[schoen]

Wow, I had no idea that we even had the technology to produce sounds at that kind of frequency, let alone that it was routinely used!

[williamscales]

The piezoelectric effect is used to do this[0]. This other wiki page[1] has some neat pictures of what the sound field looks like.

[0] https://en.wikipedia.org/wiki/Ultrasonic_transducer

[1] https://en.wikipedia.org/wiki/Ultrasonic_transducer#Transduc...