Design And Realization Of Low-Frequency Sensitivity Measurement System For Hydrophone Based On Air Acoustic Tube

With the deep development of underwater acoustic engineering technology,nowadays sonar technology is more and more developing to lower frequency,and the importance of low frequency parameters of sonar equipment is increasing day by day.As the core conversion component of acoustic signal and electrical signal in sonar equipment,the most important parameter of hydrophone is sensitivity.However,the calibration and measurement of low frequency sensitivity level of hydrophone is often accompanied by high cost and cumbersome measurement process.Therefore,in order to improve the convenience of low frequency sensitivity level measurement of hydrophone,the existing traveling wave acoustic tube technology is referred to.In this paper,the low frequency sensitivity of hydrophone is measured by air sound tube.The measurement method is to establish the planar traveling wave sound field in the circular tube waveguide to satisfy the free field condition and the sound field pressure condition required for the hydrophone calibration by the comparative method.In order to increase the speed and stability of measurement,an automatic measurement system is designed to measure the sensitivity level of hydrophone effectively and quickly.The measuring system consists of mechanical system and electronic system.The mechanical system mainly provides the necessary conditions for the establishment of the planar traveling wave sound field in the acoustic tube.The electronic system is divided into signal generation part,signal conditioning part,signal acquisition part and digital control part according to the function.The paper has completed the chip selection,circuit design and debugging,function testing and other work of the four parts of the circuit.The main function of the signal generation part is to generate the excitation signal required by the speaker.The design uses the FPGA control DAC chip to generate two independent excitation signals with adjustable parameters.The main function of the signal conditioning part is to amplify the signal received by the hydrophone,and realize the gating of two-stage amplification through the analog switch;The digital control part is responsible for the analysis of the upper computer instructions,according to the command control signal generation part and signal acquisition part to complete the signal generation,collection and data upload functions.The main control chip of digital control part uses FPGA,and the communication interface between FPGA and upper computer uses USB interface.In the signal acquisition part,ADC chip is used to convert signals into analog to digital,including the acquisition of 16 channels.The collected data is transmitted to the upper computer through USB for processing,so as to obtain the sensitivity level of the hydrophone to be calibrated.The measuring system establishes the plane wave sound field in the circular tube waveguide,and tests the deviation of sound pressure amplitude at different positions of the sound field.The test results are all below 1dB within the range of measured frequency.This paper uses the measuring system to measure the sensitivity level of the sound pressure hydrophone 8103,8104,8105 developed by Brüel & Kj?r Company and the hydrophone developed by domestic institutes.At the same time,the measurement results are basically consistent with the sensitivity level curve of the official data manual by comparing with the sensitivity curve of the official or first-level measuring station.In the frequency range of 300 Hz,the error is less than 1dB,and in the frequency range of 300Hz-700 Hz,the error is less than 1.5dB,which verifies the accuracy and reliability of the measuring system for the hydrophone sensitivity level.