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RF heating application

Posted Aug 19, 2022, 11:30 a.m. EDT 5 Replies

Manal Shlebik
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Hi everyone

I am simulating electromagnetic heating for the rib waveguide using RF Heating with the wavelength is 1550[nm], and using the ports that have an input power equal: P= [Intensity of incident field * area of the waveguide * cos(Polar angle of incidence in the air)]

The purpose of my simulation is to solve the time-harmonic wave equation for the electric field as the multiphysics couplings add the electromagnetic power dissipation as a heat source and the electromagnetic material properties can depend on the temperature.

As the Microwave Heating interface is added from the Heat Transfer>Electromagnetic Heating branch, the Electromagnetic Waves, Frequency Domain, and Heat Transfer in Solids interfaces are automatically added. I know that the modeling approach should be based on the assumption that the electromagnetic cycle time is short compared to the thermal time scale. I have no error in my simulation but I can not see the Electric Field and Temperature in the Results section (please see the attached COMSOL file).

Would you please tell me how much frequency should I put into the Preset Studies (which are: Frequency-Transient and Frequency-Stationary)?

Thanks in advance, Manal

5 Replies Last Post Aug 30, 2022, 10:43 a.m. EDT
Dave Greve
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Posted: 2 years ago Aug 19, 2022, 4:45 p.m. EDT

You need to EITHER enter the analytic form of the waveguide mode (user-defined port) OR perform a boundary mode analysis step for each port (numeric port).

I recommend that you first set up the ridge waveguide problem and get it to solve correctly. Only then introduce absorbing media and finally the heat transport.

You need to EITHER enter the analytic form of the waveguide mode (user-defined port) OR perform a boundary mode analysis step for each port (numeric port). I recommend that you first set up the ridge waveguide problem and get it to solve correctly. Only then introduce absorbing media and finally the heat transport.
Manal Shlebik
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Posted: 2 years ago Aug 19, 2022, 9:48 p.m. EDT

Hi Dave

Many thanks for your responce.

I followed your advice and was able to solve the electric field correctly both before and after the addition of the absorbing media. However, when trying to solve the heat transfer using both the Time-Dependent Study and the Frequency-Stationary Study, I received the attached error messages.

Would you please let me know which Study type I should select to get the correct dependent temperature values?

I would appreciate it if you could tell me why I got these error messages since I believe it should have come from the Frequency-Stationary feature due to selecting the Electromagnetic Heating feature within the Multiphysics branch.

All the best, Manal

Hi Dave Many thanks for your responce. I followed your advice and was able to solve the electric field correctly both before and after the addition of the absorbing media. However, when trying to solve the heat transfer using both the Time-Dependent Study and the Frequency-Stationary Study, I received the attached error messages. **Would you please let me know which Study type I should select to get the correct dependent temperature values?** I would appreciate it if you could tell me why I got these error messages since I believe it should have come from the Frequency-Stationary feature due to selecting the Electromagnetic Heating feature within the Multiphysics branch. All the best, Manal
Dave Greve
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Posted: 2 years ago Aug 20, 2022, 1:24 p.m. EDT
  1. Add another Wave Equation node, apply to the absorbing material only
  2. Select Refractive index for Electric displacement field model for this node
  3. There was a perfect electric conductor assigned all around waveguide so field in the absorbing material was zero. Delete the second perfect electric conductor node.
  4. (reset solver to default before solving)

You should be able to verify that the electric field in the absorbing material is nonzero and that the total power dissipation emw.Qh is nonzero.

NOW you can add a Frequency-Stationary node. It must be a step after the boundary mode analysis steps.

Be aware that these multiphysics heating problems may solve very slowly with the default solvers, especially for transients. It may be necessary to mess with the solver settings.

1. Add another Wave Equation node, apply to the absorbing material only 2. Select Refractive index for Electric displacement field model for this node 3. There was a perfect electric conductor assigned all around waveguide so field in the absorbing material was zero. Delete the second perfect electric conductor node. 4. (reset solver to default before solving) You should be able to verify that the electric field in the absorbing material is nonzero and that the total power dissipation emw.Qh is nonzero. NOW you can add a Frequency-Stationary node. It must be a step after the boundary mode analysis steps. Be aware that these multiphysics heating problems may solve very slowly with the default solvers, especially for transients. It may be necessary to mess with the solver settings.
Manal Shlebik
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Posted: 2 years ago Aug 22, 2022, 8:22 a.m. EDT

Hi Dave

Thank you very much for answering all my inquiries, from your answers I could solve all my problems easily,

Your help is really appreciated,

All the best, Manal

Hi Dave Thank you very much for answering all my inquiries, from your answers I could solve all my problems easily, Your help is really appreciated, All the best, Manal
Manal Shlebik
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Posted: 2 years ago Aug 30, 2022, 10:43 a.m. EDT
Updated: 2 years ago Aug 30, 2022, 6:59 p.m. EDT

Hi everyone,

Hi Dave,

I would like to compute S-parameters. As it is known that the S11 parameter describes the reflections, and the S21 parameter measures the wave that is transmitted through Port 2 when the waveguide is excited at Port 1.

I have used the S-parameters that are available as built-in expressions, ready for evaluation in postprocessing but I can only see two values ( S11 and S21) and I think that is incorrect because I should have a line graph (line graph results from several values of frequencie written in Frequeny Domain Study).

I have tried another way which is creating the Global Evaluation node and writing in the Expression section the below equations: intA(emw.Qrh)/(Port input power) >> for Absorption (intR(-emw.Poavx))/(Port input power) >> for Reflection intT(emw.Poavx)/(Port input power) >> for Transmission (intR(-emw.Poavx)+intA(emw.Qrh)+intT(emw.Poavx))/(Port input power) >> (A+R+T)=1

However, I believe that my results are incorrect since the summation of (A+R+T) should equal 1.

My results are: Absorption = 6.1072E12, Reflection = -1.2194E13, Transmission = 5.6967E12, and (A+R+T) = -3.8973E11, as shown in the attached COMSOL file

Would you please show me how I can compute the S parameters correctly?

Thanks in advance, Manal

Hi everyone, Hi Dave, I would like to compute S-parameters. As it is known that the S11 parameter describes the reflections, and the S21 parameter measures the wave that is transmitted through Port 2 when the waveguide is excited at Port 1. I have used the S-parameters that are available as built-in expressions, ready for evaluation in postprocessing but I can only see two values ( S11 and S21) and I think that is incorrect because I should have a line graph (line graph results from several values of frequencie written in Frequeny Domain Study). I have tried another way which is creating the Global Evaluation node and writing in the Expression section the below equations: intA(emw.Qrh)/(Port input power) >> for Absorption (intR(-emw.Poavx))/(Port input power) >> for Reflection intT(emw.Poavx)/(Port input power) >> for Transmission (intR(-emw.Poavx)+intA(emw.Qrh)+intT(emw.Poavx))/(Port input power) >> (A+R+T)=1 However, I believe that my results are incorrect since the summation of (A+R+T) should equal 1. My results are: Absorption = 6.1072E12, Reflection = -1.2194E13, Transmission = 5.6967E12, and (A+R+T) = -3.8973E11, as shown in the attached COMSOL file Would you please show me how I can compute the S parameters correctly? Thanks in advance, Manal

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