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Help with vector calculus in reflection and transmission of plane wave

  1. Jun 3, 2013 #1
    This is not a homework, this is concerning reflection and transmission of electromagnetic wave ( plane wave) at a flat planar boundary between two media. But the work in question is pure vector calculus. I ultimately want to proof if ##\vec E_I=\hat y E_I## then ## \vec E_R## and ##\vec E_T## are ##\hat y## direction also. I have a lot of difficulty in this as it is very long. I have the first road block that I need someone to check my work.

    As shown in the figure, the ##\vec E_I,\;\vec E_R,\;\hbox { and }\;\vec E_T## are all in xz plane and the boundary is the xy plane at z=0.

    At z=0, ##\vec E_I|_{z=0}=\vec E_{0I},\;\vec E_R|_{z=0}=\vec E_{0R},\;\hbox { and }\;\vec E_T|_{z=0}=\vec E_{0T}##

    [PLAIN]http://i40.tinypic.com/kaj5x.jpg[/PLAIN]

    We let:
    ##\vec E_{0I}=\hat y E_{0I}##.
    ##\vec E_{0R}=\hat x E_{0R_x}+\hat y E_{0R_y} + \hat z E_{0R_z}##
    ##\vec E_{0T}=\hat x E_{0T_x}+\hat y E_{0T_y} + \hat z E_{0T_z}##
    ##\hat k_I=\hat x\sin\theta_I+\hat z \cos\theta_I##, ##\hat k_R=\hat x\sin\theta_R-\hat z \cos\theta_R## and ##\hat k_T=\hat x\sin\theta_T+\hat z \cos\theta_T##.

    This is the boundary equations of J D Jackson p304 (7.37) that is being used here
    ##[\epsilon(\vec E_0+\vec E_0'')-\epsilon'\vec E_0']\cdot \hat n=0## (7.37a) for normal E.
    ##[\hat k \times \vec E_0+\hat k''\times\vec E_0''-\hat k'\times\vec E_0']\cdot \hat n=0## (7.37b) for normal B.
    ##(\vec E_0+\vec E_0''-\vec E_0')\times\hat n=0## (7.37c) for tangential E.
    ##\left[\frac 1 {\mu}(\hat k \times \vec E_0+\hat k''\times\vec E_0'')-\frac 1 {\mu'}(\hat k'\times\vec E_0')\right]\times\hat n=0## (7.37d) for tangential B.

    Where ##\hat k=\hat k_I,\;\hat k'=\hat k_T,\;\hat k''=\hat k_R##
    ##\vec E=\vec E_I,\;\vec E'=\vec E_T,\;\vec E''=\vec E_R,\;\hat n=\hat z##


    (7.37a)##\Rightarrow\;[\epsilon_1(\vec E_{0I}+\vec E_{0R})-\epsilon_2\vec E_{0T}]\cdot \hat z=0## (A).
    (7.37b)##\Rightarrow\;[\hat k_I \times \vec E_{0I}-\hat k_R \times\vec E_{0R}-\hat k_T \times\vec E_{0T}]\cdot \hat z=0## (B).
    (7.37c)##\Rightarrow\;(\vec E_{0I}+\vec E_{0R}-\vec E_{0T})\times\hat z=0## (C).
    (7.37d)##\Rightarrow\;\left[\frac 1 {\mu_1}(\hat k_I \times \vec E_{0I}-\hat k_R\times\vec E_{0R})-\frac 1 {\mu_2}(\hat k_T\times\vec E_{0T})\right]\times\hat z=0## (D).

    From (C) ##[\vec E_{0I}+\vec E_{0R}-\vec E_{0T}]\times\hat z=0\;\Rightarrow\;\hat y E_{0I_y}\times \hat z + (\hat x E_{0R_x}+\hat y E_{0R_y} + \hat z E_{0R_z})\times \hat z + (\hat x E_{0T_x}+\hat y E_{0T_y} + \hat z E_{0T_z})\times \hat z=0##
    ##\Rightarrow\; \hat x E_{0I_y}-\hat y E_{0R_y}+\hat x E_{0R_y}+\hat y E_{0T_x}-\hat x E_{0T_y}=0##

    Therefore ## E_{0I_y}+E_{0R_y}-E_{0T_y}=0\;\hbox { and }\;E_{0R_x}=E_{0T_x}## (E)


    From (B) ##[\hat k_I \times \vec E_{0I}+\hat k_R \times\vec E_{0R}-\hat k_T \times\vec E_{0T}]\cdot \hat z=0##
    Also according to Snell's Law, ##\theta_I=\theta_R##. Let ##\theta_1=\theta_I=\theta_R## and ## \theta_2=\theta_T## here.

    \begin{align}\Rightarrow\; &[(\hat x \sin\theta_1+\hat z \cos\theta_1)\times \hat y E_{0I_y}+(\hat x \sin\theta_1-\hat z \cos\theta_1)\times(\hat x E_{0R_x}+\hat y E_{0R_y} + \hat z E_{0R_z})\\
    &-(\hat x \sin\theta_2+\hat z \cos\theta_2)\times(\hat x E_{0T_x}+\hat y E_{0T_y} + \hat z E_{0T_z})]\cdot \hat z=0
    \end{align} Because of the ##\cdot \hat z ## at the end, only the ##\hat x \times \hat y## terms in the equation remain:
    ##\Rightarrow\; E_{0I_y} \sin\theta_1 +E_{0R_y}\sin\theta_1 - E_{0T_y}\sin\theta_2=0##.(F)

    If you compare (E) to (F)
    It cannot be both true as ##\theta_1## is not equal to ##\theta_2##. Can anyone check my work, I have check 3 times already and I cannot see the problem.

    Thanks
     
    Last edited by a moderator: Jun 3, 2013
  2. jcsd
  3. Jun 3, 2013 #2
    Anyone?

    I have another question: The wave function is really defined as:
    [tex]\vec E_R = \vec E_{0R} e^{-jk_R(x\sin\theta_1 - z\cos\theta_1)}=\hat k_R E_{0R} e^{-jk_R(x\sin\theta_1 - z\cos\theta_1)}[/tex]
    which the amplitude vary sinusoidally along the path of ##\vec k_R##. I should still use ##\vec E_R(\vec k_R)=\hat x E_{R_x}+\hat y E_{R_y}+\hat z E_{R_z}##. Is this true?
     
    Last edited: Jun 3, 2013
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