Design Of Underwater Acoustic Sensor Based On PZT Piezoelectric Thin Film And Reaserch Of Its Orientation Algorithm

As an important part of the sonar, the underwater acoustic sensor is a general term for sensors used to receive and measurement signals under the water. At this stage, the underwater acoustic sensor not only needs to detect the presence of sound in the water, but also needs to sense the direction of the sound waves, which is the location of the sound source. From the above two goals, a series of work is carried out in this thesis. The whole system of the underwater acoustic sensor for sound source detection is analyzed, designed and optimized. Through the design of the sensor structure, array and post processing algorithm in this thesis, it can effectively achieve the purpose of detecting sound waves and be used in various marine activities.In this thesis, the underwater acoustic sensor and its positioning technology are described firstly. The characteristics of piezoelectric materials and the electromechanical coupling coefficient are also introduced. Then, the PZT piezoelectric thin film is used as the sensitive components of the underwater acoustic sensor. Three different structures of the piezoelectric sensing unit are analyzed, and the fixed supported rectangular structure are selected as the sensor structure. The dimensions of the sensor structure are optimized from two aspects of sensitivity and- 3d B bandwidth. The modal and harmonic response of the optimized structure are analyzed, and the effective electromechanical coupling coefficient of the structure is also derived in this thesis. It is proved that the performance of the optimized structure is obviously better than the un-optimized structure. This thesis provides the basis for the later research of a fixed supported rectangular piezoelectric sensing unit. In addition, the sound source localization by the sensor array is analyzed in this thesis. A normal tetrahedral body-centered array model is built on the basis of the normal tetrahedral array, and the expressions of the directional angle and pitch angle of the sound source in respect of the pseudo range as well as the expressions of errors are deduced. A numerical analysis of the array is developed, which proves that the array error is small and the performance is favorable. Then the optimization analysis of an arbitrary array of five elements is carried out, and the equation satisfying the best formation is given in this thesis. Finally, the time delay estimation algorithm is researched. The process of using the LMS algorithm to estimate the time delay is simulated in the two cases of noise and two cases of high SNR and low SNR were compared. The LMS algorithm is modified in this thesis and the variable step size is taken into account. A modified variable step size LMS algorithm, named GSVS-LMS, is proposed comparing with the traditional algorithms. This GSVS-LMS algorithm adds a parameter based on the SVS-LMS algorithm of the Sigmoid function. A better performance can be acquired by adjusting this parameter. The modified algorithm proposed in this thesis can be directly used in the future time delay estimation post processing design.