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boundary mode study for electromagnetism

Posted Apr 6, 2011, 3:32 p.m. EDT Version 4.1 3 Replies

Yuting Huang
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Hi!

I'm doing wave propagation in a 3D waveguide.My model is just like the adapter model in the module library. I have two numerical ports. For the study, I have two boundary mode analysises for the ports, and then frequency domain analysis. I realize my result changes when I change the "Desired Number of Modes". For some frequencies, there are more than one mode, for example, like 3 modes possible in the waveguide, should I always put 3 for the desired mode number for example? Or if I just want the 3rd lowest mode, then should I put in 1?

I don't know how the desired mode number influences my solution here. Can someone help please? I don't know if I get a single mode or a combination of all possible single modes depending on the desired number of modes I choose?

Thanks!

Tina H.
3 Replies Last Post Apr 8, 2011, 2:28 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 7, 2011, 1:50 a.m. EDT
Hi

I'm not sure I fully understand your model description, but if you use the modal solvers, in all generality, they are based on modal development, to 1,2,3 ...n modes order so the more you add (the longer it takes) but the more precise it "should" be.

It all depends on how to sort the modes, sometimes it's not the three first that are the most important, from what I understand with COMSOL you can only choose, currently, the 1 to n first, and not (yet?) randomly from a list

--
Good luck
Ivar
Hi I'm not sure I fully understand your model description, but if you use the modal solvers, in all generality, they are based on modal development, to 1,2,3 ...n modes order so the more you add (the longer it takes) but the more precise it "should" be. It all depends on how to sort the modes, sometimes it's not the three first that are the most important, from what I understand with COMSOL you can only choose, currently, the 1 to n first, and not (yet?) randomly from a list -- Good luck Ivar
Yuting Huang
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Posted: 1 decade ago Apr 7, 2011, 4:41 p.m. EDT
Hi Ivar,

Thanks for your reply!

So just to clarify, if I put n in the "Desired Number of Modes" in the boundary mode study, I get the 1st, 2nd, ....., and the nth modes seperately? But in the result I only get one mode, so I don't which mode I'm getting, can be any of n modes right? Or am I get a superposition of the 1-n th modes together?

Tina H.
Hi Ivar, Thanks for your reply! So just to clarify, if I put n in the "Desired Number of Modes" in the boundary mode study, I get the 1st, 2nd, ....., and the nth modes seperately? But in the result I only get one mode, so I don't which mode I'm getting, can be any of n modes right? Or am I get a superposition of the 1-n th modes together? Tina H.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 8, 2011, 2:28 a.m. EDT
Hi

from my understanding, but I haven't really tested the waveguide examples that much, the easiest way to answer is to plot the modes shapes for your ports (plot the results of the stored solutions) these show you the field at the ports, clearly, if several modes might coexist and you as for 3 it will take the three closest to the "search for ...", Exactly which modes I'm not sure, you must deduce that from the E field shapes.

I'm rather sure your E field results will depend strongly on the E field of the input port(s), hence on the modes and number of modes all over,
But I also believe that even if you have several modes at the input, depending on what you are doing in the waveguide, then you might not get all natural port modes at the output

--
Good luck
Ivar
Hi from my understanding, but I haven't really tested the waveguide examples that much, the easiest way to answer is to plot the modes shapes for your ports (plot the results of the stored solutions) these show you the field at the ports, clearly, if several modes might coexist and you as for 3 it will take the three closest to the "search for ...", Exactly which modes I'm not sure, you must deduce that from the E field shapes. I'm rather sure your E field results will depend strongly on the E field of the input port(s), hence on the modes and number of modes all over, But I also believe that even if you have several modes at the input, depending on what you are doing in the waveguide, then you might not get all natural port modes at the output -- Good luck Ivar

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