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Far-field calculations bug in COMSOL version 4.1

Posted 22.03.2011, 05:28 GMT-4 RF & Microwave Engineering Version 4.1 0 Replies

Martin Ploschner
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For those of you doing calculations of far-field in RF module, please be aware of the fact that it works correctly only for vacuum case. I have compared scattering cross-sections of gold nanoparticles with Mie and it works very well for vacuum around the particle. However, the moment you switch to different medium, the scattering cross-sections of Mie and COMSOL differ significantly. COMSOL support told me that it will be fixed in next release in May or June. If you need the correct results right now, here are some workarounds

1) Going few lambda away from the scatterer and integrating scattered field usually gives good results, but the number of mesh points is huge.

2) Introducing very thin vacuum layer around the scatterer and integrating far-field on the surface in the middle of this vacuum layer works well, but the mesh requirements are again huge.

3) Let's say you need solution for lambda0=800nm in water n_w=1.33. You can run the simulation for lambda0/1.33 with n_w=1 and change the permittivity of gold from e_re(f)-i*e_im(f) to 1/(1.33^2)*(e_re(f/1.33)-i*e_im(f/1.33)). This results in equivalent problem and built-in Stratton-Chu far-field works well.

Might be a bug in other versions of COMSOL too. I would check it if I were you.

Hope this helps.

Martin
0 Replies Last Post 22.03.2011, 05:28 GMT-4
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