Ultrasonic microprobe hydrophones
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Miniature, bilaminar ultrasonic hydrophones have been constructed with elements of piezoelectric lead titanate (PbTiO3), lead metaniobate (PbNb2O6), and poly(vinylidene fluoride) (PVDF). The overall shape of the bilaminar element was cubical, with dimensions of about 0.8 mm for the PbTiO3 and PbNb2O6 probes and 1.3 mm for the PVDF probe. When used with a 19‐dB‐gain, 100‐pF‐input capacitance preamplifier, the sensitivities ranged from − 229 dB//IV/μPa for the PbTiO3 to − 236 dB//1V/μPa for the PVDF probe. The resonance frequency of the PbTiO3 and PbNb2O6 probes, about 0.9 MHz, was lower than expected; this is probably due to the relatively high percentage of epoxy used in constructing the elements. If one defines the useful frequency range as that for which the response is flat within ± 1 dB and the beam pattern is omnidirectional within ± 1 dB, the useful upper frequency limit extends to 100 kHz for the (larger) PVDF probes and to 200 kHz for the PbTiO3 and PbNb3O6 microprobes. These upper frequency limit...