Advances in measurements of ultrasound fields in the frequency range 20-60 MHz

A powerful measurement technique suitable for virtually continuous calibration of ultrasonic hydrophone probes in the frequency range 250 kHz-60 MHz is described and frequency responses of PVDF polymer hydrophones are presented. The validity of the calibration results was examined using independent calibration techniques. The values of sensitivity in V/Pa obtained using a linear swept frequency technique were compared with those which were determined from the measurements employing nonlinear wave propagation. Also, the sensitivity against frequency data obtained here were compared with the data provided by an independent national laboratory. The overall agreement between the calibration results obtained using different techniques mentioned above was within ±1 dB at frequencies up to 25 MHz. The uncertainty increased gradually with increasing frequency and was determined to be ±2.5 dB at 60 MHz. A spatial averaging correction model is being developed to minimize this uncertainty. The near continuous frequency plots in the 40-60 MHz bandwidth were not reported so far and reveal that the ultrasonic hydrophone probes response is largely controlled by their design architecture.