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I read about magnetic induction communication on Lockheed Martin's wireless mining communication system

In this interview Warren Gross said:

We generate a signal and send it through a loop that's wrapped around a pillar in the mine. When you send the signal through a loop of wires it creates a magnetic moment or a magnetic field. That magnetic field essentially creates a bubble of magnetic energy which rises to the surface.

I thought magnetic field will be around the object(coil or magnet) and doesn't shift or move away. Does magnetic field or magnetic bubble rise to the surface like air bubble in some condition?

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I think the author is talking about the diffusion of the magnetic field throught a conducting medium (the earth) of conductivity sigma. – Shaktyai Aug 9 '12 at 12:51

2 Answers 2

I read the interview, and I think the confusion arises from really imprecise wording. He could mean that

  • He's sending an alternating current through the coil of wire (AC), and that's creating a fluctuating magnetic field, so basically what he is creating is an electromagnetic wave that will reach the surface. But these aren't "magnetic" waves, and at a certain frequency range are radio waves.
  • The magnetic field created is so strong that it reaches all the way up to the surface, and is detected there.

Since he has mentioned that it isn't radio waves and is instead a "bubble of magnetic energy", I suspect it's the second choice, but unless you can find another report that details this mechanism, I don't think we can actually say which one it is.

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Perhaps what was meant is that the magnetic field surrounding the (metal) pillar extends to the surface (and the field strength at the surface is detectable).

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