Message from @Sari
Discord ID: 522502744326668308
Behind it all is Carol Aebersold and her twin daughters Chanda Bell and Christa Pitts, who kicked off the craze in 2005 when Carol and Chanda published a book called The Elf on a Shelf . Since then, their company, Creatively Classic Activities and Books, based in metro Atlanta, has expanded to a larger franchise.Dec 13, 2013
HRC & John Kerry in India
So what should you do when your Scout Elf is accidentally touched? First, don't worry! ... Sprinkle a little cinnamon next to your Scout Elf. Cinnamon is like vitamins for your elf and it will help him or her get back to the North Pole where the elf doctors can give them a quick check-up!Dec 11, 2017
The Unofficial Elf on the Shelf Guide for Parents. Note: There are two main rules when it comes to the official Elf on the Shelf. First, the elf is to be moved to a different location in your house every night while your children are asleep. ... If your kids accidentally touch him, they can write an apology letter to Santa ...
Extremely low frequency (ELF) is the ITU designation[1] for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively.[2][3] In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz.[4][5] 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.
Extremely low frequency
Frequency range
3 to 30 Hz
Wavelength range
100,000 to 10,000 km, respectively
1982 aerial view of the U.S. Navy Clam Lake, Wisconsin ELF transmitter facility, used to communicate with deeply submerged submarines. The rights of way of the two perpendicular 14 mile (23 km) overhead transmission lines that constituted the ground dipole antenna which radiated the ELF waves can be seen at lower left.
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.[6][7][8][9][10][11][12][13] The U.S. facilities were used between 1985 and 2004 but are now decommissioned.[9]
3 - 30hz?
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.[14] The World Health Organization (WHO) have used ELF to refer to the concept of "extremely low frequency (ELF) electric and magnetic fields (EMF)"[17] 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."[17]
Extremely Low Frquency = ELF
Due to their extremely long wavelength, ELF waves can diffract around large obstacles, and are not blocked by mountain ranges or the horizon and can travel around the curve of the Earth. ELF and VLF waves propagate long distances by an Earth-ionosphere waveguide mechanism.[5][18] The Earth is surrounded by a layer of charged particles (ions) in the atmosphere at an altitude of about 60 km at the bottom of the ionosphere, called the D layer which reflects ELF waves. The space between the conductive Earth's surface and the conductive D layer acts as a parallel-plate waveguide which confines ELF waves, allowing them to propagate long distances without escaping into space. In contrast to VLF waves, the height of the layer is much less than one wavelength at ELF frequencies, so the only mode that can propagate at ELF frequencies is the TEM mode in vertical polarization, with the electric field vertical and the magnetic field horizontal. ELF waves have extremely low attenuation of 1–2 dB per 1000 km,[18][19] giving a single transmitter the potential to communicate worldwide.
ELF waves can also travel considerable distances through "lossy" media like earth and seawater, which would absorb or reflect higher frequency radio waves.
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 great circle path interfere with each other.[20] At certain frequencies these oppositely directed waves are in phase and add (reinforce), causing standing waves. In other words, the closed spherical Earth-ionosphere cavity acts as a huge cavity resonator, enhancing ELF radiation at its resonant frequencies. These are called Schumann resonances after German physicist Winfried Otto Schumann who predicted them in 1952,[21][22][23][24] and were detected in the 1950s. Modeling the Earth-ionosphere cavity with perfectly conducting walls, Schumann calculated the resonances should occur at frequencies of[20]
f
n
=
7.49
[
n
(
n
+
1
)
]
1
/
2
Hz
{\displaystyle f_{n}=7.49[n(n+1)]^{1/2}\;{\text{Hz}}}
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 the resonance could be used to monitor global warming.[25][20]
The United States Navy utilized extremely low frequencies (ELFs) as radio band and radio communications. The Submarine Integrated Antenna System (SIAS) was a research and development effort to communicate with submerged submarines.[26] The Soviet/Russian Navy also utilized ELFs for submarine communications system, ZEVS.[27] The Indian Navy has an operational ELF communication facility at the INS Kattabomman naval base to communicate with its Arihant class and Akula class submarines.[28][29] A Chinese ELF facility on Hainan island, which is also the location of the Yulin Naval Base for nuclear submarines, has a military section which may be involved in submarine communications.[30]
Because of its electrical conductivity, seawater shields submarines from most higher frequency radio waves, making radio communication with submerged submarines at ordinary frequencies impossible. Signals in the ELF frequency range, however, can penetrate much deeper. Two factors limit the usefulness of ELF communications channels: the low data transmission rate of a few characters per minute and, to a lesser extent, the one-way nature due to the impracticality of installing an antenna of the required size on a submarine (the antenna needs to be of an exceptional size in order to achieve successful communication). Generally, ELF signals have been used to order a submarine to rise to a shallow depth where it could receive some other form of communication.
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One of the difficulties posed when broadcasting in the ELF frequency range is antenna size, because the length of the antenna must be at least a substantial fraction of the length of the waves. Simply put, a 3 Hz (cycle per second) signal would have a wavelength equal to the distance EM waves travel through a given medium in one third of a second. Taking account of refractive index, ELF waves propagate slightly slower than the speed of light in a vacuum. As used in military applications, the wavelength is 299,792 km (186,282 mi) per second divided by 50–85 Hz, which equals around 3,500 to 6,000 km (2,200 to 3,700 mi) long. This is comparable to the Earth's diameter of around 12,742 km (7,918 mi). Because of this huge size requirement, to transmit internationally using ELF frequencies, the Earth itself forms a significant part of the antenna, and extremely long leads are necessary into the ground. Various means, such as electrical lengthening, are used to construct practical radio stations with smaller sizes.
The US maintained two sites, in the Chequamegon-Nicolet National Forest, Wisconsin and in the Escanaba River State Forest, Michigan (originally named Project Sanguine, then downsized and rechristened Project ELF prior to construction), until they were dismantled, beginning in late September 2004. Both sites used long power lines, so-called ground dipoles, as leads. These leads were in multiple strands ranging from 22.5 to 45 kilometres (14.0 to 28.0 mi) long. Because of the inefficiency of this method, considerable amounts of electrical power were required to operate the system.
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There have been some concerns over the possible ecological impact of ELF signals. In 1984 a federal judge halted construction, requiring more environmental and health studies. This judgment was overruled by a federal appeals court on the basis that the US Navy claimed to have spent over $25 million studying the effects of the electromagnetic fields, with results indicating that they were similar to the effect produced by standard power distribution lines. The judgment was not accepted by everyone and, during the time that ELF was in use, some Wisconsin politicians such as Senators Herb Kohl, Russ Feingold and Congressman Dave Obey called for its closure. Similar concerns have, in the past, been raised about electromagnetic radiation and health.
Naturally occurring ELF waves are present on Earth, resonating in the region between ionosphere and surface seen in lightning strikes that make electrons in the atmosphere oscillate.[32] Though VLF signals were predominantly generated from lightning discharges, it was found that an observable ELF component—slow tail—followed the VLF component in almost all cases.[33] Also, the fundamental mode of the Earth-ionosphere cavity has the wavelength equal to the circumference of the Earth, which gives a resonance frequency of 7.8 Hz. This frequency, and higher resonance modes of 14, 20, 26 and 32 Hz appear as peaks in the ELF spectrum and are called Schumann resonance.
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 off 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 magnetars. The pulsar in the Crab nebula radiates powers of this order at 30 Hz.[34] Radiation of this frequency is below the plasma frequency of the interstellar medium, thus this medium is opaque to it, and it cannot be observed from Earth.
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In electromagnetic therapy and electromagnetic radiation and health research, electromagnetic spectrum frequencies between 0 and 100 hertz are considered extremely low-frequency fields.[35] A common source of exposure of the public to ELF fields is 60 Hz electric and magnetic fields from high-voltage electric power transmission lines and secondary distribution lines, such as those supplying electricity to residential neighborhoods.[17][36][35]
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
