The ubiquitous FLEXBARTM transducer element for low-frequency, broadband high-power sonar projector arrays

Abstract

The piezoceramic FLEXBARTM, a modified free-free flexure bar, is a sonar projector element of extraordinary versatility and superior performance. It represents a cost-effective, mature transducer technology that is uniquely suitable for projectors of virtually any configuration; viz., planar, cylindrical, spherical, or conformal. Piezoceramic FLEXBARTM projectors have been designed to operate at frequencies from ∼250 Hz to ∼5 kHz, with source levels and beam patterns only constrained by the available power and the allowable array envelope. In conjunction with pressure-equalizing oil-filled internal cavities, FLEXBARTM projectors are operational to essentially any depth. For example, REFLEXDUCERTM model RFD-420/A, a cylindrical array comprised of 32 FLEXBARTMs, and incorporated into a housing 20 cm D×40 cm H, has the following performance characteristics: resonant frequency to f0≂2000 Hz; quality factor Qm≂3; bandwidth B/W≂670 Hz (−3 dB); source level SL≂210 dB//μPa/m; electric power in Pwr(e)≂12 500 W; acoustic power out Pwr(a)≂8125; electro-acoustic efficiency ηea≂65%. The unit, including an internal 1:5 step-up transformer with a tuned secondary, weights approximately 66 kg so that its effective acoustic power-to-weight ratio is ≂120 W/kg (≂55 W/lb). A conformal submarine-sail design is shown covering a bandwidth of 1–5 kHz at a source level of SL≂245 dB//μPa/m, with steerable midband vertical beam patterns of θv≂10 degrees (−3 dB) and steerable horizontal patterns of θh≂5 degrees (−3 dB).