Due to the penetration ability of ELF radiation, the US Navy incorporates it for submarine communication. An antenna, buried underground in Maine, provides a link from the land-based transmitter to underwater submarines. Unfortunately, the required high power (due to low antenna efficiency) and long antenna lengths prevent submarines from communicating with land bases. The Navy conducted experiments with underwater antenna communication in the 1960's but gave up the effort. Published data from these investigations depicting reduced effective antenna wavelength is shown below :

Tabular data taken from the above plot.

According to these datas, the effective 60Hz air wavelength of 15,600,000 feet is reduced to 600 feet in sea water. This is a substantial reduction. Two factors are responsible for this reduction. The dielectric constant of sea water is ~80 and accepted conductivity is 5 S/m. Permeability of the surrounding antenna medium also exhibits a significant effect toward wavelength reduction.

Reference : Antenna Roundup, Tom Kneitel, Volume 2, Prentice Hall Publications, 1966

The plot above, shows the phase velocity reduced wavelength for an ELF antenna
in seawater (published by the US Navy in 1960's), in air and also in a pure iron powder (for the System-G).

See also : The System-G equations solver by J-L Naudin

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