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The correct measurement of the broadband nonlinearly distorted pulses as emitted by diagnostic ultrasound equipment requires hydrophones working over a broad frequency range. Commonly, the hydrophones used are not ideal, e.g. the transfer functions show variations in the frequency range of interest. The new upcoming international standard “IEC 62127-1, Ultrasonics – Hydrophones – Part 1: Measurement and characterization of medical ultrasonic fields up to 40 MHz using hydrophones“ provides the application of the impulse deconvolution method in such cases [1]. However, besides the amplitude response that has classically been applied solely, the corresponding phase response of the hydrophone used is needed for this procedure. Therefore, the Ultrasonics Section of PTB has worked intensively for the past few years on the necessary extension of the hydrophone calibration techniques and has meanwhile reached the leading position on an international scale [2-5]. Accordingly, there has been no possibility so far for comparison with results of other independent calibration laboraties or metrology institutions. In anticipation of the new standard, a large European manufacturer of medical diagnostic ultrasound devices has now for the first time ordered the complex-valued calibration (1 MHz ? 50 MHz) – for one of the hydrophones to be used for exposimetry [6] in the manufacturer’s internal testing labs – which was successfully provided by the PTB.
| [1] |
V. Wilkens and C. Koch: “Improvement of hydrophone measurements on diagnostic ultrasound machines using broadband complex-valued calibration data,“ in Journal of Physics: Conference Series 1, Advanced Metrology for Ultrasound in Medicine, 27–28 April 2004, NPL, UK, IoP Publishing, pp. 50-55. |
| [2] |
C. Koch, “Amplitude and phase calibration of hydrophones by heterodyne and time-gated time-delay spectrometry,“ IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 50, pp. 344-348, 2003. |
| [3] |
V. Wilkens, “Characterization of an optical multilayer hydrophone with constant frequency response in the range from 1 to 75 MHz,“ J. Acoust. Soc. Am., vol. 113, no. 3, pp. 1431-1438, 2003. |
| [4] |
V. Wilkens and C. Koch, “Amplitude and phase calibration of hydrophones up to 70 MHz using broadband pulse excitation and an optical reference hydrophone,“ J. Acoust. Soc. Am., vol. 115, no. 6, pp. 2892-2903, 2004. |
| [5] |
V. Wilkens and W. Molkenstruck, “Broadband PVDF Membrane Hydrophone for Comparisons of Hydrophone Calibration Methods up to 140 MHz,“ IEEE Trans. Ultrason., Ferroelect., Freq. Contr., accepted for publication. |
| [6] |
V. Wilkens: “Megapascal und Milliwatt? Ultraschallexposimetrie im Dienste der Patientensicherheit,“ PTB-Mitteilungen, vol. 117, no. 1, pp. 31-34, 2007. |
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