Discussion Forum

Hi

for me it looks like your lateral sides are not "Perfectly" matched and you have reflexion from mthe lateral sides interacting, but this is just a guess.

In which version are you ? use the new forum tags, it helps us others udnerstand better too ;)

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Good luck
Ivar

I am experiencing the same issue in a scattering model using Comsol 4.0.0.937. The particle is located at the origin, then we have some space and the outer subdomain is a PML boundary (See attached file pml_air.png).

If I use air in the surrounding and the PML subdomains, the solution looks nice. If I switch both permittivities to some value unequal 1, I get severe errors in the solution. (See pml_glass.png). I also tried setting the permittivity of the PML region equal to 1 and the surrounding of the particle to some value unequal 1. Same wrong results.

Seems like these are UPML (UnPerfectly Matched Layers ;o)). Unfortunately, the documentation is not of much help here. Has anyone experienced the same issue or does anyone have an idea?

Best regards!

For the expression of incident wave in 'Scalar Variables', the wavevector k0 should be corrected as sqrt(epsilon)*k0, in which the epsilon is the permittivity of surrounding. My COMSOL version is 3.5a, and I did not know if this solution would work in COMSOL4.0. Good luck!

Hi

an check that you have latest patch, fo me today this means 4.0.0.993, see tha main COMSOL web site

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Good luck
Ivar

Hi!

Thanks for hinting me at the wave vector definition. sqrt(epsilon)*k0 indeed did the trick. This is somehow inconvenient, because when changing the material of the surrounding domain, you'll also have to change the incident field definition. The only solution I see so far is to adding a global variable with the refractive index.

By the way: Is there a complete variable reference for emw.*? Haven't been able to find one so far.

Thanks and best regards!

Christian

I also have not seen variable of this kind. :)


He Kaiting

Hi

but epsilon and "n" the refractive index are linked to the spped of light no ?

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Good luck
Ivar

Hi!

In a medium with refractive index n the speed of light is c=c0/n, where c0 is the _vacuum_ speed of light. In terms of the wave vector, in a medium with refractive index n, the wave vector is k=k0*n. The refractive index and the permittivity epsilon are related by sqrt(epsilon)=n.
So in the Comsol model, we use the free space wave vector emw.k0 to specify the wave. This is somewhat confusing, because I would have expected Comsol to scale the wave vector automatically in a medium with n!=1, but it seems like it does not.

Hi

ideally we should have this confirmed by COMSOL support, no ?
(PS I'n not by COMSOL ;)

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Good luck
Ivar

Yes, you are right. I had this issue in 3.5a already and the support told me to rescale the wave vector. I'll contact the support.