Gr. Harris et Pm. Gammell, Sensitivity measurements of piezoelectric polymer hydrophones from 0.2-2 MHz using a broadband-pulse technique, J ACOUST SO, 105(2), 1999, pp. 725-731
It is widely recognized that the sensitivity of hydrophones used to measure
medical diagnostic ultrasound fields should be uniform over several octave
s above the center frequency (i.e., above the mean of the upper and lower -
3 dB frequencies in the transmitted acoustic-pressure spectrum). However. a
bandwidth extending to at least ten times below the diagnostic pulse-cente
r frequency is needed for accurate (error approximate to 5%) measurement of
the peak rarefactional pressure. Since at present it is not common for man
ufacturers of medical-use hydrophones to provide sensitivity information be
low 1-2 MHz, a study was undertaken to determine these low-frequency sensit
ivities. The technique uses broadband, plane-wave pressure pulses generated
by electrical short-pulse excitation of a thick piezoelectric ceramic disk
. The hydrophone response is calculated from measurements of the source tra
nsducer and hydrophone-voltage waveforms. The frequency responses of both n
eedle-type and spot-poled membrane polymer hydrophones were measured using
this technique. The spot-poled membrane hydrophones had -3-dB bandwidths ex
tending below 0.2 MHz, the lower limit for the calibration technique. The n
eedle-type hydrophones studied, however, all exhibited a response roll-off
of greater than 3 dB in the frequency range studied. Therefore, given the a
bove bandwidth criterion as a function of diagnostic pulse-center frequency
, the sensitivity to at least 0.2 MHz should be established for diagnostic-
use hydrophones, because a uniform response below I MHz cannot be assumed.
[S0001-4966(99)01002-4].