Design And Calibration Of Low-noise Vector Hydrophone

The vector hydrophone(VH)has been widely used in many underwater applications because of its high sensitivity and excellent cosine directivity at low frequency over past decade.The VH and VH based array have become the main receiver for low frequency target detection application.Not only high sensitivity of the receiver is important for weak signal acquisition at low frequency,but also alos the equivalent self-noise should be sufficiently low.Research on the self-noise reduction of VH carried out in this paper.A complete low noise vector hydrophone(LNVH)theoretical design and measurement method are purposed which provide a theoretical basis for the design and verification of the LNVH.The equivalent self-noise measurement system is established for the self-noise level of the LNVH evaluated accurately,which provides the reference for LNVH and LNVH array research.Firstly,the self-noise design method of the piezoelectric acceleratormeter,the suspension structure and the preamplifier circuit of the vector hydrophone is studied.The cable equivalent model is given for the different preamplifier circuit input forms as well.The design principle of LNVH is given based the sensing device,suspension structure,cable and preamplifier circuit as a whole VH system.According to the design principle,the self-noise level of the two different piezoelectric acceleration sensitive devices combined of two pre-amplifier circuit is analyzed.The research results show that the combination of IEPE acceleration-sensitive devices and low-noise operational amplifiers provide the lower self-noise for the VH.design and production of two low-noise vectors using the preferred acceleration-sensitive devices and preamplifiers Sample The two prototype of the LNVH are manufactured.Secondly,in order to improve self-noise of the LNVH measurement precision,both the measurement methods and measurement systems are studied in this paper.The dual hydrophone cross-spectrum method(DHCM)is proposed as the measurement method.The best conditions of the DHCM process though the simulation of when the ambient background noise,the sensitivity of the two measured VHs and the sampling data length are not the same.the vacuum and the water medium environment measurement system are developed.The measurement results by using DHCM in the above measurement system show that the equivalent self-noise pressure level of the designed LNVH is below ambient noise at sea states zero in the frequency range of 100-1000 Hz,wherein reaches 55.5dB/?Hz at 200 Hz.The self-noise level is close to and part of exceeded the tunnelling accelerometer based vectorhydrophone in 100-1000 Hz,which has the lowest self-noise.Finally,a transient calibration method for calibrating the sensitivity of the LNVH with large-sized preamplifier circuits in low-frequency limited space water tank is proposed.The principle of low frequency limited space is studied by using the low frequency sound field distribution in the limited space of the tank.The correction method of transient calibration sensitivity based on transient calibration technique is proposed as well.The calibration results show that the transient sensitivity calibration method can be used in the finite space for the free-field sensitivity calibration of the LNVH.This method effectively expands the low frequency limit of the sensitivity calibration of the VH and provides a new method for phase calibration of the low-frequency vector hydrophone array.