Wireless Communication With Mine

choi

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Kris Maher, New Tool May Reach Trapped Miners;
Lockheed Martin Is Testing Wireless Communication System to Help Locate
Workers After Accidents
Wall Street Journal, July 20, 2010.
http://online.wsj.com/article/SB10001424052748704720004575377232010729558.html
("to send a fully wireless signal through the layers of earth and rock above
mines. * * * Using the magnetic waves, the system has successfully
transmitted signals through mines to depths in excess of 1,550 feet in tests
. Radio waves, by contrast, can usually penetrate only a few feet of earth")
Note:
(a) Sago Mine disaster

http://en.wikipedia.org/wiki/Sago_Mine_disaster
(b) electromagnetic radiation
http://en.wikipedia.org/wiki/Electromagnetic_radiation

The illustration of Electromagnetic spectrum shows where "radio waves" are
located. I am uncertain where "magnetic waves" lie in the spectrum.

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