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Failed current stimulation

Posted 27 feb 2012, 00:35 GMT-5 Low-Frequency Electromagnetics Version 4.2a 6 Replies

Kim Donghyeon
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Hi, all

I want to simulate current stimulation, so i made a simple brain model and attached 2 electrodes

one electrode output 1A and the other electrode input 1A using terminal.

but, it cannot be solved by direct solver.

I think, there is a problem of setting boundary condition, but i could not find it.

What is a problem?

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6 Replies Last Post 7 mar 2012, 05:43 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 feb 2012, 01:32 GMT-5
Hi

what if you replace terminal 2 by a GND node on the same boundary ?

Furthermore you should add an epsilonr = 1 to your materials, even if its not needed for the solver, its needed for many of the postprocessing variables, but so long you do not use them it might be OK

--
Good luck
Ivar
Hi what if you replace terminal 2 by a GND node on the same boundary ? Furthermore you should add an epsilonr = 1 to your materials, even if its not needed for the solver, its needed for many of the postprocessing variables, but so long you do not use them it might be OK -- Good luck Ivar
Kim Donghyeon
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Posted: 1 decade ago 27 feb 2012, 01:55 GMT-5
Thanks for quickly reply.

I'v replaced terminal 2 by GND node and it works well

but, when i checked current output using Derived Values,

Output current is about 360mA.

I don't know whether measuring current is incorrect or simulation condition is incorrect.
Thanks for quickly reply. I'v replaced terminal 2 by GND node and it works well but, when i checked current output using Derived Values, Output current is about 360mA. I don't know whether measuring current is incorrect or simulation condition is incorrect.

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 feb 2012, 02:23 GMT-5
Hi

both are "correct", but it seems that you have not read carefully the KB about flux calculations.

if you use a Derived Values Globa Evaluation - variable electric current - port and terminal + ec.I0_1
you will then get a more accurate value obtained with the weak formulation (already integrated over the port area)

if you change the mesh density on your pads you will notice the current change, by the way use rather

ec.normJ = sqrt(realdot(ec.Jx,ec.Jx)+realdot(ec.Jy,ec.Jy)+realdot(ec.Jz,ec.Jz)) Current density norm

than your product, ... or ?

--
Good luck
Ivar
Hi both are "correct", but it seems that you have not read carefully the KB about flux calculations. if you use a Derived Values Globa Evaluation - variable electric current - port and terminal + ec.I0_1 you will then get a more accurate value obtained with the weak formulation (already integrated over the port area) if you change the mesh density on your pads you will notice the current change, by the way use rather ec.normJ = sqrt(realdot(ec.Jx,ec.Jx)+realdot(ec.Jy,ec.Jy)+realdot(ec.Jz,ec.Jz)) Current density norm than your product, ... or ? -- Good luck Ivar
Kim Donghyeon
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Posted: 1 decade ago 27 feb 2012, 04:42 GMT-5
Stupid question, what's KB?

first of all, thanks

Stupid question, what's KB? first of all, thanks
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 feb 2012, 04:59 GMT-5
Hi

sorry, it the Knowledge BASE see

www.comsol.com/support/knowledgebase/browse/900/

There are no stupid questions, at most stupid answers ;)

--
Good luck
Ivar
Hi sorry, it the Knowledge BASE see http://www.comsol.com/support/knowledgebase/browse/900/ There are no stupid questions, at most stupid answers ;) -- Good luck Ivar
Kim Donghyeon
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Posted: 1 decade ago 7 mar 2012, 05:43 GMT-5
Hi

Thank you for your adviser.

By reading KB, I know that when I set terminal condition to the electrode, it is hard to get exact flux value on that surface which I give the terminal condition

Then, If I calculate flux in the other surface, can I sure that value?

For example, I made cylinder electrode in the rectangle model and I set 1mA on the upper side.
After calculation, I measure the current on the lower side of the electrode by surface integration

Then, is the output current proper?

Hi Thank you for your adviser. By reading KB, I know that when I set terminal condition to the electrode, it is hard to get exact flux value on that surface which I give the terminal condition Then, If I calculate flux in the other surface, can I sure that value? For example, I made cylinder electrode in the rectangle model and I set 1mA on the upper side. After calculation, I measure the current on the lower side of the electrode by surface integration Then, is the output current proper?

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