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MEMS - Electorstatic actuators

Posted 18 nov 2011, 17:51 GMT-5 MEMS & Nanotechnology, MEMS & Piezoelectric Devices Version 4.2 4 Replies

Andrija Milojevic
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Hi.

I am trying to do a simple simulation of electrostatic actuator in Comsol 4.2. My system consist of two electrode, one electrode is fixed and another is free to move. I want when I apply voltage to one electrode to induce electrostatic force that will move another electrode. I want to show displacement of the second electrode. I would be very grateful if any one can help me how to do this? I don't know which module to use? I presume that I need to couple two physics electrostatic in AC/DC module and solid mechanics in Structural Mechanics module, because I need to apply fixed boundary condition to one electrode. But I don't know how to couple these two physics? I know that in Comsol version 4.2a exist electrostatics in Structural Mechanics module that has these two physics already coupled, but as I sad I have only Comsol version 4.2.

Thanks

Andrija
4 Replies Last Post 26 lug 2012, 07:57 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 19 nov 2011, 09:32 GMT-5
Hi

the principle of coupling is to use results from one physics to drive BC's or physics for another. In your case the geometry and voltage will give you an electricfield, which induces electric forces. You need to couple these electrically induced forces to the solid boundary loads. This you do by either calling in the forces variable from the other physics into the solid boundary condition, or you let COMSOl do it, normally you have a pull down menu that appears when COMSOL detects force variables from other physics, to propose to use these, advantage, you do not need to rememer the variable name.

You should also ask yourself which forces and how, loads are defined as forces per boundary surface, hence in pressure units, be sure you get the corresponding varaible wth correct units, if you select the names.

Then for your model to be correct you need to ensure that the deformation of the solid, induces a change in electrode distance, to induce changes in voltage. This is typically done via ALE (or DG) or spatial frame induced deformations.

Finally in MEMS with electroes, the closer they come the more force you apply, this is a positive feedback system, if your solid pring deformation force is not large enough, you have "snap in" effects which are so non-linear that the solver might not get to the end, be aware and do your home works: some hand calculations to estimate the overall behaviour of any/the model

--
Good luck
Ivar
Hi the principle of coupling is to use results from one physics to drive BC's or physics for another. In your case the geometry and voltage will give you an electricfield, which induces electric forces. You need to couple these electrically induced forces to the solid boundary loads. This you do by either calling in the forces variable from the other physics into the solid boundary condition, or you let COMSOl do it, normally you have a pull down menu that appears when COMSOL detects force variables from other physics, to propose to use these, advantage, you do not need to rememer the variable name. You should also ask yourself which forces and how, loads are defined as forces per boundary surface, hence in pressure units, be sure you get the corresponding varaible wth correct units, if you select the names. Then for your model to be correct you need to ensure that the deformation of the solid, induces a change in electrode distance, to induce changes in voltage. This is typically done via ALE (or DG) or spatial frame induced deformations. Finally in MEMS with electroes, the closer they come the more force you apply, this is a positive feedback system, if your solid pring deformation force is not large enough, you have "snap in" effects which are so non-linear that the solver might not get to the end, be aware and do your home works: some hand calculations to estimate the overall behaviour of any/the model -- Good luck Ivar
Andrija Milojevic
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Posted: 1 decade ago 19 nov 2011, 10:00 GMT-5
Thank you so much Ivar, you explain everything to me in details. You helped me so much.
I will try to do this and write to you if I succeed.

Thanks once again.

Andrija
Thank you so much Ivar, you explain everything to me in details. You helped me so much. I will try to do this and write to you if I succeed. Thanks once again. Andrija
B G sheeparamatti basavaprabhu
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Posted: 1 decade ago 15 dic 2011, 05:12 GMT-5
sir,
I need a simple electrostatic beam cantilever where voltage is applied to cantilever and deflects towards ground electrode ... just applying voltage and seeing displacement
sir, I need a simple electrostatic beam cantilever where voltage is applied to cantilever and deflects towards ground electrode ... just applying voltage and seeing displacement
Utk Singh
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Posted: 1 decade ago 26 lug 2012, 07:57 GMT-4
Hey, i have been to design the same electrostatically actuated cantilever beam and facing the same problem. I have understood the theory but can you please exactly specify the steps how to realize the coupling between the electrostatic and structural physics.
Hey, i have been to design the same electrostatically actuated cantilever beam and facing the same problem. I have understood the theory but can you please exactly specify the steps how to realize the coupling between the electrostatic and structural physics.

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