Abstract:

A 3-kHz class VII flextensional transducer was developed at NUWC. The class VII flextensional is a modified class IV shape having concave radiating surfaces rather than convex. This transducer is commonly referred to as a ``dogbone`` flextensional because of its similar shape. This design, originally described by Merchant in U.S. Patent 3,258,738 (28 June 1966), has the advantages that all the surfaces of the shell radiate in-phase and a positive compressive stress is maintained on the ceramic driver as the operation depth increases. The shell can support thinner walls, since hydrostatic pressures do not have to be overcome in order to keep the piezoelectric ceramic driver under compression, as in a conventional class IV transducer. The transducer was designed using two different modeling approaches: finite element modeling (using ATILA) and an equivalent circuit model based on plane-wave and lumped parameters. Based on the modeled results, a transducer was fabricated and then tested in August 1996. The transducer volume is 5 in. (12.7 cm) high, 5 in. (12.7 cm) long, and 2.5 in. (6.35 cm) wide, the shell material is stainless steel, and the ceramic stack is composed of 30 0.1-in. (2.54-mm)-thick PZT-8 plates, two of which are unpoled and used for insulators. The in-air weight is 10 lbs. The transducer performed exceptionally, matching the modeled data while producing an SL of 202 dB at 10 kV/in., a resonance frequency of 3050 Hz, a mechanical Q of 5, an in-water effective coupling coefficient of 30% (typical of class IV transducers), and an electro-acoustic efficiency of 80%. [Work supported by ONR.]