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how to design an unbiased resonator
Posted 16.03.2012, 09:51 GMT-4 MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 4.2a 2 Replies
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I want to design a mems resonator similar to the example model in the model library - mems.
Here the example biased_resonator_2d_freq is interesting for me.
To understand how comsol uses the parameter internally, I wanted to try an unbiased resonator, which is just actuated by an AC voltage to see the unbiased displacement of the resonator vs. the frequency in a sweep around the resonance frequency (instead of like in the example a actuation AC voltage + a DC bias).
In the example the study prestressed analysis, frequency domain is used, which contains a stationary part and a frequency domain part.
As far as I understand it, the DC bias is represented by the electric potential in electromechanics - electric potential 3 and the AC actuation by the electric potential in electromechanics - electric potential 3 - harmonic perturbation 1.
But if I just want the AC actuation and set the DC bias to 0 an error occurs.
Can I instead use only a frequency domain study for analyzing the unbiased case. But here I have only the option of the electric potential in electromechanics - electric potential 3 (which represented the DC voltage), The harmonic perturbation does not have any effect on the result (as far as I can say). Do I have to use the effective voltage of the AC actuation for the electric potential or is this model also not suited to solve the unbiased resonator?
How can I simulate the problem instead?
I hope somebody can give me a tip how to solve it.
Hello Stefan Wagner
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if you have an unbiased model, with a continuous AC excitation of sinus type, it's enough to run a simple frequency domain solver either with one frequency, or for several as a sweep (range(...)), It is when you add a bias that you ned to use special cases to "stress" your model first, then use that point as a linearisation point for next frequency domain solving. COMSOL has added a few special solver cases, that looks after this for certain physics, check your do (v4.3 in particular)
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Good luck
Ivar