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Dealing with Periodic Boundary Conditions, PMLs and interfaces.

Posted 09.11.2012, 05:36 GMT-5 RF & Microwave Engineering, Geometry, Mesh, Parameters, Variables, & Functions Version 4.2a 2 Replies

Yggdrasil
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Hello, I'm trying to simulate a nanoparticle array over a substrate in order to study its extinction cross-section. To do so I've made a cell with periodic boundary conditions on the sides and two PMLs under and above. I'm starting with a simple model, just two medias of different refractive index and a plane wave propagating in the perpendiuclar direction to the interface.

I'm solving for the scattered field and I set my background field as a plane wave. My first doubt comes here, if I have two different medias, should I define analytically different plane waves for each media (changing the refractive index in the exponential)? Or can I just define the plane wave in the first media and comsol will do the rest, provided the refractive index of the other material?

I use Scattered Boundary Conditions in the external faces of my PMLs, should I use it in all the external faces or just the perpendicular to the direction of the wave (setting PBC on the sides)?

Another problem that I have with respect to the PMLs is that I don't know how to do a swept mesh correctly. I always get problems of geometrical mismatch in the face near the other meshed domain.

Any help will be highly appreciated.
2 Replies Last Post 19.11.2012, 06:34 GMT-5
Alexander Kuznetsov
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Posted: 1 decade ago 12.11.2012, 15:42 GMT-5
don't use scattered field formulation. Instead, use "port" boundary condition to set up excitation.It makes the setup much easier.

Scattered BC is good for PML. But it general it shouldn't matter. It PML's BC change anything - then your PML is not large enough.
don't use scattered field formulation. Instead, use "port" boundary condition to set up excitation.It makes the setup much easier. Scattered BC is good for PML. But it general it shouldn't matter. It PML's BC change anything - then your PML is not large enough.
Yggdrasil
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Posted: 1 decade ago 19.11.2012, 06:34 GMT-5
Thanks for the suggestion, Alexander.

In principle if I use Total Field formulation the setting would be much easier because I would only need to set the incoming wave and COMSOL would solve the propagation too. But with PBC and different substrates I think I would have to set a great number of port conditions to ensure that I don't get unphysical reflections (I can't put PMLs on the sides). Also, I need the Scattered Field in order to calculate the extinction cross-section. Otherwise I think I would have to simulate the model two times to get the scattered field: one without the NP and another one with the NP. That seems like a waste of resources. Anyway, I still haven't use Total Field formulation in deep so probably I'm talking nonsense... I will try some things, anyway.


With Scattered Field Formulation I just have to calculate analitically the propagation of the wave, set it manually as the background field and just extract the scatterred field (E-Eb).

Also, I still haven't found the way to swept meshing the PMLs... Anyone know how to properly mesh a rectangular substrate into layers?
Thanks for the suggestion, Alexander. In principle if I use Total Field formulation the setting would be much easier because I would only need to set the incoming wave and COMSOL would solve the propagation too. But with PBC and different substrates I think I would have to set a great number of port conditions to ensure that I don't get unphysical reflections (I can't put PMLs on the sides). Also, I need the Scattered Field in order to calculate the extinction cross-section. Otherwise I think I would have to simulate the model two times to get the scattered field: one without the NP and another one with the NP. That seems like a waste of resources. Anyway, I still haven't use Total Field formulation in deep so probably I'm talking nonsense... I will try some things, anyway. With Scattered Field Formulation I just have to calculate analitically the propagation of the wave, set it manually as the background field and just extract the scatterred field (E-Eb). Also, I still haven't found the way to swept meshing the PMLs... Anyone know how to properly mesh a rectangular substrate into layers?

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