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Homework Help: Electromagnetic Absorption/MATLAB calculaiton

  1. Apr 2, 2012 #1
    1. The problem statement, all variables and given/known data
    Hey guys, I am trying to draw out the electromagnetic absorpton vs frequency graph for a known dielectric constant ε in a medium but I am kind of stucked.

    I am studying from the Griffiths' book if you can catch me up from there, equations are on pg. 394, in chapter 9.4 Absorption and dispersion, 3rd edition

    2. Relevant equations
    Well, after a long proof, Griffiths concludes that the electromagnetic waves are (not suprisingly);

    E(z,t) = E 0 e-κz e i(kz-ωt)
    B(z,t) = B 0 e-κz e i(kz-ωt)

    where κ is the complex part, and k is the real parts of the "wave number"

    3. The attempt at a solution
    After we all know this given information I just tried to put all the values I know (like the frequency range, ε, σ, etc.) and excluded the imaginary(E) to find absorption. (and then simply plot it on MATLAB.)

    Where am I mistaken? I believe I should not simply plot the imaginary part. But what should I do to get a nice Absorption vs frequency spectrum?

    Cheers and thank you in prior!
  2. jcsd
  3. Apr 5, 2012 #2
    Absorption refers to the INTENSITY of energy flow ratio between incident wave and wave after traveling in the media for some distance, and the instantaneous intensity of the energy flow is the amplitude of the Poynting flux S~ExB. The time averaged intensity must be averaged over the period. For each frequency there's a different ratio of this time-averaged intensity.
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