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Coupling Surface Charge Density from Electrostatics to Electrical Circuit

Posted 31.03.2013, 07:18 GMT-4 Low-Frequency Electromagnetics, MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Studies & Solvers Version 4.3a 3 Replies

Jeffrey Fong
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Hi,

I have made a model of a varying overlap capacitor with an electric potential on one side as an electret. It seems to work with just ES and ALE but once I add in CIR and set the top electrodes as circuit terminals for the electric circuit, the study takes much too long and doesn't finish so I don't believe that will result in a correct answer.

I have instead integrated the surface charge density over the surface of the top electrodes and am able to show that it changes over time, hence a current (shown in image). But how can I couple this current to the electric circuit model?

Thanks,
Jeffrey
3 Replies Last Post 06.04.2013, 05:11 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 01.04.2013, 16:21 GMT-4
HI

I'm not by my WS so I cannot open your model, but when you ay you use ES, do not forget that there is no current flow, so if you add in CIR physics, be sure you connect to a lumped port/terminal so that you get the voltage distributed over the full desired area = BC. Also as there is no current I'm not sure how this is back coupled into CIR

I woudl suggest to check how this works on a simple well known and easily analyed model

--
Good luck
Ivar
HI I'm not by my WS so I cannot open your model, but when you ay you use ES, do not forget that there is no current flow, so if you add in CIR physics, be sure you connect to a lumped port/terminal so that you get the voltage distributed over the full desired area = BC. Also as there is no current I'm not sure how this is back coupled into CIR I woudl suggest to check how this works on a simple well known and easily analyed model -- Good luck Ivar
Jeffrey Fong
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Posted: 1 decade ago 05.04.2013, 22:07 GMT-4
Maybe my way of thinking is not correct but here it is, when you place a positive electrode in close proximity to a conductor, you will induce negative surface charges. Then you suddenly switch from the positive electrode to a negative one and then positive surface charges are now induced. Hence a flowing current, no?

Thanks,
Jeffrey
Maybe my way of thinking is not correct but here it is, when you place a positive electrode in close proximity to a conductor, you will induce negative surface charges. Then you suddenly switch from the positive electrode to a negative one and then positive surface charges are now induced. Hence a flowing current, no? Thanks, Jeffrey
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 06.04.2013, 05:11 GMT-4
Hi

I agree if you apply a varying voltage, to get this voltage to "propagate" you need to move the charges, hence you induce current.
But on the other side you need to carefully read the hypothesis of ACDC and ES versus EC, in very summary first ACDC means small objects compared to the wavelength of any oscillating electric field (magnetics are not considered in ES nor in EC) this means also that propagation is instantaneous, no true time delay so you do not "see" the current flow.

Then for ES (static in contrary to EC dynamic current flow) you do not look at the electron flow, when you apply a potential to a boundary it appears all over, there is no resolution of the current flow, no resistance effets, nor Joule heating (all that is in EC, but not part of ES) This allows for easier solving and quicker solutions. But all this remains a "model" simplified w.r.t. natue, and in nature it's the full ACDC + RF electric AND magnetic solution one must apply, with all it's extra complexity

--
Good luck
Ivar
Hi I agree if you apply a varying voltage, to get this voltage to "propagate" you need to move the charges, hence you induce current. But on the other side you need to carefully read the hypothesis of ACDC and ES versus EC, in very summary first ACDC means small objects compared to the wavelength of any oscillating electric field (magnetics are not considered in ES nor in EC) this means also that propagation is instantaneous, no true time delay so you do not "see" the current flow. Then for ES (static in contrary to EC dynamic current flow) you do not look at the electron flow, when you apply a potential to a boundary it appears all over, there is no resolution of the current flow, no resistance effets, nor Joule heating (all that is in EC, but not part of ES) This allows for easier solving and quicker solutions. But all this remains a "model" simplified w.r.t. natue, and in nature it's the full ACDC + RF electric AND magnetic solution one must apply, with all it's extra complexity -- Good luck Ivar

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