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Ultrasound power and radiation force balances

Measurement of acoustic output power

A radiation force balance is used to determine the output power of a transducer system. We can measure the output power generated by transducers and reference sources, such as those produced by NIST and Precision Acoustics, to standard IEC 61161 & 62555:

  • Over the range 1 mW to 20 W, between 1 MHz and 20 MHz, using radiation force balances
  • At HIFU levels (reaching over 300 W), typically between 1 MHz and 5 MHz, by the buoyancy change method based on the thermal expansion of castor oil

High Intensity Therapeutic Ultrasound (HITU), used clinically for treating a wide range of conditions, is a rapidly growing field, and measurement methods are now in place at NPL for customers providing HITU-level power measurement capability on highly focused transducers. The technique has been tested successfully at power levels in excess of 300 W.

Calibration of radiation force balances

Power measurement devices can be calibrated for power levels up to:

  •  1 W by comparison with our Primary Standard Balance, for frequencies up to 25 MHz
  •  20 W by comparison with our Secondary Standard Balance, for frequencies up to 5 MHz

Relevant standards:

  • IEC 61161:2013 - Ultrasonics - Power measurement - Radiation force balances and performance requirements.
  • IEC 61689:2013 - Ultrasonics - Physiotherapy systems - Field specifications and methods of measurement in the frequency range 0.5 MHz to 5 MHz
  • IEC 62555:2013 - Ultrasonics - Power measurement - High intensity therapeutic ultrasound (HITU) transducers and systems.


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