Megahertz-frequency sound waves with submillimeter wavelengths are widely used to probe the interior regions of many types of structures. When human tissues are exposed to ultrasound for diagnostic or therapeutic purposes, the applied power levels must be both known and minimized. Calibration of ultrasonic equipment used in industry, medicine, and research is supported by NIST ultrasound power measurement services based on a radiation force balance (RFB) constructed at NBS in 1974. In this apparatus, incident waterborne ultrasound exerts on an absorptive target a radiation force proportional to the time-averaged spatially-integrated power. Special RFB design features allow this force to be isolated from confounding ones consequent to buoyancy, surface tension, and vibration, and to be balanced by a counterforce generated by an actuator calibrated against reference masses using dc current as the transfer variable. Minimization of instrumental measurement uncertainties for the RFB has required the development of equipment and techniques which, while perhaps too elaborate for general use in ultrasound power measurements, are described as elements of possible solutions to other measurement problems.
Proceedings Title: Proceedings of the 1995 ASME International Mechanical Engineering Congress & Exposition, 95-WA/NCA-18 (The American Society of Mechanical Engineers)
Conference Dates: November 12-17, 1995
Conference Location: San Francisco, CA
Conference Title: 1995 ASME International Mechanical Engineering Congress and Exposition
Pub Type: Conferences
Medical ultrasonic, Ultrasonics, Ultrasound power measurement