Discussion Forum

Dasant,

I assume you saw “Hepatic Tumor Ablation” from Comsol model library. Indeed, this model uses DC current.

You can use the following steps to create model with AC current:

1. Go to Model Wizard Window.
2. Click Next.
3. In the Add physics tree, Select AC/DC>Electric Currents (ec) and click Add Selected.
4. In the Add physics tree, select Heat Transfer>Bioheat Transfer (ht) and click Add Selected.
5. Click Next.
6. In the Select Study Type, expand Custom Studies and select Preset Studies for Some Physics>Frequency Domain
7. Click Finish.
8. Click Study 1>Step 1: Frequency Domain node and go to Study Settings for Frequency Domain. Clear green check mark in the Solve for section for Bioheat Transfer. Set up frequency in Frequencies section. This will be driving frequency for your AC current.
9. Right-click Study 1 node and select Study Steps>Time Dependent.
10. Go to Study Settings for Time Dependent and clear green check mark in Solve for section for Electric currents.

Thus, in Step 1, you will be solving AC current only. Solution from this Step will be used in Step 2: Time Dependent.

Of course, you will need properly set up both physics and define Heat Source in ht interface.

Good luck,

Sergei Yushanov

Hello Sergei Yushanov,
Thanks for your helpful response
Yes exactly I want to make a model like “Hepatic Tumor Ablation” from Comsol model library with AC current
I did the steps as you told me, but the result of the temperature distribution were different from the case of the DC current, the photo of my result attached in this message and I also want to get the electric field distribution, please help me if you know what the problem in my model
thanks a lot

Basant,

It is hard to tell what is wrong without seeing your model but seems that heat source is not defined properly. Make sure that setting for heat source is correct. I did quick run of the model with AC current source and results are quite close to the DC case. Let me know if you still have issues with your model and I upload AC version of mph file for you.

Regards,
Sergei

Hello Sergei,
I reviewed my model again; I did the steps exactly as in comsol dynamic help and the steps you told me for AC current, I found that when the time in “3D plot Group” sitting is greater than 400 sec the result of temperature distribution become close to the DC case.

This is the link for downloading my model, because I couldn’t attach my model in this message: www.4shared.com/file/xl7rUuQC/my_model.html

In "3D plot Group 2" the temperature distribution at 60 sec and in "3D plot Group 3" the temperature distribution at 600 sec you can see the difference between the two results.please help me if you know what the problem in my model.

thanks a lot

Basant,

I have difficulties with downloading mph file from your website. If you can clear meshes, delete solver settings, results and email your mph file to me along with screenshots of results which concern you then I'll take a look at the model setup.

Regards,
Sergei

Hello Sergei,

this is my model but without mesh and results, i wish you review it and especially the "study 1" setting. also there are screenshots of my results attached in this message, and note that the frequency of AC current is 500000 HZ

thanks a lot

Basant,

The problem with your model was that you were still solving DC case (look at the equation – there is no frequency entering into Current Conservation law).
So, I did the following modification in your model:
1) Changed Electric Currents equation form to Frequency Domain;
2) Assigned (arbitrary) relative permittivity to all materials.
Modified model is attached.

Regards,
Sergei

Hello Sergei,

I can’t open the attached file because when I opening it I find this message “Model created by a later version of comsol multiphysics”, my comsol version is “4.0 a”
And I tried to do the steps you told me,
> I assigned the relative permittivity to all materials
> In electric currents setting > advanced sittings > equation form: frequency domain, frequency: user defined, 500[kHZ]
But I got error, please try to send the Modified model again, where I can open it with my COMSOL version.

Thanks a lot for your help

Basant,

I am afraid that issues for this particular model are realted to 4.0a version. I built this model for AC case in 4.0a and results seems very wrong. Again, the same AC model in 4.3a gave me very reasonable results.

Regards,
Sergei

Hello Sergei,

It’s difficult to get 4.3a version, but I find "COMSOL 4.0a Update" on this link: www.comsol.com/support/updates/comsol40ap/ my version is 4.0.0.982, I would like to know if this update will be useful or not, or if you know another solution for my problem

Thanks a lot for your help

Hello Sergei,

i would like to ask you to send me the model "my model 2_AC_sy_reset .mph" again in version 4.0a, because when i try to did the modification for AC current, i get error.

thanks very much

Basant,

I suspect, error you are getting is related to the time-dependent solver setting. Try to change default time-dependent iterative solver to direct.

Regards,
Sergei

Hello Sergei,

I attached in this message a presentation of radiofrequency ablation model, it was presented in comsol conference 2012, I would like to ask you is this model different from the "Tumor Ablation” in Comsol model library, or the electrode shape is only the difference.

thanks a lot

Basant,

Presentation suggests that electrical part of the problem is solved in the frequency domain which includes conductive and displacement current (exactly what you are interested in), while model "Tumor Ablation” in Comsol library uses DC current only.

However, Governing Equations in Slide 4 of the presentation are quite misleading: I don’t see there term “j*omega*epsilon*E” for the displacement current, although permittivity of the liver is given in the presentation (BTW, liver relative permittivity 2770 seems too high).

Regards,
Sergei

Concerning the tumor ablation model, can someone tell how to get the volume of tissue heated within an isothermal surface. In the model an isothermal surface of 50˚C was done after 8minutes, however, I not only want to find the volume of tissue within this isothermal surface but also want to know the value of the volume with changing time, from t=0 to t=8minutes. How can I calculate the volume at each time instant?
Thanks plenty.