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Hi,
I am having issues with running a simulation on a model that im trying to recreate. Im trying to recreate the model in the following article. You can click the link to reach the article or you can simply download it from the attachment. I have created the model and im getting results that are not meaningful. I've only created topology A from the article. I've gone through the tutorials but i couldnt fix the issue no matter how much i tried. Can you help me fix please?
Link to the article
https://onlinelibrary.wiley.com/doi/abs/10.1002/mop.33959
Hi Ali,
I will have a look.
Best regards,Torben Voigt
You accidentally entered MHz instead of GHz I also recommend FEM for such closed waveguides, as the simulation is significantly faster and saves more memory than with MoM, see attached model.
Note, I didn't check correctness of the dimaensions in your model, also didn't check if mesh needs to be refined.
Best regards,Torben
At first glance, it looks as if the dipoles are not centered in the z-direction. Is that correct?
And I believe that the overlapping dipoles should have different lengths (L1 and L2), right?
Hi Ali, You accidentally entered MHz instead of GHz I also recommend FEM for such closed waveguides, as the simulation is significantly faster and saves more memory than with MoM, see attached model. Note, I didn't check correctness of the dimaensions in your model, also didn't check if mesh needs to be refined. Best regards,Torben
Hi Torben,
i think you are running an old version of feko. Because i get some kind of incompatibility error while trying to open the file on the attachment. Thanks for the effort though.
Best regards,
Ali
Hi Torben, i think you are running an old version of feko. Because i get some kind of incompatibility error while trying to open the file on the attachment. Thanks for the effort though. Best regards, Ali
I'm using the latest release, which is Feko 2024.0.1 (Feko 2024.1 is about to be released in the next days).
Once you have installed Feko 2024 and updated to 2024.0.1, you should use the new attached model test_FEM_newly_created.cfx. I recreated it based on the paper and the results look promising:
Hi Ali, Once you have installed Feko 2024 and updated to 2024.0.1, you should use the new attached model test_FEM_newly_created.cfx. I recreated it based on the paper and the results look promising: Best regards,Torben
It appears that as a student ı can only access the 2023 version of feko. I wont be able to open the project you sent me. Would you please tell me the changes you ve made on my project?
Sincerely
At first glance, it looks as if the dipoles are not centered in the z-direction. Is that correct? And I believe that the overlapping dipoles should have different lengths (L1 and L2), right?
I didnt realize that the dipoles were not centered in the z axis. Also the length of L1 and L2 are the same i think.
I just re-build the model again from scratch in Feko 2023.1.2. Please check, if length and width of the dipoles is correct. For me, the information in the paper is somehow unclear.
Hi Ali, I just re-build the model again from scratch in Feko 2023.1.2. Please check, if length and width of the dipoles is correct. For me, the information in the paper is somehow unclear. Best regards,Torben
Your model works very well. Thank you for your time and work. I ve learned a lot from your model. I tried to mimic your model to get the same results but even so, i failed. Can you show me what i am missing? Thanks in advance.
Sincerely,
It is very important to pay attention to whether the outer surfaces of the dipoles are defined as "PEC" or "default"! With "default", they become dielectric boundaries as soon as you set the inner surface to Air. If I were you, I would simply define the dipoles as PEC rectangles (as in my model 2023_FEM_newly_created.cfx). The thickness of 35 µm is thick enough that no losses due to skin effects are to be expected. You get a simpler model and faster results with PEC rectangles
I recorded the steps I did, so you can see how I apply the changes to your model.
I see now that the results in the "RepairedModel" are still significantly different from mine. I'll have to check what you did differently.
Ok, now I see that you used different lengths for the dipoles. I used "L1" (29.4 mm) and "L2" from the paper, you used 20 mm. Also for the widths of the dipoles I used "w1" (2 mm )and "w2" (2 mm) from the paper, you used 1.5 mm.
Thus, the models are different.
My model has been corrected for the most part thanks to your efforts. But one small issue is that i see a ripple other than the 2 resonant frequencies. Any idea why this happens? Your model with the Rectangular dipoles had it as well but it was relatively smaller. I sketched the same model in CST studio and the results dont show any ripples. Thanks in advance.
Ali Emir Uğurluoğlu
Hi Torben, My model has been corrected for the most part thanks to your efforts. But one small issue is that i see a ripple other than the 2 resonant frequencies. Any idea why this happens? Your model with the Rectangular dipoles had it as well but it was relatively smaller. I sketched the same model in CST studio and the results dont show any ripples. Thanks in advance. Sincerely, Ali Emir Uğurluoğlu
This sometimes occurs when using "continuous (interpolated) range". It is possible that an improved mesh will fix this, but you would have to try it out. I would start by meshing the dipoles a little more finely. If you were to use "linearly spaced discrete points", you would probably not have this problem, but you would probably have to simulate several thousand frequencies...
Try this:
It works for me in Feko 2024.0.1
Try this: It works for me in Feko 2024.0.1
I made the change and it didn't work at all. Do you have any other suggestions?
Here is my model and results. Not sure why your model behaves different, but most likely your dipoles (cuboids) require much finer meshing. As I said, I recommend rectangles.
I should do it with rectangles i guess. cant get rid of the ripples even testing with many frequencies. Thanks for the help Torben, you're doing god's work!
I should do it with rectangles i guess. cant get rid of the ripples even testing with many frequencies. Thanks for the help Torben, you're doing god's work! Sincerely, Ali Emir Uğurluoğlu
For the sake of interest, I will also try it with 35 µm thick cuboids.
Here is my model with physical thickness. There is no ripple in the result. I think with such thin regions you have to measure accordingly fine. In my case, the dipoles are meshed with 35 µm * 20. You can investigate whether you can enlarge the mesh again until the ripples reappear. Fortunately, such a fine mesh in FEM does not immediately mean that memory and runtime explode (in contrast to MoM).
You probably know that one should always perform a Mesh Convergence Stufy to check whether the mesh is fine enough. Of course, in 99% of cases you don't feel like it and don't do it...:) If you don't want to do this manually, you can use AMRFEKO. I would recommend setting the threshold to Low. Here is a video about AMRFEKO: https://www.youtube.com/watch?v=pmKj63tsXVQ&t=597s
AMRFEKO didnt work, though the ripple was smaller. The interesting issue is that i dont get any ripples at topology B where the same sided dipoles are not parallel but 45 degrees apart. You changed the meshing of dipole faces to 35e-3* 20. you mean by 35 micrometer *20 , its 35e-3 right?
As I said, ripples sometimes occur when continuous frequency range is used. In many cases this can be remedied by using a finer mesh (here 20* thickness of cuboids). You have to bear in mind that with your dipoles with a physical thickness of only 35 µm, there is an extremely small distance between the top and bottom of the dipoles. This can lead to the need for such a fine mesh. Apparently, interesting phenomena occur there at a certain frequency. I chose the value more or less at random, a larger mesh might also work.
With rectangles instead of cuboids, we wouldn't even be having this whole discussion
