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[AC/DC & MEMS modules, 3.5a version] Microcantilever magnetic dynamic actuation

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Hi to all,
I'm working on the magnetic dynamic actuation of a microcantilever placed near a permanent magnet.
The cantilever is a bi-layer structure with a magnetization assigned to the upper layer.
My goal is to find with a frequency responce analysis the "resonane curve" (amplitude vs excitation frequency) under the magnetic load.
To simplify things I have realized a trial multiphysics model in 2d.
I have coupled plane stress module with the AC/DC/Quasi-static Magnetic/perpendicular corrents/small signal analysis module.
Magnetic force acting on the cantilever is given as boundary force through the Maxwell stress tensor.
In the static case (i.e. a static magnetic field deflects the cantilever) everything seems work correctly.
I'm not sure instead on the results obtained performing the frequency sweep.
Should I have, for instance, to split the magnetic force in a static component (whose name is set in the subdomain settings of the "bias" application mode) and a dynamic component (whose name is set in the subdomain settings of the "time-harmonic" application mode) and assign both of them to the cantilever boundaries?
To my knowledge there are no Comsol models dealing with the electro- or magneto-dynamics actuations of microstructures.
Any suggestion about such a problem is welcome.

Alessandro Ricci

4 Replies Last Post Oct 19, 2009, 8:30 AM EDT

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Posted: 10 years ago Oct 9, 2009, 2:55 AM EDT
Hi

have you seen similar effects as the 2-3 discussion of Shu Zhou ? static forces from the Maxwell tensor calculations when you do not expect them, due to meshing assymetries ?

It would be nice to have a few such models in the ModelExchange, so if you can pls keep us informed.

Personally I would have a closer look to the Virtual work approach for the magnetic forces, I believe it is more robust than the Maxwell tensor approach, evn though more complex to set up.

Except perhaps if you work in 1/4 symmetry and calculate the total Maxwell stress tensor forces by symmetry.

Good luck
Ivar
Hi have you seen similar effects as the 2-3 discussion of Shu Zhou ? static forces from the Maxwell tensor calculations when you do not expect them, due to meshing assymetries ? It would be nice to have a few such models in the ModelExchange, so if you can pls keep us informed. Personally I would have a closer look to the Virtual work approach for the magnetic forces, I believe it is more robust than the Maxwell tensor approach, evn though more complex to set up. Except perhaps if you work in 1/4 symmetry and calculate the total Maxwell stress tensor forces by symmetry. Good luck Ivar

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Posted: 10 years ago Oct 9, 2009, 4:44 AM EDT
Hi Ivar,
at this stage I not interested in an accurate calculation of the magnetic forces acting on the cantilever. Therefore even if maybe Maxwell stress tensor it is not the best choice, I think it is sufficient for my modelling pourposes.
I have read almost all the discussions of Shu Zhou, and his problem is different from mine since I am dealing with the dynamic actuation while the static one seems to work correctley in my case.
My question is more about a precedure and not about the degree of accuracy of the results.
I would like to understand how to correcly set up a frequency sweep analysis where the external load is a magnetic field which varies sinusoidally in time and has a frequency which ranges from two values which are around the resonance frequency of the cantilever.
Comsol documentation unfortunately is not detailed for such a problem (while more than one tutorial is dedicated to static problems).
I will try by myself. If I obtain a "good" model I will post it in the model exchange.
Hi.

Alessandro
Hi Ivar, at this stage I not interested in an accurate calculation of the magnetic forces acting on the cantilever. Therefore even if maybe Maxwell stress tensor it is not the best choice, I think it is sufficient for my modelling pourposes. I have read almost all the discussions of Shu Zhou, and his problem is different from mine since I am dealing with the dynamic actuation while the static one seems to work correctley in my case. My question is more about a precedure and not about the degree of accuracy of the results. I would like to understand how to correcly set up a frequency sweep analysis where the external load is a magnetic field which varies sinusoidally in time and has a frequency which ranges from two values which are around the resonance frequency of the cantilever. Comsol documentation unfortunately is not detailed for such a problem (while more than one tutorial is dedicated to static problems). I will try by myself. If I obtain a "good" model I will post it in the model exchange. Hi. Alessandro

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Posted: 10 years ago Oct 18, 2009, 3:01 AM EDT
Hi again

Following our discussion at Milano
I would to propose some good litterature on modal analysis (and modal mass participation factors, see §4.5)

"Vibration Dynamics and Control", by Gienacarlo GENTA, Springer, 2009, ISBN 978-0-387-79579-9

But as I understood you know the author

there is also this other series (I have myself only vol3):

Vol3 Modelling of Mechanical Systems: Fluid-Structure Interaction, F. Axisa & J. Antunes, 2007, B&H-Elsevier, ISBN 978-0 750-66847-7

for the others, probably as good and well written

Vol2 is on "Structural Elements", and Vol 1 on "Discrete systems", all three by F. Axisa


Have a nice reading ;)
Ivar

Hi again Following our discussion at Milano I would to propose some good litterature on modal analysis (and modal mass participation factors, see §4.5) "Vibration Dynamics and Control", by Gienacarlo GENTA, Springer, 2009, ISBN 978-0-387-79579-9 But as I understood you know the author there is also this other series (I have myself only vol3): Vol3 Modelling of Mechanical Systems: Fluid-Structure Interaction, F. Axisa & J. Antunes, 2007, B&H-Elsevier, ISBN 978-0 750-66847-7 for the others, probably as good and well written Vol2 is on "Structural Elements", and Vol 1 on "Discrete systems", all three by F. Axisa Have a nice reading ;) Ivar

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Posted: 10 years ago Oct 19, 2009, 8:30 AM EDT
Hi Ivar,
nice to meet you again on the forum!
Thanks a lot for the links.
I will read them accurately as soon as possible.
Have a nice day!

Alessandro
Hi Ivar, nice to meet you again on the forum! Thanks a lot for the links. I will read them accurately as soon as possible. Have a nice day! Alessandro

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