Help with vector calculus in reflection and transmission of plane wave

In summary, the conversation is discussing the reflection and transmission of an electromagnetic wave at a flat planar boundary between two media. The focus is on using vector calculus to prove that if the incident electric field is in the y direction, then the reflected and transmitted electric fields will also be in the y direction. The conversation also includes equations and diagrams to support the discussion. The speaker is asking for someone to check their work and has a question about the definition of the wave function.
  • #1
yungman
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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
 
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  • #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?
 
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FAQ: Help with vector calculus in reflection and transmission of plane wave

1. What is vector calculus?

Vector calculus is a branch of mathematics that deals with operations on vector fields, which are quantities that have both magnitude and direction. It includes concepts such as differentiation and integration of vector fields, as well as the use of vector operations like dot and cross products.

2. How is vector calculus used in the reflection and transmission of plane waves?

In the context of electromagnetic waves, vector calculus is used to analyze the behavior of wave propagation at boundaries between different materials. This is because the electric and magnetic fields of the wave can be represented as vector fields, and their behavior at the boundary can be described using vector calculus operations.

3. What is the importance of understanding vector calculus in this context?

Understanding vector calculus is crucial in this context because it allows us to accurately predict and analyze the behavior of plane waves at boundaries. This can help us design and optimize devices such as antennas, optical fibers, and waveguides.

4. What are some key concepts in vector calculus that are relevant to the reflection and transmission of plane waves?

Some key concepts in vector calculus that are relevant to this topic include vector field differentiation and integration, the divergence and curl of a vector field, and the use of boundary conditions to solve for the behavior of fields at boundaries.

5. Are there any resources available for further learning about vector calculus in the context of plane wave reflection and transmission?

Yes, there are many textbooks and online resources available that cover vector calculus in the context of electromagnetic waves and their behavior at boundaries. Some recommended resources include "Electromagnetic Field Theory Fundamentals" by Bhag Singh Guru and Hüseyin R. Hiziroglu and "Introduction to Electrodynamics" by David J. Griffiths.

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