Research Of Highly Directional Second-order Hydrophone Based On Vector Hydrophones

Underwater small and medium sized measurement platforms are the common equipment for detecting and positioning surface and underwater targets.The space of platform is small,not suitable for underwater acoustic sensor array with a large aperture.Application of single vector hydrophone in the platform played a good role on improving the performance of the platform.The beamwidth of vector hydrophone is large,the blunt directivity is difficult to obtain high azimuth resolution in the process of target location,and multiple targets in short distance is more difficult to distinguish.So more peaked highly directive hydrophones are needed to develope for the small and medium sized measurement platforms.Highly directional second-order hydrophone is a new concept of underwater acoustic sensors,relative to the vector hydrophone,the second-order hydrophone has more sharpening quadrupole directivity,and its outstanding feature is the ability of sound field measurement of second-order tensor.Therefore to carry physical basic research and engineering studies for highly directional second-order hydrophone are necessary.Firstly,the basis of the theory of highly directional second-order hydrophone is analyzed.Starting from the study of sound pressure decomposition theory for various physical quantities measured by second-order hydrophone in the fluid sound field,explore the physical meaning of particle velocity and velocity gradient,and discuss the relationship of velocity gradient and acoustic common physical quantities.Theoretical analysis shows that the fundamental of fluid micelles movement is pressure inhomogenetities within the fluid micelles.Particle velocity can describe the translational motion of fluid micelles,and velocity gradient can describe the deformation and rotation of fluid micelles.The directivity performance of second-order hydrophone is analyzed,and theoretical analysis shows that the directivity performance of a second-order hydrophone is better than a vector hydrophone.This dissertation studies the design theory of highly directional second-order hydrophone.The measurement principle of second-order hydrophone is discussed.A kind of second-order hydrophone based on vector hydrophone is designed,and spatial structure of second-order hydrophone that combined by six vector hydrophones and one pressure hydrophone is given.The equivalent circuit of second-order hydrophone is analyzed,and the pressure sensitivity characteristic equations are derived.Analysis of the relationship between the second-order hydrophone measurement principle and hydrophone operating band,and the influence of vector hydrophones mismatch are studied.The directivities of second-order hydrophone are analyzed by simulation when mismatch exist.Three types of second-order hydrophone are designed.Small sized uniaxial second-order hydrophone limit the operating frequency 2kHz,medium sized uniaxial second-order hydrophone limit the operating frequency 2.5kHz,complex structure triaxial second-order hydrophone limit the operating frequency 1.6kHz.Pressure sensitivity of each channel of second-order hydrophone is calculated according to the basic theory.The acoustic scattering of second-order hydrophones in the sound field are analyzed by FEM software,and simulated the directivity of each channel of second-order hydrophone and vector hydrophone mismatch caused by acoustic scattering.The performances of three types of second-order hydrophone are tested.The directivity patterns and pressure sensitivity curves are given,and test results and the theoretical values agree well.The vector hydrophone mismatch is analyzed by test data,and the phenomenon is same with the finite element simulation.The measurement errors of second-order hydrophone are estimated,and the second-order hydrophone smaplers meet the design requirements.