Tutorial 2-Intracavitary Applicator

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    Department of Electromagnetic Field Intracavitary applicatorFEI CTU in Prague COMSOL Multiphysics 

    v. 1.0

    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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    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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    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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      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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