Design And Realization Of Hydrophone Self-noise Spectral Level Measurement System

Hydrophone is an important part of sonar system,which can convert acoustic signals into electrical signals.It is widely used in underwater acoustic communication,underwater target detection,Marine environmental noise monitoring and other practices.Hydrophone self-noise is an important performance parameter of hydrophone,which has an important influence on the work of sonar system.It is very important for designers and users to understand the self-noise of hydrophones clearly.The sound and vibration in the environment will cause serious interference to the hydrophone when the equivalent noise sound pressure spectrum level is measured.The sensitive components,electronic components and cables of hydrophones are also subject to electromagnetic interference in the environment.In the absence of any shielding measures,the sound pressure spectrum level of equivalent noise of hydrophone obtained from self-noise data acquisition and analysis is quite different from the real situation.Therefore,in order to obtain the hydrophone self-noise data accurately,the measuring equipment should fully eliminate the interference of sound,vibration and electromagnetic.At good sound isolation,vibration isolation and electromagnetic shielding environment,the self-noise signal output by hydrophone is very weak.The equivalent input noise of the data acquisition system should be significantly lower than the output self-noise signal of the hydrophone.Otherwise,the self-noise signal of hydrophone will be drowned in the background noise of data acquisition system,and the data acquisition system cannot collect effective self-noise data of hydrophone.This paper designs a measuring system which can effectively measure the self-noise spectrum level of sound pressure hydrophone and vector hydrophone.The measuring principle of the system and the calculation method of equivalent noise sound pressure spectrum level of hydrophone are described in detail.The measurement system consists of mechanical system and data acquisition system.The circuit part and the mechanical device cooperate with each other,using wireless data transmission,to avoid the vibration interference brought by cable connection.The mechanical system adopts vacuum sound isolation,two-stage vibration isolation and double-layer electromagnetic shielding,which can effectively shield the sound,vibration and electromagnetic interference in the environment.The data acquisition and processing system is designed around low-noise signal acquisition.It consists of power supply unit,signal conditioning unit,analog-digital conversion unit,communication control unit and data processing program.It can realize continuous data acquisition of self-noise signal of hydrophone,calculate equivalent noise sound pressure spectrum level of hydrophone,compare the calculated results with level 0 sea state and Marine environment noise,and evaluate the self-noise level of hydrophone.In the measurement frequency band range of 10Hz～30k Hz,the effective values of the equivalent input noise of the four channels of the data acquisition and processing system are all less than1μV,and the maximum equivalent input noise density is 5.6 nV/(?) 。In this paper,the equivalent noise sound pressure spectrum level of Teledyne RESON’s hydrophone TC4014 is measured by using this measurement system.The measured TC4014 equivalent noise sound pressure spectrum level curve of hydrophone is compared with the equivalent noise sound pressure spectrum level curve given by TC4014 data manual.The accuracy of self-noise measurement of hydrophone can be verified.In this paper,the equivalent noise sound pressure spectrum levels of vector hydrophones and pressure hydrophone are measured by using the measurement system.The reliability of the measurement system is verified.When some hydrophones with preamplifiers are used for self-noise measurement,the background noise of the hydrophone self-noise spectral level measurement system is less than the equivalent noise sound pressure of the hydrophone30 dB～50dB within the 10Hz～30kH bandwidth.