Relationship between acoustic power and frequency

lupok2001

Hi everybody,
I am working with ultrasound-induced cavitation (i.e. what is used in ultrasonic water-bath cleaners) and I can't make my mind around the concept. I recon cavitation happens when the acoustic pressure (p) induced by the sound waves is greater than the hydraulic pressure of the medium through which the waves are traveling.

The acoustic pressure is calculated as
p = √(P Z A^-1)

Where P is the acoustic power, Z is the impedance of the medium and A is the surface area of the wave-front.

By looking at just the physics it seems that the acoustic pressure does not depend on the frequency of the sound wave. However, only ultrasounds (> 20 kHz) are used for cavitation. What am I missing? Is the acoustic power related to the frequency?

Thanks for the help
Fabio