Medical ultrasonic standards at NPL

Absolute measurement of the acoustic output of medical ultrasonic equipment in the megahertz frequency range is discussed, together with the methods developed at NPL for the determination of the total ultrasonic power using a radiation pressure balance and the measurement of spatial and temporal field quantities with miniature piezoelectric hydrophones. The principles of the radiation pressure balance and the absolute calibration of hydrophones, which form the basis of the NPL ultrasonic standards programme, are described. Finally, beam calibration systems, which have been specially developed for the rapid and quantitative evaluation of ultrasonic fields, are briefly discussed.