[scientizscht (OP)]

Hello!

Is 500kHz ultrasound harmful to humans?

For how long?

Thanks!

[Bored chemist]

At a high enough power, and for long enough.
However I suspect the range  of 500 KHz ultrasound in air is so small as to be not worth bothering with.

[alancalverd]

Any source of vibration will produce some heating effect and a low-frequency high-amplitude pulse can be focussed to break up kidney stones. It all depends on the intensity and duration of the exposure.