Abstract
The calorimeter absorbs, in a flow of castor oil, a fraction of the acoustic power output of an ultrasound transducer. It has been used to measure powers of between 1 mW and 10 W at frequencies from 1.5 to 3 MHz. Examples are given of results obtained for an ultrasound therapy unit and an ultrasonic pulse-echo scanner. Sources of inaccuracy are defined. It appears that constant-flow calorimetry offers a potentially very sensitive method for the absolute measurement of acoustic power.