含玻璃微球的黏弹性复合材料覆盖层的水下吸声性能分析

水下吸声覆盖层对潜艇的隐身具有重要的意义, 因此得到了广泛的关注. 本文对含有玻璃微球的黏弹性复合材料覆盖层的水下吸声性能进行了理论分析. 采用等效参数法计算了玻璃微球的体积含量对复合材料的力学和声学性能的影响. 应用声波在多层介质中传播的一维模型, 计算了不同玻璃微球体积含量的单层复合材料覆盖层的吸声性能.结果表明, 增加玻璃微球的体积含量可以提高覆盖层的低频吸声性能, 但是其高频吸声性能降低.采用遗传算法对玻璃微球在覆盖层厚度方向上的体积含量分布进行优化. 优化的多层结构可以在一定的频带内改善覆盖层的表面与水的声阻抗匹配, 在保证覆盖层的高频吸声系数大于某一限值(0.7)的前提下, 提高其低频吸声性能.另外, 多层优化结构覆盖层不含宏观的空腔结构, 不影响覆盖层的耐压性能.其结构简单, 对制备工艺的要求不高.因此, 本文形成的理论方法适用于水下吸声覆盖层的设计. 关键词： 水下吸声 黏弹性复合材料 玻璃微球 遗传算法     

具有压电分流电路薄板的吸声特性Ⅰ.理论分析

首次从理论上分析了粘有压电陶瓷片薄板的低频吸声特性和吸声机理.根据压电陶瓷薄片外接分流电路时的等效柔顺性系数,应用拉格朗日方程建立了粘有压电陶瓷片薄板的运动方程.该方程中包含了薄板和压电片的质量、弹性、阻尼以及压电片分流电路的电阻和电感.给出了粘有压电片薄板的表面阻抗和吸声系数的数值计算方法,数值计算表明调节分流电路参数可明显改善薄板一阶模态处的吸声特性.     

具有压电分流电路薄板的吸声特性Ⅱ.数值和实验分析

利用数值计算和实验方法研究了压电分流阻尼技术控制薄板吸声特性的机制,分析了串联电阻和电感与薄板吸声系数、相对声阻和相对声抗之间的关系.数值计算和实验结果表明:通过调节分流电路中电感和电阻等参数,可使电路谐振和机械谐振出现强耦合,进而明显提高薄板一阶模态处的吸声系数和吸声带宽.     

0.7Pb(Mg1/3 Nb2/3)O3-0.3PbTiO3单晶/环氧树脂1-3型复合材料的压电性能研究

模拟了0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3(PMN-0.3PT)单晶1-3型压电复合材料的性能与单品体积分数的关系,得出性能最优时压电相的体积分数为64%,在这一体积分数下,采用切割-填充法,并使用了不同类型的环氧树脂填充制备复合材料.系统地研究了聚合物相对复合材料性能的影响,研究表明,减小聚合物相的刚度系数c和密度ρ有利于提高复合材料的性能,且聚合物相与压电相的结合强度对性能的影响非常明显,制备的PMN-0.3 PT单晶1-3型复合材料的厚度伸缩机电耦合系数k1高达90.1%,压电系数d33大于1000 pC/N,机械品质因数Qm为10.39,声阻抗Z也大大降低,性能明显优于传统的Pb(Zrx,Ti1-x)O3(PZT)陶瓷及其1-3复合材料,在压电换能器和传感器中显示出广阔的前景.     

不同压电分流电路对声子晶体梁带隙的影响

通过在匀质基体梁上周期性对贴连有分流电路的压电片,可以形成一维声子晶体结构.不同分流电路将决定梁的带隙特性.电阻分流电路能够对梁的模态共振有一定的抑制作用,而且可以通过改变压电效应的强弱使Bragg带隙结构发生变化.LC分流电路会使梁产生局域共振带隙,其带隙是由压电片激励LC电路产生电磁振荡形成.引入电阻后会使LC电路的共振作用变弱,使得带隙衰减幅值变小,但可以扩宽带隙频率范围.     

含空腔的功能梯度声学覆盖层水下吸声特性

针对传统的声学覆盖层吸声频带窄的问题,基于功能梯度材料的特点提出了一种含空腔结构的水下功能梯度声学覆盖层结构,引入梯度有限元法建立了功能梯度型声学覆盖层的水下声学计算模型,研究了功能梯度声学覆盖层结构的水下吸声特性。与传统的功能梯度结构声学建模方法相比,在保证计算精度和计算效率的基础上,文中所建立的功能梯度结构声学计算模型可适用于更复杂的功能梯度声学结构声学性能评估。研究结果表明,功能梯度声学覆盖层能够有效改善中高频段的吸声性能,获得较好的宽频吸声效果。此外,空腔形状采用锥型空腔结构或者组合型空腔结构可以有效地拓宽功能梯度声学覆盖层的吸声频带。      

聚合物电导率对0-3型压电复合材料极化性能的影响

建立了0-3型压电复合材料的等效电学模型.分析了聚合物电导率对复合材料极化性能的影响，研究了聚苯胺改性0-3型锆钛酸铅/聚偏氟乙烯复合材料极化性能与聚合物电导率之间的关系.理论分析和实验结果均表明，提高聚合物电导率可以提高复合材料的极化性能. 关键词： 压电复合材料 电导率 极化 聚偏氟乙烯     

0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3单晶/环氧树脂1-3型复合材料的压电性能研究

模拟了0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃(PMN-0.3PT)单晶1-3型压电复合材料的性能与单晶体积分数的关系,得出性能最优时压电相的体积分数为64%, 在这一体积分数下,采用切割-填充法,并使用了不同类型的环氧树脂填充制备复合材料.系统地研究了聚合物相对复合材料性能的影响,研究表明,减小聚合物相的刚度系数c和密度ρ有利于提高复合材料的性能,且聚合物相与压电相的结合强度对性能的影响非常明显,制备的PMN-0.3 PT单晶1-3型复合材料的厚度伸缩机电耦合系数k_t高达90.1%,压电系数d₃₃大于1000pC/N,机械品质因数Q_m为10.39,声阻抗Z也大大降低,性能明显优于传统的Pb(Zr_xTi_1-x)O₃(PZT)陶瓷及其1-3复合材料,在压电换能器和传感器中显示出广阔的前景. 关键词： PMN-PT单晶 压电复合材料 压电相 聚合物相     

内嵌不同形状散射子的局域共振型黏弹性覆盖层低频吸声性能研究

最近研究表明,将声子晶体中的局域共振现象引入到水下吸声材料的设计中,可以观察到由局域共振引起的低频声吸收现象.为了进一步揭示局域共振低频吸声机理并获得更优的水下低频声吸收性能,研究了内嵌不同形状散射子的黏弹性声学覆盖层.利用晶格和散射子在空间排布的对称性,传统有限元方法得到简化,从而节约了计算时间和存储空间,并通过将简化有限元法计算得到的结果与传统有限元法计算的结果进行对比,验证了简化有限元方法的正确性.结合位移云纹图,考察了特定频率点上振动模态与相应的局域共振吸声峰之间的关系,揭示了内嵌圆柱形散射子的黏弹性覆盖层的吸声机理.进一步讨论了相同体积下不同形状的圆柱形散射子对黏弹性覆盖层吸声性能的影响,给出了提升覆盖层低频吸声性能的优化思路.通过讨论不同芯体材质对内嵌圆柱形散射子的黏弹性覆盖层吸声性能的影响,找到了改变第一共振峰位置的方法,从而可以通过调整第一共振峰来实现特定频率范围内的宽带吸声.     

压电复合材料换能器

压电复合材料是将压电陶瓷与聚合物材料按一定的连通方式、一定的体积百分比和一定的空间分布复合而成的。它可以提高材料的某些压电性能,并具有常用压电陶瓷材料所没有的某些优良性能。在过去的十几年中材料研究者们做了大量工作并取得实用性进展。     

Singular variation property of elastic constants of piezoelectric ceramics shunted to negative capacitance

Piezoelectric shunt damping has been widely used in vibration suppression, sound absorption, noise elimination, etc.In such applications, the variant elastic constants of piezoelectric materials are the essential parameters that determine the performances of the systems, when piezoelectric materials are shunted to normal electrical elements, i.e., resistance,inductance and capacitance, as well as their combinations. In recent years, many researches have demonstrated that the wideband sound absorption or vibration suppression can be realized with piezoelectric materials shunted to negative capacitance. However, most systems using the negative-capacitance shunt circuits show their instabilities in the optimal condition, which are essentially caused by the singular variation properties of elastic constants of piezoelectric materials when shunted to negative capacitance. This paper aims at investigating the effects of negative-capacitance shunt circuits on elastic constants of a piezoelectric ceramic plate through theoretical analyses and experiments, which gives an rational explanation for why negative capacitance shunt circuit is prone to make structure instable. First, the relationships between the elastic constants c_(11), c_(33), c_(55) of the piezoelectric ceramic and the shunt negative capacitance are derived with the piezoelectric constitutive law theoretically. Then, an experimental setup is established to verify the theoretical results through observing the change of elastic constant c_(55) of the shunted piezoelectric plate with the variation of negative capacitance.The experimental results are in good agreement with the theoretical analyses, which reveals that the instability of the shunt damping system is essentially caused by the singular variation property of the elastic constants of piezoelectric material shunted to negative capacitance.     

Multimode shunt damping of piezoelectric smart panel for noise reduction

Multimode shunt damping of piezoelectric smart panel is studied for noise reduction. Piezoelectric smart panel is a plate structure on which a piezoelectric patch is attached with an electrical shunt circuit. When an incidence sound is impinged on the panel structure, the structure vibrates and the attached piezoelectric patch produces an electrical energy, which can be effectively dissipated as heat via the electrical shunt circuit. Since the energy dissipation strongly depends on the vibration mode of the panel structure, many patches are required for multiple vibration modes. Instead of using multiple piezoelectric patches, a single piezoelectric patch is used in conjunction with a blocked shunt circuit for multimode shunt damping. Modeling, shunt parameter tuning, and implementation of the blocked shunt circuit along with an acoustic test of the panel are explained. A remarkable reduction of the transmitted noise was achieved for multiple modes of the panel. Since this technology has many merits in terms of compactness, low cost, robustness, and ease of installation, practical applications in many noise problems can be anticipated.     

A multiple degree of freedom electromechanical Helmholtz resonator

The development of a tunable, multiple degree of freedom (MDOF) electromechanical Helmholtz resonator (EMHR) is presented. An EMHR consists of an orifice, backing cavity, and a compliant piezoelectric composite diaphragm. Electromechanical tuning of the acoustic impedance is achieved via passive electrical networks shunted across the piezoceramic. For resistive and capacitive loads, the EMHR is a 2DOF system possessing one acoustic and one mechanical DOF. When inductive ladder networks are employed, multiple electrical DOF are added. The dynamics of the multi-energy domain system are modeled using lumped elements and are represented in an equivalent electrical circuit, which is used to analyze the tunable acoustic input impedance of the EMHR. The two-microphone method is used to measure the acoustic impedance of two EMHR designs with a variety of resistive, capacitive, and inductive shunts. For the first design, the data demonstrate that the tuning range of the second resonant frequency for an EMHR with non-inductive shunts is limited by short- and open-circuit conditions, while an inductive shunt results in a 3DOF system possessing an enhanced tuning range. The second design achieves stronger coupling between the Helmholtz resonator and the piezoelectric backplate, and both resonant frequencies can be tuned with different non-inductive loads.     

高频宽带嵌套式复合材料换能器*

研制了一种嵌套式高频宽带复合材料换能器,利用1-3型压电复合材料Q值较低、频带较宽的特点,采用组合式的结构拓展换能器的工作带宽。通过切割框型压电陶瓷、灌注环氧树脂得到压电复合材料框型敏感元件,再将不同厚度的框型敏感元件沿轴向嵌套从而制成多层嵌套的压电复合材料敏感元件。建立1-3型压电复合材料中压电小柱的等效电路,根据等效电路计算出压电小柱的谐振频率,并与1-3型压电复合材料的谐振频率理论计算结果进行对比。通过ANSYS软件对敏感元件结构进行仿真,并根据仿真结果确定了敏感元件的最佳设计方案。最终制作出的换能器进行水下测试,该换能器的谐振频率为310kHz,最大发送电压响应为188.5dB,-3dB带宽可达130kHz,接收灵敏度最大可达-186.8dB,-3dB带宽可达90kHz,谐振频率处-3dB的指向性开角约为2.4°。该嵌套式敏感元件可实现换能器宽带发射与接收声波的目标。     

Investigations of thickness-shear mode elastic constant and damping of shunted piezoelectric materials with a coupling resonator

Shear-mode piezoelectric materials have been widely used to shunt the damping of vibrations where utilizing surface or interface shear stresses. The thick-shear mode(TSM) elastic constant and the mechanical loss factor can change correspondingly when piezoelectric materials are shunted to different electrical circuits. This phenomenon makes it possible to control the performance of a shear-mode piezoelectric damping system through designing the shunt circuit. However, due to the difficulties in directly measuring the TSM elastic constant and the mechanical loss factor of piezoelectric materials, the relationships between those parameters and the shunt circuits have rarely been investigated. In this paper, a coupling TSM electro–mechanical resonant system is proposed to indirectly measure the variations of the TSM elastic constant and the mechanical loss factor of piezoelectric materials. The main idea is to transform the variations of the TSM elastic constant and the mechanical loss factor into the changes of the easily observed resonant frequency and electrical quality factor of the coupling electro–mechanical resonator. Based on this model, the formular relationships are set up theoretically with Mason equivalent circuit method and they are validated with finite element(FE) analyses. Finally, a prototype of the coupling electro–mechanical resonator is fabricated with two shear-mode PZT5 A plates to investigate the TSM elastic constants and the mechanical loss factors of different circuit-shunted cases of the piezoelectric plate. Both the resonant frequency shifts and the bandwidth changes observed in experiments are in good consistence with the theoretical and FE analyses under the same shunt conditions. The proposed coupling resonator and the obtained relationships are validated with but not limited to PZT5 A.     

含三聚氰胺多孔材料分层复合介质吸声特性*

三聚氰胺泡沫材料是一种具有高开孔率的多孔材料,具备优良的吸音、防火隔热及环保性能,可以作为吸声材料与弹性板、空腔介质形成复合结构,在建筑、航空、交通工具等工程领域有广泛的应用。该文基于Biot理论和分层介质在交界面处的不同边界条件,建立非均匀复合介质背衬刚性壁面结构的理论声学模型,详细分析了多孔材料布局对复合结构吸声特性的影响。该文理论模型计算的结果与阻抗实验得到的垂直入射吸声系数基本一致,验证了理论模型的正确性。结果表明:在多孔材料前面增加空气层可以改善高频吸声特性;在多孔材料后面增加空气层可以改善复合结构低频吸声特性。通过合理配置多孔材料,可以在应用需求频段上达到满意的吸声效果。     

PSPICE controlled-source models of analogous circuit for Langevin type piezoelectric transducer

The design and construction of wide-band and high efficiency acoustical projector has long been considered an art beyond the capabilities of many smaller groups. Langevin type piezoelectric transducers have been the most candidate of sonar array system applied in underwater communication. The transducers are fabricated, by bolting head mass and tail mass on both ends of stacked piezoelectric ceramic, to satisfy the multiple, conflicting design for high power transmitting capability. The aim of this research is to study the characteristics of Langevin type piezoelectric transducer that depend on different metal loading. First, the Mason equivalent circuit is used to model the segmented piezoelectric ceramic, then, the impedance network of tail and head masses is deduced by the Newton's theory. To obtain the optimal solution to a specific design formulation, PSPICE controlled-source programming techniques can be applied. A valid example of the application of PSPICE models for Langevin type transducer analysis is presented and the simulation results are in good agreement with the experimental measurements.     

A study of a 1-3-2 type piezoelectric composite

A novel 1-3-2 type piezoelectric composite is developed. There are piezoelectric ceramic framework supports at transverse and longitudinal directions in its structure, so it is free from the influence of any outside mechanic impact and environmental temperature change. The sample characteristic is good coherence. It has many advantages, such as a high piezoelectricity, lower density and acoustic impedance matching with water and tissue easily. Based on Newnham's series and parallel theory of composites, the calculation formulae of dielectric and piezoelectric constants of a 1-3-2 type piezoelectric composite are deduced. The sample's characteristics indicate that a 1-3-2 type piezoelectric composite's theoretic calculation values are in good agreement with the measurement results. Element samples have been designed, manufactured and measured. The results indicate that the resonant frequency, resonant impedance, piezoelectricity and static capacity of these samples are stable. It is easy to design sensor array elements using this material.     

压电陶瓷非线性对大功率换能器结构参数匹配 影响的计算分析

在Guyomar非线性模型基础上,通过机电等效法将晶堆前向负载作为等效质量和阻尼加入振动方程的质量项和阻尼项,推导了换能器振速、辐射声压级和谐振频率偏移率等表达式,计算分析了压电陶瓷非线性参数和结构参数对换能器声辐射性能的影响,研究了压电陶瓷的非线性对换能器结构参数匹配的影响。结果表明,换能器节面靠前,前盖板厚度越小,前盖板大径越小,都可以减少压电陶瓷非线性引起的换能器频率偏移。当设计频率确定时,压电陶瓷处于非线性工作域的换能器的结构参数有所减小。换能器加入辐射端匹配后,可以改善压电晶堆前向负载匹配,降低换能器的谐振频率偏移率。换能器激励电流也会出现频率偏移现象。在提高换能器激励电压时,换能器的结构参数应适当减小。得到的结论可为换能器设计提供理论依据和帮助。