【作者】 陈思；

【导师】 杨士莪；

【作者基本信息】 哈尔滨工程大学 ， 水声工程， 2011， 博士

【摘要】 随着减振降噪技术的进步,传统被动声纳探测潜艇遇到了困难,远距离探测潜艇需要低频主动声纳。低频大功率发射换能器的研究是远程主动声纳的关键技术之一。弯张换能器是水声领域一种典型的低频、大功率、小尺寸换能器,但由于其机械品质因数较高,带宽通常较窄,使其应用受到了一定的限制。新型弛豫铁电单晶材料在准同型相界附近具有非常优异的压电性能。本文的主要工作是利用压电单晶作为驱动材料研究弯张换能器的宽带发射问题。本文提出了利用弯张换能器的一阶弯曲振动、膜振动、二阶弯曲振动的耦合实现宽带的思想,并且研制了一种压电单晶驱动的长轴加长型弯张换能器样机。首先,运用矩阵变换法推导得到了沿[001]方向极化的铌镁酸铅—钛酸铅PMNT单晶的介电常数、柔性常数和压电常数的矩阵形式和独立的常数分量个数,作为研究压电单晶驱动的弯张换能器的基础。然后,采用有限元法,利用ANSYS软件研究了压电单晶Ⅳ型弯张换能器的主要振动模态及特征、换能器的发送电压响应及带宽特性以及换能器的结构尺寸对主要振动模态和宽带发送电压响应的影响,进而提出了利用多模态耦合的原理设计宽带弯张换能器需要解决的两个实际问题。在此基础上,提出了加高Ⅳ型弯张换能器和端面辐射型弯张换能器的解决方案,详细讨论了各种解决方案对于弯张换能器频带拓展所起到的具体作用,并最终提出了长轴加长型弯张换能器的设计思想。利用有限元软件ANSYS,对压电单晶驱动的长轴加长型弯张换能器进行了研究,建立了换能器空气中与水中的有限元模型,分析了换能器实现宽带的基本原理以及振动、辐射特性并进行了宽带性能的优化设计。长轴加长型弯张换能器首先以端面辐射型弯张换能器为基础,解决了二阶弯曲振动的响应凹谷问题。接着通过长轴加长型弯张壳体的设计,改变了换能器膜振动模态在频带内的相对位置,使之处于一阶、二阶弯曲振动模态频率之间,利用膜振动的辐射能力进一步解决了弯张换能器一阶、二阶弯曲振动之间响应起伏较大的问题。从而利用一阶弯曲振动、膜振动、二阶弯曲振动之间的耦合形成宽带,实现了弯张换能器的频带拓展,并且借助于压电单晶材料低声速、高应变的特点降低换能器的工作频率,提高换能器的发送电压响应。最后,设计并制作了PMNT单晶与PZT-4压电陶瓷驱动的Ⅳ型弯张换能器并进行了水池测试。结果表明：同种结构尺寸的Ⅳ型弯张换能器,利用PMNT做驱动材料相比PZT-4,谐振频率降低17%,谐振时的电导值大5倍,获得的发送电压响应高5dB。对PMNT单晶驱动的长轴加长型弯张换能器进行了制作和测试,在1.6kHz～16kHz的频率范围内,压电单晶长轴加长型弯张换能器的最大发送电压响应136dB,响应起伏7.8dB,带宽达到3个倍频程以上,可以实现弯张换能器的宽带发射。更多还原

【Abstract】 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 ClassⅣflextensional 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 ClassⅣflextensional 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.更多还原