Discussion Forum

Posted: 1 decade ago Jan 22, 2011, 1:15 a.m. EST

Try setting width of your PML to lambdaS_xyz where xyz is the suffix of the application mode you are using.

Posted: 1 decade ago Jan 22, 2011, 1:18 a.m. EST

Just to clarify, I don't mean the actual geometrical width of the object, but in the subdomain settings where you enable PML, there is an option of width. Remove the original thing with the one I mentioned above.

Posted: 1 decade ago Jan 24, 2011, 10:39 a.m. EST

Hi, Thanks for replying. I am guessing that'll stretch the coordinate of the PML region and make it one lambda thick, right? That doesn't seem to be working, unfortunately. it did not fix my problem and I am still getting reflections from the PML. I think the reflection would have something to do with trying to terminate a negative epsilon medium. But I am not sure what I can change to fix that. Yan

Posted: 1 decade ago Jan 24, 2011, 10:45 a.m. EST

Hi For your PML "material properties" are you using "air" or the same as the surrounding material? You might need to split your PML and adapt to the non PML boundary material to avoid reflexions, if I remember right -- Good luck Ivar

Posted: 1 decade ago Jan 24, 2011, 12:17 p.m. EST

Upload your model. May be we can discuss after having a look at it. I have in the past dealt with the issue of metallic waveguides with negative permittivity extending into PMLs. And reflections did disappear, at least to the point of becoming invisible in the absolute field plot. And that is always as far as I have gone. Numerical effects always make sure that something comes back, however strong or weak.

Posted: 1 decade ago Jan 24, 2011, 1:10 p.m. EST

Hi, thanks a lot for taking a look. I have to reset the model because it was too big. You will have to remesh it before running. I used 'mapped mesh' for domain 1,2,3&9. The rest is just 'free mesh'. To summarize the model, I am looking for the eigenmode of the plasmonic waveguide (it's a leakymode), which is a metallic slot sandwiched in between air and glass. thanks.

Attachments:

• modeIndex_plasmonic_lossless_1550nm_comsolExchange.mph

Posted: 1 decade ago Jan 25, 2011, 11:41 a.m. EST

Sorry Yan, I didn't realize you were talking with respect to mode analysis problem. I have dealt with harmonic propagation problems in which metals conveniently protrude into PMLs without trouble. But this case does seem strange and I could not find any meaningful solution despite tweaking with various parameters.

Posted: 1 decade ago Jan 25, 2011, 12:20 p.m. EST

Hey, thanks a lot for trying to fix my model. I think despite using eigenmode simulation vs. harmonic propagation, the way that the PML is set up should be the same. It's weird that Comsol help is not responding lately. I think it used to give me a case number before anyone takes a look, but I haven't been getting that automatic reply at all. Does this happen to you lately? I am just curious...

Posted: 1 decade ago Jan 25, 2011, 3:10 p.m. EST

Hi Ivar, I did not use air as the material property. It's the same as it's non-PML neighbor. Yan

Posted: 1 decade ago Jan 26, 2011, 5:25 a.m. EST

Hello, no changes were made in the way notification messages from COMSOL Support are sent out. Here is how it works: * If you have no open case tickets, a mail message to support@comsol.com will generate an automatic notification to you with case number included. * If you already have an open case ticket, a new email to support@comsol.com will be silently appended to that open case. The support engineer who is assigned to the support case, as well as your COMSOL sales rep will get a notification and a copy of your mail. *If you have more than one open case tickets, you can control which case your email will end up in by using the syntax [Case: NNNN] included in the subject header. I hope this answers your questions. Niklas Rom, COMSOL [QUOTE] Hey, thanks a lot for trying to fix my model. I think despite using eigenmode simulation vs. harmonic propagation, the way that the PML is set up should be the same. It's weird that Comsol help is not responding lately. I think it used to give me a case number before anyone takes a look, but I haven't been getting that automatic reply at all. Does this happen to you lately? I am just curious... [/QUOTE]

Posted: 1 decade ago Feb 9, 2011, 1:20 a.m. EST

Hi, I m making a model of metamaterials in COMSOL. In my model PML is used around a glass slab. Can anyone suggest about the subdomain settings for PML having rank tensor properties?????? Or normal subdomain settings for PML so that glass slab shows reflectivity?? Please help me... Its urgent for me..

Posted: 1 decade ago Feb 9, 2011, 2:09 a.m. EST

Hi are you saying that you want the PML to be an infinite "metamaterial" ? I normally always have "air/vacuum" around my models so the PML is air, I have though used one "glass" and then cut up my PML radially (cylindrical symmetry) such to have part of it as an infinite glass slab and the rest air, to minimise any reflection from the transition material to PML. As by beams were roughly radial at PML level the edge and material change in the PML region did not distub me. I'm not sure how to make a PML fully anisotropic, or if the equations are compatible, one would need to look into the equation view, and make afew tests on simple cases -- Good luck Ivar

Posted: 1 decade ago Feb 9, 2011, 2:26 a.m. EST

Hi, Thanks for replying. I have attatched my geomatery file. please saw it. The entire geometry is made of six parts. R1 is the glass slab, R2-R5 are the PML and R6 is a rectangle whose sub domain properties are those of air. Now my question is this, what are the subdomain settings for PML, so that it slab shows reflectivity.

Posted: 1 decade ago Feb 9, 2011, 2:27 a.m. EST

The geomaery file is attached with this.

Attachments:

• geomatery.docx

Posted: 1 decade ago Feb 9, 2011, 3:38 a.m. EST

Hi if you have "air" around your PML should also be "air", by the way I mostly use circular PML centered at "0,0" I have noticed these mostly solve better -- Good luck Ivar

Posted: 1 decade ago Mar 30, 2011, 8:17 a.m. EDT

[QUOTE] are you saying that you want the PML to be an infinite "metamaterial" ? I normally always have "air/vacuum" around my models so the PML is air, I have though used one "glass" and then cut up my PML radially (cylindrical symmetry) such to have part of it as an infinite glass slab and the rest air, to minimise any reflection from the transition material to PML. As by beams were roughly radial at PML level the edge and material change in the PML region did not distub me. I'm not sure how to make a PML fully anisotropic, or if the equations are compatible, one would need to look into the equation view, and make afew tests on simple cases [/QUOTE] Dear all, We've also encountered problems with full rank tensor medium PML (in our case, the PML should model a infinite plasma medium), and worked a bit with the support on our case. So, here is what we experienced. It appears that COMSOL PML works generally fine when dealing with air/vacuum media (as Ivar Kjelberg explained it : metamaterial geometry are often located in the middle of the simulation space, and air-PML are put at the edges). However, things get more complicated for anisotropic (and/or negative index permittivity) media PML. In some case, it may be interesting to change the sign of the PML equations, for example changing the (1-i) into (1+i). But this may not work in all situations and as far as I know for the moment (v3.5 or v4.1), the COMSOL PML can't deal with all tensorial permittivity (especially when negative index are used). Best regards