Broadband acoustic projector for low-frequency synthetic aperture sonar application

Possibilities for increased mine detection and classification techniques have established a need for broadband, underwater acoustic projectors. An advanced version of a low frequency synthetic aperture sonar (SAS) for the mine reconnaissance hunter program has recently been developed. The transducer is resonant at 100 kHz but has been designed to deliver constant high sound pressure levels over an operating frequency range of 10 kHz to 100 kHz. This wide band operation is accomplished because of an absence of spurious modes within the operational frequency decade. The actual projector is constructed with a two layered 1-3 piezocomposite material stacked in mechanical series and electrically wired in parallel. This arrangement was selected in order to maximize the source level output. The center electrode of the monolithic 1-3 piezocomposite layers has been segmented to offer four individual elements such that combinations of the sectors offer the ability to access nine different apertures. A constant source level is maintained through the use of a preshaped transformer between the driver and the projector. The combination of the transformer design with the clean spectrum response of the composite material results in an acoustic projector with constant source level.