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How to simulate the thermal noise in microphone using COMSOL

Posted 2025年3月10日 GMT+8 16:58 Structural & Acoustics, Acoustics & Vibrations, MEMS & Piezoelectric Devices Version 6.2 1 Reply

Rowan
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For a Microphone device, SNR should be an important performance metric, defined as the difference between sensitivity and noise. I have noticed that the COMSOL case library includes a simulation case for MEMS Microphones. However, as I understand it, this case only includes results for sensitivity and frequency response. For actual devices, thermal noise introduced by the Brownian motion of air molecules and electrical noise from the amplification circuit are the main factors. The electrical noise is not considered for now. How can I calculate thermal noise using COMSOL?

1 Reply Last Post 2025年3月11日 GMT+8 16:01
Edgar J. Kaiser Certified Consultant
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Posted: 6 months ago 2025年3月11日 GMT+8 16:01

Hi Rowan,

this is an interesting topic and I was doing a little research. I found this quite extensive Stack Exchange thread that has a couple of literature references: https://physics.stackexchange.com/questions/110540/how-loud-is-the-thermal-motion-of-air-molecules I find it interesting that the Brownian noise level is far below human hearing sensitivity but not far from animal hearing, e.g. cats. Everybody who has a cat knows how sensitive they are. So, sensitive microphones are likely to be limited by Brownian noise as well. The thread is not showing how to implement Brownian noise in a numeric simulation. One option may be to implement a pressure boundary condition to the active microphone boundaries with suitable temporal and spatial random pressure fluctuations. The required intensity may be taken from the literature sources. Electronic noise depends a lot on the amplifier frontend, active component (e.g. transistor, J-FET, tube, etc.), matching circuitry, etc. The first preamplifier stage is typically the dominant electric noise source. Hope this can help a little. It would be interesting to hear about your progress. I cannot really contribute on the modeling side. I do a lot of acoustics, but I don't have the MEMS module.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Hi Rowan, this is an interesting topic and I was doing a little research. I found this quite extensive Stack Exchange thread that has a couple of literature references: https://physics.stackexchange.com/questions/110540/how-loud-is-the-thermal-motion-of-air-molecules I find it interesting that the Brownian noise level is far below human hearing sensitivity but not far from animal hearing, e.g. cats. Everybody who has a cat knows how sensitive they are. So, sensitive microphones are likely to be limited by Brownian noise as well. The thread is not showing how to implement Brownian noise in a numeric simulation. One option may be to implement a pressure boundary condition to the active microphone boundaries with suitable temporal and spatial random pressure fluctuations. The required intensity may be taken from the literature sources. Electronic noise depends a lot on the amplifier frontend, active component (e.g. transistor, J-FET, tube, etc.), matching circuitry, etc. The first preamplifier stage is typically the dominant electric noise source. Hope this can help a little. It would be interesting to hear about your progress. I cannot really contribute on the modeling side. I do a lot of acoustics, but I don't have the MEMS module. Cheers Edgar

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