The Study Of Piezoelectric Single Crystal Flextensional Transducer

Along with the development of technologies of vibration and noise reduction, it causes great difficulties in submarine detection by passive sonar, and active sonar has been introduced as an important means for detection of distant submarine. Design and manufacture of high-power, low-frequency projectors is one of the most important technologies for long range active sonar system. Flextensional transducer is a typical low frequency, high-power and small size transducer. But the bandwidth of the transducer is narrow for its high mechanical quality factor. Thus the application is limited. Novel relaxor ferroelectric single crystal is found to exhibit excellent piezoelectric properties near the morphotropic phase boundary. The main content of this dissertation is to study the broadband transmittion of the flextensional transducer driven by piezoelectric single crystal. In this dissertation, an idea of extending the bandwidth of flextensional transducer by coupling the first flexural vibration mode, the membrane vibration mode and the second flexural vibration mode is proposed and a prototype of piezoelectric single crystal flextensional transducer with major axis lengthened is developed.Firstly, matrix transformation method is used to obtain the matrix form and the independent number of dielectric, compliance, and piezoelectric constants of PMNT single crystal polarized along [001] direction. It is the foundation of studying the flextensional transducer driven by piezoelectric single crystal.Secondly, the Classâ…£flextensional transducer driven by piezoelectric single crystal is studied using finite element software ANSYS. The researches include the main vibration modes and its characteristics, the transmitting voltage response, the bandwidth characteristics, the influence of the sizes of the transducer on the modes and broadband TVR. Then two questions which have to be dealed with for designing broadband flextensional transducer using multiple-mode-coupling are put forward. On this basis, the heightened Class IV flextensional transducer and end radial flextensional transducer are proposed. The specific effect of these kinds of solutions for extending the bandwidth of the transducer is discussed. Finally, the flextensional transducer with major axis lengthened is proposed.The flextensional transducer with major axis lengthened is analyzed using finite element software ANSYS. The finite element models of the transducer in air and water are builded. The basic principle of extending the bandwidth, the characteristics of the vibration and radiation are analyzed. The performance of its bandwidth is optimized. The flextensional transducer with major axis lengthened is proposed based on the end radial flextensional transducer whose response sunken of the second flexural vibration has been overcome. Then the relative position of the membrane mode in the bandwidth has been changed by the design of the shell with major axis lengthened. Its position has been adjusted to the region between the first and second flexural vibration modes. The large discrepancy between responses of the first and second flexural vibrations has been further overcome by the capability of radiation of the membrane mode. So the bandwidth of the flextensional transducer is extended by the coupling of the first flexural vibration mode, the membrane vibration mode and the second flexural vibration mode. Meanwhile the working frequency of the transducer is lowered by the lower sound speed of single crystal. The transmitting voltage response of the transducer is increased by the higher strain of single crystal.Finally the Classâ…£flextensional transducers driven by PMNT and PZT-4 are designed, produced and tested. It is shown that the PMNT flextensional transducer possesses a 17% lower resonance frequency,5 times more conductance and a 5dB higher transmitting voltage response than the PZT-4 flextensional transducer of the same dimensions. A flextensional transducer with major axis lengthened is produced and tested. The transmitting voltage response of the transducer reaches to 136dB with 7.8dB variation between 1.6kHz to 16kHz. The bandwidth is more than 3 octaves. The broadband transmittion of flextensional transducer has been achieved.