# Discussion Forum

## Q-Factor Calculation for Acoustic Metamaterial Resonator

Hello,

I am trying to calculate the Q-factor for an acoustic metamaterial resonator with multiple layers of Steel. I'm having trouble understanding how I should be incoporating damping/loss into my system. I'm currently using the Pressure Acoustics, Frequency Domain Module on Comsol 6.2.

My approach currently is introducing a user-defined attenuation coefficient to both the Steel and Air domains, which I've chosen to be around 0.003 dB/m and 0.2 dB/m, respectively. With a monopole point source placed in middle of my metamaterial, I then measure the Q-factor by running a Frequency Domain sweep near the resonance frequency (around 10 kHz).

I'm wondering if this is the best approach, or even correct, and if so, I struggle to know what attenuation coefficients I should be using (having difficulty finding these values in any data tables online). Any guidance on this matter would be appreciated.

Sincerely, Jeffrey

2 Replies Last Post May 22, 2024, 3:36 p.m. EDT

Posted: 3 months ago

The Pressure Acoustics interface is meant for modeling only pressure waves in fluids. So for steel, this wouldn't take into account any shear waves, surface waves, vibration modes, etc. Also you are limited by how to define the damping in terms of fluid models.

A more general approach would be to model the air with pressure acoustics. You can use a loss model such as atmospheric attenuation which is built-in. Model the steel as a linear elastic solid in Solid mechanics and couple this to Pressure Acoustics using Acoustic-Structure interaction. Losses in the steel can be modeled with an isotropic loss factor, which is available in reference tables in the literature.

Either a frequency domain sweep or an eigenfrequency study can be used to compute the Quality factor. The framework described above would require the Acoustics Module.

-Mark

Posted: 3 months ago

Thank you so much Mark! This is incredibly helpful, as I was not previously aware of the Acoustic-Structure interaction.

If I wished to find the Quality factor using an eigenfrequency study, how would that simulation look?

Thanks, Jeffrey