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Resonance frequency of beam (calculation+plot)

Posted 4 mar 2013, 11:16 GMT-5 MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization Version 4.3, Version 4.3a 4 Replies

Bahar
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HI

I want to calculate and plot resonance frequency of cantilever that I designed in MEMS module. Based on the previous discussions here I understand that I should do the study in "Eigenfrequency" and then i can get different modes of resonance frequency, is that right?
I did what I have mentioned above, and I got 6 eigenfrequency. However there are two problems.

1- I can not understand what equation comsol is using for calculating this resonance frequency. For mu theoretical calculation of first mode of resonance frequency I used this formula "f=0.162(t/L^2)squrt(E/Rho)
by using this equation I get resonance frequency of 95 K, but the simulations give me first eigenfrequency of 117K. Is this differences normal?

2-I can not plot find out how I can plot frequency vs. amplitude to have a simple resonance frequency plot with a pick on resonance frequency.

I would be grateful if someone can help me with this.

Regards
Bahar
4 Replies Last Post 7 mar 2013, 13:03 GMT-5
Edgar Kaiser
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Posted: 1 decade ago 4 mar 2013, 12:05 GMT-5
Bahar,

1. Regarding the frequency discrepancy you should check if your mesh is fine enough and your model is really equivalent to the formula.

2. You can't plot amplitude vs. frequency from an Eigenfrequency study. The study solves an Eigenvalue equation, the amplitudes you get are arbitrary. They can just show the shape of a certain eigenmode. In order to get amplitudes you must run a frequency domain study in the frequency range you got from the Eigenmode study.

Cheers
Edgar
Bahar, 1. Regarding the frequency discrepancy you should check if your mesh is fine enough and your model is really equivalent to the formula. 2. You can't plot amplitude vs. frequency from an Eigenfrequency study. The study solves an Eigenvalue equation, the amplitudes you get are arbitrary. They can just show the shape of a certain eigenmode. In order to get amplitudes you must run a frequency domain study in the frequency range you got from the Eigenmode study. Cheers Edgar
Bahar
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Posted: 1 decade ago 4 mar 2013, 12:55 GMT-5
Dear Edgar

Thanks a lot for your reply and helpful information.
I am going to do both (check my meshing and also using frequency domain study) .

Regards
Bahar
Dear Edgar Thanks a lot for your reply and helpful information. I am going to do both (check my meshing and also using frequency domain study) . Regards Bahar
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 4 mar 2013, 14:47 GMT-5
Hi

I believe I pposted a few models some years ago, perhaps these:

www.comsol.eu/community/forums/general/thread/22681/
www.comsol.eu/community/forums/general/thread/28177/

(I'm not by my WS so I cannot open them, nor check ;)

--
Good luck
Ivar
Hi I believe I pposted a few models some years ago, perhaps these: http://www.comsol.eu/community/forums/general/thread/22681/ http://www.comsol.eu/community/forums/general/thread/28177/ (I'm not by my WS so I cannot open them, nor check ;) -- Good luck Ivar
Bahar
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Posted: 1 decade ago 7 mar 2013, 13:03 GMT-5
Thanks a lot for your information Ivar.
That helps me a lot
Thanks a lot for your information Ivar. That helps me a lot

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