Spring Constant and Pull-down voltage calculation for MEMS Fixed-Fixed Beam

Hi,

I'm new to COMSOL, I had tried models already given and now imported geometry from other CAD software into COMSOL. Please briefly explain me that how can I calculate Spring Constant, k and Pull-down voltage required.

I'm confused with the study module and the units I take in results while plotting.

Can you please explain:
Which Physics is appropriate, I was using Electromechanics.

Sometimes I can not be able to add fixed constrains, like when I select the fixed constrains it doesn't add up. But for some geometries it just works.

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Regards,
Tejinder S.