some problems in my COMSOL Multiphysics model

April 16, 2016, 4:54 am

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Hi
There are some problems with my model. I build a model of the RF generator whichis a rectangular cavity and two electrodes and the sample is in the middle of the two plates. The top electrode is used as a port for radio frequency emission and the voltage is added on it. I use the joule heating module and frequency domain.
But the result is failed to calculate variable(-variable: comp1.emw.sigmabnd - defined as: material.sigmabnd; -variable: comp1.emw.Jsy- defined as: comp1.emw.tEy*sqrt((epsilon0_const*(comp1.emw.epsilonrbnd+(comp1.emw.sigmabnd/(epsilon0_const*comp1.emw.iomega))))/(comp1.emw.murbnd*mu0_const))
Failed to calculate expression(- espression: d((comp1.emw.iomega*mu0_const*(-comp1.emw.Jsx*comp1.emw.testPhystEx-comp1.emw.Jsy*comp1.emw.testPhystEy-comp1.emw.Jsz*comp1.emw.testPhystEz)/comp1.emw.Kscale)*(dvol),{test@1})
I don't know where the problem is. Please give me a detailed answer and recommendations for model。
Thank you so much~

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Is the imaginary part of the relative permittivity of Au positive or negative?

April 17, 2016, 10:20 pm

≫ Next: Transmission of rough gold film with different incident angles

≪ Previous: some problems in my COMSOL Multiphysics model

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Hello everyone.

Here is another question about "models. woptics. scattering_nanosphere". In this model, the imaginary part of the relative permittivity of Au is negative, e.g. the complex dielectric constant is
-16.8177-1.0668*i,
when the frequency of incident beam is 424THz. The data was extracted from
P. B. Johnson and R. W. Christy, "Optical Constants of the Noble Metals," Phys. Rev. B, vol. 6, pp. 4370-4379, 1972.
I downloaded the paper and found that the complex dielectric constant was defined as
(n+k*i)^2.
When the frequency of incident beam is 1.76eV (corresponding to 424THz), n=0.13 and k=4.103. Then the complex dielectric constant should be
-16.8177+1.0668*i.
I also checked some other papers about the data. It seems that most metals have a positive imaginary part of the relative permittivity.

Please help me to check it.
Thank you very much.

Transmission of rough gold film with different incident angles

April 18, 2016, 12:49 am

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Hello,

I'm new to COMSOL. And I have a question about the boundary condition of RF module. Hope someone can give me some suggestions.

I'm using COMSOL RF module to simulate the transmission of a 3D irregular gold film with different incident angles as attached picture 1. Because the surface and edge of gold film is irregular and asymmetric, so I'm wondering what boundary condition should I use in this case. Floquet periodic condition can not be work because the gold film is not asymmetric and it will have problem in meshing.
I also have tried the PML as attached picture 2. But the result is totally incorrect(as attached picture 3) because the transmission should not be more than 1 in this case.

To summarize, my question is what boundary condition should I use to simulate the transmission of a irregular gold film with different incident angles?

Hope someone can give me some suggestions. Any reply will be helpful for me.
Thanks.


Shih-Yi

confinement loss

June 5, 2012, 1:11 pm

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Hi
is imaginary part of refractive index could be positive or negative that means 1.028175433939737e-19 or -1.028175433939737e-19. I found in my simulation positive and negative values for different values of wavelength, is it possible.

Plz help me

Regards

Samiul

EMW Analysis Methodology

April 20, 2016, 9:56 pm

≫ Next: Optical absorption in MIM or MSM plasmonic structure

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Can anyone offer any specific details on the the Robust, Intermediate, and Fast settings and how they relate to the Mesh and Solver? There isn't much coverage in the reference manuals and guides and various blog posts - I've only ever seen it mentioned in passing. Thanks.

Nick

Optical absorption in MIM or MSM plasmonic structure

April 22, 2016, 6:28 am

≫ Next: Cannot use Prescribed mesh velocity in Frequency-Transient Study

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Hello,

I am studying the plasmonic effects on Metal-Si(SiO2)-Metal structure . I try to calculate the total optical absorption (1/m) on the surface of the structure using the Total Power Dissipation Density (emw.Qh). Did I use the correct option to get the logical result or should I use the other one?
However, emw.Qh gives both positive and negative value which I cannot understand. I thought that the total power dissipation density should be positive. Can you please comment on this and tell me where I am going wrong?

Best,
Hamed

Cannot use Prescribed mesh velocity in Frequency-Transient Study

April 22, 2016, 8:48 am

≫ Next: Express objective function in Optimization study of Frequency domain in Acoustics module

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I'm setting up a microwave heating model with a deformed geometry.
The microwave field is solved in the frequency domain, and the other physics (e.g. heating) in the time domain. This is accomplished with the so called Frequency - Transient study, which works like a normal time dependent study, except that it allows to enter the frequency.
The additional 'physics' of the deformed mesh contains a prediscribed mesh velocity. It does what it should do in a time dpendent study. However when I combine it with the microwave using the above mentioned frequency-transient step, then I recieve the error:

Prescribed mesh velocity is only applicable for transient studies.
- Feature: Compile Equations: Frequency-Transient

But I do have a transient study, So? This seems unintended behaviour to me. Any suggestions ?

Food & Biobased Research
Wageningen University

Express objective function in Optimization study of Frequency domain in Acoustics module

February 6, 2015, 10:55 pm

≫ Next: what is difference between "Mode analysis" and "Boundary mode analysis" in RF?

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Hi,

I want to run an optimization study in frequency domain. I have experimental values of the variable alpha for specific frequencies and I want to adjust my control variable R in order to match these results. If my experimental results are for frequencies 20, 30, 40 kHz ... then the objective functions to be minimised are:

abs(alpha(20kHz) - expermentvalue1)
abs(alpha(30kHz)- experimentvalue2)
abs(alpha(40kHz)- experimentvalue3)
....

My question is: How do I express in Comsol "alpha(20 kHz)"? Is there an operator to do so?

Thanks

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what is difference between "Mode analysis" and "Boundary mode analysis" in RF?

April 26, 2016, 8:25 am

≫ Next: Why set the conductivity as zero?

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i'm not getting , where we should use boundary mode analysis in study step and where we should use only mode analysis in 2D modal.?

Why set the conductivity as zero?

April 26, 2016, 11:16 am

≫ Next: Patch antenna with a coat of Microwave absorber

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Hello everyone.

Here is another question about "scattering_nanosphere".
In this model, the conductivity of nanosphere (composed of Au) was set as 0. But its true value should be 45.6E6[S/m]. If we use it to replace the default one, then the result will be dramatically changed.

Please tell me which value should I use.
Thank you very much.

Patch antenna with a coat of Microwave absorber

April 26, 2016, 11:17 am

≫ Next: Mesh size and dimension of the structure

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Hi,
I am studying the improvement in absorption of radiation by microstrip patch antenna, which is coated with a layer of microwave absorber that I am going to develop.

How can I define the physics for this absorber?


Thanks in advance,

Best,
Karthik

Mesh size and dimension of the structure

April 27, 2016, 10:14 am

≫ Next: time dependent EM-fields in cavity

≪ Previous: Patch antenna with a coat of Microwave absorber

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Hi Guys,

I am quite new in COMSOL, and I have three small questions about the setting of the mesh in ewfd, frequency domain study.

1. I found the results will be different if I used different size of the mesh, in this case, how could I value the setting of the mesh is suitable or not?

2. Another problem, the different dimension of my waveguide with same mesh size will also yield different results, how could I determine the right size of mesh if I change the length of my waveguide?

3. The distance between the light source and the boundary to my waveguide will also get different results, how could I choose the distance of the boundary to my waveguide.

Is there anyone have good suggestions? it would be very appreciated.

Chuan

time dependent EM-fields in cavity

April 28, 2016, 8:41 am

≫ Next: How to add a static current in Electromagnetic wave transient study

≪ Previous: Mesh size and dimension of the structure

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Hi!
First of I apologize in advance for any stupid questions but I'm a new COMSOL user and would like to model the field inside a resonator. This is no problem in the frequency domain but when I try to do this in the time domain I run into problem. I want it in time domain as I would like to have particles interact with the field. I've tried a few different options but with no success.
I've tried a few different things, both feeding the cavity with a port, coupling the magnetic field in the resonator with a magnetic loop, doing an alternating voltage source to couple the E-field etc..None of these have worked so far and COMSOL doesn't seem to like very high frequencies when you're not in the frequency domain.
Can anyone point me in the right direction as to what physics/studies I should use?

TL;DR
What physics/studies should I use if I want to have particle-field interaction in a resonator?

I appreciate any answers

How to add a static current in Electromagnetic wave transient study

April 28, 2016, 10:11 am

≫ Next: Convergence: when should I stop the model?

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Hi,

I am working on a problem using electromagnetic waves transient module. I want to study the interaction between incident EM waves and an annulus conductor in which a static current is flowing on it.

It is easy to set up the incident EM waves using scattering boundary condition. My question is how can I establish the static current in the annulus conductor?

I can establish a static current in AC/DC module, such as the MEF study by putting a voltage difference on the two ends of the conductor. But it seems in electromagnetic waves transient study I can not define a voltage on the conductor end.

Any comment would be highly appreciated.

Zhang

Convergence: when should I stop the model?

March 15, 2012, 3:55 pm

≫ Next: Question about modeling propagating plane wave (wave optics)

≪ Previous: How to add a static current in Electromagnetic wave transient study

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Hi everyone

I have been working on models that take several days to solve. One of them is running at the moment, and I just have a general question.

When I look at the Convergence Plot 2, which is "Reciprocal of step size" vs "Time step", I can see the reciprocal of step size is between 10^5 and 10^6. It has been like this for several hours, and the progress value is at 2% without increasing.

I need results for this simulation by the beginning of next week. When do you know if you should stop the simulation or let it run and solve this convergence difficulty eventually? If I stop it, and the model could have advanced and solved, then I'll lose several hours of solving. But if I don't stop it, it might be at 2% for more than a day.

What should I do? What are the general guidelines on convergence?

Thank you so much!
Sylvana

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Question about modeling propagating plane wave (wave optics)

May 1, 2016, 11:08 am

≫ Next: serval questions of heat transfer in my project

≪ Previous: Convergence: when should I stop the model?

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Hi,
I am new to Comsol, so unfortunately I have little experience. I am trying to set up a very simple model in which I have a propagating plane wave in air, normally incident upon different materials with different geometries. It is to be a 2D model. Simply put: air medium, material (different types of plastic) with different geometries, then air. I am currently doing modeling in a ray tracing solver, but I wanted to compare the results with FDTD (patterned geometries are 2mm in size, corner cube reflectors). I want to know the reflectance / transmission of this plane wave as it interacts with these media. Plus I wanted the nice visualization of the plane wave reflecting for a presentation.

Here is a video (clip on the left), that I am trying to simulate. The plane wave can be a pulse, rather than continuous if that's easier to model.

www.youtube.com/watch?v=WRGfYqqjXDo

Any advice as far as the type of solver, setup, variables, etc. would be great. I feel like I should be able to do this! As it doesn't appear to be anything to complex other than a plane wave incident upon a surface!

Thanks,
Dan

serval questions of heat transfer in my project

May 2, 2016, 11:52 pm

≫ Next: How to calculate the wave's power which pass through an edge before a PML layer?

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Hello
As the figure shows, I am using the fllowing models
(Heat Transfer>Conjugate Heat Transfer>Laminar Flow
Stationary situation
Surface-to-Surface Radiation), and try to find the temperature distribution of the air and the spheres.
I simplified the original object into two spheres,since its shape was very complex. The latter sphere has a boundary heat source.
I have some questions to solve:
1.Since the object was simplified, so the real convective area was changed, i need to modify the convective heat transfer coefficient, but I can't find the modify interface in comsol.
2.The Surface-to-Surface Radiation was considered, and the model is periodic, so I need to define the periodic boundaries as perfect mirrors (the default insulated conditions are just fine to the convective heat transfer and conduction heat transfer)， but I can't find the interface in comsol,too.
3. Since the original object was simplified into two spheres, so the heat conduction was incorrect，because the spheres are not contacted.I want to find the ht.gardT between the spheres and use the Fourier's law of heat conduction to define extra heat source on spheres, is it right?
thank you

How to calculate the wave's power which pass through an edge before a PML layer?

May 3, 2016, 11:17 am

≫ Next: Is there any difference to build 1 domain and 2 domains with the same material in RF/wave optics module?

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Hello,
I am now building a 2D structure which is half-infinite, which I should add a PML layer.
Wave incident to the structure and I would like to calculate how much power it remains after passing through it.
I know it is easy to use port BC to get S-parameter to get the Transmission, Reflection and Absorption, but if there is a PML layer, I think there is no way to set a port.
So is there a way to calculate the power at an edge?

Thanks a lot!
Han

Is there any difference to build 1 domain and 2 domains with the same material in RF/wave optics module?

May 6, 2016, 2:57 am

≫ Next: how to calculate electrical and mechanical parameters of the following design of RF MEMS Switch?

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Hey guys,
I am trying to build a model to calculate a component's absorption. The component lays on Si and the wave incidents from air to Si.
I use periodic PC and 2 periodic ports to calculate it. But the result is far to my expect.
So I made a test. I found that, if I set the component's domain to air, the E-field is still not the same as there is no component's domain,as the pics attached.
Am I wrong to build the model? What should I to fix this problem?
Thank you!

how to calculate electrical and mechanical parameters of the following design of RF MEMS Switch?

May 6, 2016, 11:20 pm

≫ Next: how to excite a plane wave in comsol

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i designed an RF MEMS Switch in comsol 5. i need to calculate the electrical and mechanical parameters like applied force, moment of inertia. i applied the pull down voltage of 5v.