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Improved hydrophone calibration

Novel measurement setup enables more comprehensive calibrations

PTBnews 3.2018
Especially interesting for

manufacturers and users of hydrophones

providers of calibration services

A novel measurement setup has been developed at PTB for the primary calibration of ultrasonic hydrophones. Hydrophones are sensors used to determine ultrasonic pressure wave in liquid media. They are mainly used in medical engineering in order to test ultrasonic equipment. The new facility covers a larger frequency range and simultaneously exhibits lower uncertainty.

Measurement setup during a measurement with the vibrometer. The vibrometer is located in the blue housing. The foil is placed in the red lens tube and lies on the water surface.

Response level (sensitivity) of a hydrophone in the frequency range from 1 MHz to 80 MHz. The gray shaded area represents the uncertainty range with a coverage factor k = 2.

Within the field of hydrophone calibration, the hydrophone’s sensitivity is defined as the ratio between the electric output voltage of the hydrophone to be calibrated and the actual ultrasonic pressure; it is then transferred as a function of the frequency via the calibration certificate.

In PTB’s new measurement facility, a high-frequency vibrometer uses an optical measurement procedure to determine the displacement of a thin foil placed on the water surface; this displacement is caused by the ultrasonic wave. The ultrasonic pressure is determined based on this measurement. Calibration is now performed using short excitation pulses at high amplitudes rather than longer, mono-frequency or tuned sound waves. Since the pulses generated by exploiting non-linear propagation in water exhibit a broad spectrum of frequencies, they allow hydrophones to be characterized in a frequency range from 1 MHz up to 100 MHz. The test assembly is mostly automated, allowing calibrations to be performed faster.

Moreover, pulse excitation allows the phase frequency response of the hydrophone to be determined easily. This piece of information is especially important when pulse deconvolution is used in order to reconstruct ultrasonic wave forms in a standardized way that is as objective as possible. The procedure is also suitable for sensors used in high-intensity ultrasonic fields that are often less responsive than conventional hydrophones.


Volker Wilkens
Department 1.6 Sound
Phone: +49 531 592-1423
Opens window for sending emailvolker.wilkens(at)ptb.de

Scientific publication

M. Weber, V. Wilkens: Using a heterodyne vibrometer in combination with pulse excitation for primary calibration of ultrasonic hydrophones in amplitude and phase. Metrologia 54, 432–444 (2017)