The FLEXBAR™: A new transducer element with applications to low‐frequency, high‐power, broadband sonar projectors

Abstract

Conventional wisdom in the sonar community has always held that the free‐free (F‐F) flexure bar, unlike its hinged‐hinged (H‐H) counterpart (i.e., the bender bar), has no useful application as an underwater transducer, presumably because it radiates as a dipole [R. S. Woollett, “The Flexural Bar Transducer,” p. 203, NUSC (1988)]. However, a simple modification converts the F‐F bar to an efficient monopole radiator, while at the same time retaining its beneficial and unique properties of nodal mounting and dynamic balance. Such a modified F‐F bar, termed a “FLEXBAR™,” has profound consequences as regards sonar projector performance. Among them is the fact that the FLEXBAR™, unlike the bender bar, can be driven at high amplitudes with essentially no mechanical coupling to or reaction on its mounting, housing, or array structure. Applications of FLEXBAR™s are illustrated by designs and predicted performances of two different liquid‐filled, tuned‐cavity projectors. The first of these is based on a cylindrical array of piezoceramic FLEXBAR™s, 21 in. in diameter × 30 in. high, covering the band of 400–800 Hz with a source level of SL≃210 dB/μPa‖m. The second unit consists of electrodynamic FLEXBAR™s in a cylindrical array 7 ft. in diameter×7.5 ft. high, and covers the band of 100–200 Hz with a source level of SL≃220 dB/μPa‖m. The calculated responses of FLEXDUCER™s (comprised of FLEXBAR™s) from their equivalent circuit representations compare favorably with their measured responses. [Work supported in part by NUSC/NLON.]