The NPL ultrasound beam calibrator

The calibrator consists of a multielement membrane hydrophone made from polyvinylidene fluoride which is mounted in a versatile test-tank and linked to a fast data acquisition and presentation system. Acoustic output parameters of both simple medical ultrasonic systems and complex automatic scanners operating in imaging modes can be determined in a straightforward manner. Designed as a comprehensive measurement system, with the calibration traceable to United Kingdom national standards and the software configured to conform with written standards, it provides a convenient and rapid method of determining the acoustic output for both manufacturers and users of medical ultrasonic equipment. A detailed description of all aspects of the beam calibrator is given. The computer operating system is described, followed by an analysis of the postprocessing calculations which are applied to the acquired waveform data for the determination of acoustical parameters. Finally, a full assessment of the sources of uncertainty in the measurements is given, together with a comparison of results obtained using a reference measurement system.