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PML problem in groove waveguide

Posted Mar 17, 2014, 2:41 p.m. EDT RF & Microwave Engineering Version 5.2a 6 Replies

Carlos Gonzalez-Ballestero
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Hi,

I have been trying to simulate the radiation pattern of a small dipole inside a groove carved into a gold substrate (transversal shape is triangular). The simulation box is rectangular, and I set 4 out of the 6 sides to Perfectly Matched Layer (the other two are the basis of the metallic region, which I set to PEC, and the face containing the dipole, where I have PMC in order to set a symmetry plane). The sides where I have PML end in a scattering boundary condition plane.

Although my box is reasonably large, I just don't manage to get rid of the reflections appearing in the electric field (in all directions!! but specially along the axis of the waveguide). I have tried varying PML thickness, PML mesh type, size and distribution, as well as PML scaling factor. I changed from version 4.2a into 4.3 to try the same as well. None of these tries reduced the reflections. Moreover, the field actually seems to be absorbed in the PMLs!! This suggests it may not be a PML problem but a size issue. However, by increasing the dimensions of my simulation box the result don't change either! I know for sure that people is able to solve this problem with smaller boxes than mine in V3.5 so I am quite perplex and don't know where the error might be. Has anyone of you had the same problem? Any clue of what may be going wrong?

Thank you all in advance. Best,

Carlos
6 Replies Last Post Oct 14, 2016, 9:55 a.m. EDT
Pu
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Posted: 1 decade ago Mar 18, 2014, 4:31 a.m. EDT
Hi, Carlos!

Good to see you here~

How's the geometry of your model looking like? It might help people here get an idea of the question that you upload a figure of the model.

Cheers!
--
Pu, ZHANG
DTU Fotonik
Hi, Carlos! Good to see you here~ How's the geometry of your model looking like? It might help people here get an idea of the question that you upload a figure of the model. Cheers! -- Pu, ZHANG DTU Fotonik
Carlos Gonzalez-Ballestero
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Posted: 1 decade ago Mar 24, 2014, 7:33 a.m. EDT
Hi Pu!

Thanks a lot for answering! I attach an image of my model :) any idea how to make the PMLs work? maybe I should switch from a rectangular box to a quarter of a sphere...

Best,

Carlos
Hi Pu! Thanks a lot for answering! I attach an image of my model :) any idea how to make the PMLs work? maybe I should switch from a rectangular box to a quarter of a sphere... Best, Carlos

Attachments:

Pu
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Posted: 1 decade ago Mar 24, 2014, 8:28 a.m. EDT
I think the problem might be due to the metal. You can check if there's decaying modes along the wedge which will become propagating in PML.

Another thing, from the image it seems the metal substrate is not very thick. Is it enough to absorb the radiation? If not, the PEC boundary could induce reflection as well.

You can try to use a dielectric instead of metal and see if the reflection persists, in order to check if it is metal that causes the problem.

Best!
--
Pu, ZHANG
DTU Fotonik
I think the problem might be due to the metal. You can check if there's decaying modes along the wedge which will become propagating in PML. Another thing, from the image it seems the metal substrate is not very thick. Is it enough to absorb the radiation? If not, the PEC boundary could induce reflection as well. You can try to use a dielectric instead of metal and see if the reflection persists, in order to check if it is metal that causes the problem. Best! -- Pu, ZHANG DTU Fotonik
Carlos Gonzalez-Ballestero
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Posted: 1 decade ago Mar 28, 2014, 5:25 a.m. EDT
Hey Pu,

Thank you very much for your suggestions. I thickened the metal region a couple hundreds of nm, that should be enough. After that, I changed the metal into a dielectric and all the problems disappeared, so you were right! :) thank you for helping me find out where the problem was!

Now I am trying to wonder how to do it if both PMLs and (I presume) Scattering BC do not work with decaying modes. Is there a BC which is suitable for absorbing these modes? I have read about Convolutional PMLs, but I am pretty sure they are not implemented in COMSOL. Any suggestion?

Thank you very much again!! BEst,

Carlos
Hey Pu, Thank you very much for your suggestions. I thickened the metal region a couple hundreds of nm, that should be enough. After that, I changed the metal into a dielectric and all the problems disappeared, so you were right! :) thank you for helping me find out where the problem was! Now I am trying to wonder how to do it if both PMLs and (I presume) Scattering BC do not work with decaying modes. Is there a BC which is suitable for absorbing these modes? I have read about Convolutional PMLs, but I am pretty sure they are not implemented in COMSOL. Any suggestion? Thank you very much again!! BEst, Carlos
Pu
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Posted: 1 decade ago Mar 28, 2014, 5:33 a.m. EDT
If the reflection does come from the evanescent wave, maybe you can extend the length of the groove and make it sufficiently decay before it reach PML?

Cheers!
--
Pu, ZHANG
DTU Fotonik
If the reflection does come from the evanescent wave, maybe you can extend the length of the groove and make it sufficiently decay before it reach PML? Cheers! -- Pu, ZHANG DTU Fotonik
Zhuanrong Xie
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Posted: 8 years ago Oct 14, 2016, 9:55 a.m. EDT
Hi


I'm trying to simulate the electric dipole emission near an IMI waveguide slabs(air-metal-air). i also found both PML and SCB doesn't work well. If you find some kind of boundary conditions which is good for absorbing these modes.


Thank you very much
Hi I'm trying to simulate the electric dipole emission near an IMI waveguide slabs(air-metal-air). i also found both PML and SCB doesn't work well. If you find some kind of boundary conditions which is good for absorbing these modes. Thank you very much

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