Jj. Bernstein et al., MICROMACHINED HIGH-FREQUENCY FERROELECTRIC SONAR TRANSDUCERS, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 44(5), 1997, pp. 960-969
Millimeter-sized ferroelectric monomorph sonar transducers have been b
uilt using sol-gel PZT on micromachined silicon wafers. First generati
on transducer arrays with diaphragms varying in size from 0.2 to 2 mm
were tested. Second generation 8 X 8 arrays have also been built and t
ested in water in the frequency range of 0.3 to 2 MHz. Improvements to
the sol-gel process have yielded high-quality, crack-free PZT films u
p to 12 mu m in thickness, which leads directly to higher sensitivity
and figure of merit for acoustic transducers. The longitudinal piezoel
ectric coefficient d(33) is 140 to 240 pC/N, measured through a double
beam laser interferometer. Remanent polarization of 28 mu C/cm(2), a
coercive field of 30 kV/cm, and dielectric constant of 1400 were measu
red on 4-mu m thick films. Test results are presented, including frequ
ency response: beam patterns, and sensitivity. High-resolution acousti
c images have been generated using these transducers and a four-elemen
t underwater acoustic lens. Potential applications for these transduce
rs include high-frequency imaging sonars, medical ultrasound, ultrason
ic communication links, and flaw detection (NDT).