Research On High Frequency Spherical Broadband Transducer

The ocean is the lifeblood of the earth,covering 71%of the earth’s surface.Acoustic transducers play an important role in the exploration of the ocean.According to the requirements of underwater small target detection,high-speed underwater acoustic communication,underwater mapping and imaging for high-frequency omnidirectional underwater acoustic transducer,this thesis carries out the research of high-frequency spherical broadband transducer.Based on the structural design and performance optimization of 1-3 piezoelectric composite,a spherical piezoelectric composite sensing element structure is proposed to realize the high-frequency and omnidirectional characteristics of the transducer.This thesis also proposes to combine the preparation of spherical composite with the curved surface forming technology of matching layer to realize the dual-mode resonant coupling of piezoelectric elements,and then expand the bandwidth of the transducer.Finally,the prototypes of high-frequency spherical omnidirectional broadband underwater acoustic transducer are developed.The details are as follows:1.Based on the constitutive relationship of 1-3 piezoelectric composite,combined with the mechanical and electrical homogenization methods of composite,the equivalent parameter model of spherical piezoelectric composite with double polymer is established,and the whole electroelastic constants of piezoelectric composite under the series connectivity of two polymer layers are successfully predicted.Through the equivalent parameter model,the variation of electromechanical coupling performance,acoustic characteristics and hydrostatic characteristics of piezoelectric composite with each component in the composite are analyzed,which lays a theoretical foundation for the design of transducer elements.2.The equivalent finite element model of spherical piezoelectric composite is established by using the joint simulation method based on lumped parameter theory and ANSYS finite element software.The influence of structural parameters on resonant characteristics of transducer is simulated and analyzed,and then the relationship between the resonant frequency of spherical composite and the radius and thickness of materials is obtained.The finite element model of the spherical transducer in the fluid domain is established,and the variation law of the electroacoustic performance and sound field radiation characteristics of the transducer in water with the structural parameters of the composite material is analyzed,so as to design the structure of the transducer.Finally,the electroacoustic performance of the spherical broadband transducer with matching layer in fluid is simulated and analyzed,and the broadband design scheme of the spherical transducer is proposed.3.Based on the "dice and fill" and "injection molding" method,an improved spherical piezoelectric composite molding process is designed,and piezoelectric composite spherical shells with different sizes are prepared.At the same time,the surface of piezoelectric composites spherical shell is coated with matching layer,and the piezoelectric composite spherical shell elements with matching layer are made.The piezoelectric,dielectric and frequency response characteristics of the elements are tested.The results show that the performances of the piezoelectric composite spherical shell element meet the design requirements of the transducer,especially the double harmonic coupling vibration appears in the vibration characteristics of the element,which lays a foundation for the broadband design of the transducer.4.According to the optimization results of finite element,the structure of spherical transducer is designed,the assembly process and packaging technology of transducer are explored,and the spherical piezoelectric composite broadband transducer prototypes are prepared.The experimental results show that the resonant frequency of the spherical transducer can reach 270 kHz,the transmitting voltage response can reach 157.1 dB,the receiving voltage sensitivity can reach-221.4 dB,and the bandwidth can reach 110 kHz.The radiated sound field of the transducer presents ideal spatial omnidirectional characteristics,which shows that the development goal of highfrequency broadband omnidirectional transmitting and receiving sound wave of the transducer is realized.