Electromechanical simulation for MEMS combdrive actuator (Not converge for high voltage)

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Dear all

Hi, I am currently conducting a 2D electromechanical simulation for MEMS comb-drive actuator using COMSOL 5.4.

I have attached a very rough schematic of my geometry. (sorry for the bad drawing, I wish I was able to upload the COMSOL file for a better explanation, but I can`t upload it due to the Information security policy.)

Here is my question. I believe that all the setting including boundary condition, mesh is fine since the simulation converges from the certain voltage range (0 to 70 or 80 V depending on the spring constant of the system)

However, the simulation does not converge at high voltage (above 70 or 80 V) with an error message below.

Failed to find a solution for all parameters, even when using the minimum parameter step. No convergence, even when using the minimum damping factor. Returned solution is not converged. Not all parameter steps returned.

Is this because that the simulation setup considers 70 or 80 V is sort of pull-in voltage? Even more strange thing is that the simulation does not converge when 60 V was applied as a single parameter, where this value was converged when using auxiliary sweep range from 0 to 70 V.

In this case, the error message is as below.

Undefined value found. - Detail: Undefined value found in the equation residual vector. - There are 6777 degrees of freedom giving NaN/Inf in the vector for the variable comp1.spatial.u. at coordinates: (0.000283859,0.00043186), (0.000282939,0.000432316), (0.000283399,0.000432088), (0.000294359,0.00043186), (0.000293439,0.000432315), ... There are 6777 degrees of freedom giving NaN/Inf in the vector for the variable comp1.spatial.v. at coordinates: (0.000283859,0.00043186), (0.000282939,0.000432316), (0.000283399,0.000432088), (0.000294359,0.00043186), (0.000293439,0.000432315), ...

Could anyone have any idea about this? Thank you in advance and stay safe in the pandemic era.



2 Replies Last Post 2020年8月3日 GMT-4 下午9:52
Henrik Sönnerlind COMSOL Employee

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Posted: 6 months ago 2020年7月27日 GMT-4 上午2:02

It is probable that you have reached the pull-in voltage. Also, the fact that you do not get convergence in a single step at a somewhat lower voltage indicates that. Already at 60 V, there is a significant nonlinearity.

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Henrik Sönnerlind
COMSOL
It is probable that you have reached the pull-in voltage. Also, the fact that you do not get convergence in a single step at a somewhat lower voltage indicates that. Already at 60 V, there is a significant nonlinearity.

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Posted: 6 months ago 2020年8月3日 GMT-4 下午9:52

It is probable that you have reached the pull-in voltage. Also, the fact that you do not get convergence in a single step at a somewhat lower voltage indicates that. Already at 60 V, there is a significant nonlinearity.

Thanks for your reply. I will look into my simulation again based on your comments.

Best regards

>It is probable that you have reached the pull-in voltage. Also, the fact that you do not get convergence in a single step at a somewhat lower voltage indicates that. Already at 60 V, there is a significant nonlinearity. Thanks for your reply. I will look into my simulation again based on your comments. Best regards

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