Wrong Q factor

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I am simulating 1/4 of a SiN membrane suspended with 4 thin arms and clamped to the surrounding substrate, the membrane is very thin (100nm) but very wide and long (high aspect ratio managed using Swept function in the mesh) and the entire structure has an isotropic damping equal to 1/Q where Q is set to 100.

Performing an eigenfrequency study, I am expecting to find for all the modes a value of Q (that COMSOL evaluates automatically) equal to the value I set (100). Unfortunately, for the fundamental mode this doesn't happen; precisely, the Q of the fundamental mode is sometimes higher (120,130,150) and sometimes smaller (70, 80) than 100. In addition, every time I launch a new simulation run (even though I do not change nothing) the value of Q (and consequently the Real and Imaginary parts of the eigenfrequency) changes.

Is it normal? Is it a big issue?



2 Replies Last Post Apr 9, 2026, 10:51 a.m. EDT
Acculution ApS Certified Consultant

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Posted: 6 hours ago Apr 9, 2026, 8:58 a.m. EDT

Not an expert in the field, but had a quick look. The geometry is very thin relative to its other dimensions, and that might lead to some ill-conditioning? Would it be an idea to model with shells instead?

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René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
Not an expert in the field, but had a quick look. The geometry is very thin relative to its other dimensions, and that might lead to some ill-conditioning? Would it be an idea to model with shells instead?

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Posted: 4 hours ago Apr 9, 2026, 10:51 a.m. EDT

Not an expert in the field, but had a quick look. The geometry is very thin relative to its other dimensions, and that might lead to some ill-conditioning? Would it be an idea to model with shells instead?

I cannot use Shell due to other contraints. And actually I also noticed that if I add a pre-stress to my membrane, the value of Q is completely wrong for all the modes.

>Not an expert in the field, but had a quick look. The geometry is very thin relative to its other dimensions, and that might lead to some ill-conditioning? Would it be an idea to model with shells instead? I cannot use Shell due to other contraints. And actually I also noticed that if I add a pre-stress to my membrane, the value of Q is completely wrong for all the modes.

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