Micromachined high frequency ferroelectric sonar transducers

Millimeter-sized ferroelectric monomorph sonar transducers have been built using sol-gel PZT on micromachined silicon wafers. First generation 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 tested 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 up to 12 mu m in thickness, which leads directly to higher sensitivity and figure of merit for acoustic transducers. The longitudinal piezoelectric 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 measured on 4-mu m thick films. Test results are presented, including frequency response: beam patterns, and sensitivity. High-resolution acoustic images have been generated using these transducers and a four-element underwater acoustic lens. Potential applications for these transducers include high-frequency imaging sonars, medical ultrasound, ultrasonic communication links, and flaw detection (NDT).