Analysis On Performance Of Piezoelectric Infrasound Hydrophone

The infrasonic sensor with low frequency and high sensitivity is urgently necessary to be applied in the fields of nuclear explosion monitoring,earthquake monitoring and prediction,tsunami prediction and volcanic eruption monitoring.Compared with other monitoring environment,the deep water zone has smaller environment noise.Therefore the deep water environment is helpful to detect valuable infrasound information.However,it is a challenge for the infrasound sensor to seal and endure deep water pressure.The sound pressure hydrophone can detect underwater acoustic signal since it can output a voltage which is proportional to the sound pressure.The sound pressure hydrophone is an indispensable equipment of underwater sound detection,and is also the core part of the passive sonar systems.Piezoelectric hydrophones are widely used in the field of underwater acoustic detection owing to advantages of piezoelectric ceramics,such as high electromechanical coupling coefficient,good stability and high plasticity.So far,the investigation of piezoelectric hydrophone focuses on high frequency.However,the low-frequency piezoelectric hydrophone,especially the piezoelectric infrasound hydrophone(PIH),has received little attention.Therefore,the study of PIH has important application value.We propose three kinds of PIH models,which are piezoelectric bimorph infrasound hydrophone(PBIH),circular tube PIH(CTPIH)and laminated ring PIH(LRPIH).Two types of structural forms of underwater cavity and overflow are put forward for the three models,which are suitable for shallow water and deep water environment respectively.The infrasound detection performance of three kinds of IPHs with two types of structural forms is studied.The research mainly includes:Firstly,based on the linear piezoelectric theory and principle of structural dynamics,theoretical models of CTPIH and LRPIH have been established to study its basic performance in the air environment.Moreover,the expressions for estimating the sensitivity of CTPIH and LRPIH are derived from the static hypothesis.The finite element calculation results of ANSYS agree well with that of the theoretical model,which verifies the correctness of the theoretical model.The influence of structural parameters on the receiving sensitivity is further discussed.Further,the finite element models of PBIH,and of longitudinal composite hydrophones of CTPIH and LRPIH are established based on ANSYS.The numerical calculation and analysis of the mechanical-electrical coupling and fluid-solid coupling are carried out.Performances of the three kinds of PIHs are investigated,mainly including the vibration mode in the air,the sensitivity and operating bandwidth of the underwater cavity form and overflow form.The feasibility of these structure forms for infrasound detection is analyzed.In addition,the effects of the structural parameters and matching layer on the performance of the hydrophones are studied.Finally,the material selection and structural optimization of the PIHs are carried out in the allowable range of the manufacturing process.The parameters of the PIH models with good performance are given.The numerical results illustrate that reducing the natural frequency of the structure can increase the sensitivity of the PIHs,but makes operating frequency band narrower;the performance of the three kinds of PIHs with overflow form is worse than that with cavity form;there exists an optimal thickness of matching layer which can make hydrophone maximal sensitivity.After being optimized on parameters,three kinds of PIH models with cavity form have good infrasound detection performance,which are suitable for shallow water environment.The available maximum water depth can be obtained by strength check.The PIH models with overflow form can withstand a large deep water pressure.Nevertheless,for the three types of IPHs,only the overflow form of LRPIH can meet the performance requirements of the infrasound detection in deep water environment.A PIH model is obtained through optimization for deep water environment,which owns the sensitivity of-181.3 dB and bandwidth of 0.1 Hz to 120 Hz.In summary,the effects of the model parameters on the receiving sensitivity and bandwidth are obtained through theoretical analysis and numerical calculation of the theoretical models and finite element models of the IPHs.Furthermore,the model parameters of three kinds of PIHs with two types of structural forms have been optimized.Meanwhile,a theoretical basis and research methods are provided for the design and research of the PIH.