Precision Acoustics
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Power Measurement

Precision Acoustics manufactures Radiation Force Balances and Check Sources which can be used to measure ultrasound power according to the IEC Standard 61161. All products are supplied with a calibration from The National Physical Laboratory, LONDON.

  • Description and Feature
  • Specification

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    Radiation Force Balance      CW Ultrasound Check Source        Apertures & Masks

    Radiation Force Balance for Diagnostic and Therapeutic Medical Ultrasound

    Ultrasonic power is a primary acoustic quantity and its measurement is required by international specification standards for both diagnostic and therapeutic ultrasound systems. In order to comply with the US FDA 510(k) regulatory requirements, IEC61157 and IEC61689, medical equipment manufacturers are required to measure ultrasonic power. The ability to measure it accurately is vital to ensuring the correct operation and safe use of ultrasound in medicine.

    Typically scanned hydrophone measurements of acoustic power have an uncertainty that is no better than 20%, whereas commercial power balances can measure to 10%.

    The Radiation Force Balance (RFB) from Precision Acoustics is a highly specified model, which can be used for the measurement of medical diagnostic and physiotherapy equipment in the frequency range 1MHz to 10MHz and the power range 10mW to 100W+.

    The Precision Acoustics RFB  can be used either with an ‘absorbing well’ target or with a suspended target which allows the design to be tailored to individual requirements for frequency, power and transducer geometry.

    The RFB can be used as a stand-alone device or connected to a PC to provide a permanent record of results in an approved Quality System.

    Each RFB is supplied with:

    ◇ Two targets –an absorbing well and a suspended target suitable for the power levels

    to be measured.

    ◇ A NPL calibration certificate, traceable directly to the UK Primary Standard for ultrasound power.

    ◇ Approved measurement protocol and user instructions.

    ◇ Software for data acquisition and analysis.

    ◇ Retort stand to hold the transducer under test.

    CW Ultrasound Check Source

    Traceable measurement of the acoustic power output of ultrasonic diagnostic and therapeutic equipment is essential for compliance with regulatory, safety and quality standards. To meet this need, the calibration of measuring equipment such as radiation force balances and power meters should be checked regularly against reference standards.

    The CW Check Source has been developed as a cost-effective route to providing traceability to National Measurement Standards. It has been designed to produce a known acoustic output power at two discrete frequencies in the diagnostic and lower-end therapeutic levels.

    NPL Apertures for effective radiation area measurement

    The NPL aperture provides a measurement capability to the quality assessment of physiotherapy ultrasound equipment with its aperture accessory for radiation force balances.

    A set of novel precision-formed apertures provide a cost-effective and reliable estimate of the effective radiating area (ERA) of physiotherapy treatment heads. They are specifically designed for use with commercially available radiation force balances commonly used for equipment testing. Without apertures measurement of the key safety parameter has demanded the use of expensive and time-consuming beam-plotting techniques using miniature hydrophones.

    To use, the NPL apertures are simply placed in front of the physiotherapy treatment head, with the resulting reduction in power being measured using the radiation force balance.

    The method is described in the paper, A new method for measuring the effective radiating area of physiotherapy treatment heads (BajramZeqiri and Mark Hodnett, Ultrasound in Medicine & Biology, Vol. 24:5, 1998, pp. 761-770), and also in the, Guidelines for the testing and calibration of physiotherapy ultrasound machines, (IPEM Report No. 84, Institute of Physics and Engineering in Medicine, 2001).

    Key Features

    The apertures are fabricated from the NPL HAMA absorber material which allows ERA measurements to be made on the majority of treatment heads used in clinical practice.

    Each pack includes a set of apertures ranging in diameter from 4mm to 30mm supplied in a handy carrying box and a comprehensive user guide.

    Radiation Force Balance-RFB

    Precision Acoustics RFB’s  is for a highly specified model suitable for the majority of medical diagnostic and physiotherapy ultrasound equipment: Using the suspended target the power generated by HIFU transducers can be measured

    ◇ Calibrated frequency range:1MHz to 10MHz*.

    ◇ Power range 20mW to 100W+ but the calibration range is 20mW to 10W*.

    ◇ Overall measurement uncertainty* – for 50mW to 5W, less than +/-7% at 95% confidence.

    ◇ For power levels greater than 100mW the typical type A (random) measurement uncertainties is typically 

    only 1%.

    ◇ Maximum transducer diameter for absorbing well target  5cm* but the suspended target will accommodate large transducers -contact us with your specific requirements.

    * The RFB may be used outside of this range with increased uncertainty levels

    Listed are the options available for NPL calibrations which are traceable to the UK’s Primary Standard.

    ◇ Calibration at 1 and 3MHz, Powers: 0.1W, 0.5W, 1W, 5W and 10W.

    ◇ Calibration at single frequency at Powers to be agreed.

    ◇ Calibration at 1 and 3MHz, Powers: 0.1W, 0.5W, 1W, 5W and 10W AND 3 Outputs in the range 10mW to

     1W at 0.928MHz and 3.151MHz AND 2 Outputs in the range 10mW to 200mW at 5.287MHz and

    7.415MHz and 9.541MHz.

    CW Ultrasound Check Source


    Up to two continuous-wave outputs at specified   frequencies


    One or two transducers selected from 1,2,3.5,5,7   or 10MHz.

    All 19mm diameter except for 1MHz which is 23mm   diameter

    Nominal Power Output

    20mW100mW or 500mW-front panel selected


    Power output stable to better than +/- 2.5%   during 1000hrs of use

    Calibration accuracy

    Supply voltage 80-250V50-60Hz

    Electrical input

    +/- 7% as standard