Research On Vector Hydrophone Based On PVDF Piezoelectric Film

Vector hydrophones have been widely used in various fields of hydroacoustic engineering for their advantages of low operating frequency,good directivity and high sensitivity,especially the vector hydrophone’s own figure-of-eight directivity,which gives it a unique advantage in hydrophone array applications.However,co-osscillating structure requires both the overall average density of the hydrophone to be close to the density of the water medium in the design and its overall geometry to be much smaller than the wavelength corresponding to the upper operating frequency,so the size and weight of its internal core device,the accelerometer,must be small to meet the design requirements.The paper starts from piezoelectric materials,comparing piezoelectric ceramics,piezoelectric single crystal and other relatively dense materials,and selects PVDF piezoelectric film with low density and light weight as the sensitive material to design the internal core device accelerometer of vector hydrophone.In order to give full play to the advantages of high flexibility and high voltage electric voltage constant of PVDF piezoelectric thin film material,the thesis proposes the idea of designing a new membrane structure bending accelerometer by using thin film material as base based on the analysis of traditional bending accelerometer consisting of PVDF piezoelectric thin film and metal base.Therefore,based on the theory of free vibration of thin film under edge solid support boundary conditions,the paper uses the multi-physics field coupling method of membrane physical field + solid mechanics + electrostatic of COMSOL Multiphysics finite element analysis software to simulate and optimize the design of the characteristic frequency and sensitivity parameters of the membrane structure bending accelerometer with various membrane base structures,and obtains the simulation of the membrane physical field under the application of different pre-stress to the membrane base The simulation results were obtained when different pre-stresses were applied to the membrane base.The simulation results show that the PVDF piezoelectric accelerometer designed with thin film base can not only obtain a smaller scale and lighter mass,but also obtain a higher operating frequency or sensitivity by applying different pre-stress to the film base.At the same time,considering the relationship between the form factor design and the operating frequency of the co-osscillating vector hydrophone,the paper starts from the analysis of the scattering characteristics of the spherical and columnar vector hydrophone in the sound field,and uses COMSOL finite element analysis software to study the influence of the sound field distortion caused by its own scale on the 8-letter directivity and sensitivity of the vector hydrophone at different frequencies after the vector hydrophone enters the sound field.The simulation results show that the vector hydrophone still has good figure-of-eight directivity when the ka is close to or even greater than 1,while the sensitivity will change,thus providing a basis for the shape design of the co-osscillating vector hydrophone.Four new membrane structure bending accelerometers were developed based on theoretical analysis and simulation optimization design,and two single-channel co-osscillating vector hydrophones were fabricated by matching the vector hydrophone with the composite material of epoxy resin and glass beads.The sensitivity of the accelerometer and the sensitivity and pointing characteristics of the vector hydrophone were tested on the shaker and in the standing wave tube,respectively.The results showed that the sound pressure sensitivity of the two vector hydrophones at 100 Hz was-232 d B and-226 d B(0 d B re 1 V/μPa)in the operating frequency band of 20～1000 Hz and 20～500 Hz,which is basically in line with the trend of 6d B increase per octave,and has good cosine pointing characteristics.