Fresnel Equations Simulation in 2D: How to Avoid Side Entry in Comsol?

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Discussion Overview

The discussion revolves around simulating the Fresnel equations in 2D using Comsol, specifically addressing issues related to reflectance and transmission for TE and TM waves at varying angles of incidence. Participants explore the challenges of side entry of electromagnetic waves into the dielectric material and seek solutions to avoid this phenomenon.

Discussion Character

  • Technical explanation, Experimental/applied, Debate/contested

Main Points Raised

  • One participant reports difficulties in simulating the Fresnel equations in Comsol, noting discrepancies between simulated values and analytical solutions for larger angles of incidence.
  • The same participant suspects that electromagnetic waves are entering the dielectric from the sides due to the configuration of the model and the use of Floquet periodic boundary conditions.
  • Another participant indicates they resolved the issue but does not provide details initially.
  • A later reply requests clarification on how the problem was solved.
  • A participant explains that the issue was related to the propagation constant of the ports, emphasizing the importance of the vertical component of the wave vector and its sign for proper wave propagation direction.

Areas of Agreement / Disagreement

The discussion includes multiple viewpoints regarding the simulation challenges, with some participants agreeing on the nature of the problem while others seek clarification on the solution. The resolution of the issue is not fully detailed, leaving some aspects unresolved.

Contextual Notes

Limitations include potential misunderstandings of the propagation constant and the implications of boundary conditions, which may affect the simulation outcomes.

MarcelComsol
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Hi there,

I'm failing in simulating the fresnel equations in 2D with Comsol.

As you can see in the model added to this post, the reflectance and transmission in the global plots both for TE-waves ("Port, senkrecht polarisiert", Plot "Reflektion und Transimission, senkrecht") and TM-waves ("Port, parallel poralisiert", Plot "Reflektion und Transmission, paralell") seems to be correct for small angles of alpha. But for bigger angles of alpha, the simulated values differ strongly from the analytical solutions. I suspect that the wave from the upper port is also entering from the sides of the dielectrica (side 1 and 6), since we have also an electrical field in the dielectrica for alpha equals 90 degrees(see picture below). How can I avoid the electromagnetic wave entering from the sides 1 and 6 (i chose floquet periodic boundary conditions)?

upload_2019-3-19_8-20-12.png

Picture above: TM waves, alpha=90 degrees, but still a wave is entering my dielectrica(the lower half)

I would be very happy about every help in this problem!
Best wishes

model: https://drive.google.com/open?id=107LINBOhmZtR_uzkJhYKgNb8POFVLMX6
 

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I was able to solve the problem in the meantime :-)
 
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MarcelComsol said:
I was able to solve the problem in the meantime :-)
Can you tell us how you did it?
 
Hi DrClaude

The problem was the propagation constant of my ports...

My current understanding of the propagation constant is that it must correspond to the vertical component of the wave vector. It must also have a positive sign, otherwise the wave will propagate upwards.
(Provided that the wave should propagate in the negative y-axis and the coordinate system is defined that the y-axis points upwards)
 
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