Extremely low frequency
Frequency range | 3 to 30 Hz |
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Wavelength range | 100,000 to 10,000 km, respectively |
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Extremely low frequency (ELF) is the
ELF radio waves are generated by
Alternative definitions
ELF is a subradio frequency.[14] 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[15] and 50–80 Hz.[16] United States
Government agencies, such as NASA, describe ELF as non-ionizing radiation with frequencies between 0 and 300 Hz.
Propagation
Due to their extremely long wavelength, ELF waves can
ELF waves can also travel considerable distances through "lossy" media like earth and seawater, which would absorb or reflect higher-frequency radio waves.
Schumann resonances
The attenuation of ELF waves is so low that they can travel completely around the Earth several times before decaying to negligible amplitude, and thus waves radiated from a source in opposite directions circumnavigating the Earth on a
The actual frequencies differ slightly from this due to the conduction properties of the ionosphere. The fundamental Schumann resonance is at approximately 7.83 Hz, the frequency at which the wavelength equals the circumference of the Earth, and higher harmonics occur at 14.1, 20.3, 26.4, and 32.4 Hz, etc. Lightning strikes excite these resonances, causing the Earth–ionosphere cavity to "ring" like a bell, resulting in a peak in the noise spectrum at these frequencies, so the Schumann resonances can be used to monitor global thunderstorm activity.
Interest in Schumann resonances was renewed in 1993 when E. R. Williams showed a correlation between the resonance frequency and tropical air temperatures, suggesting that the resonance could be used to monitor
Submarine communications
Since ELF radio waves can penetrate seawater deeply, to the operating depths of submarines, a few nations have built naval ELF transmitters to communicate with their submarines while submerged. It was reported in 2018 that China had constructed the world's largest ELF facility roughly the size of New York City in order to communicate with its submarine forces without requiring them to surface.[26] The United States Navy in 1982 built the first ELF submarine communications facility, two coupled ELF transmitters at Clam Lake, Wisconsin, and Republic, Michigan.[27] They were shut down in 2004. The Russian Navy operates an ELF transmitter called ZEVS (Zeus) at Murmansk on the Kola Peninsula.[28] The Indian Navy has an ELF communication facility at the INS Kattabomman naval base to communicate with its Arihant-class and Akula-class submarines.[13][29]
Explanation
Because of its
Difficulties of ELF communication
One of the difficulties posed when broadcasting in the ELF frequency range is
The United States maintained two sites: in the
Other uses
Transmitters in the 22 Hz range are also used in pipeline maintenance, or pigging. The signal is generated as an alternating magnetic field, and the transmitter is mounted to, or to part of, the "pig", the cleaning device inserted into the pipe. The pig is pushed through a mostly metal pipeline. The ELF signal can be detected through the metal, allowing its location to be detected by receivers located outside of the pipe.[30] It is used to check whether a pig has passed a certain location or to locate a stuck pig.
Some radio hobbyists record ELF
Since the 2000s, very low frequencies have been used successfully at sea for oil geophysical prospecting.[31]
Natural sources
Naturally occurring ELF waves are present on Earth, resonating in the region between
ELF waves have also been tentatively identified on Saturn's moon Titan. Titan's surface is thought to be a poor reflector of ELF waves, so the waves may instead be reflecting from the liquid–ice boundary of a subsurface ocean of water and ammonia, the existence of which is predicted by some theoretical models. Titan's ionosphere is also more complex than Earth's, with the main ionosphere at an altitude of 1,200 km (750 mi) but with an additional layer of charged particles at 63 km (39 mi). This splits Titan's atmosphere into two separate resonating chambers. The source of natural ELF waves on Titan is unclear, as there does not appear to be extensive lightning activity.[32]
Huge ELF radiation power outputs of 100,000 times the Sun's output in visible light may be radiated by
Exposure
In
Conspiracy theories
Since the late 1970s, various conspiracy theories have risen around exposure to ELF electric and magnetic fields (EMF).[36] External ELF magnetic fields induce electric fields and currents in the body, which, at very high field strengths, cause nerve and muscle stimulation and changes in nerve cell excitability in the central nervous system.[citation needed]
ELF at human-perceivable kV/m levels was said to create an annoying tingling sensation in the areas of the body in contact with clothing, particularly the arms, due to the induction of a surface charge by the ELF. Of the volunteers, 7% described the spark discharges as painful when the subject was well-insulated and touched a grounded object within a 5 kV/m field, whereas 50% described a similar spark discharge as painful in a 10 kV/m field.[37]
Leukemia
There is high uncertainty regarding
No other study has found any evidence to support the hypothesis that ELF exposure is a contributing factor to leukemia in children.[39][40]
A 2014 study estimated the cases of childhood leukemia attributable to exposure to ELF magnetic fields in the
Ecological impact
There have been some concerns over the possible ecological impact of ELF signals. In 1984 a federal judge halted construction,[
Patents
- Tanner, R. L., U.S. patent 3,215,937, "Extremely low-frequency antenna", 1965
- Hansell, Clarence W., U.S. patent 2,389,432, "Communication system by pulses through the Earth"
- Altshuler, U.S. patent 4,051,479, ELF vertical dipole antenna suspended from aircraft
See also
- Ultra low frequency
- List of initialisms
- Infrasound
- Skin effect
- TACAMO
- Wardenclyffe Tower
- Naval Communication Station Harold E. Holt
- Magnetic pulsations
References
Notes
- ^ "Rec. ITU-R V.431-7, Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). ITU. Archived from the original (PDF) on 31 October 2013. Retrieved 20 February 2013.
- ^ "Extremely Low Frequency". ANL Glossary. NASA. Archived from the original on 4 March 2016. Retrieved 28 September 2013.
- ^ "Extremely low frequency". ANL Glossary. Archived from the original on 29 October 2013. Retrieved 9 August 2011.
- ^ Liemohn, Michael W. and A. A. CHAN, "Unraveling the Causes of Radiation Belt Enhancements". Archived 27 May 2010 at the Wayback Machine. 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.
- ^ .
- ^ Wolkoff, E. A.; W. A. Kraimer (May 1993). "Pattern Measurements of U.S. Navy ELF Antennas" (PDF). ELF/VLF/LF Radio Propagation and Systems Aspects. Belgium: AGARD Conference proceedings 28 Sep – 2 October 1992, NATO. pp. 26.1–26.10. Archived (PDF) from the original on 5 April 2014. Retrieved 17 February 2012.
- ISBN 978-0-7864-2662-1.
- ^ ISBN 978-1-85109-732-6.
- S2CID 119798336.
- ^ Jacobsen, Trond (2001). "ZEVS, The Russian 82 Hz ELF Transmitter". Radio Waves Below 22 kHz. Renato Romero webpage. Retrieved 17 February 2012.
- IHS Jane's Defence Weekly. Archived from the originalon 23 February 2014. Retrieved 23 February 2014.
- ^ a b "Navy gets new facility to communicate with nuclear submarines prowling underwater". The Times of India. 31 July 2014.
- ^ a b NASA.gov, page 8. ">0 to 300 Hz ... Extremely low frequency (ELF)". Archived 21 July 2011 at the Wayback Machine.
- PMID 16620992.
- ^ ESTECIO, Marcos Roberto Higino and SILVA, Ana Elizabete. Alterações cromossômicas causadas pela radiação dos monitores de vídeo de computadores Archived 20 February 2005 at the Wayback Machine. Rev. Saúde Pública [online]. 2002, vol. 36, n. 3, pp. 330–336. ISSN 0034-8910. Republished by docguide.com. Accessed 8 February 2010.
- ^ a b c "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."
- ^ a b S. Basu; J. Buchau; F. J. Rich; E. J. Weber; E. C. Field; J. L. Heckscher; P. A. Kossey; E. A. Lewis; B. S. Dandekar; L. F. McNamara; E. W. Cliver; G. H. Millman; J. Aarons; J. A. Klobuchar; M. F. Mendillo (1985). "Ionospheric Radio Wave Propagation" (PDF). In Jursa, Adolph S. (ed.). Handbook of Geophysics and the Space Environment (4th ed.). Air Force Geophysics Laboratory, U.S. Air Force. pp. 10.25–10.27.
- ^ Barr, et al (2000) ELF and VLF radio waves (Archived 5 April 2014 at the Wayback Machine), p. 1695, 1696 (fig. 3).
- ^ a b c Barr, et al. (2000) ELF and VLF radio waves (Archived 5 April 2014 at the Wayback Machine), p. 1700–1701.
- S2CID 96060996.
- .
- S2CID 122643775.
- S2CID 6546863.
- S2CID 26708495.
- ^ "China's NYC-Sized 'Earthquake Warning System' Array Sounds More Like a Way to Talk to Submarines". 31 December 2018.
- ^ "U.S. Navy: Vision...Presence...Power" (Archived 20 April 2015 at the Wayback Machine). SENSORS – Subsurface Sensors. US Navy. Accessed 7 February 2010.
- ^ ZEVS, the Russian 82 Hz ELF transmitter.
- ^ James Hardy (28 February 2013). "India makes headway with ELF site construction". IHS Jane's 360. Archived from the original on 23 February 2014.
- ISBN 978-2-7430-0972-4. 332 p.
- ^ Stéphane Sainson, Electromagnetic seabed logging, A new tool for geoscientists. Ed. Springer, 2016
- ^ a b "Titan's Mysterious Radio Wave". Jet Propulsion Laboratory. 1 June 2007. Archived from the original on 3 June 2007. Retrieved 2 June 2007. Republished as "Casini - Unlocking Saturn's Secrets - Titan's mysterious radio wave Archived 24 December 2010 at the Wayback Machine". 22 November 2007. NASA. Accessed 7 February 2010.
- ^ Tepley, Lee R. "A Comparison of Sferics as Observed in the Very Low Frequency and Extremely Low Frequency Bands" (Archived 5 June 2011 at the Wayback Machine). Stanford Research Institute Menlo Park, California. 10 August 1959. 64(12), 2315–2329. Summary republished by American Geophysical Union. Accessed 13 February 2010.
- ^ "Pulsars". www.cv.nrao.edu. Archived from the original on 12 November 2020. Retrieved 31 December 2018.
- ^ ISBN 0-7172-8244-9.
- ^ a b c d Electromagnetic fields and public health (Report). Fact Sheet No. 322. World Health Organization. June 2007. Archived from the original on 1 July 2007. Retrieved 7 February 2010.
- ^ Extremely Low Frequency Fields Environmental Health Criteria (Report). Monograph No. 238. World Health Organization. chapter 5, page 121. Archived from the original on 29 June 2007.
- PMID 20877339.
- PMID 25689995.
- ISBN 978-981-10-5121-0.
- PMID 24161447.
- ^ Electric and magnetic fields from power lines and electrical appliances (Report). Government of Canada. 25 November 2020.
- ^ "Expertise de l'Afsset sur les effets sanitaires des champs électromagnétiques d'extrêmement basses fréquences". afsset.fr (in French). 6 April 2010. Retrieved 23 April 2010.
- PMID 18245151.
- ^ Scientific Committee on Emerging Newly Identified Health Risks-SCENIHR (January 2009). Health effects of exposure to EMF (PDF) (Report). European Directorate General for Health & Consumers. Brussels, Belgium: European Commission. pp. 4–5. Retrieved 27 April 2010.
General information
- Non-ionizing radiation, Part 1: Static and Extremely Low-Frequency (ELF) Electric and Magnetic Fields (2002) by the IARC. (Non-Ionizing Radiation)
External links
- Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).
- Extremely low frequency (ELF) fields (EHC 35, 1984)
- "Radio waves below 22kHz: Nature's signals and strange emission at very low frequency" - a site specialising in low-frequency signals .
- Jacobsen, Trond, "ZEVS, the Russian 82 Hz ELF transmitter: An Extrem Low Frequency transmission-system, using the real longwaves" ALFLAB, Halden, Norway.
- NASA live streaming ELF -> VLF Receiver