Direct-immersion horn type ultrasonic generator.

Hi,

I was wondering if anyone knows how to calculate the intensity of ultrasonic irradiation from a ultrasound machine (direct immersion horn type). Fequency 20kHz, maximum wattage 750W. If the amplitude is at 30% with pulse 3seconds (3s on and 3s off), wht would the intensity, in mW/cm2 be? thanks

regards

CJ