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surface charge density - RF module
Posted Oct 21, 2014, 8:33 a.m. EDT Version 4.3a, Version 4.3b 2 Replies
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Hello everyone,
I am a little bit confused and I would be grateful for your help regarding the calculation of surface charge density on a gold nanoparticle in glass in comsol (RF module). Here is how I get the surface charge density on the gold nano sphere surface (by using Gauss Law):
Rho = (d(emw.Ex,x)+d(emw.Ey,y)+d(emw.Ez,z))*n_glass^2
where, n_glass = 1.5, which is the refractive index of the glass.
Is this correct/best way to do this or is there any other/better way of getting the charge density?
My surface plot for this 'Rho' looks really coarse even though I have a really high resolution during Meshing.
ps: On the related note, could someone tell me how could I get the polarization charge distribution?
Any light on this topic would be much appreciated :)
Thanks in advance,
I am a little bit confused and I would be grateful for your help regarding the calculation of surface charge density on a gold nanoparticle in glass in comsol (RF module). Here is how I get the surface charge density on the gold nano sphere surface (by using Gauss Law):
Rho = (d(emw.Ex,x)+d(emw.Ey,y)+d(emw.Ez,z))*n_glass^2
where, n_glass = 1.5, which is the refractive index of the glass.
Is this correct/best way to do this or is there any other/better way of getting the charge density?
My surface plot for this 'Rho' looks really coarse even though I have a really high resolution during Meshing.
ps: On the related note, could someone tell me how could I get the polarization charge distribution?
Any light on this topic would be much appreciated :)
Thanks in advance,
2 Replies Last Post Oct 23, 2014, 3:53 a.m. EDT
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Posted:
1 decade ago
I'll address the first part of your question.
First, it looks like your approach was to try to compute a volume charge density, not a surface charge density. In a perfect conductor, the surface charge density follows from Gauss's law, and is directly proportional to the normal component of the electric field at the surface, so you you don't need to compute the divergence of E. (This change will probably help you a lot, in terms of numerical noise.)
So in your case, this would be:
surface charge density = epsilon0_const*(nx*emw.Ex+ny*emw.Ey+nz*emw.Ez)*n_glass^2
p.s. Don't forget the factor: epsilon0_const . You left that out in your expression (it is not part of n_glass).
Also, be sure to evaluate the above as a surface plot upon the surface in question, and not as volume plot, slice plot, etc., because otherwise Comsol may not understand the surface unit normal (nx,ny,nz) variables properly.
First, it looks like your approach was to try to compute a volume charge density, not a surface charge density. In a perfect conductor, the surface charge density follows from Gauss's law, and is directly proportional to the normal component of the electric field at the surface, so you you don't need to compute the divergence of E. (This change will probably help you a lot, in terms of numerical noise.)
So in your case, this would be:
surface charge density = epsilon0_const*(nx*emw.Ex+ny*emw.Ey+nz*emw.Ez)*n_glass^2
p.s. Don't forget the factor: epsilon0_const . You left that out in your expression (it is not part of n_glass).
Also, be sure to evaluate the above as a surface plot upon the surface in question, and not as volume plot, slice plot, etc., because otherwise Comsol may not understand the surface unit normal (nx,ny,nz) variables properly.
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Posted:
1 decade ago
First of all thank you for your quick response! That answered my question to the point. You are right about the epsilon0_const, by mistake I forgot to include that when i was writing the post. So the equation I used was for the total charge density (for the volume case) with the del dot E. Please correct me if I am wrong.
I have another question though, I want to plot this surface charge distribution in matlab now and I know how to export the data from comsol to matlab, but I am having a hard time plotting the 3D surface charge density plot. Any convenient way of doing it? I tried mphplot function with Matlab LiveLink but I wanted to use the streamslice function of Matlab to show the electric field lines around the sphere's surface and I cannot control that with mphplot or could I?
Thanks once again for your kind help. My confusion is gone :)
I have another question though, I want to plot this surface charge distribution in matlab now and I know how to export the data from comsol to matlab, but I am having a hard time plotting the 3D surface charge density plot. Any convenient way of doing it? I tried mphplot function with Matlab LiveLink but I wanted to use the streamslice function of Matlab to show the electric field lines around the sphere's surface and I cannot control that with mphplot or could I?
Thanks once again for your kind help. My confusion is gone :)