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Waht is Background Electric Field?

August 20, 2014, 10:14 pm
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Hi Guys,

I can not understand the meaning of background electric field.
In scattered field solution, one has to specify background electric field.
What does it mean?
What is the difference between Full Field and Scattered Field study?
I appreciate guys answering my question.

Thanks,
Mohammad
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Boundary Mode Analysis Undefined Variable

September 30, 2014, 12:17 pm
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Simple waveguide problem. I make a rectangular block of air, 2 cm x 1 cm x 10 cm surrounded by the default PEC boundaries. Ports at each end. Ports both set to Numeric. Add study -> Boundary Mode Analysis Frequency domain. I set the frequency of the mode analysis and frequency domain to be 10 GHz. Everything else defaults. I click compute. Bang:

Undefined value found.
- Detail: Undefined value found in the equation residual vector.
There are 1 degrees of freedom giving NaN/Inf in the vector for the variable comp1.emw.S2x.
at coordinates: (0,0,0), ...
- Feature: Stationary Solver 1 (sol1/s1)

What's this undefined value? If I make one of the ports rectangular, no error. But both numeric, Undefined value. What's the deal here? Obviously I'm missing something obvious with regard to how boundary mode analysis and numeric ports work. What is it? The docs on this topic (as usual) are pretty thin.
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Unable to change the frequency of the model due to some error

January 16, 2016, 11:57 pm
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Hi guys,

I need some help regarding some kind of error message received, I had been doing the modelling regarding the heat radiation of a cell phone and wireless router to the human head/body. I am currently using the model that is already available inside the Comsol library, and whenever i change the frequency of the cell phone (PCB board) ) more than 2.3Ghz, there is a error message as shown below,

====================================================
Undefined value found.
- Detail: NaN or Inf found when solving linear system using SOR.
- Feature: Stationary Solver 1 (sol1/s1)
====================================================

Does this mean that I can't do the simulation with a higher frequency? I have search the web regarding similar problem and the solution i gotten is to change the mesh size to a finer size. But after i try it, the same error still pop out.

I really appreciate if someone can help to share their solution over here, so that others who have similar problem can learn.

Regards,
Boon Heng
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Material melted in combustion chamber

January 21, 2016, 8:08 am
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Dear All
I am modelling a combustion Chamber, which contains an inflow and outlow.
This means the material enters in solid phase, it warms up and leaves the chamber in liquid phase. I need to have a specified material rate.
But I am not sure which physics are suitable for my case??
I mean for definig the material flow which enters and leaves the chamber in different phases, which physic is suitable??


Any suggestion is highly appreciated.

Regards
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Simulating chiral media

January 30, 2015, 4:20 am
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Hi,
I am trying to simulate chiral media as explained in "alphard.ethz.ch/hafner/Workshop/Comsol2009.pdf". My understanding of adding the chiral expression for the electric displacement is that I add a wave equation to the EM physics and then select my domain (in the middle of the structure) and then change the equations for that domain. I found the electric displacement equation and changed it accordingly for all three E components, unlike what is shown in the presentation here (only one equation). First of all is this correct?
Secondly once I simulate it for linearly polarized light, what I find odd is that the E field before reaching the chiral domain has also been affected. What could I be doing wrong? I found the equation for the B field it was curl of E, and hence I assumed no change was required to it as it would be calculated in accordance to the changes made to D. Could this be the problem?
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Reduce Degree of Freedom antenna array

February 8, 2016, 3:16 pm
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Hello,

I am using RF module and have a created a model of antenna array, with which I would like to observe scattering of EM waves when penetrating dielectric material (permittivity 50-70)

The antenna array is used to focus radiation in one place. Since antenna array works only in far field, I need a volume at least 1.5-2 wavelengths to observe the scattering of waves in material. This is why I have enclosed antenna array in tall cylinder shape.

When I try to mesh the model, the DOF number is too large for computer to solve (because of large permittivity of material). Are there any ways to reduce DOF's in particular model?

Thank you,
Arturs
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Electric Field from a point source

March 8, 2015, 5:44 pm
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Hi, I am new to COMSOL. I want to model a point source from which Electric Field spreads out in x,y directions. I am working in 2D plane.
I started of by creating a geometry with air, and then specified my point. How do I assign electric field to my point?
Any help would be greatly appreciated.
Regards
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incident plane wave configuration

February 17, 2016, 4:54 pm
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Dear all,
I'm trying to figure out electromagnetic model of QWIP. I have used scattering bounday conditions and applied Ex=Ez=377 incident electric field. Field polarization direction is y-direction.
As default, incident wave directions are -emw.nx, -emw.ny, -emw.nz. For my application, how should I change the incident wave direction configurations?
Thank you in advance,
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simulating a solar cell

February 21, 2016, 6:54 am
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Helo
I am a new user and I have a question, any body knows how to get the Absorption and the Absorption Enhancement when simulating a thin solar cell?
Thanks in advance
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Magnetic shielding

February 21, 2016, 8:14 am
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How to simulate magnetic flux density in and around the magnetic shielding?
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S21, RF attenuation between two cross-sections

February 22, 2016, 6:02 pm
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Hello,

I am trying to simulate a circular wave guide below cut-off to be used as an attenuator. I started with just a cylinder whose boundaries were PECs and each end defined as a port. The S21 agreed with calculation.

Now I am exciting the TE11 mode with two parallel wires using a lumped port voltage between them. After simulation I can view the field profile and it is the desired mode. However I would like to know S21 between a short distance after the end of the wires to the end port.

Apparently comsol does not let you define internal boundaries so I am not sure how to do it. I have included a screen shot of my geometry.

Thank you.
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Study1 is sweep of the wavelength and the consequence is used in Study 2, but how to get the curves of Study 2 which is sweep the wavelength of Study 1?

July 14, 2014, 5:44 pm
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Hello all !
I'm puzzled that how to calculate the EQE of the solar cell , I used the light(rf module) to calculate the G (sweep of the wavelength) and electrostatics1 to calculate the phi0; two transport of diluted species to calculate the nc & pc; electrostatics 2 to calculate the phi. I want to get the EQE with the function of wavelength, and the J-V profile, but don't know how to set the whole module, Study1 is sweep of the wavelength and the consequence is used in Study 2, but how to get the curves of Study 2 which is sweep the wavelength of Study? Could you help me to check and modification my .mph file?and Thank you very much！
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Simulating chiral media

January 29, 2015, 10:20 pm
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Hi,
I am trying to simulate chiral media as explained in "alphard.ethz.ch/hafner/Workshop/Comsol2009.pdf". My understanding of adding the chiral expression for the electric displacement is that I add a wave equation to the EM physics and then select my domain (in the middle of the structure) and then change the equations for that domain. I found the electric displacement equation and changed it accordingly for all three E components, unlike what is shown in the presentation here (only one equation). First of all is this correct?
Secondly once I simulate it for linearly polarized light, what I find odd is that the E field before reaching the chiral domain has also been affected. What could I be doing wrong? I found the equation for the B field it was curl of E, and hence I assumed no change was required to it as it would be calculated in accordance to the changes made to D. Could this be the problem?
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RF module or Wave Optics ??

March 3, 2015, 3:19 am
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Hi,

I am trying to simulate the wavelength/ frequency transmission and reflection of a nanoscale cross-dipole antenna on a dielectric substrate.

For this I have taken the approach of the RF module (emw) "Freq Selective Surface with a Split Ring resonator" example as a starting point. Resonance as at 4.6 GHz but I have scaled the frequency up and the geometry down for resonance at around a wavelength 6-10 um. Two ports and S parameters are used to calculate reflection and transmission. Simulations run, but I do not feel very certain about the results

A more suitable approach maybe to use the Wave Optics module (ewfd) ???
Any idea's or comments on this ?

I am not very familiar with COMSOL in RF design and I am using 4.4 at the moment.

Thanks,
Ger
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Electric Field from a point source

March 8, 2015, 11:44 am
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Hi, I am new to COMSOL. I want to model a point source from which Electric Field spreads out in x,y directions. I am working in 2D plane.
I started of by creating a geometry with air, and then specified my point. How do I assign electric field to my point?
Any help would be greatly appreciated.
Regards
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Calculation of far field scattering pattern

March 21, 2015, 5:36 pm
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Hello everyone....

I have a doubt regarding calculation of scattering pattern in far field domain.

I have simulated a model which gives the scattering pattern of nano sphere. But i want to calculate the scattering pattern in far field domain so at what distance i should put my PML boundary ??

I have simulated the model by putting my PML at lamda/2 distance. I think it is not ok for calculating far field pattern.

Please Help me out
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How to plot the electric field of circular polarized light?

January 25, 2016, 4:56 am
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Hello

I simulate a meta-surface model when a circular polarized light is normal incident, the polarization state of transmitted light is circular polarized too, and how can I plot the transmitted electric field of circular polarized and light? Could the "expression" in the "plot" be written as "ewfd.Ex+i*ewfd.Ey"?

it could be explained intuitively in attach file.
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How can I find the fundamental mode of PCF (photonic crystal fiber)?

January 28, 2016, 10:19 pm
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Hi, I'm facing a problem in finding the fundamental mode of PCF (photonic crystal fiber). For step index fibers, the fundamental mode can be easily found by setting "search for modes around" higher than the refractive index of the core. But, for PCFs, this technique doesn't work. How can I find the fundamental mode of PCF?
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About the Comsol with Matlab

January 29, 2016, 5:53 pm
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Hi, everyone
When I am trying to plot a function, and an error is occurred : Failure loading MATLAB libraries. This model requires that MATLAB is available. - File: csmatlab.dll - Function: Sigma_G.

I am new to comsol with matbal, and how can I solver the problem?
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What kind of boundary condition should be applied to the edge of PML region?

January 31, 2016, 11:18 pm
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Hi, I'm trying to calculate confinement loss of optical fibers. What kind of boundary condition should be applied to the edge of PML region (the red line in the figure attached)?
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