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Calculating Impedance?

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Hello All,
I am trying to include impedance calculations in my model (I have Comsol 4.2a).

To keep it simple, let's consider my model to be AC/DC analysis with a multi-turn coil domain above an aluminum plate.

The model is in the frequency domain and sweeps through a range of frequencies--in this case 0-20kHz.

How do I include impedance in the calculation/analysis?

(I've also attached the model I'm working on for your convenience)

Thank you in advance for your help!


5 Replies Last Post Apr 25, 2012, 10:20 a.m. EDT

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Posted: 1 decade ago Mar 28, 2012, 4:00 p.m. EDT
From looking at the model, while this does not directly answer your question, your mesh is fairly intense where you have the left and right coils attached to the magnet. This is because in your geometry, you have the coil blocks seated a little too high up into the magnet block. See attached file. Making the geometry fit a little better definitely cuts down on unknowns and speeds up the simulation.


For finding impedance for the coil, you just need to use a global evaluation under derived values and pick your quantity of interest.

dennis

From looking at the model, while this does not directly answer your question, your mesh is fairly intense where you have the left and right coils attached to the magnet. This is because in your geometry, you have the coil blocks seated a little too high up into the magnet block. See attached file. Making the geometry fit a little better definitely cuts down on unknowns and speeds up the simulation. For finding impedance for the coil, you just need to use a global evaluation under derived values and pick your quantity of interest. dennis


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Posted: 1 decade ago Apr 24, 2012, 12:42 a.m. EDT
Thank's for the response!
Forgive my inexperience, but I guess I am still unclear as to how to add impedance to a model in general. It would be ideal to model a multi-turn coil sending continuous wave excitation over a range of frequencies through an aluminum plate while the coil is in the presence of a static magnetic field. This is in an attempt to model an Electromagnetic Acoustic Transducer (EMAT) and get the impedance (of the wave traveling through an aluminum plate) vs frequency.

But for now, I just want to know how to plot impedance (y-axis) vs Frequency (x-axis) in general before I move on to specific uses. I also dont know where I would take the impedance, would I select the aluminum plate, the magnet, or the coil? Any help is greatly appreciated!

Thank's for the response! Forgive my inexperience, but I guess I am still unclear as to how to add impedance to a model in general. It would be ideal to model a multi-turn coil sending continuous wave excitation over a range of frequencies through an aluminum plate while the coil is in the presence of a static magnetic field. This is in an attempt to model an Electromagnetic Acoustic Transducer (EMAT) and get the impedance (of the wave traveling through an aluminum plate) vs frequency. But for now, I just want to know how to plot impedance (y-axis) vs Frequency (x-axis) in general before I move on to specific uses. I also dont know where I would take the impedance, would I select the aluminum plate, the magnet, or the coil? Any help is greatly appreciated!

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Posted: 1 decade ago Apr 24, 2012, 10:46 a.m. EDT
I made the assumption that you have set your physics up correctly so I did not check into it all that much. Your file simulated and looks ok.

After the simulation finishes, under Derived Values, you add a global evaluation. From there, you can change the default expression. You will see some default calculations, one for coil parameters.

If you want to sweep freq, then in the freq domain step, just add in the freqs you want by hand or use the little pop up tool. Setting up to do a xy plot is easy to do with doing a multi freq sweep. Let us know if you cannot figure it out. Give it a shot. I have attached a solved file in ver42a.
I made the assumption that you have set your physics up correctly so I did not check into it all that much. Your file simulated and looks ok. After the simulation finishes, under Derived Values, you add a global evaluation. From there, you can change the default expression. You will see some default calculations, one for coil parameters. If you want to sweep freq, then in the freq domain step, just add in the freqs you want by hand or use the little pop up tool. Setting up to do a xy plot is easy to do with doing a multi freq sweep. Let us know if you cannot figure it out. Give it a shot. I have attached a solved file in ver42a.


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Posted: 1 decade ago Apr 24, 2012, 6:01 p.m. EDT
Thanks, Dennis! I looked at your model and input range(100,100,10000) for the frequency range.

I also noticed the expression emqa.ZCoil_1 added to the global definitions. Did adding that global definition allow me to use that as one of the expressions for the Y-Axis data when creating a 1D line graph?

Also, I'm not quite sure which point or line to select for the impedance, because it seems like any point i select, the output of the graph is just a single point in the center of the graph rather than over the frequency ranges.
Thanks, Dennis! I looked at your model and input range(100,100,10000) for the frequency range. I also noticed the expression emqa.ZCoil_1 added to the global definitions. Did adding that global definition allow me to use that as one of the expressions for the Y-Axis data when creating a 1D line graph? Also, I'm not quite sure which point or line to select for the impedance, because it seems like any point i select, the output of the graph is just a single point in the center of the graph rather than over the frequency ranges.

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Posted: 1 decade ago Apr 25, 2012, 10:20 a.m. EDT
You are not really selecting a point or line for impedance. It is a global value based on the coil domain you have set up in the physics.

Take a look at this new file as I have added some new items. Does this help at all? I solved it with your freq range.

It also looked like you want to do a 2D revolution plot. I have something pretty generic in here but to do a 2D revolution plot you have to use a 3D plot in the results. I just did something to show the point and not to solve completely.

You will have to rerun the simulation as I deleted the soln's to make the file smaller. It was around 13MB before so uploading it here was a bit too much.
You are not really selecting a point or line for impedance. It is a global value based on the coil domain you have set up in the physics. Take a look at this new file as I have added some new items. Does this help at all? I solved it with your freq range. It also looked like you want to do a 2D revolution plot. I have something pretty generic in here but to do a 2D revolution plot you have to use a 3D plot in the results. I just did something to show the point and not to solve completely. You will have to rerun the simulation as I deleted the soln's to make the file smaller. It was around 13MB before so uploading it here was a bit too much.

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