In Reply to: low frequency, low power ultrasound posted by Roger Paul on 10/25/02 at 11:07 AM:
Here are some Ultrasonic links I found earlier this year.
Generating a 20kHz signal is no problem and buffering it produce 2-3 Watts is no problem.
I do think that 2-3 Watts is a lot of power unless you know what you are doing. Make sure you start at a much lower power and work your way up. I would hate to see you damage yourself or the neighborhood animals.
For circuits I found:
Educational project (you might have to email the authors):