Research On Second-order Multimode Hydrophone

In the underwater acoustic detection,the hydrophone's directivity is a very important indicator of the sonar system.Conventional vector hydrophones have a wide beamwidth,and in target detection,it is difficult to distinguish accurately if the multi-target distance is close.So how to develop a more directional high-level directional hydrophones become a new research goal.In this paper,based on the radial polarization of the piezoelectric tube,the second-order multi-mode hydrophone was studied.In this paper,the sound pressure in the sound field for Taylor series expansion,and the expansion of the order and the corresponding series of vector up.The sensitivity formula of each stage vector is deduced,and a connection method is proposed to improve the sensitivity of piezoelectric ceramic tube.The natural directivity of the second-order vector and the combinatorial directivity of each class are discussed.The influencing factors of the second-order vector hydrophone operating frequency band are proposed.Based on the theoretical derivation,the sound pressure of the hydrophone,the first-order vector and the second-order vector channel are designed.The appropriate piezoelectric ceramic tube is selected and the impedance characteristic curve is measured and cut.The epoxy resin is used as the backing of the piezoelectric tube and the outside is filled with polyurethane to produce a second-order multimode vector hydrophone with a size of ?65 ?50 mm and a working frequency band of the sound pressure channel of 20 Hz to 8000 Hz,a vector channel Working frequency band 2500Hz~8000Hz,second-order vector channel operating frequency of 3000 Hz ~ 6500 Hz.The results show that the sound pressure channel of the hydrophone is better than that of the omnidirectional,and the sensitivity fluctuates between-181 d B~-187 d B(0d B =1V/?Pa),and The theoretical value of-184 d B is not much difference.The direction of the vector channel of the hydrophone is more consistent with the cosine directivity in both directions,and the sensitivity is lower than the theoretical value-194 d B(4000Hz,0d B = 1V/?Pa).The directionality of the second-order vector channel can be observed in the transverse quadrupole directivity.After the data processing,the second-order pure bias direction is not ideal,but the trend of narrowing the beam is generally shown.