Research On High-sensitivity Low-frequency Piezoelectric Sound Pressure Hydrophone

With the development of hydroacoustic technology,sound pressure hydrophones have attracted much attention.Its most important application is in the military field.The main requirements for hydrophones have begun to tend to low frequency,small size,high sensitivity,wide operating bandwidth,and non-directional.In this paper,two types of sound pressure hydrophones,longitudinal vibration tonpilz hydrophone and flextensional cylindrical hydrophone,are studied.Lead zirconate titanate(PZT-4)is used as the sensitive element.First,the analysis methods of the hydrophone are introduced.The theoretical model of the longitudinal vibration tonpilz hydrophone is derived by using the equivalent circuit method,and the function expressions about frequency of the receiving sensitivity and the admittance are derived.The finite element method and sound field reciprocity principle are introduced.An example of a longitudinal vibration tonpilz hydrophone is simulated using the finite element software ANSYS 18.0,and the receiver sensitivity of the hydrophone is calculated based on the sound field reciprocity principle.A comparative analysis of the deduced results of the equivalent circuit method reveals that as for the equivalent circuit method,the material parameters and structural parameters are both reflected in mathematical formulas,which directly express the physical meaning of each structural component;ANSYS finite element simulation is closer to the actual situation in terms of modeling,modal analysis,and application of boundary conditions.Considering the longitudinal and lateral modal coupling of the hydrophone and the fluid-solid coupling interface between the front cover and the contact surface near the water field,and compared with the equivalent circuit method,finite element method is more in line with the actual situation.Then,using ANSYS finite element software to optimize the structural parameters of sound pressure hydrophones for longitudinal vibration tonpilz hydrophone,the main structural parameters were studied to find the impact on receiving sensitivity,operating bandwidth,and anti-resonant frequency.The experimental prototype of the optimized longitudinal vibration tonpilz hydrophone: the peak value of the receiving sensitivity is about-169.1 dB,and the corresponding frequency here is the first-order anti-resonant frequency of 11400 Hz.Its receiving sensitivity fluctuates less than 3 dB in the low frequency band below 2800 Hz,with an average of-186 dB.The next,using ANSYS finite element software to optimize the structural parameters of sound pressure hydrophones for flextensional cylindrical hydrophone,the main structural parameters were studied to find the impact on receiving sensitivity,operating bandwidth,and anti-resonant frequency.The experimental prototype of the optimized flextensional cylindrical hydrophone: the peak of receiving sensitivity is about-174.2 dB,and the first-order anti-resonant frequency is 6000 Hz.Its receiving sensitivity has a relatively flat response in the low frequency band below 4200 Hz,of which the fluctuation doesn't exceed3 dB,with an average of-180 dB.Finally,the above two hydrophones are processed and manufactured,and the underwater testing system and principle are introduced,and their conductance,receiving sensitivity and directivity in water are tested.For longitudinal vibration tonpilz hydrophones,tests have shown that in the 2000-15000 Hz frequency band,the measured curve is close to the theoretical calculations,and in the low frequency band of 20-2000 Hz,the hydrophone has poor receiving performance,large fluctuation and the value is very low.In this frequency band,the curve has a relatively flat response only in the range of 60-600 Hz.The average receiving sensitivity value is only-198 dB,and the directivity is concentrated along the central axis of symmetry.For flextensional cylindrical hydrophones,tests show that the measured curve in the 20-4000 Hz frequency band is very close to the curve calculated by the finite element method,and the fluctuation does' t exceed 3 dB,and the average receiving sensitivity reaches-180 dB.In addition,the hydrophone have good directivity in this band.