Hello all, I also have similar problem. I managed to use flux regions to surround the sphere, do both null run and sample run and calculate absorption out of it by normalizing it to incident light intensity. However, the curve shows artificial peaks. By looking at the flux density for the null run. I found that even I used light source extends to PML layer, the plane wave isn't so exact. There is still a little divergence at the other direction. Furthermore, the intensity of incident light and exiting light from the box also have some differences. ( I was doing a 2-D simulation) As Alex mentioned that flux-box is the correct one to use for calculation, I looked up flux-box reference and it seems we need to do some scripting at C++ level as they were not wrapped to high-level yet. Look forward for some detailed explanation on that.
Message: 6 > Date: Wed, 22 Sep 2010 11:25:19 +0000 > From: jack swagger <[email protected]> > Subject: [Meep-discuss] Regarding Near field enhancement and > Scattering cross section > To: <[email protected]> > Message-ID: <[email protected]> > Content-Type: text/plain; charset="iso-8859-1" > > > Dear MEEP users! > As i mentioned before that i am trying to calculate the Near > field enhancement and scattering cross section of a nano sphere. Some of you > had made a few comments, thanks to them (especially to Stephan). But that > comments was not enough for me to solve the problem. > > In the code below i have tried to calculate the scattering cross section. > At 1st i run the simulation without a sphere, which was the total field, > then in the 2nd run i included the sphere and collect the field at each side > as given in the code. So the Scattered field would be: E-scattered = E_total > - E_incident, But i am not sure that this is correct or not. Please make a > few comments on this. > > I have also seen on the MEEP GROUP that Mr. Alexander S. McLeod has > suggested someone how to calculate the near field enhancement and the > scattering cross section. Sir, i have some questions from you. > - You have mentioned that to compute near field enhancement, just output > field values Ex, Ey, and Ez in the region of interest of your simulation > using a 2- or 3-D volume. Enhancement is given by > |E|^2=|Ex|^2+|Ey|^2+|Ez|^2. My question is that to find Ex, Ey and Ez, > should i choose three plans i.e. xy, yz and zx ? but in all these plans i > have to change the position and size of the source as well. For example in > the code given below, the postion of the source is (0 0 -0.6) and its size > is (1 1 0) and this is zx-plane, so to find Ey i will choose this plane. For > the xy-plane the position of the source would be (-0.6 0 0) and its size > would be (0 1 1), so here i will find Ez and so on. Am i correct. Please > clarify me here. > - You have also mentioned that to calculate the scattering cross section > you have to define 2-D volume surfaces that surround your structure in a > cubic fashion, and output the in-plane E and B-field components for each of > these volumes. Do the same with a "normalization" run. Obtain "scattered > field" values as E_scat=E_total-E_norm for each field component. My question > here is that from 2D volume surfaces you mean the same three planes as i > mentioned above i.e. xy, yz and zx ? And also tell me how to calculate > E_norm. Please clarify me here. I will be very thankful to you. > > Best regards, > Jack > > > > > (set! eps-averaging? false) > > (set! geometry-lattice (make lattice (size 1 1 2))) > > (set! geometry > > (list > > (make sphere (center 0 0 0) (radius 0.125) > > (material (make dielectric (epsilon 1) > > (polarizations > > (make polarizability > > (omega 1e-20) > > (gamma 0.052) > > (sigma 2.45e44)) > > )))) > > )) > > (set! pml-layers (list (make pml (thickness 0.2)))) > > (set! resolution 50) > > (define fcen 1.29) ; Pulse center frequency > > (define-param df 2) ; Pulse width (in frequency) > > (set! sources (list > > (make source > > (src(make gaussian-src (frequency fcen) (fwidth df))) > > (component Ey) > > (center 0 0 -0.6) > > (size 1 1 0) > > ) > > ) > ) > > (define-param nfreq 300) > > (define incident1 > > (add-flux fcen df nfreq > > (make flux-region > > (center 0 0 0.7) (size 1 1 0) (direction Z) > > ) > > )) > > (define incident2 > > (add-flux fcen df nfreq > > (make flux-region > > (center 0 0 -0.7) (size 1 1 0) (direction Z) > > ) > > )) > > (define incident3 > > (add-flux fcen df nfreq > > (make flux-region > > (center 0 0.7 0) (size 1 0 1) (direction Y) > > ) > > )) > > (define incident4 > > (add-flux fcen df nfreq > > (make flux-region > > (center 0 -0.7 0) (size 1 0 1) (direction Y) > > ) > > )) > > (define incident5 > > (add-flux fcen df nfreq > > (make flux-region > > (center 0.7 0 0) (size 0 1 1) (direction X) > > ) > > )) > > (define incident6 > > (add-flux fcen df nfreq > > (make flux-region > > (center -0.7 0 0) (size 0 1 1) (direction X) > > ) > > )) > > (run-sources+ (stop-when-fields-decayed 30 Ey (vector3 -0.65 0 0) 1e-3) > > (to-appended "y-efield" output-efield-y) > > ) > > (display-fluxes incident1 incident2 incident3 incident4 incident5 > incident6) > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://ab-initio.mit.edu/pipermail/meep-discuss/attachments/20100922/605c4b0a/attachment.htm > > > > ------------------------------ > > _______________________________________________ > meep-discuss mailing list > [email protected] > http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss > > End of meep-discuss Digest, Vol 55, Issue 17 > ******************************************** > -- Mike
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