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Impedance in RF module & Transmission Line module

Posted 16.07.2015, 03:37 GMT-4 RF & Microwave Engineering, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3 3 Replies

Jack Palmer
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Hi !

I am currently on a project. I am trying to model human liver and the reaction of tissues due to the heat. There are models already set up in COMSOL. They are called "tumor_ablation" and "microwave_cancer_therapy" and they are placed in the " Heat transfert module" library.

It's the exact thing that I want but I would like to upgrade it.

I have an electrical modeling of liver, that let me know the impedance in function of the frequency.

So my objective is to use the geometric of the "tumor_ablation" model, using the "microwave_cancer_therapy" physics (especially the RF module), changing the impedance of tissues by my function.

1) Is it possible ? (I mean to change the impedance by my function )

1 bis) Is it possible using the Transmission Line module?

2) If yes , how ?

Thanks for your consideration, it's the first time that I meet this software so I just know few things that I have learned watching COMSOL videos.
3 Replies Last Post 22.07.2015, 03:09 GMT-4
Chris Nadovich
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Posted: 9 years ago 17.07.2015, 13:07 GMT-4
I don't understand your use of the word "impedance" here. Impedance is a lumped element characteristic. It's the ratio of voltage to current at a specific point. Impedance is also a characteristic of a transmission line. Again it's a voltage/current ratio and it's determined by the geometry of the line and the characteristics of the materials within it.

The liver is a 3D object made of a material distributed in space. We might talk about the conductivity or permittivity of that material. These may be functions of frequency. COMSOL is very good at modelling fields and electromagnetic heating within geometries of materials described by frequency dependent permittivity/conductivity.

I don't understand your use of the word "impedance" here. Impedance is a lumped element characteristic. It's the ratio of voltage to current at a specific point. Impedance is also a characteristic of a transmission line. Again it's a voltage/current ratio and it's determined by the geometry of the line and the characteristics of the materials within it. The liver is a 3D object made of a material distributed in space. We might talk about the conductivity or permittivity of that material. These may be functions of frequency. COMSOL is very good at modelling fields and electromagnetic heating within geometries of materials described by frequency dependent permittivity/conductivity.
Jack Palmer
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Posted: 9 years ago 20.07.2015, 04:43 GMT-4
Well, in Comsol, in the "Electric Currents" and the "Electromagnetics waves" module there is an option ( in the Terminal/Port Sweep Settings ) that is called Reference impedance and it's a value named Zref in Ohm. So that's that kind of impedance that I'm talking about.

In a previous project a student have created an electrical model of the liver summarizing the system ( of liver tissues and the electrode). The result was a study that describe the value of the impedance of the system ( tissues + electrode ) in function of the frequency applied.

My point is to implement this model to comsol. The result of the previous study is a transfer function like
H(s)= Ztissues/Ztissues+Zelectrode.
Do you see ?

see en.wikipedia.org/wiki/Electrical_impedance
Well, in Comsol, in the "Electric Currents" and the "Electromagnetics waves" module there is an option ( in the Terminal/Port Sweep Settings ) that is called Reference impedance and it's a value named Zref in Ohm. So that's that kind of impedance that I'm talking about. In a previous project a student have created an electrical model of the liver summarizing the system ( of liver tissues and the electrode). The result was a study that describe the value of the impedance of the system ( tissues + electrode ) in function of the frequency applied. My point is to implement this model to comsol. The result of the previous study is a transfer function like H(s)= Ztissues/Ztissues+Zelectrode. Do you see ? see https://en.wikipedia.org/wiki/Electrical_impedance
Jack Palmer
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Posted: 9 years ago 22.07.2015, 03:09 GMT-4
An other point, I study the system in a alternative signal so the value of U and I ( as Z= U/I ) depnd on frequency > U=u*Sin(wt) and I=i*Sin(wt+phy)

So for me it's correct when I say that my impedance is in function of the frequency.
An other point, I study the system in a alternative signal so the value of U and I ( as Z= U/I ) depnd on frequency > U=u*Sin(wt) and I=i*Sin(wt+phy) So for me it's correct when I say that my impedance is in function of the frequency.

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