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difference between eigenfrequency and frequency .

Posted May 27, 2011, 6:01 a.m. EDT MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Studies & Solvers Version 4.1 4 Replies

Vikram Kumar Singh
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hi

can anyone explain what is the difference between eigenfrequency and frequency .

let us consider an eigenfrequency : 2.34567e5i or 4.87965e7 + 2.567e8i

so what will be frequency in both case .?
4 Replies Last Post May 30, 2011, 4:27 a.m. EDT
Edgar Kaiser
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Posted: 1 decade ago May 27, 2011, 7:59 a.m. EDT
Hi,

an eigenfrequency is a special case of an eigenvalue, which is a general mathematical term. You can have a look at en.wikipedia.org/wiki/Eigenvalues_and_eigenvectors

Cheers
Edgar
Hi, an eigenfrequency is a special case of an eigenvalue, which is a general mathematical term. You can have a look at http://en.wikipedia.org/wiki/Eigenvalues_and_eigenvectors Cheers Edgar
Vikram Kumar Singh
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Posted: 1 decade ago May 28, 2011, 1:21 a.m. EDT
thank u sir for ur reply

ya i understood in general what is eigenfrequency but

while simulating(comsol model) my model i am getting some eigenfrequency which is complex.

but i need resonant frequency in order to calculate Q factor

so how can i extract that frequency from eigenfrequency.

needed the help

waiting for ur reply sir
thank u sir for ur reply ya i understood in general what is eigenfrequency but while simulating(comsol model) my model i am getting some eigenfrequency which is complex. but i need resonant frequency in order to calculate Q factor so how can i extract that frequency from eigenfrequency. needed the help waiting for ur reply sir
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 30, 2011, 1:43 a.m. EDT
Hi

another point I believe you are referring to is that complex frequency values means that you have damping, hence you should rather use Bodee plots with amplitude phase information (with abs() and atan2(imag(),real()) operators)

when you do a frequency domain plot, you will see that COMSOL proposes equations for the physics that are derived as harmonic time developments. While if you choose eigenfrequency, its the "classical" matrix eigenvalue that is used

--
Good luck
Ivar
Hi another point I believe you are referring to is that complex frequency values means that you have damping, hence you should rather use Bodee plots with amplitude phase information (with abs() and atan2(imag(),real()) operators) when you do a frequency domain plot, you will see that COMSOL proposes equations for the physics that are derived as harmonic time developments. While if you choose eigenfrequency, its the "classical" matrix eigenvalue that is used -- Good luck Ivar
Edgar Kaiser
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Posted: 1 decade ago May 30, 2011, 4:27 a.m. EDT
Hi,

to my knowledge in a complex eigenfrequency the real part stands for the system's resonance frequency in the undamped case and the imaginary part stands for the damping.
So, the imaginary part is already a measure for the quality.
If you kick such a system with a real part omega and imaginary part delta with delta << omega (damping is small) it will oscillate with the frequency sqrt(omega^2 - delta^2), which is lower than the undamped eigenfrequency.

Cheers
Edgar

Hi, to my knowledge in a complex eigenfrequency the real part stands for the system's resonance frequency in the undamped case and the imaginary part stands for the damping. So, the imaginary part is already a measure for the quality. If you kick such a system with a real part omega and imaginary part delta with delta

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