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The 'penalty method' in the 'Pull-in of an RF MEMS switch' model

Posted 6 mars 2014, 08:31 UTC−5 5 Replies

Senna
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In comsol 4.4 this model provides a very valuable method to calculate the pull-in time of an RF MEMS switch through transient analysis, but I'am a little confused about the parameter 'tn=5e5 pa'( input estimate of the contact force). How can I set the appropriate value of 'tn' to make sure 'the elastic stiffness and the contact force' has been correctly tuned?
Any help is appreciated.Thanks in advance.
5 Replies Last Post 28 sept. 2016, 10:40 UTC−4
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Hello Senna

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Yuanyu Yu
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Posted: 1 decade ago 14 juil. 2014, 07:36 UTC−4
I am also confused about how to set this value for different device with different material.
Have you found a way?
I am also confused about how to set this value for different device with different material. Have you found a way?
Fandi Hamid
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Posted: 9 years ago 24 juin 2015, 23:33 UTC−4
Hallo Senna...have u got the answer for your question

"In comsol 4.4 this model provides a very valuable method to calculate the pull-in time of an RF MEMS switch through transient analysis, but I'am a little confused about the parameter 'tn=5e5 pa'( input estimate of the contact force). How can I set the appropriate value of 'tn' to make sure 'the elastic stiffness and the contact force' has been correctly tuned?
Any help is appreciated.Thanks in advance."

Can u share with me..how to set appropriate value of 'tn'?
Hallo Senna...have u got the answer for your question "In comsol 4.4 this model provides a very valuable method to calculate the pull-in time of an RF MEMS switch through transient analysis, but I'am a little confused about the parameter 'tn=5e5 pa'( input estimate of the contact force). How can I set the appropriate value of 'tn' to make sure 'the elastic stiffness and the contact force' has been correctly tuned? Any help is appreciated.Thanks in advance." Can u share with me..how to set appropriate value of 'tn'?
Henrik Sönnerlind COMSOL Employee

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Posted: 9 years ago 25 juin 2015, 03:01 UTC−4
Hi,

A penalty method is an approximate way of computing contact, where a stiff spring is inserted between the contacting boundaries. If you do not supply the contact force (actually: contact pressure) estimate, then there will be an overlap between the contacting boundaries such that F_contact = k*d where k is the penalty stiffness and d is the overlap (= gap g with but with positive sign).

So in order to decrease the artificial overlap you should have a high penalty stiffness. But a too high penalty stiffness is detrimental to the numerics. A good starting point is to use something of the order E/h where E is the Young's modulus, and h is a characteristic element size in the contact region.

Adding a reasonable contact force estimate 'tn' will also decrease the overlap, since the contact force will then be computed as F_contact = k*d + tn, and that would reduce 'd'. But the contact force input is not necessary, it only improves the accuracy.

If you have no idea about what contact pressures to expect, try to do the analysis once with tn=0, and then look at the results. You can then enter the resulting contact pressure as input, and do a refined analysis.

Regards,
Henrik
Hi, A penalty method is an approximate way of computing contact, where a stiff spring is inserted between the contacting boundaries. If you do not supply the contact force (actually: contact pressure) estimate, then there will be an overlap between the contacting boundaries such that F_contact = k*d where k is the penalty stiffness and d is the overlap (= gap g with but with positive sign). So in order to decrease the artificial overlap you should have a high penalty stiffness. But a too high penalty stiffness is detrimental to the numerics. A good starting point is to use something of the order E/h where E is the Young's modulus, and h is a characteristic element size in the contact region. Adding a reasonable contact force estimate 'tn' will also decrease the overlap, since the contact force will then be computed as F_contact = k*d + tn, and that would reduce 'd'. But the contact force input is not necessary, it only improves the accuracy. If you have no idea about what contact pressures to expect, try to do the analysis once with tn=0, and then look at the results. You can then enter the resulting contact pressure as input, and do a refined analysis. Regards, Henrik
Fandi Hamid
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Posted: 9 years ago 25 juin 2015, 03:10 UTC−4
Hi...tq for your answer Henrik.

May i know how to determine 'h' (characteristic element size) in the PUll in Of an RF MEMS Switch model.Tq in advance

Regards
Fandi
Hi...tq for your answer Henrik. May i know how to determine 'h' (characteristic element size) in the PUll in Of an RF MEMS Switch model.Tq in advance Regards Fandi
Dorra Bahloul
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Posted: 8 years ago 28 sept. 2016, 10:40 UTC−4
Hi Fandi,

I have the same preoccupation as you for the estimation of the contact force. Did you find a method to calculate the characteristic element size (h)?

Regards,
Dorra
Hi Fandi, I have the same preoccupation as you for the estimation of the contact force. Did you find a method to calculate the characteristic element size (h)? Regards, Dorra

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