THE EFFECTIVE PROPERTIES OF PIEZOELECTRIC COMPOSITE MATERIALS WITH TRANSVERSELY ISOTROPIC SPHERICAL INCLUSIONS

The effective properties of piezoelectric composite materials are very important in engineering. In this paper, the closed_form solutions of the constraint_strain and the constraint_electric_field of a transversely isotropic spherical inclusion in an infinite non_piezoelectric matrix are obtained. The dilute solutions of piezoelectric composite materials with transversely isotropic spherical inclusions are also given. The solutions in the paper can be readily utilized in analysis and design of piezoelectric composite materials or smart materials and smart structures.

A Single-Layer Piezoelectric Composite Separator for Durable Operation of Li Metal Anode at High Rates

Piezoelectric ceramic and polymeric separators have been proposed to effectively regulate Li deposition and suppress dendrite growth,but such separators still fail to satisfactorily support durable operation of lithium metal batteries owing to the fragile ceramic layer or low-piezoelectricity polymer as employed.Herein,by combining PVDF-HFP and ferroelectric BaTiO_(3),we develop a homogeneous,single-layer composite separator with strong piezoelectric effects to inhibit dendrite growth while maintaining high mechanical strength.As squeezed by local protrusion,the polarized PVDF-HFP/BaTiO_(3)composite separator generates a local voltage to suppress the local-intensified electric field and further deconcentrate regional lithium-ion flux to retard lithium deposition on the protrusion,hence enabling a smoother and more compact lithium deposition morphology than the unpoled composite separator and the pure PVDF-HFP separator,especially at high rates.Remarkably,the homogeneous incorporation of BaTiO_(3)highly improves the piezoelectric performances of the separator with residual polarization of 0.086 pC cm^(-2)after polarization treatment,four times that of the pure PVDF-HFP separator,and simultaneously increases the transference number of lithium-ion from 0.45 to 0.57.Beneficial from the prominent piezoelectric mechanism,the polarized PVDF-HFP/BaTiO_(3)composite separator enables stable cyclic performances of Li||LiFePO_(4)cells for 400 cycles at 2 C(1 C=170 mA g^(-1))with a capacity retention above 99%,and for 600 cycles at 5 C with a capacity retention over 85%.

Phase Compensation of Composite Material Radomes Based on the Radiation Pattern

Some compensation methods have been pro- posed to mitigate the degradation of radiation characteris- tics caused by composite material radomes, however most of them are complex and not applicable for large radomes, for example, the modification of geometric shape by grinding process. A novel and simple compensation strat- egy based on phase modification is proposed for large reflector antenna-radome systems. Through moving the feed or sub-reflector along axial direction opportunely, the modification of phase distribution in the original aperture of an enclosed reflector antenna can be used to reduce the phase shift caused by composite material radomes. The distortion of far-field pattern can be minimized. The modification formulas are proposed, and the limitation of their application is also discussed. Numerical simulations for a one-piece composite materials sandwich radome and a 40 m multipartite composite materials sandwich radome verify that the novel compensation strategy achieves sat- isfactory compensated results, and improves the distortion of the far-field pattern for the composite material radomes. For one-piece dielectric radome, more than 60% phasedifference caused by radome is reduced. For multipartite radome, the sidelobe level improves about 1.2 dB, the nulling depth improves about 3 dB. The improvement of far-field pattern could be obtained effectively and simply by moving the feed or sub-reflector according to phase shift of the radome.

Analysis on vibration characteristics of large-size rectangular piezoelectric composite plate based on quasi-periodic phononic crystal structure

Based on the theory of composite materials and phononic crystals(PCs),a large-size rectangular piezoelectric composite plate with the quasi-periodic PC structure composed of PZT-4 and epoxy is proposed in this paper.This PC structure can suppress the transverse vibration of the piezoelectric composite plate so that the thickness mode is purer and the thickness vibration amplitude is more uniform.Firstly,the vibration of the model is analyzed theoretically,the electromechanical equivalent circuit diagram of three-dimensional coupled vibration is established,and the resonance frequency equation is derived.The effects of the length,width,and thickness of the piezoelectric composite plate at the resonant frequency are obtained by the analytical method and the finite element method,the effective electromechanical coupling coefficient is also analyzed.The results show that the resonant frequency can be changed regularly and the electromechanical conversion can be improved by adjusting the size of the rectangular piezoelectric plate.The effect of the volume fraction of the scatterer on the resonant frequency in the thickness direction is studied by the finite element method.The band gap in X and Y directions of large-size rectangular piezoelectric plate with quasi-periodic PC structures are calculated.The results show that the theoretical results are in good agreement with the simulation results.When the resonance frequency is in the band gap,the decoupling phenomenon occurs,and then the vibration mode in the thickness direction is purer.

Parity-time symmetric acoustic system constructed by piezoelectric composite plates with active external circuits

Researches on parity-time(PT)symmetry in acoustic field can provide an efficient platform for controlling the travelling acoustic waves with balanced loss and gain.Here,we report a feasible design of PT-symmetric system constructed by piezoelectric composite plates with two different active external circuits.By judiciously adjusting the resistances and inductances in the external circuits,we obtain the exceptional point due to the spontaneous breaking of PT symmetry at the desired frequencies and can observe the unidirectional invisibility.Moreover,the system can be at PT exact phase or broken phase at the same frequency in the same structure by merely adjusting the external circuits,which represents the active control that makes the acoustic manipulation more convenient.Our study may provide a feasible way for manipulating acoustic waves and inspire the application of piezoelectric composite materials in acoustic structures.

Vibration characteristics of piezoelectric functionally graded carbon nanotube-reinforced composite doubly-curved shells

This paper presents an analytical solution for the free vibration behavior of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) doubly curved shallow shells with integrated piezoelectric layers. Here, the linear distribution of electric potential across the thickness of the piezoelectric layer and five different types of carbon nanotube(CNT) distributions through the thickness direction are considered. Based on the four-variable shear deformation refined shell theory, governing equations are obtained by applying Hamilton's principle. Navier's solution for the shell panels with the simply supported boundary condition at all four edges is derived. Several numerical examples validate the accuracy of the presented solution. New parametric studies regarding the effects of different material properties, shell geometric parameters, and electrical boundary conditions on the free vibration responses of the hybrid panels are investigated and discussed in detail.

THE OPCM STRAIN GAUGES FOR STRAIN AND STRESS MEASUREMENT OF ORTHOTROPIC MATERIAL STRUCTURES

The orthotropic mechanical sensor of piezoelectric compositematerial made from piezoelectric ceramic and resin materials andtheir sensing mechanism are presented. The sensing equations of thead- hered- and embedded-type sensing units are deduced, which areused to detect the stresses in orthotropic material structures. Thesurface strain of the orthogonal plate is measured under the actionof the planar stress field, and the error is analyzed.

Novel mechanical behavior of periodic structure with the pattern transformation

Abstract In periodic cellular structures, novel pattern transformations are triggered by a reversible elastic instability under the axial compression. Based on the deformation-triggered new pattern, periodic cellular structures can achieve special mechanical properties. In this paper, the designed architecture materials which include elastomer matrixes containing empty holes or filled holes with hydrogel material are modeled and simulated to investigate the mechanical property of the periodic materials. By analyzing the relationship between nominal stress and nominal strain of periodic material, and the corresponding deformed patterns, the influence of geometry and shapes of the holes on the mechanical property of architecture material is studied in more details. We hope this study can provide future perspectives for the deformation-triggered periodic structures.

Effects of an attached functionally graded layer on the electromechanical behaviors of piezoelectric semiconductor fibers

In this paper,we propose a specific two-layer model consisting of a functionally graded(FG)layer and a piezoelectric semiconductor(PS)layer.Based on the macroscopic theory of PS materials,the effects brought about by the attached FG layer on the piezotronic behaviors of homogeneous n-type PS fibers and PN junctions are investigated.The semi-analytical solutions of the electromechanical fields are obtained by expanding the displacement and carrier concentration variation into power series.Results show that the antisymmetry of the potential and electron concentration distributions in homogeneous n-type PS fibers is destroyed due to the material inhomogeneity of the attached FG layer.In addition,by creating jump discontinuities in the material properties of the FG layer,potential barriers/wells can be produced in the middle of the fiber.Similarly,the potential barrier configuration near the interface of a homogeneous PS PN junction can also be manipulated in this way,which offers a new choice for the design of PN junction based devices.

Electroelastic interaction between piezoelectric screw dislocation and circularly layered inclusion with imperfect interfaces

The interaction between a piezoelectric screw dislocation and an interphase layer in piezoelectric solids is theoretically investigated. Here, the dislocation located at arbitrary points inside either the matrix or the inclusion and the interfaces of the interphase layer are imperfect. By the complex variable method, the explicit solutions to the complex potentials are given, and the electroelastic fields can be derived from them. The image force acting on the dislocation can be obtained by the generalized Peach- Koehler formula. The motion of the piezoelectric screw dislocation and its equilibrium positions are discussed for variable parameters. The important results show that, if the inner interface of the interphase layer is imperfect and the magnitude of degree of the interface imperfection reaches the certain value, two equilibrium positions of the piezoelectric screw dislocation in the matrix near the interface are found for the certain material combination which has never been observed in the previous studies （without considering the interface imperfection）.

A Novel Rectangular Element for Piezoelectric Laminated Plates

Based on the classical laminated plate theory, a novel finite element formulation is presented for modeling the static response of laminated composites containing distributed piezoelectric ceramic subjected to electric loadings. A four-node rectangular composite element with an additional voltage freedom per piezoelectric layer is implemented for the analysis. The element can predict more accurately the bending response of the structure because of its new displacement radixes. Numerical examples ere performed and the calculated data compare very well with existing results in the literatures.

KNbO_(3)/PVDF/棉织物压电传感器的制备及其性能

为克服无机压电传感器柔性差和有机压电材料传感性能差的缺陷,将无机压电体KNbO_(3)和有机柔性压电体聚偏氟乙烯(PVDF)复合,以舒适性良好的棉织物为基体制备出KNbO_(3)/PVDF/棉织物压电型压力传感器。通过X射线衍射仪、扫描电子显微镜、傅里叶变换红外光谱仪、X射线电子能谱仪对所制备材料的微观形貌和结构进行表征,研究了KNbO_(3)/PVDF/棉织物材料组分变化对压力传感性能的影响。结果表明:正交相KNbO_(3)颗粒均匀分布在PVDF中,并与棉织物基底形成稳定结合;当KNbO_(3)/PVDF/棉织物材料中KNbO_(3)质量分数为5%时具有最优的压电性能,峰值电压为3.46 V,是PVDF/棉织物的3.2倍。研究结果为织物基有机-无机复合压电传感材料的开发提供了研究思路,有助于推动柔性智能纺织材料的实际应用。

一种改进型1-3-2压电复合材料的研究

高质量的压电换能器需要具备较高的机电耦合系数和灵敏度。该文在传统型1-3-2压电复合材料的基础上提出了一种改进型1-3-2压电材料,提高了压电换能器的机电耦合系数和换能器的接收灵敏度。通过有限元仿真分析了不同间距对改进型1-3-2压电材料敏感元件的谐振频率、反谐振频率及机电耦合系数的影响,并与传统1-3-2型压电复合材料进行了对比。结果表明,与传统型1-3-2压电复合材料相比,在相同间距条件下,改进型压电材料的机电耦合系数约大0.03。制做的3种不同间距改进型压电材料表明,间距为1 mm的改进型压电材料的机电耦合系数较大,约为0.68。

压电弹性体复合材料的制备与应用进展

压电材料可将人体运动等环境中离散的机械能转化为电能,实现可穿戴传感器和自供电设备等的能源供给。与聚偏氟乙烯、尼龙11等压电聚合物基体相比,高分子弹性体材料具有较低的杨氏模量和较高的应变能力,作为复合材料基体时可大大提高压电陶瓷的体积分数,赋予复合材料优异的柔韧性,产生小应力大形变,赋予材料优异的应变传递能力。因此,压电弹性体复合材料兼具压电陶瓷优异压电性能和弹性体大形变的优势,得到了科学界的广泛关注。本文概述了压电弹性体复合材料的研究现状及发展趋势,归纳了压电弹性体复合材料的种类,如硅橡胶基复合材料、聚氨酯弹性体基复合材料和聚烯烃基复合材料等;总结了各复合材料的制备与成型方法;综述了压电功能复合材料在自供电电子器件、能量收集和生物医疗等领域的应用现状,探讨了压电弹性体复合材料未来的发展方向。

小型图像声呐发射换能器优化设计

在复杂水下环境中,图像声呐因其高分辨率、高效率的探测优势,在水下目标识别时发挥着重要作用。多波束图像声呐的发射换能器多采用弧形阵,其具有大波束开角,但存在指向性边缘起伏较大的问题,影响信号强度均匀性。此外,图像声呐发射换能器通常用匹配层技术拓宽工作带宽,以获取更多信息,同时,匹配层的阻抗介于激励源和介质之间,更有利于声能的辐射。该文设计了一款弧形发射换能器,通过对阵列加权的方式来控制波束,减小指向性起伏,并添加了一层匹配层,用以拓展带宽。实际测试结果表明,换能器在130°水平开角内的指向性起伏从3 dB降低至1.5 dB,中心频率为402 kHz,带宽拓宽至217.3 kHz,优化效果显著。

压电/压磁复合楔形结构耦合场的奇异性研究:反平面问题

研究了反平面变形状态下压电/压磁复合楔形结构耦合场的奇异性.应用复变函数理论和本征函数展开方法,推导了16种机械、电学和磁学组合边界条件下关于奇异性指数本征方程的显函表达式.基于得到的本征方程,通过数值算例表明了楔角、边界条件和材料组合类型对耦合场奇异性的影响,发现压电效应和压磁效应之间的相互作用导致压电/压磁复合楔磁电弹场的奇异性比压电复合楔电弹场的奇异性更加复杂.

Electromechanical coupling of 2-2 piezo-composite material

A dynamic mode) for 2-2 piezo-composite material was developed,in which the acoustic plane waves propagating along the interface were solved and their dispersion curves were obtained.By taking the resonator thickness as half a wavelength or its odd fold,the resonant frequencies of the composite transducers are in agreement with the dispersion curves.From the dynamic model the piezoelectric coupling coefficients for the thickness vibration of the composite could be obtained as a function of the composite thickness as well as the volume fraction of the ceramic phase.The results show that when the thickness vibration mode is decoupled with the lateral periodical vibration mode,the piezoelectric coupling reaches its maximum.This condition gives a maximum frequency bandwidth and a greatest piezoelectric coupling coefficient for the composite material.

Random Vibration Control of Laminated Composite Plates with Piezoelectric Fiber Reinforced Composites

This paper presents an analysis of the active control of random vibration for lami- nated composite plates using piezoelectric fiber reinforced composites （PFRC）. With Hamilton＇s principle and the Rayleigh-Ritz method, the equation of motion for the resulting electromechani- cal coupling system is derived. A velocity feedback control rule is employed to obtain an effective active damping in the suppression of random vibration. The power spectral density and mean- square displacements of the random vibration for laminated plates under different control gains are simulated and the validity of the present control strategy is confirmed. The effect of piezoelec- tric fiber orientation in the PFRC layer on the random vibration suppression is also investigated. The analytical methodology can be expanded to other kinds of random vibration.

随机分布非椭球夹杂压电复合材料变分上下界

压电复合材料因其具有高机电耦合系数和压电常数及低密度和高声阻抗,被广泛应用于水声工程、医学和超声检测的领域.人们通过预测压电复合材料有效模量界限可以更好地优化压电复合材料的结构。目前,对于压电复合材料有效模量上下界的研究普遍集中于包含椭球形夹杂的压电复合材料,而对于非椭球形夹杂的压电复合材料研究甚少.本文在传统的Hashin-Shtrikman变分上下界方法的基础上,利用体现夹杂物分布特性及形状的微结构参数,求解横观各向同性压电复合材料有效模量的上下界.该方法适用于任意形状夹杂:当椭球域与椭球形夹杂形状相同时,该方法与传统的压电复合材料Hashi-Shtrikman上下界方法一致.当椭球域与椭球形夹杂物形状不同且夹杂含量较低时,本方法所得到的部分有效模量的上下界更紧凑.此外,本文计算了横观各向同性的压电基体含正方体夹杂的复合材料有效模量上下界,结果表明材料整体表现为横观各向同性且与椭球形夹杂时的有效模量上下界差异较小,本文建立了考虑夹杂物分布和夹杂物形状的压电复合材料上下界的计算方法,对压电复合材料的研究有一定的参考价值。

柔性压电催化复合膜的制备及其降解有机染料实验设计

将科学研究的前沿热点压电效应及压电催化引入实验课教学,通过查阅文献和课堂讲解相结合,在拓宽学生催化降解领域视野的同时,也让学生了解科技进步与环境保护之间的关系。该综合实验设计内容符合科教融合的发展需求,采用开放式条件实验的形式,引导学生探索染料降解机制,有助于加深学生对知识点的综合理解,培养学生的实践和探索精神。