Study On Low Frequency Broadband Underwater Acoustic Transducer

In modern oceanic expedition,low frequency,broadband,high-power,deep-water operating underwater acoustic transducers are urgently needed for oil and gas resources exploration field and the marine environmental monitoring field based on acoustic methods,also for active anti-submarine warfare and long-distance underwater acoustic communication.The researches about low frequency,high-power acoustic transducer is also be taken great intention.In addition,ship radiated noise and marine biological noise mainly distributed in ultra-low frequency band from tens of hertz to several hundred hertz,so it is imperative that development of ultra-low frequency underwater acoustic transducers for noise simulation,acoustic decoys,jammer and other underwater acoustic equipment.The main content of this paper consists of two parts:1.Developed a Janus-Helmholtz underwater transducer using Janus longitudinal vibration transducer plus Helmholtz resonator,the working frequency band of the transducer is 400Hz-3kHz,with source level not less than 200dB,and working depth not less than 1000m.A multi-cavity Janus-Helmholtz transducer based on the structure of Janus-Helmholtz transducer is proposed for expanding the upper band of working frequency.Firstly,several basic theoretical problems of the Janus-Helmholtz transducer are studied.The broadband operating mechanism of the transducer is studied,the effect of cavity’s elastic property on the vibration performance of fluid cavity is studied,and the effect of mutual radiation caused by different part vibration on the performance of the transducer is studied.Secondly,Janus-Helmholtz transducer is researched by using the finite element method.The structure parameters of Janus-Helmholtz transducer are optimized by ANSYS.The effect of several major structural dimensions on the operation bandwidth and fluid cavity resonance frequency is studied,and the structure size of prototype design is obtained.Finally,production process of the Janus-Helmholtz transducer is studied.Watertight scheme and supporting structure are designed,three Janus-Helmholtz transducer prototypes at low,medium,and high frequency band respectively are produced,the electro-acoustic performance of the three prototypes were tested in anechoic tank.Test results show good agreement with the design results.2.A new type of moving coil transducer is developed based on a new type of magnetic circuit.Operating frequency band of the transducer is 20Hz-500Hz,the average sound source level is 162 dB,and the working depth is 150m.Firstly,vibration and sound radiation properties of moving coil transducer are studied based on the theory of mechanical vibration and sound radiation.The equivalent circuit of moving coil transducer is given.Secondly,a dual-gap magnetic circuit is designed,magnetic circuit structure optimization is carried out based on ANSYS for improving the output Lorentz force.Then,movable components of the vibrator are optimized.Shape optimization of the radiation plate is carried out to increase the upper limit of operating frequency.Optimal design of the helical springs and coil has carried out in order to increase security reliability and continuous working time;pressure compensation system is designed to ensure for work in great depth.Finally,production process of the new moving coil transducer is studied,and prototype is manufactured,the electro-acoustic performance of the prototypes was tested in anechoic tank.Test results show good agreement with the designing expectation.