Research Of Sandwiched Flexural Vector Hydrophone

Vector hydrophones are one of the underwater receiving transducers which can measure acoustic vector information,such as sound pressure gradient,particle velocity,particle acceleration.They have natural low-frequency directivity so that they are of great value to marine research and military applications.The vector hydrophones can be classified into inertial type and non-inertial type according to sensing mode.Inertial vector hydrophones are widely used because of their high sensitivity at low frequency,but the performance can be easily affected by suspensions.Non-inertial vector hydrophones are convenient to mount,while their sensitivity is usually low and bandwidth is narrow.In general,it is necessary to apply new structures and theories to vector hydrophone design with the purpose of improving the performance and applicability.In this study,a sandwich-type flexural vector hydrophone is investigated.The non-inertial vector hydrophone design is based on composite bar that has low flexural resonance frequency in small size.Therefore,low-frequency response to input acoustic excitations of the vector hydrophone can be improved by using bending vibration mode.Besides,this structure has the advantage of simple installation.Firstly,Timoshenko’s beam theory is applied to analyze the vibration characteristics of the sandwich beam structure,and the deflection displacement is calculated.With the deflection solutions,equivalent electro-acoustic parameters of the vector hydrophone are deduced by energy method,and the driving force and induced mass of equivalent circuit are obtained based on acoustic principle.Thus,the equivalent circuit for sandwich-type vector hydrophone is given.Then the receiving characteristics of the vector hydrophone can be calculated.Secondly,finite element analysis software COMSOL is used to analyze the vector hydrophone.A validation of the theoretical analysis is performed by comparing the simulation results and theoretical calculations.Meanwhile,the influence of structural parameters variation on bending resonance frequency and receiving sensitivity is studied.According to the theoretical and FEM analysis,the structure of vector hydrophone is optimized to improve the performance.At last,the structural parameters of the vector hydrophone prototype are determined.Finally,a sandwich-type vector hydrophone prototype on the basis of optimization results is designed and fabricated.Performance of the prototype is measured in the pool.And the results of experiments show good agreement with the computation ones.It is proved that the sandwich-type non-inertial vector hydrophone working in flexural mode can meet the requirements of small size,high sensitivity and easy installation.