How to emit 18 kHz to 22 kHz ultrasound?

Question

Is there a program that I can use to make a sound (30 sec) in the 18 kHz to 22 kHz range?

Answer 1

You can write some simple code to generate the output of a simple cos() function at say 21 kHz

A*cos(2*pi*fx*n) , n=0 to T, where A is your amplitude.
You may want to sample at least 4x the frequency (Nyquist sampling theorem). Then send the data to a DA converter.

However, your DA needs to support that frequency as well, otherwise your tone will never be transmitted.