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Expansion of services for the calibration of ultrasonic hydrophones


The construction of a novel setup for hydrophone calibration was finalized by conducting extensive comparisons with further test sites at PTB. After publishing the results of these comparisons and conducting an internal audit, hydrophone calibration services up to 100 MHz can now be offered. Additionally, the results of primary calibrations are available to customers for the first time.

In recent years, a new measurement setup has been developed for primary hydrophone calibration in the Sound department. The system uses a laser vibrometer to determine ultrasonic pressure via optical means. By applying broadband ultrasonic pulses for excitation purposes, a frequency range of up to 100 MHz can now be covered. Earlier systems were able to provide calibration services only up to 50 MHz. As a standard feature, this new technique offers modulus and phase data (or the real and imaginary part of complex-valued data) of the hydrophone’s sensitivity with a frequency resolution of 0.1 MHz. This eliminates the need for additional, separate phase response determination services. Another advantage for PTB’s customers is the fact that calibration uncertainties are reduced due to the new technique being a primary method and because an increase in uncertainties resulting from the usage of transfer standards in secondary methods no longer takes place.



 Image 1: Overview of the novel test facility. The water tank with the ultrasonic transducer in the bottom is located below the laser vibrometer (blue housing unit).


PTB possesses several measurement systems that utilize different methods to calibrate and characterize hydrophones. All these facilities have now been extensively compared [1], and consistent results have been achieved with all methods under consideration of the uncertainties. This comparison also linked the new methods to the last international key comparison [2], in which PTB participated while still using the former primary standard.

After a detailed set of documentation of the test facility had been created and an internal audit successfully performed, the calibration system was incorporated into the quality management system of PTB. This has allowed hydrophone calibrations, which are particularly important for traceable measurements of medical ultrasonic fields, to now be offered to customers in an extended frequency range up to 100 MHz. It is also planned to issue digital calibration certificates in addition to the current paper certificates. This will reliably link calibration certificates and automatically readable calibration data sets, thus providing greater protection for users against accidentally selecting the wrong data set.



[1] Weber, M. & Wilkens, V. A Comparison of Different Calibration Techniques for Hydrophones Used in Medical Ultrasonic Field Measurement, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control Volume: 68, Issue: 5, Pages 1919 - 1929, May 2021 DOI: 10.1109/TUFFC.2020.3046751 Opens external link in new windowLink

[2] Rajagopal, S.; Fury, C. R.;Zeqiri, B.; Brandt, M.; Wilkens, V.; Koch, C.; Matsuda, Y.; Yoshioka, M.; Ping, Y.; Yan, Z.; Wenping, B.; Felix, R. P. & Oliveira, E. G. Report on BIPM/CIPM Key Comparison CCAUV.U-K4: Absolute Calibration of Medical Hydrophones in the Frequency Range 0.5 MHz to 20 MHz, National Physical Laboratory: Acoustics and Ionising Radiation Division, 2016 Opens external link in new windowLink



Volker Wilkens, FB 1.6, E-Mail: Opens local program for sending emailvolker.wilkens(at)ptb.de