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MEMS micromirror oszillation air damping

Posted 21.07.2014, 10:40 GMT-4 MEMS & Nanotechnology, MEMS & Piezoelectric Devices Version 4.4 3 Replies

Martin Günter
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Hello,
I want to do a timedependent simulation of a micromirror with piezoelecric actuators. The actuators are stimulated with different voltages and the behaviour of the micromirror over the time are simulated.
My question is: How can I pay attention o the air damping of the surrounding air? Do I have to put a sphere of air around my modell? Or is there a better way because I don't want to simulate the behaving of the air. I only want that the air damping of the oszillating mirror is noticed in the simlation.

Thank you :)
3 Replies Last Post 30.07.2014, 11:12 GMT-4
Pieter Westerik
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Posted: 1 decade ago 25.07.2014, 06:41 GMT-4
If you want to do it completely correctly you have to simulate the complete behaviour of the air as well. However for certain geometries, fluid properties and frequencies you can put all kinds of simplifications. For example if you have two parallel plates, one fixed, the other moving, close to each other (but at least a few free path lengths away from each other) you can use a squeeze film damping boundary condition instead of simulating the complete behaviour of the air between the plates. The gap should be small compared to the size of the plates by the way.
If you want to do it completely correctly you have to simulate the complete behaviour of the air as well. However for certain geometries, fluid properties and frequencies you can put all kinds of simplifications. For example if you have two parallel plates, one fixed, the other moving, close to each other (but at least a few free path lengths away from each other) you can use a squeeze film damping boundary condition instead of simulating the complete behaviour of the air between the plates. The gap should be small compared to the size of the plates by the way.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 28.07.2014, 11:44 GMT-4
Hi Martin,

I agree with Pieter. In some cases you need to explicitly model the gas/air and in others you can make some simplifying assumptions, such as the squeeze film damping boundary. Check out this webinar for a MEMS example where we explicitly modeled the surrounding air www.comsol.com/video/simulating-fluid-structure-interaction-comsol-multiphysics. Also, check out Model #1432 in the COMSOL Model Gallery for an example on how to account for the gas damping without explicitly modeling it.

Nagi Elabbasi
Veryst Engineering
Hi Martin, I agree with Pieter. In some cases you need to explicitly model the gas/air and in others you can make some simplifying assumptions, such as the squeeze film damping boundary. Check out this webinar for a MEMS example where we explicitly modeled the surrounding air http://www.comsol.com/video/simulating-fluid-structure-interaction-comsol-multiphysics. Also, check out Model #1432 in the COMSOL Model Gallery for an example on how to account for the gas damping without explicitly modeling it. Nagi Elabbasi Veryst Engineering
Martin Günter
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Posted: 1 decade ago 30.07.2014, 11:12 GMT-4
Thank you very much.
Thank you very much.

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