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The buoyancy method - a potential new primary ultrasound power standard.

Rajagopal, S; Shaw, A (2012) The buoyancy method - a potential new primary ultrasound power standard. Metrologia, 49 (3). pp. 327-339.

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The acoustic output power produced by medical ultrasound equipment is a key quantity representing the safety to the exposure of ultrasound during diagnostic or therapeutic applications. At present the wideley used method for estimating the total output power from ultrasound sources is by measuring the radiation force using a gavimetric balance. The method described here is a non-radiation force method using a form of calorimetry where the average temperature change in the medium is inferred from its volume change. This method has been previously validated using radiation force method at 1 MHz and 3 MHz for powers in the range 1 W to 350 W. Estimated systematic uncertainties at 95 % confidence interval was 3.4 % for 1 MHz at 50 W measured power and typical overall uncertainties were in the order of 4 %.The same method is now extended and validated up to 9.5 MHz using a improved target and powers in the range of 100 mW to 1 W are investigated. The investigation into higher frequencies and modified data analysis has improved understanding of two important systematic effects. First, the heat loss from the acoustic entry membrane of the castor oil target, which was found to be a function of insonation time and significant at higher frequencies. Second, the effect of energy stored in the heating element on determining the buoyancy sensitivity by electrical heating. At a 95 % confidence level, the estimated systematic uncertainty in the incident power with the improved target is 2.6 % for 50 W acosutic power at 3 MHz for the transducer tested in the original paper which is an improvement over the figure of 3.5 % from the previous design.

Item Type: Article
Keywords: Ultrasound, Output power, Buoyancy, Calorimetry, Calibration, Heat loss
Subjects: Acoustics
Acoustics > Ultrasound
Identification number/DOI: 10.1088/0026-1394/49/3/327
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5493

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