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Floating Potential

Posted May 2, 2012, 4:35 p.m. EDT Low-Frequency Electromagnetics, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 4.2 13 Replies

Bahar
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I have a question about floating potential condition. I have 2 metals (like electrodes) which are not directly connected to voltage source and i want to use them to measure the signal (or voltage variation in my medium). According to some of the posts here i should use floating potential option as my boundary conditions for these metals. Is that right?
And if it is correct, then what should i assign in its terminal charge value section (in floating potential option)?

Best
Bahareh
13 Replies Last Post May 11, 2017, 1:51 a.m. EDT
Edgar Kaiser
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Posted: 1 decade ago May 3, 2012, 3:40 a.m. EDT
Hi Bahareh,

yes a floating object can act as a probe for the field it is rurrounded by. The terminal charge should be zero, otherwise you would observe a shift in the floating voltage.

Cheers
Edgar
Hi Bahareh, yes a floating object can act as a probe for the field it is rurrounded by. The terminal charge should be zero, otherwise you would observe a shift in the floating voltage. Cheers Edgar
R. F. Hamou
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Posted: 1 decade ago May 3, 2012, 4:48 a.m. EDT
Hi,

I would say that your terminal charge value depends on your initial condition! It can be zero or equal to another value that you are assuming (reflecting a certain value of potential at a certain position of your electrode or time) since that you want to probe the potential within a medium!

Cheers
Hi, I would say that your terminal charge value depends on your initial condition! It can be zero or equal to another value that you are assuming (reflecting a certain value of potential at a certain position of your electrode or time) since that you want to probe the potential within a medium! Cheers
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 3, 2012, 5:57 a.m. EDT
Hi

or to add another possibility, use a SPICE model of your voltage monitoring electronics impedance

--
Good luck
Ivar
Hi or to add another possibility, use a SPICE model of your voltage monitoring electronics impedance -- Good luck Ivar
Bahar
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Posted: 1 decade ago May 3, 2012, 11:14 a.m. EDT
Thanks for the reply.
However, do you have nay idea what if i don't set any special boundary for my metals and leave them as their initial values? Because i also tried this case and the simulation was done without any error! However since the problem is complex i can not use theoretical method to verify my final results.
This is the reason i get a bit confused!
Do you think leaving them as initial value, which is V=0 is a wrong approach?


Best
Bahar
Thanks for the reply. However, do you have nay idea what if i don't set any special boundary for my metals and leave them as their initial values? Because i also tried this case and the simulation was done without any error! However since the problem is complex i can not use theoretical method to verify my final results. This is the reason i get a bit confused! Do you think leaving them as initial value, which is V=0 is a wrong approach? Best Bahar
Bahar
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Posted: 1 decade ago May 3, 2012, 11:17 a.m. EDT
This approach seems more accurate. I will look in to tutorials to see how i can do this. I never combine these two software together. However, can you give me you idea about not setting any boundary at all. I mean if i leave the metal condition as its initial value, will that be a wrong approach?
This approach seems more accurate. I will look in to tutorials to see how i can do this. I never combine these two software together. However, can you give me you idea about not setting any boundary at all. I mean if i leave the metal condition as its initial value, will that be a wrong approach?
Bahar
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Posted: 1 decade ago May 3, 2012, 11:20 a.m. EDT
Thanks for adding some information on this issue. What i also have in my mind is that double layer capacitance which will be formed when the metal will be placed in medium will affect the charges on the boundary. However still i have no idea what value should i choose for that. May be i should look more deeper in this issue!

Thanks for adding some information on this issue. What i also have in my mind is that double layer capacitance which will be formed when the metal will be placed in medium will affect the charges on the boundary. However still i have no idea what value should i choose for that. May be i should look more deeper in this issue!
Edgar Kaiser
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Posted: 1 decade ago May 3, 2012, 11:45 a.m. EDT

I would recommend to test the different options in a very simple model, i.e. a parallel plate capacitor and check whether they behave as expected from theory.

Cheers
Edgar
I would recommend to test the different options in a very simple model, i.e. a parallel plate capacitor and check whether they behave as expected from theory. Cheers Edgar
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 3, 2012, 4:12 p.m. EDT
Hi

interesting question, I tried it out, while guessing the results, I got close but not fully right, Once you think it over, you get convinced that COMSOL is allthough right, given the forgotten assumptions betweeen ES and EC ;)
so there is everytime things to learn

My example is slightly mixed but tracking the solvers one get it right

--
Good luck
Ivar
Hi interesting question, I tried it out, while guessing the results, I got close but not fully right, Once you think it over, you get convinced that COMSOL is allthough right, given the forgotten assumptions betweeen ES and EC ;) so there is everytime things to learn My example is slightly mixed but tracking the solvers one get it right -- Good luck Ivar

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Bahar
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Posted: 1 decade ago May 4, 2012, 10:26 a.m. EDT
Thanks for your advice
Thanks for your advice
Bahar
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Posted: 1 decade ago May 4, 2012, 10:27 a.m. EDT
Thanks for your helpful example Ivar
Thanks for your helpful example Ivar
R. F. Hamou
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Posted: 1 decade ago May 5, 2012, 12:16 p.m. EDT
Concerning the double layer that can be formed at electrode/medium interface:

This is possible if the electric charges in your medium are free to move and to accumulate near charged surfaces, i.e., can be affected by the electric field caused by the "charged electrode surface". This would be governed by the equation that you are assuming for your medium.

In reality, there should be some charges present at the surface of your electrode due to various natural effects.
So you have to take into account the nature of your medium and see if there should be some effects, which reflect the terminal charge.

Good luck

Concerning the double layer that can be formed at electrode/medium interface: This is possible if the electric charges in your medium are free to move and to accumulate near charged surfaces, i.e., can be affected by the electric field caused by the "charged electrode surface". This would be governed by the equation that you are assuming for your medium. In reality, there should be some charges present at the surface of your electrode due to various natural effects. So you have to take into account the nature of your medium and see if there should be some effects, which reflect the terminal charge. Good luck
Khawar Hussain
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Posted: 9 years ago Oct 23, 2015, 2:41 p.m. EDT
Hi
i am new to comsol and trying a simulate a unimorph piezoelectric cantilever beam using strain charge equations in comsol .As i studied i came to know that floating potential is used to specify the charge ....i have confusion that when we apply vibrations to piezo material it generates charge at output and that charge should be applied in floating potential ..so from where i get that specific value of charge ...or correct me if i am wrong ??
and how to couple piezo and electrosatic study in comsol 4.3b?

Thanks in advance ...
Khawar
Hi i am new to comsol and trying a simulate a unimorph piezoelectric cantilever beam using strain charge equations in comsol .As i studied i came to know that floating potential is used to specify the charge ....i have confusion that when we apply vibrations to piezo material it generates charge at output and that charge should be applied in floating potential ..so from where i get that specific value of charge ...or correct me if i am wrong ?? and how to couple piezo and electrosatic study in comsol 4.3b? Thanks in advance ... Khawar
Ritu Goel
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Posted: 8 years ago May 11, 2017, 1:51 a.m. EDT
The charge which will be generated in the piezoelectric device, can be collected into the floating potential electrode. Also, use solid mechanics and electrostatics module to get the effect of piezoelectricity in your version of COMSOL.
The charge which will be generated in the piezoelectric device, can be collected into the floating potential electrode. Also, use solid mechanics and electrostatics module to get the effect of piezoelectricity in your version of COMSOL.

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