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TEM Wave Propagation

Posted Dec 10, 2010, 1:08 p.m. EST RF & Microwave Engineering, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.0, Version 4.0a, Version 4.1 3 Replies

Nathan Ridling
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Greetings,

I am trying to do some second harmonic generation (in 2D) by sending a wave packet in from a boundary as a function of space and time. I am specifying the wave as a propagating Gaussian. The problem seems to be that COMSOL 4.0 and up will not allow this to work properly. In version 3.5, the wave propagates without problem, but with 4.0 and later the wave sits on the boundary. The time dependent portion looks to be working, but the spacial part does not. I imagine that when I use an expression such as cos( k*x - omega*t ) on a boundary, the value that is used for x is the x coordinate of the boundary only (which is a single value because the boundary is vertical).

If anyone has any ideas, they would be most appreciated. I have attached a version 4.1 file to this post since it is fairly small. It is a time dependent study, so if you run the solver, you will want to view the animation in the player.

Thanks so much,
Nathan

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3 Replies Last Post Dec 16, 2010, 2:04 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 12, 2010, 9:32 a.m. EST
Hi

first of all when you do the movie you have the usual autoscale effect that gives very wrong impressions. Try to step through time plot by time plot.
But then to understand it better use a more symmetric boundary conditions (I disables you right scattering condition and the bottom perfect magnetic conduction, keeping all perfect electric conduction.

Then by looking at the Ez field along the left scattering boundary (line plot) I notice its rather clipped, so your waist is rather large compared to the modelling domain and the edge effects are rather large, and finally by cutting the block into 4 identical sub blocks by adding two split lines passing by the rectangle centre I observe a Ez field (line plot) that is nicely absorbed, I do not really see what is wrong ?

--
Good luck
Ivar
Hi first of all when you do the movie you have the usual autoscale effect that gives very wrong impressions. Try to step through time plot by time plot. But then to understand it better use a more symmetric boundary conditions (I disables you right scattering condition and the bottom perfect magnetic conduction, keeping all perfect electric conduction. Then by looking at the Ez field along the left scattering boundary (line plot) I notice its rather clipped, so your waist is rather large compared to the modelling domain and the edge effects are rather large, and finally by cutting the block into 4 identical sub blocks by adding two split lines passing by the rectangle centre I observe a Ez field (line plot) that is nicely absorbed, I do not really see what is wrong ? -- Good luck Ivar
Nathan Ridling
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Posted: 1 decade ago Dec 15, 2010, 12:09 p.m. EST
The problem is that I want the wave to propagate through the solution space, not get absorbed on the left boundary.
The problem is that I want the wave to propagate through the solution space, not get absorbed on the left boundary.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 16, 2010, 2:04 a.m. EST
Hi

and that is what I see when I look at the images one by one in the main view, but the movie has a "global" colour scale that give the impression that nothing is radiating

--
Good luck
Ivar
Hi and that is what I see when I look at the images one by one in the main view, but the movie has a "global" colour scale that give the impression that nothing is radiating -- Good luck Ivar

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