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Near field/Far Field of scatered light from a nanoparticle

Posted Mar 30, 2013, 4:43 a.m. EDT 9 Replies

Snehanshu MAiti
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Hi,I am simulating in Comsol 4.2.

In my simulation domain ,2 micrometer by 2 micrometer,the upper portion is air and the lower surface is glass.A nanoparticle of 300 nm is placed at the interface(halfway in my simulation domain).I want to analyse the fields(near and far field) after light been incident from the top surface of my simulation domain and scattered by the particle.
I am using scattered boundary conditions for my simulation domain boundaries (i dont kno if that is correct)

I want to know how to analyse the far field here.I will be looking forward to the detailed steps.I also want to know if my boundary conditions are correct.I am using 2D model

I will be waiting eagerly for the kind reply and the solution

Regards
9 Replies Last Post Apr 1, 2013, 6:35 a.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Mar 30, 2013, 6:53 a.m. EDT
Hi,

you must define a far field domain under the emw node. This will make the far field variables available in the post processing.
3D far field post processing is very expensive. A 3D far field plot may take longer to calculate than the solution of the model. 2D plots like typical antenna radiation patterns are fairly fast.

Cheers
Edgar
Hi, you must define a far field domain under the emw node. This will make the far field variables available in the post processing. 3D far field post processing is very expensive. A 3D far field plot may take longer to calculate than the solution of the model. 2D plots like typical antenna radiation patterns are fairly fast. Cheers Edgar
Snehanshu MAiti
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Posted: 1 decade ago Mar 31, 2013, 9:09 a.m. EDT
Please tell me about the boundary conditions of my simulation domain.I have taken scattering boundary condition across all the 4 boundaries.IS it okay?Or do i need to introduce PEC bondary condition instead of scatter
Please tell me about the boundary conditions of my simulation domain.I have taken scattering boundary condition across all the 4 boundaries.IS it okay?Or do i need to introduce PEC bondary condition instead of scatter
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Mar 31, 2013, 9:46 a.m. EDT
With a PEC at the outer boundary all radiation gets reflected into the domain. That is probably not what you want if you are interested in the far field.

You should probably add a PML around the scattering boundary.

--
Edgar J. Kaiser
www.emphys.com
With a PEC at the outer boundary all radiation gets reflected into the domain. That is probably not what you want if you are interested in the far field. You should probably add a PML around the scattering boundary. -- Edgar J. Kaiser http://www.emphys.com
Snehanshu MAiti
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Posted: 1 decade ago Mar 31, 2013, 12:42 p.m. EDT
i have attached the images of my simulation;one for normalized far field and the other for magnetic field(Hz)
The plot for Hz makes sense but not the Far field plot.I assume there is some terrible mistake in my simulation as far as the result is concerned.Kindly Help
i have attached the images of my simulation;one for normalized far field and the other for magnetic field(Hz) The plot for Hz makes sense but not the Far field plot.I assume there is some terrible mistake in my simulation as far as the result is concerned.Kindly Help

Attachments:

Snehanshu MAiti
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Posted: 1 decade ago Mar 31, 2013, 12:45 p.m. EDT
it seems as if at the interface from the left most cornet light is coming.There is a tiny white spot there which come s out while finding Farfield norm.I donot understand why this crazy result is ha penning!!This comes only during far field simulation
it seems as if at the interface from the left most cornet light is coming.There is a tiny white spot there which come s out while finding Farfield norm.I donot understand why this crazy result is ha penning!!This comes only during far field simulation
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Mar 31, 2013, 1:48 p.m. EDT

Without seeing the model and all the settings it is difficult to say what's wrong.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
Without seeing the model and all the settings it is difficult to say what's wrong. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Snehanshu MAiti
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Posted: 1 decade ago Apr 1, 2013, 2:31 a.m. EDT
As i have mentioned I am using a 2D model in COMSOL4.2

GEOMETRY AND MATERIALS:
In my simulation domain ,4 micrometer by 4 micrometer,the upper portion is air(4micro*1 micro)and the lower portion is glass.A nanoparticle(say polysterene) of 300 nm is placed at the interface(halfway in my simulation domain).The materials have their usual refractive indices 1,2.37 and 2.51

ELECTROMAGNETIC WAVES:
In the EM WAVE section I have taken the In-plane vector wave(want for TM case) and analyzing the total field(there is option of total field/scattered field).
I am using scattering boundary conditions for my simulation domain boundaries (i don't know if that is correct/if something else might be appropriate)the sc1.png takes into account one scattering boundary and sc2.png takes into account the top boundary condition where light is excited.The farfield settings are shown(there might be some mistake here).(farfield.png)
What i have done is I have taken glass as my FAR FIELD DOMAIN SELECTION and taken the lowest boundary in my boundary selection .
The frequency domain analysis is done and computed.
my wavelength is 632 nm
The plots which i have obtained (HZ and Efarnorm) are the same which i have attached in the previous post.



As i have mentioned I am using a 2D model in COMSOL4.2 GEOMETRY AND MATERIALS: In my simulation domain ,4 micrometer by 4 micrometer,the upper portion is air(4micro*1 micro)and the lower portion is glass.A nanoparticle(say polysterene) of 300 nm is placed at the interface(halfway in my simulation domain).The materials have their usual refractive indices 1,2.37 and 2.51 ELECTROMAGNETIC WAVES: In the EM WAVE section I have taken the In-plane vector wave(want for TM case) and analyzing the total field(there is option of total field/scattered field). I am using scattering boundary conditions for my simulation domain boundaries (i don't know if that is correct/if something else might be appropriate)the sc1.png takes into account one scattering boundary and sc2.png takes into account the top boundary condition where light is excited.The farfield settings are shown(there might be some mistake here).(farfield.png) What i have done is I have taken glass as my FAR FIELD DOMAIN SELECTION and taken the lowest boundary in my boundary selection . The frequency domain analysis is done and computed. my wavelength is 632 nm The plots which i have obtained (HZ and Efarnorm) are the same which i have attached in the previous post.
Snehanshu MAiti
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Posted: 1 decade ago Apr 1, 2013, 2:40 a.m. EDT
I am attaching the model file here.
Kindly have a look at this.
I think i am making a mistake which is giving me erroneous results

Thanks
I am attaching the model file here. Kindly have a look at this. I think i am making a mistake which is giving me erroneous results Thanks

Attachments:

Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 1, 2013, 6:35 a.m. EDT

Hi,

I think the far field surface plot doesn't make much sense. You are probably interested in the far field along the bottom or lateral boundaries.
Try a 1D line plot along those boundaries and you will see that it gives reasonable results.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
Hi, I think the far field surface plot doesn't make much sense. You are probably interested in the far field along the bottom or lateral boundaries. Try a 1D line plot along those boundaries and you will see that it gives reasonable results. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com

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