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Modelling the scattering cross section off an infinite cylinder

Posted Dec 14, 2020, 3:21 p.m. EST RF & Microwave Engineering, Geometry, Parameters, Variables, & Functions Version 5.6 4 Replies

Koorosh Esteki
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Hello Everyone,

I am new user of COMSOL, my intension is to derive the optical properties of an infinite cylinder such as scattering, extinction and absorption cross sections. I already simulated the the results using the Mie theory in matlab, but my simulation using the COMSOL does not match. I know the matlab one is correct, but they do not match. I have gone through the steps by this tutorial: https://www.youtube.com/watch?v=8u4pNpf0N2o Instead I have cylinder rather than sphere. I also changed the length of my cylinder to be 20 times the diameter so that it is long enough. So, my question is that how you model an infinite cylinder? Thank you

4 Replies Last Post Dec 17, 2020, 11:50 a.m. EST
Robert Koslover Certified Consultant
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Posted: 4 years ago Dec 15, 2020, 5:06 p.m. EST
Updated: 4 years ago Dec 15, 2020, 5:14 p.m. EST

Perhaps you could post your model to the forum? In a 3D model, have you considered employing a cylinder that is modeled as centered within a cylindrical computational volume, where your scattering cylinder is continuous from one computational end-cap boundary to the other, and then making use of Floquet boundary conditions on the end-cap faces (i.e., those perpendicular to the cylinder axis), so as to effectively extend the cylinder to infinity? (I also wonder if you might even be able to get away with simple scattering boundary conditions, in this case.)

-------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
Perhaps you could post your model to the forum? In a 3D model, have you considered employing a cylinder that is modeled as centered within a cylindrical computational volume, where your scattering cylinder is continuous from one computational end-cap boundary to the other, and then making use of Floquet boundary conditions on the end-cap faces (i.e., those perpendicular to the cylinder axis), so as to effectively extend the cylinder to infinity? (I also wonder if you might even be able to get away with simple scattering boundary conditions, in this case.)
Koorosh Esteki
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Posted: 4 years ago Dec 17, 2020, 11:19 a.m. EST
Updated: 4 years ago Dec 19, 2020, 3:57 a.m. EST

Thanks for your reply. It is 3D model. I have attached it for you.

Thanks for your reply. It is 3D model. I have attached it for you.
Robert Koslover Certified Consultant
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Posted: 4 years ago Dec 17, 2020, 11:48 a.m. EST

I haven't taken the time to understand your whole model, but I can see that your electric field and k vector are both in a plane perpendicular to the axis of the cylinder. This makes your problem easier! Combined with the fact that you are interested in an infinitely long cylinder, this means you should probably do this whole problem in 2D, representing the cylinder by a circle (the effectively-infinite cylinder would be perpendicular to your 2D plane). So I encourage you to attack the problem in 2D. If that works well, you can consider more general wave incidence conditions in a 3D model.

-------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
I haven't taken the time to understand your whole model, but I can see that your electric field and k vector are both in a plane *perpendicular* to the axis of the cylinder. This makes your problem easier! Combined with the fact that you are interested in an infinitely long cylinder, this means you should probably do this whole problem in 2D, representing the cylinder by a circle (the effectively-infinite cylinder would be perpendicular to your 2D plane). So I encourage you to attack the problem in 2D. If that works well, you can consider more general wave incidence conditions in a 3D model.
Koorosh Esteki
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Posted: 4 years ago Dec 17, 2020, 11:50 a.m. EST

Ok, I will try it in 2D.

Ok, I will try it in 2D.

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