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Electromagnetic Wave Propagation

  1. Apr 20, 2008 #1
    Hi All,

    Em waves propagate in varying ground conditons, in the ground the velocity of em waves is reduced since it is dependant on the relative dielectric permittivity, the realtive magnetic permiability & electrical conductivity.

    This will more than likely make no sense at all?

    My question is:

    Instead of using all the above formula's to try to simulate this, can it be done by another method?

    By the resistivity of the ground conditions, or doesn't this apply to the em wave propagation through the ground?

    Thanks
     
  2. jcsd
  3. Apr 20, 2008 #2
    conductivity is the reciprocal of resistivity - i.e. different ways of looking at the same thing:

    conductivity=resistivity-1

    resistivity=conductivity-1

    I'm really not sure what you're trying to get at........?
     
  4. Apr 20, 2008 #3
    Thanks billiards,

    I am attempting to get an idea of em wave amplitude through various ground conditions from a known primary coil pulsed flux intensity, different ground conditions hinder the em wave amplitude & depth penetration & also from a target response signal to a reciever-i.e
    in mineralised soils etc.

    I was thinking that by adding on an Ohm's resistance value to the driving primary coil specifications --(reducing flux intensity) & to the reciever coil that this may simulate the resistivity of particular ground conditions & give me a smillar outcome instead of all the formulas for relative dielectric permittivity, the realtive magnetic permiability & electrical conductivity.

    I can find or determine the ground resistivity figures but at am at a loss to to find the figures to apply into the other formulas for various ground conditions.
    I may be totally wrong with trying to do this via soil resistivity numbers & adding an Ohm's resistance to try to simulate this but it was just an idea & any help would be greatly appreciated.

    Thank You
     
  5. Apr 20, 2008 #4
    Are you trying to send and receive signals using the Earth as a conductor instead of using the Earth as one side of a Marconi antenna?
     
  6. Apr 20, 2008 #5
    Hi pinestone,

    Simmilar to a GPR -Ground Penetrating Radar- or Metal Detector etc.
     
  7. Apr 20, 2008 #6
    Ground communication has been utilized for many years. The US Navy and Soviets used ELF, sub-terrestrial waves to communicate with their submerged submarines. The main drawback to this type of system has been its inefficient use of power. Some experimenters have tried many different coupling methods and frequencies that would raise the efficiency to a useful level, but I haven't heard or read of anyone who can compete with a typical Earth-sky Marconi radiator. Here's one such effort and test data:

    http://www.borderlands.com/newstuff/research/FelixRadio/FelixRadio.htm

    Recently, HAARP has utilized the Earth for one component of their system:

    http://www-star.stanford.edu/~vlf/pars/pars.htm#A.6 Excitation of ULF and Lower-ELF Waves
     
  8. Apr 20, 2008 #7
    oops...missed the point completely.
     
  9. Apr 20, 2008 #8
    Hi pinestone,

    Sorry i should have elaborated more about the simulations i am trying to achieve, it is not for Radio communication but for detection & response signal of underground metalic objects--ferrous & non ferrous. I am just looking for a simplified way to allow for the em wave amplitude through various soil conditions in my simulations.
    I thought i may be able to do this via ground resistivity figures like mentioned above.
     
  10. Apr 21, 2008 #9
    I'm a bit confused as to why you would add a resistance value to an inductive component.
     
  11. Apr 21, 2008 #10
    If you're using a GPR bear in mind that the frequency and the antenna separation will both have a first order affect on depth penetration. The geological conditions are also important, in particular, the presence of water which has an extraordinarily high permittivity relative to other geologically occuring substances. I believe that the dielectric contrast between layers is important in governing the amount of reflected energy, similar to acoustic impedance contrast in seismology.

    As for electrical resistivity surveys, depth penetration is also affected by electrode separation. Although in practice if there is a highly conductive body in the shallow then you won't get any deeper than that.

    As a disclaimer I advise you not to take any of what I've said at face value :-)
     
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