A new approach to low frequency wide-band projector design

Long-range, underwater, acoustic systems require low frequency signals covering a broad frequency band. We have exploited a novel approach, using a narrowband medium-output high-efficiency resonator, which transmits a frequency sweep by mechanically tuning a resonator to match the frequency and phase of the reference signal. The design begins with a symmetrical pressure balanced Tonpilz driver consisting of two pistons separated by preloaded ceramic stacks. The driver is placed between two coaxially mounted resonator tubes. This is a simple, efficient, narrow-band projector, which operates at any ocean depth. The resonant tubes have slots (or vents) progressively covered or uncovered by sliding coaxial sleeves over them. The frequency is varied by the sleeve position. A computer-controlled, electro-mechanical actuator moves the sleeves along the resonator tubes keeping the projector in resonance at the instantaneous frequency of a swept frequency modulated signal. The projector prototype was first tested at the Woods Hole Oceanographic Institution (WHOI) dock in Woods Hole, MA, and later in the Pacific Ocean during a voyage of the research vessel "PT SUR", November 2001.