Broadband Underwater Acoustic Transducer Based On Relaxation Ferroelectric Single Crystal

Underwater acoustic transducer is the window of transmitting and receiving signals of sonar equipment,and its quality will directly affect the performance of sonar system.A significant reduction in the size and weight of the sonar equipment will greatly improve platform maneuverability and increase the system’s payload capacity.At the same time,in order to improve the detection accuracy and environmental adaptability,the sonar system is required to have ultra-wide frequency band coverage.Therefore,the underwater acoustic transducer with small volume,large bandwidth and high performance is an important guarantee to improve the effectiveness of sonar system.The relaxation ferroelectric single crystal breaks through the limitations of traditional piezoelectric ceramics in terms of elastic stiffness coefficient,electromechanical coupling coefficient and energy density,and has the potential to greatly reduce the volume weight of the underwater acoustic transducer,expand the frequency band width and improve the sound source level.However,the bandwidth of the transducer cannot be greatly improved by directly replacing the piezoelectric ceramic with a relaxation ferroelectric single crystal.Therefore,to give full play to the performance advantages of single crystal,it is necessary to study the bandwidth expansion mechanism of single crystal underwater acoustic transducer,and the specific research content is as follows.Firstly,according to Stanfield criterion,the matching relationship between the effective electromechanical coupling coefficient keff and the mechanical quality factor Qm,and the relationship between bandwidth and the effective electromechanical coupling coefficient were revealed,and the realization mechanism of the broadband of the underwater acoustic transducer with low mechanical quality factor was explored,the material properties of the front mass block were determined,and the structural parameters were optimized.Secondly,the electromechanical-acoustic equivalent circuit model of the longitudinal vibration hydroacoustic transducer driven by single crystal 32 transverse stretching vibration mode is established to characterize the underwater admittance and transmission voltage response of the transducer.Thirdly,the influences of the material parameters,structural parameters and the number of single crystal oscillators on the mechanical quality factor of the single crystal transducer are explored,the above parameters are regulated and the mechanical quality factor of the single crystal transducer is optimized.Furthermore,32 transverse stretching vibration modes,front mass bending modes and transverse resonant orthogonal beam(TROB)modes are coupled to design a multi-mode coupled UWB transducer.Finally,in order to verify the bandwidth expansion mechanism,a longitudinal vibrating underwater transducer driven by relaxation ferroelectric single crystal 32 transverse telescopic mode was prepared to test the performance of underwater conductance and transmission voltage response.The results show that according to Stansfield criterion,the optimal matching relationship between the effective electromechanical coupling coefficient and the mechanical quality factor of the transducer is.The equivalent circuit model of single crystal transducer can accurately characterize the relationship between effective electromechanical coupling coefficient mechanical quality factor and bandwidth of the transducer.The results show that the premass material with low density and high Young’s modulus can effectively reduce the mechanical quality factor of the transducer.The mechanical quality factor of the optimized single crystal transducer can be reduced to 1.85,and the bandwidth can reach 66%(Stansfield criterion).32 Single crystal transducer coupled with transverse stretching vibration mode,front mass bending mode and TROB mode achieves the response bandwidth of-3d B transmission voltage covering17.5～82.6k Hz,up to 130%.Finally,the bandwidth of the longitudinal vibration transducer driven by the transverse stretching vibration mode of single crystal 32 is 53%.And the transmission voltage response achieves the broadband transmission with the fluctuation of less than 3d B within the resonant frequency of 14～31k Hz,reaching 76%.32 Single crystal transducer coupled with transverse stretching vibration mode,front mass bending mode and TROB mode achieves the response bandwidth of-3.2d B transmission voltage covering16.5～73.0k Hz,up to 126%,which is in good agreement with the theoretical results.Therefore,the bandwidth expansion mechanism in this paper is of guiding significance for the design of wideband single crystal transducers.