10,000 kilometers.〔(【引用サイトリンク】title=Extremely Low Frequency )〕〔(【引用サイトリンク】title=Extremely low frequency )〕 In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz.〔Liemohn, Michael W. and A. A. CHAN, "(Unraveling the Causes of Radiation Belt Enhancements )". EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION, Volume 88, Number 42, 16 October 2007, pages 427-440. Republished by NASA and accessed online, 8 February 2010. Adobe File, page 2.〕 In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands. ELF radio waves are generated by lightning and natural disturbances in Earth's magnetic field, so they are a subject of research by atmospheric scientists. Because of the difficulty of building antennas that can radiate such long waves, ELF frequencies have been used in only a very few human-made communication systems. ELF waves can penetrate seawater, which makes them useful in communication with submarines. The US, Russia, and India are the only nations known to have constructed ELF communication facilities.〔 at the (Federation of American Scientists website )〕〔〔(【引用サイトリンク】title=Navy gets new facility to communicate with nuclear submarines prowling underwater )〕 The U.S. facilities were used between 1985 and 2004 but are now decommissioned.〔 ELF waves can also penetrate significant distances into earth or rock, and "through-the-earth" underground mine communication systems use frequencies of 300 to 3000 Hz. The frequency of alternating current flowing in electric power grids, 50 or 60 Hz, also falls within the ELF band, making power grids an unintentional source of ELF radiation. ==Alternate definitions== ELF is a ''subradio frequency''.〔(NASA.gov ), page 8. ">0 to 300 Hz ... Extremely low frequency (ELF)" 〕 Some medical peer reviewed journal articles refer to ELF in the context of "extremely low frequency (ELF) magnetic fields (MF)" with frequencies of 50 Hz and 50–80 Hz.〔 ESTECIO, Marcos Roberto Higino and SILVA, Ana Elizabete. (Alterações cromossômicas causadas pela radiação dos monitores de vídeo de computadores ). Rev. Saúde Pública (). 2002, vol.36, n.3, pp. 330-336. ISSN 0034-8910. Republished by docguide.com. Accessed 8 February 2010.〕 United States Government agencies, such as NASA, describe ELF as non-ionizing radiation with frequencies between 0 and 300 Hz.〔 The World Health Organization (WHO) have used ELF to refer to the concept of "extremely low frequency (ELF) electric and magnetic fields (EMF)"〔"(Electromagnetic Fields and Public HealthL - Extremely Low Frequency (ELF) )". Fact Sheet N205. November 1998. World Health Organization. Accessed 12 February 2010. "ELF fields are defined as those having frequencies up to 300 Hz. ... the electric and magnetic fields act independently of one another and are measured separately."〕 and have also referred to "ELF electric and magnetic fields in the frequency range >0 to 100,000 Hz (100 kHz)."〔 The WHO also stated that at frequencies between 0 and 300 Hz, "the wavelengths in air are very long (6000 km at 50 Hz and 5000 km at 60 Hz), and, in practical situations, the electric and magnetic fields act independently of one another and are measured separately."〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Extremely low frequency」の詳細全文を読む スポンサード リンク
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