Acoustic modes are incorrect for leaky waveguides

[thariq-shanavas]

I am trying to simulate a leaky acoustic waveguide for forward SBS, where a significant fraction of phonons are expected to leak into the substrate. COMSOL simulations suggest that the acoustic quality factor of the waveguide is expected to be around 500 to 1000 taking into account only the phonons lost to the substrate. It would probably be in the 200 to 500 range if material absorption is also considered.

The calculated acoustic modes are incorrect because the acoustic waves are reflected back from the boundary of the simulation. (As mentioned in Literature example 4). What would be the best way to work around this?

I am aware the main fork of NumBAT is at https://github.com/michaeljsteel/NumBAT, but that repo does not permit raising issues.
Thank you so much for the time and effort that went into building this software package, and making it open source!

cc @michaeljsteel

[michaeljsteel]

Hi Thariq, Yeah, no doubt this is a problem. The absence of open boundaries/PML in numbat is the biggest missing feature and presents real challenges for certain structures. I would like to get this added but it's a far from trivial task and I don't currently have a student keen or capable of doing this. It's something that is proving a problem for us at times, so I'm definitely pushing towards making it happen, but can't promise anything in the short to medium term. Incidentally, I've now turned on Issues in my repo. I'm glad NumBAT is proving useful, notwithstanding the leaky modes problem. If you haven't updated to the current tree you'll find a lot of improvements in usability I think. There are few API change to deal with, but it's worth it. Best wishes Mike

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________________________________ From: Thariq Shanavas ***@***.***> Sent: Friday, 27 October 2023 6:50 AM To: bjornsturmberg/NumBAT ***@***.***> Cc: Michael Steel ***@***.***>; Mention ***@***.***> Subject: [bjornsturmberg/NumBAT] Acoustic modes are incorrect for leaky waveguides (Issue #10) I am trying to simulate a leaky acoustic waveguide for forward SBS, where a significant fraction of phonons are expected to leak into the substrate. COMSOL simulations suggest that the acoustic quality factor of the waveguide is expected to be around 500 to 1000 taking into account only the phonons lost to the substrate. It would probably be in the 200 to 500 range if material absorption is also considered. The calculated acoustic modes are incorrect because the acoustic waves are reflected back from the boundary of the simulation. (As mentioned in Literature example 4). What would be the best way to work around this? I am aware the main fork of NumBAT is at https://github.com/michaeljsteel/NumBAT, but that repo does not permit raising issues. Thank you so much for the time and effort that went into building this software package, and making it open source! cc @michaeljsteel<https://github.com/michaeljsteel> — Reply to this email directly, view it on GitHub<#10>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AGIAAPD6K632E4ZRQFFCMO3YBK5G5AVCNFSM6AAAAAA6RX3V6GVHI2DSMVQWIX3LMV43ASLTON2WKOZRHE3DIMRWHEYDANQ>. You are receiving this because you were mentioned.