[mehc]

I want to extract polyphenols from my tea sample by sonication for 2 hours. As the polyphenols are readily oxidized by light, I have to cover my flasks completely.
If I wrap my flask with aluminum foil completely except from bottom, Will ultrasound energy pass easily through the flask?

[azmanam]

yes, but any foil in the water will disintegrate.  one other option is to take an old cardboard box and build yourself a little boxed-in cave.