Determining the Quality factor of resonator

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The discussion focuses on determining the quality factor (Q) of a piezoelectric rectangular plate MEMS resonator using COMSOL Multiphysics. The user is struggling with defining damping in their model and is seeking guidance on how to calculate Q based on eigenfrequencies. They mention obtaining purely imaginary eigenvalues, which suggest an infinite Q, while they expect a finite value. The user has already identified the desired contour mode but is confused by the complex eigenvalues that do not align with their expected results. Assistance is requested urgently to clarify how to accurately find the quality factor for their specific geometry.
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Respected members,
PLEASE help me in determining quality factor of a piezoelectric rectangular plate MEMS RESONATOR in COMSOL multiphysics.there is a need to define some 'damping'.where should i define that..
PLS HELP ME ITS URGENT
thank you and best
 
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mohit21 said:
Respected members,
PLEASE help me in determining quality factor of a piezoelectric rectangular plate MEMS RESONATOR in COMSOL multiphysics.there is a need to define some 'damping'.where should i define that..
PLS HELP ME ITS URGENT
thank you and best

Welcome to the PF.

How is the quality factor "Q" defined? How are you modelling the mechanical oscillations in COMSOL so far? Can you show us what you have done so far?
 
thanks for your quick reply

I am working on piezoelectric (aluminium nitride) vibrating contour mode resonators and filters.i am using COMSOL multyphysics 4.0a.
i have a rectangular plate geometry and i want to find contour mode that i got already.i got desired eigenmode(contour) at some eigenfrequency.
this is the thing i want to design (http://www.seas.upenn.edu/~piazza/Papers/Piazza_JMEMS_jan07.pdf
but i want to find Quality factor according to each eigenfrequency of desired mode.
i search in help there was a formula for Q. they r calculating Q by eigenvalue(lemda) as imaginary part divided by twice real part of lemda.thats ok
but i am getting purely imaginary lemda according to desired mode in comsol.means infinite Q
but it should be some definite value...

i am getting some complex lemdas also.which r not according to desired eigenmode.by formula Q will comes order of e-7 or lesser.

MEANS I DONT KNOW HOW TO FIND Q OF A GIVEN GEOMETRY ??
 
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