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Problems of Electromechanics/Electrostatics in assembly geometry mode.

Posted Mar 25, 2014, 4:39 a.m. EDT Low-Frequency Electromagnetics, MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Geometry, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3, Version 4.3a, Version 4.3b 7 Replies

Yu Y.Y
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Hi,
I want to model a capacitor whose top plate is to be pulled down upon the bottom plate under a large bias voltage(above the pull-in voltage). Electromechanics physics with stationary study is employed for simulation. Contact pairs are defined on the bottom of top plate and the surface of the bottom plate. Identity pairs are also defined between the plate and the air gap.
At the first stage, only an external force is applied as the boundary load without any bias voltage for simulating the contact phenomenon. The top plate contacts to the bottom plate as expected.
Then a DC voltage is applied as the terminal condition with a ground condition, but the Segregated solver cannot converge! Because the gap is air, in the emi physics the Identity pairs could not be set asContinuity condition.
I guess that the problem is caused by the geometry of assembly. For I change to "Form union" to build the geometry, the top plate is deflected as expected. But the "assembly" geometry is necessary for contact analysis.
I don't know how to set the condition for applying electrical voltage in contact analysis. It has confused me for some days.
Would you please give me some advices? Thanks a lot!

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7 Replies Last Post Apr 9, 2014, 5:23 a.m. EDT
Yu Y.Y
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Posted: 1 decade ago Mar 26, 2014, 11:42 p.m. EDT
I found that by adding the Identity pair with "Electric Potential" in the Electromechanics->Pairs->Electrical, the solver could work well. But I just defined the value of electric potential as "V". But the top plate was not deflected so much, although the applied voltage is far above the pull-in voltage.
Any suggestion is appreciated!
I found that by adding the Identity pair with "Electric Potential" in the Electromechanics->Pairs->Electrical, the solver could work well. But I just defined the value of electric potential as "V". But the top plate was not deflected so much, although the applied voltage is far above the pull-in voltage. Any suggestion is appreciated!
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Apr 2, 2014, 9:19 a.m. EDT
I suggest you check two things: (i) the force generated from the electric field in COMSOL and compare it to the theoretical value for force between parallel plates, and (ii) the deflection of the plate in a structural-only stationary analysis due to the same force.

Nagi Elabbasi
Veryst Engineering
I suggest you check two things: (i) the force generated from the electric field in COMSOL and compare it to the theoretical value for force between parallel plates, and (ii) the deflection of the plate in a structural-only stationary analysis due to the same force. Nagi Elabbasi Veryst Engineering
Yu Y.Y
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Posted: 1 decade ago Apr 3, 2014, 4:53 a.m. EDT
Hi, Nagi,
Thank you for your suggestions. Strangely, there is no electrostatic force (zero) betweent the plate. But the electric field value is effective. And the global derived values, such as the total electric energy, the electric potential, the terminal charge and the capacitance are right.
However, if I modified the geometry form from "Assembly" to "Union", the electrostatic force value is OK (non zero). I don't know what BC should be set in the assembly mode.
Hi, Nagi, Thank you for your suggestions. Strangely, there is no electrostatic force (zero) betweent the plate. But the electric field value is effective. And the global derived values, such as the total electric energy, the electric potential, the terminal charge and the capacitance are right. However, if I modified the geometry form from "Assembly" to "Union", the electrostatic force value is OK (non zero). I don't know what BC should be set in the assembly mode.
Yu Y.Y
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Posted: 1 decade ago Apr 4, 2014, 3:03 a.m. EDT
The electric potentials over the indentity pair are plotted. To my surprise, even though this pair is defined as electric potential pair in BC with the same value of 'V', the values are out of phase!!!
And I also attached a 2D surface plot of potential and a arrow plot of electric field. It seems that there is no problem for the overall polarity of potential.
The electric potentials over the indentity pair are plotted. To my surprise, even though this pair is defined as electric potential pair in BC with the same value of 'V', the values are out of phase!!! And I also attached a 2D surface plot of potential and a arrow plot of electric field. It seems that there is no problem for the overall polarity of potential.
Yu Y.Y
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Posted: 1 decade ago Apr 4, 2014, 3:15 a.m. EDT
And the electric potential along the axial is attached. The plot shows that there is no invert polarity in the range.
And the electric potential along the axial is attached. The plot shows that there is no invert polarity in the range.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Apr 6, 2014, 2:17 p.m. EDT
Hi Yu, it’s hard to follow the problem without a model. If you post a model maybe someone from the Forum can take a look. Regarding the out-of-phase electric potential graphs you posted, they are not out-of-phase. The x-axis on the graph is arc-length and one seems to be measured relative to the right end and the other relative to the left end. Replacing arc-length with the axial (X?) coordinate should fix it.

Nagi Elabbasi
Veryst Engineering
Hi Yu, it’s hard to follow the problem without a model. If you post a model maybe someone from the Forum can take a look. Regarding the out-of-phase electric potential graphs you posted, they are not out-of-phase. The x-axis on the graph is arc-length and one seems to be measured relative to the right end and the other relative to the left end. Replacing arc-length with the axial (X?) coordinate should fix it. Nagi Elabbasi Veryst Engineering
Yu Y.Y
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Posted: 1 decade ago Apr 9, 2014, 5:23 a.m. EDT
Hi, Nagi
Thank your for your assistance! I have modified the x-axis, as a result, the potentials are in phase as you said.
I also tried a simplifed model in es physis, the result is same. There is no electrostatic force value in the assembly geometry mode. If the geometry is changed into union mode, the force value is available.
These two models are attached for your reference. Thanks again!
Hi, Nagi Thank your for your assistance! I have modified the x-axis, as a result, the potentials are in phase as you said. I also tried a simplifed model in es physis, the result is same. There is no electrostatic force value in the assembly geometry mode. If the geometry is changed into union mode, the force value is available. These two models are attached for your reference. Thanks again!

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