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EM waves penetration

  1. Sep 1, 2010 #1
    When an EM wave has a higher frequency, it is able to penetrate materials more easily.

    However, why does a microwave able to penetrate haze while visible light can't? Why visible light is able to enter our atmosphere while those of gamma can't?
     
  2. jcsd
  3. Sep 1, 2010 #2

    Dale

    Staff: Mentor

    This is not generally true. E.g.
    http://en.wikipedia.org/wiki/File:Water_absorption_spectrum.png [Broken]
     
    Last edited by a moderator: May 4, 2017
  4. Sep 2, 2010 #3
    First assuming TEM mode (no field component in the propagation direction).

    In addition to the above poster, the attenuation of a material could be viewed upon as the sum of three things
    1) Reflection, at the first boundary of the material
    2) Multi-reflection, inside the material between the boundaries of the material
    3) Absorption in the material itself

    1) and 3) tend to increase the attenuation and 2) increase it.
    1) is often just a simple function of the different wave impedances of the two regions (that is from where the wave came from and into the material we are talking about).

    The absorption (3) is highly dependent on the material parameters in our "shield material".
    E.g. to attenuate low frequency magnetic fields, you need a material with a high permeability value. Also all of this is of course frequency dependent, HOWEVER you cannot assume it to be linear :-)
     
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