Transverse resonance orthogonal beam (TROB) mode for broadband underwater sound generation

New-generation relaxor-based single crystals exhibit excellent transverse piezoelectric properties and extremely high Poisson's ratio, making possible a drive mode for underwater sound generation, hereafter referred to as the Transverse Resonance Orthogonal Beam (TROB) mode. Unlike conventional transverse width (CTW) mode in which the resonating direction and the acoustic beam direction are identical, in the TROB mode, the active material is set in resonance in half-wavelength mode in one transverse direction and the acoustic beam is generated in the CTW beam direction, the latter being orthogonal to the resonating transverse direction. For direct drive (pistonless) projectors made of [011]-poled PZN-5.5%PT single crystal of ≤62 mm3 in volume, the source levels of underwater sound generated via respective TROB and CTW modes are comparable and can be >180 dB re 1 μPa @ 1 m, which can be combined to advantage to form a broad bandwidth underwater projector. Due to low sound velocities in lead-based relaxor single crystals, the lateral dimensions of direct drive projectors utilizing the TROB excitation mode can be kept at or less than λw/2 in the design, λw being wavelength of sound of the design frequency in water. This makes possible the fabrication of broadband projector arrays via the TROB mode.