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Very simple cantilever pull-in voltage problem

Posted Sep 26, 2015, 8:23 a.m. EDT MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Studies & Solvers Version 5.0 3 Replies

Sotiris Thomas
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Hi,

Im having a problem trying to simulate the pull-in behavior of a cantilever. Essentially, Im following the biased_resonator_2d_model but instead of VdcSP I'm using E_est, a variable for Young modulus. The model doesnt work and the error message Im getting is:
"There are 1 void equations (empty rows in matrix) for the variable comp1.E_est. at coordinates: (0,0), ... and similarly for the degrees of freedom (empty columns in matrix). Returned solution is not converged."
Im setting the initial value to 1000e9. I'm feeling Im missing something obvious. Any help appreciated.

Best,
Sotiris

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3 Replies Last Post Dec 17, 2015, 9:35 a.m. EST
COMSOL Moderator

Hello Sotiris Thomas

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Duy Duc Nguyen
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Posted: 9 years ago Dec 10, 2015, 11:57 a.m. EST
Hi Thomas
I am new in COMSOL and I also want to find Pull-in Voltage of a clamped beam.

Therefore, I am looking for Pull-in reference. However, I can not find any information about Pull-in in COMSOL User Guide 5.0. It seems that you understand it better since you know what is VdcSP and E_est. Can you give me any information?

Thank you very much
Best

Hi Thomas I am new in COMSOL and I also want to find Pull-in Voltage of a clamped beam. Therefore, I am looking for Pull-in reference. However, I can not find any information about Pull-in in COMSOL User Guide 5.0. It seems that you understand it better since you know what is VdcSP and E_est. Can you give me any information? Thank you very much Best
Sotiris Thomas
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Posted: 9 years ago Dec 16, 2015, 9:41 a.m. EST
Hi Duy,

The way I figured out to do it is by running an Auxiliary sweep with the "continuation" option on the parameter of interest (in your case the pull-in voltage). Start by defining Vpi as something very llow (that you dont expect pull-in) and sweep it to higher values. When pull-in occurs, the stationary solver will not converge and the sweep will automatically backtrack to a smaller Vpi value in an effort to find a value that converges.

The smaller the step in the sweep the higher the accuracy the Vpi will be pinpointed to.

After this is finished, you can find your Vpi by looking at the log and see the last run that the solver managed to converge and give a solution. Hope that helps.

PS: E_est is a parameter relevant in my own design only :)

Hi Duy, The way I figured out to do it is by running an Auxiliary sweep with the "continuation" option on the parameter of interest (in your case the pull-in voltage). Start by defining Vpi as something very llow (that you dont expect pull-in) and sweep it to higher values. When pull-in occurs, the stationary solver will not converge and the sweep will automatically backtrack to a smaller Vpi value in an effort to find a value that converges. The smaller the step in the sweep the higher the accuracy the Vpi will be pinpointed to. After this is finished, you can find your Vpi by looking at the log and see the last run that the solver managed to converge and give a solution. Hope that helps. PS: E_est is a parameter relevant in my own design only :)
Duy Duc Nguyen
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Posted: 9 years ago Dec 17, 2015, 9:35 a.m. EST
Hi Thomas

Thank you very much.

Best regards
Duc
Hi Thomas Thank you very much. Best regards Duc

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