Ultra-broadband underwater acoustic projector based on transverse resonance orthogonal beam (TROB) mode and acoustic matching layer technique

An acoustic matching layer can improve energy transmission between the projecting surface of an underwater acoustic projector and hence increase the frequency bandwidth. However, the conventional acoustic matching layer is mostly designed to match the fundamental resonance of the projector. This work investigates the effect of the acoustic matching layer on bandwidth improvement of dual-mode underwater acoustic projectors driven by Pb(Zn1/3Nb2/3)O3-5.5%PbTiO3 (PZN-5.5%PT) ferroelectric single crystals. The results show that when the melamine formaldehyde quarter-wavelength acoustic matching layer is designed to match the higher-frequency transverse resonance orthogonal beam (TROB) resonance of the dual-mode projector, an ultra-broad -3 dB frequency bandwidth of 76% (82 kHz-183 kHz), and a high transmission voltage response of 143.5 dB can be achieved. This work also systematically investigates and elaborates the influence of matching frequency on the performance of multi-mode projectors. In addition, due to the low sound velocities in the relaxor-PT ferroelectric single crystals, the lateral dimensions of the fabricated projector element can be kept at or less than the half-wavelength of sound of the design frequency in water, making possible fabrication of compact and ultra-broadband arrays.