This International Standard • specifies a method of determining the total emitted acoustic power of ultrasonic transducers based on the use of a radiation force balance; • establishes general principles for the use of radiation force balances in which an obstacle (target) intercepts the sound field to be measured; • establishes limitations of the radiation force method related to cavitation and temperature rise; • establishes quantitative limitations of the radiation force method in relation to diverging and focused beams; • provides information on estimating the acoustic power for diverging and focused beams using the radiation force method; • provides information on assessment of overall measurement uncertainties. This International Standard is applicable to: • the measurement of ultrasonic power up to 1 W based on the use of a radiation force balance in the frequency range from 0,5 MHz to 25 MHz; • the measurement of ultrasonic power up to 20 W based on the use of a radiation force balance in the frequency range 0,75 MHz to 5 MHz; • the measurement of total ultrasonic power in well-collimated, diverging and focused ultrasonic fields; • the use of radiation force balances of the gravimetric type or force feedback type. (See also Clause A.1) NOTE 1 A focused beam is converging in the pre-focal range and diverging beyond focus. NOTE 2 Ultrasonic power measurement in the high intensity therapeutic ultrasound (HITU) range, i.e. beyond 1 W or 20 W, respectively, is dealt with in the future IEC 62555.