Reciprocity calibration of ultrasonic piezoelectric disks in air
Not peer reviewed
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The phase response of a transducer acting as a transmitter or receiver of sound is important in many industrial applications, such as fiscal measurements of natural gas, therein multipath ultrasonic transit-time flow meters, measurements on the velocity of sound in the gas, as well as quality measurements on natural gas. A recurring challenge when attempting to measure the phase response of transducers acoustically are the estimates of both the separation distance between the transmitter and receiver as well as the speed of sound in the media. Small deviations in both are associated with large deviations in the measured phase. For example, at 100 kHz given a sound speed in air of 343 m/s, a deviation of only ±1 mm in the measured distance between the transmitter and receiver gives a phase deviation of ±105º, and for 300 kHz the phase deviation is ±315º. In the current work, laser sensors are employed to determine the separation distance between the transmitter and receiver. The uncertainty associated with the distance measurement is estimated to be 40 µm. Utilizing the lasers, piezoelectric disks operating in air are calibrated using the reciprocity method for both magnitude and phase. The calibrated quantities are the transmitting voltage response and the receiving voltage sensitivity, and the frequency range of primary interest is 70-125 kHz, where a SNR larger than 40 dB is expected. The calibrated quantities are compared to FE-simulations, and around 90-105 kHz the deviations between the simulated and measured phases are less then 15º for the receiving voltage sensitivity, and approximately 6.5º for the transmitting voltage response. 8 measurements on the repeatability of the measurement set-up have been performed and the standard deviation about the mean is calculated to 2º for the same frequency range. The measurement uncertainties are developed for magnitude and indicates an uncertainty of approximately 0.3 dB. This is comparable to the uncertainties provided by commercial transducer producers, such as Brüel & Kjær.
PublisherThe University of Bergen
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