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Far field problem in RF 3D mode

Posted Aug 23, 2010, 11:33 a.m. EDT RF & Microwave Engineering, Geometry, Mesh, Results & Visualization, Studies & Solvers Version 3.5a, Version 4.0a 4 Replies

Jing Wen
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HI,
I have a question about far-field transformation in RF 3D mode.
A nano particle is lied on the substrate with a thin cladding on top of the particle. Material parameters of the substrate, cladding, air satisfied the single mode dielectric waveguide. The fields which is scattered by the particle can propagate inside the waveguide. I want to compute the far field radiation pattern from this nanoparticle.

The particle is on the substrate and covered with a cladding. And I have to define a boundary of far-field transformation which surround the particle. The thing is that if the particle is surrounded by homogenous air, this problem is easy to do, because the boundary is homogenous.
However, when the particle is standing on the substrate and covered with a cladding, the boudnary of the far-field transformation consist of substrate,air and cladding which is inhomogeneous.
Is COMSOL possible to deal with such a problem? Can Stratton-Chu formula deal with inhomogeneous boudnary?
Anyone has similar problems? and any ideas?
4 Replies Last Post Aug 9, 2011, 2:57 a.m. EDT
Robert Koslover Certified Consultant
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Posted: 1 decade ago Aug 24, 2010, 8:31 p.m. EDT
Although you can *probably* get away with using the set of inhomogeneous material surfaces as your source boundaries for the Stratton-Chu integration, I recommend that you instead introduce an additional, simpler bounding surface (which could be set up with continuity boundary conditions, so it is effectively invisible) that covers all the possibly-complicated radiating source(s) of interest to you, including some air or vacuum as well. In 3D, this might be a simple cylinder or sphere (or a half- or quarter- section of one, if you can leverage symmetry planes that may apply). If that new surface becomes your outermost boundary, then be sure to assign it scattering boundary condtions (to absorb the wave). But again, the surface used for aperture integration does not have to be the outermost surface of the problem. Regardless, always make sure you provide some distance within the model for the waves to propagate at least slightly away from your source(s), and to allow the radiating waves to be absorbed in a scattering-boundary condition surface. Otherwise, you may get seriously-inaccurate results.
Although you can *probably* get away with using the set of inhomogeneous material surfaces as your source boundaries for the Stratton-Chu integration, I recommend that you instead introduce an additional, simpler bounding surface (which could be set up with continuity boundary conditions, so it is effectively invisible) that covers all the possibly-complicated radiating source(s) of interest to you, including some air or vacuum as well. In 3D, this might be a simple cylinder or sphere (or a half- or quarter- section of one, if you can leverage symmetry planes that may apply). If that new surface becomes your outermost boundary, then be sure to assign it scattering boundary condtions (to absorb the wave). But again, the surface used for aperture integration does not have to be the outermost surface of the problem. Regardless, always make sure you provide some distance within the model for the waves to propagate at least slightly away from your source(s), and to allow the radiating waves to be absorbed in a scattering-boundary condition surface. Otherwise, you may get seriously-inaccurate results.
Jing Wen
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Posted: 1 decade ago Aug 25, 2010, 4:56 a.m. EDT

Although you can *probably* get away with using the set of inhomogeneous material surfaces as your source boundaries for the Stratton-Chu integration, I recommend that you instead introduce an additional, simpler bounding surface (which could be set up with continuity boundary conditions, so it is effectively invisible) that covers all the possibly-complicated radiating source(s) of interest to you, including some air or vacuum as well. In 3D, this might be a simple cylinder or sphere (or a half- or quarter- section of one, if you can leverage symmetry planes that may apply). If that new surface becomes your outermost boundary, then be sure to assign it scattering boundary condtions (to absorb the wave). But again, the surface used for aperture integration does not have to be the outermost surface of the problem. Regardless, always make sure you provide some distance within the model for the waves to propagate at least slightly away from your source(s), and to allow the radiating waves to be absorbed in a scattering-boundary condition surface. Otherwise, you may get seriously-inaccurate results.


Hi,
Thanks a lot for your answer. If I understand you right, you suggest to introduce a larger sphere which completely include all the radiation source. But the thing is that the substrate and the cladding is much larger (maybe 30 times)than the nanoparticle (scattering source) which is embedded between them. If I introduce additional boundary, that means the substrate and the cladding will come to an end before they reach the introduced boundary. In the space which is between the ending of the substrate/cladding and the introduced boundary, the field will be scattered out from the substrate/cladding. I guess this will modify the result compared to the original physical phenomenon.
However, I am confused about the first sentence of your answer. Can the boundaries where Stratton-Chu formula is computed set to be different materials ?
[QUOTE] Although you can *probably* get away with using the set of inhomogeneous material surfaces as your source boundaries for the Stratton-Chu integration, I recommend that you instead introduce an additional, simpler bounding surface (which could be set up with continuity boundary conditions, so it is effectively invisible) that covers all the possibly-complicated radiating source(s) of interest to you, including some air or vacuum as well. In 3D, this might be a simple cylinder or sphere (or a half- or quarter- section of one, if you can leverage symmetry planes that may apply). If that new surface becomes your outermost boundary, then be sure to assign it scattering boundary condtions (to absorb the wave). But again, the surface used for aperture integration does not have to be the outermost surface of the problem. Regardless, always make sure you provide some distance within the model for the waves to propagate at least slightly away from your source(s), and to allow the radiating waves to be absorbed in a scattering-boundary condition surface. Otherwise, you may get seriously-inaccurate results. [/QUOTE] Hi, Thanks a lot for your answer. If I understand you right, you suggest to introduce a larger sphere which completely include all the radiation source. But the thing is that the substrate and the cladding is much larger (maybe 30 times)than the nanoparticle (scattering source) which is embedded between them. If I introduce additional boundary, that means the substrate and the cladding will come to an end before they reach the introduced boundary. In the space which is between the ending of the substrate/cladding and the introduced boundary, the field will be scattered out from the substrate/cladding. I guess this will modify the result compared to the original physical phenomenon. However, I am confused about the first sentence of your answer. Can the boundaries where Stratton-Chu formula is computed set to be different materials ?
Yevgeniy Davletshin
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Posted: 1 decade ago Sep 1, 2010, 2:41 p.m. EDT
Refer to this forum
www.physicsforums.com/showthread.php?t=306393&page=2
Refer to this forum http://www.physicsforums.com/showthread.php?t=306393&page=2
TIAN ZHOU
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Posted: 1 decade ago Aug 9, 2011, 2:57 a.m. EDT
dear Robert

thanks a lot for your post. i am very interested in the 'some distance within the model for the waves to propagate at least slightly away from your source' part. i am wondering if you or anyone reading this post has a rule of thumb about this distance? should i use several wavelength or use the criteria that separates the near and far field?

thanks a lot


Although you can *probably* get away with using the set of inhomogeneous material surfaces as your source boundaries for the Stratton-Chu integration, I recommend that you instead introduce an additional, simpler bounding surface (which could be set up with continuity boundary conditions, so it is effectively invisible) that covers all the possibly-complicated radiating source(s) of interest to you, including some air or vacuum as well. In 3D, this might be a simple cylinder or sphere (or a half- or quarter- section of one, if you can leverage symmetry planes that may apply). If that new surface becomes your outermost boundary, then be sure to assign it scattering boundary condtions (to absorb the wave). But again, the surface used for aperture integration does not have to be the outermost surface of the problem. Regardless, always make sure you provide some distance within the model for the waves to propagate at least slightly away from your source(s), and to allow the radiating waves to be absorbed in a scattering-boundary condition surface. Otherwise, you may get seriously-inaccurate results.


dear Robert thanks a lot for your post. i am very interested in the 'some distance within the model for the waves to propagate at least slightly away from your source' part. i am wondering if you or anyone reading this post has a rule of thumb about this distance? should i use several wavelength or use the criteria that separates the near and far field? thanks a lot [QUOTE] Although you can *probably* get away with using the set of inhomogeneous material surfaces as your source boundaries for the Stratton-Chu integration, I recommend that you instead introduce an additional, simpler bounding surface (which could be set up with continuity boundary conditions, so it is effectively invisible) that covers all the possibly-complicated radiating source(s) of interest to you, including some air or vacuum as well. In 3D, this might be a simple cylinder or sphere (or a half- or quarter- section of one, if you can leverage symmetry planes that may apply). If that new surface becomes your outermost boundary, then be sure to assign it scattering boundary condtions (to absorb the wave). But again, the surface used for aperture integration does not have to be the outermost surface of the problem. Regardless, always make sure you provide some distance within the model for the waves to propagate at least slightly away from your source(s), and to allow the radiating waves to be absorbed in a scattering-boundary condition surface. Otherwise, you may get seriously-inaccurate results. [/QUOTE]

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