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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Paolo Togni 1/11Michal Cifra
Intracavitary applicator on 2.45 GHz for thermal abblationTutorial for COMSOL Multiphysics
This document was created in the framework of FRVŠ project 2300/2008
• Introduction
This tutorial describes how modeling an intracavitary microwave applicator for thermo-ablation.Thanks to the symmetrical properties of this applicator around its axis, it is possible to model itin two dimensions (2D) saving a great computation-power and solving-time. To find thetemperature distribution as a function of time, it is necessary to solve both, electromagneticand thermal problem. To do this it is necessary to set the domain and boundaries parameterfor both problems and solve setting electromagnetic field as source for the thermal solver.
The results of this tutorial result is a 2D time varying temperature distribution which can bevisualized as animation with steps of 30s interloped to 1s.
• Model drawing
Open Comsol Multiphysics, in the Model navigator select: S p a ce d i m e n s i o n : 2 D He a t T r a n s f e r M o d u l e : B i o h e a t Eq u a t i o n
RF Mo d u l e : El e c t r om a g n e t i c W a v e s , TM w a v e s
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Applicator drawing:
D r a w menu , S p e ci f y O b j e c t s , Re c t a n g l e and set the following parameters:
Repeat the operation above setting the following parameters:
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Paolo Togni 3/11Michal Cifra
In D r a w menu, Cr e a t e C om p o s i t e O b j e c t and Se t F o r m u l a “ R 2 - R 3 ” :
Repeat the operation above setting the formula “ C 0 1 - R 4 ” .
• Parameter Settings
Constant Setting:
Select O p t i o n menu, Co n s t a n t s and write the values below:
Note: It is possible to save this values in a text file in order to use it for other modelspressing the Sa v e button in the window above.
Select Ph y s i c s menu, S ca l a r V a r i a b l e s and substitute the E x p r e s s i o n ofn u _ r f w with f r e q :
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Now select So l v e menu, So l v e r P a r a m e t e r s , select T im e d ep e n d e n t in S o l v e rsection and fill the T im e s box in T im e s t e p p i n g section as shown below:
• Subdomain Settings (electromagnetic solver)
Here we will define the electromagnetic characteristics of the model materials for the
electromagnetic section:
Select Mu l t y P h y s i c s menu, TM W a v es ( r f w h ) Select Ph y s i c s menu, Su b d om a i n Se t t i n g s and in the S u b d om a i n s e l e ct i o n
select n° 1
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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In the fill the r and σ boxes with the expression indicated below:
Repeat the operation above also for the Subdomain selection n° 2 filling the boxesaccording to the table below:
s e l e c t i o n 2
reps_w
σ
sigma_w
• Boundary Settings (electromagnetic solver):
Here we will define the boundary condition of the model for the electromagnetic section. Select Ph y s i c s menu, B o u n d a r y Settings and select G r o u p s tab
Create the group s im _ a x i s writing its name in the N a m e box and pressing buttonN e w
In B o u n d a r y s o u r c e s a n d c o n t a i n s section, set the box B o u n d a r y c o n d i t i o n to
A x i a l Symmetry.
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Paolo Togni 6/11Michal Cifra
Create the other groups according to the table below:
Group Boundary Condition
scattering Scattering boundary condition
continuity Continuitypec Perfect electric conductor
Press B o u n d a r i e s tab and in Bondaries selection select simultaneously the
boundaries n° 1 , 3 . Select “s im _ a x i s ” in G r o u p box assigning in such a way this to boundaries to the
group “ s im _ a x i s ” . Assign the other boundaries to the other groups according to the table below:
Boundary n° Group
2,12,14,15 scattering
4,13 continuity
5,6,7,9,10,11 pec
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Select now the boundary n°8 and set according to the picturebelow:
Select P o r t tab and in P o r t d e f i n i t i o n section set the Mo d e s p e c i f ic a t i o n box to
Coa x i a l
• Subdomain Settings (thermal solver)
Here we will define the termal characteristics of the model materials for the thermal section: Select Mu l t y P h y s i c s menu, B i o h e at Eq u q t i o n ( h t b h ) Select Ph y s i c s menu, Su b d om a i n Se t t i n g s and in the S u b d om a i n s e l e ct i o n
select n°1 Check the box A c t i v e in t h i s d om a i n for this section Fill in the boxes in Thermal properties and heat source/sink section according to
the picture below:
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Select I n i t tab and in the I n i t i a l v a l u e section set T ( t o ) box to 3 1 0 . 1 5
Select n°2 in S u b d om a i n s e le c t io n and verify that box A c t iv e i n t h i s d om a n is NOT checked
•
Boundary Settings (thermal solver):
Here we will define the boundary condition of the model for the thermal section. Select Ph y s i c s menu, B o u n d a r y Settings and select G r o u p s tab Create the group i n s u l a t i o n writing its name in the N a m e box and pressing button
N e w
In B o u n d a r y s o u r c e s a n d c o n s t r a i n s section, set the box B o u n d a r y c o n d i t i o n
to T h e r m a l i n s u l a t io n .
Press B o u n d a r i e s tab and in Boundaries selection select simultaneously theboundaries n° 1 , 2 , 4 , 1 3 , 1 4 , 1 5 .
Select “i n s u l a t i o n ” in G r o u p box assigning in such a way this to boundaries to thegroup “ i n s u l a t i o n ” .
• Mesh setting
To discretized our model in order to calculate the electromagnetic field quantity it is neccessaryto define a mesh. A Basic mesh can be easily defined as follow:
Select Me s h menu , Re f in e M e s h
• Problem Solving
To solve the problem:
Select So l v e menu, S o lv e Pa r am e t e r s and set the boxes as in the picture
below:
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Select again So l v e menu, So l v e Pr o b l em . Number of d e g r e e s o f f r e e d om is 1 2 0 8 9 4
Solution time 3 2 8 s using an Intel Centrino Duo T2300 1.6 GHz
• Postprocessing
Temperature distribution Select P o s t p r o c e s s i n g menu, P lo t P a r am e t e r s Select s l i c e tab and in P r e d e f i n e d q u a n t i t i e s select Tem p e r a t u r e Select A n im a t io n tab and set the parameters as in the picture below:
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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Press St a r t A n i m a t i o n button and if the model is correct the animation shouldstart as in the first picture below and finish as in the second (animationpreparation can take a few minutes):
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Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics
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