基于可逆畴变的压电圆环多层致动器应变响应研究

压电致动器在现代工业中发挥着非常重要的作用。然而,目前应用的压电致动器均是基于线性压电效应,最大应变一般只有0.1-0.15%,实现大的致动应变一直是该领域学者追求的目标。本文中,我们提出了两种经过特殊设计的基于可逆非180°电畴翻转的PZT圆环多层致动器,一种是径向极化、部分电极（RPPE）的4层圆环,另一种是周期性正交极化（POP）的4层圆环,以期能够实现大的致动应变,而且圆环构型层数增加时也不容易发生失稳等问题。实验结果表明,在相同的驱动电场（2kV/mm,0.1Hz）下,4层RPPE最大致动应变为0.27%,约为普通PZT圆环的2倍,但表面变形很不均匀。相比之下,4层的POP圆环致动器的最大输出应变为0.36%,是普通PZT圆环的2.7倍。这两种致动器的致动应变都是随着频率的增加而减小, RPPE致动器在超过1Hz后稳定在0.19%, POP致动器在超过5Hz后稳定在0.2%。而且, POP圆环致动器重复性能很好,经过2万次致动循环后致动应变几乎不变。这种POP PZT多层圆环致动器具有结构稳定、输出应变大等优点,在致动领域具有很好的应用前景。     

智能板振动控制的分布压电单元法

提出了一个用于振动控制的分布压电单元法，该方法中采用将分布压电传感器和致动器分割成若干相互独立的单元的方法，来设计压电模态传感器与压电模态致动器．压电模态传感器所观测的模态坐标和模态速度，可从各传感单元的输出电荷及电流中提取出来；而压电模态致动器则通过调制施加于其上的电压的空间分布来实现．在此基础上对智能板进行了模态控制     

用两种功能材料综合控制智能梁的振动

给出了用两种材料对梁进行振动控制的综合控制方法。采用多层分布压电层进行精密主动控制时,将压电传感层和压电致动层分割成若干单元来设计压电模态传感器和压电模态致动器,进而实现了梁的模态控制,同时利用形状记忆合金的超弹性特性对梁进行被动控制来抑制梁的大振幅振动,取得了很好的控制效果。     

一种新型压电作动器的设计及其特性研究

提出了一种新型压电作动器,这种作动器由一片压电片粘贴在一个弓型梁金属底座上构成.对其变形放大原理进行了理论分析,实验测定了这种压电作动器自由状态下输出变形随驱动电压变化曲线.推导了约束状态下该作动器的输出作动弯矩与驱动电压的关系式;实验测得了约束状态下其中点位移响应幅频特性曲线.实验结果表明本文设计的新型压电作动器与传统压电片作动器相比具有较大的变形输出,具有较宽的稳定工作频率范围,而所需的驱动能量与传统压电片作动器相同,同时在使用上具有可预制、安装方便、可拆卸、对结构表面适应性好等优点.     

双向变步长大位移压电作动器

提出一种基于蠕动式运动原理的新型双向变步长的大位移压电作动器,建立了该作动器的动力学模型。在30Hz作动频率下,采用MATLAB-SIMULINK软件进行了仿真。设计了含有高电压驱动器的作动器实验系统,作动器样机整体机构由嵌位部分、作动部分和轨道间距微调部分组成。研究结果表明,该作动器实际可提供±8mm的双向往返运动,实际作动曲线与计算机仿真结果在0.1μm级精度条件下吻合良好。     

层合结构压电器件的机电耦合效应

压电传感器和致动器都可以看成是一种复合材料层合板结构，由压电材料层和非压电(弹性)材料层交替铺设而成。对于这类任意铺设的层合板悬臂梁结构，我们推导出了表示力学变形与外加电场之间耦合效应的解析表达式。进而，又推导出了两类(一类为单层压电-弹性层，另一类为双层压电-弹性层)层合型悬臂梁结构机电耦合性能的解析公式。在该机电耦合模型中，包括了两个压电常数d211和d222。此外，还建立了含压电材料的有限元算式，进行了实验测量。最后，通过比较解析解(包括考虑了d222参数的理论值和没有考虑d222参数的理论值)，实验值以及有限元计算结果，发现它们吻合得很好，而且考虑d222是十分必要的。     

附磁压电悬臂梁流致振动俘能特性分析

流致振动蕴含巨大的能量,本文基于流致振动理论,设计了一种附加磁力激励的压电悬臂梁流致振动俘能器,并通过理论和实验研究其振动俘能特性.该俘能器由压电悬臂梁、圆柱绕流体和磁铁组成;首先基于Euler-Bernoulli梁理论,推导了流致振动附磁压电俘能器的能量函数,利用Hamilton原理建立了流致振动附磁压电俘能器的机电耦合方程;利用数值方法研究详细分析了流速、圆柱绕流体直径和长度、磁间距、磁极和外接电阻等系统参数对压电俘能器振动特性和输出电压的影响.分析结果表明,该型压电俘能器的振动幅值在低流速条件下产生涡激振动,并产生最大的输出电压;磁力可以降低压电俘能器的共振频率并能够拓宽压电俘能器频带带宽,因此,附磁压电俘能器具有相比没有附磁的压电俘能器更适用于低速层流环境;实验结果与数值结果吻合较好,验证了附磁压电悬臂梁流致振动俘能器的理论分析的正确性.     

附磁压电悬臂梁流致振动俘能特性分析

流致振动蕴含巨大的能量, 本文基于流致振动理论,设计了一种附加磁力激励的压电悬臂梁流致振动俘能器,并通过理论和实验研究其振动俘能特性.该俘能器由压电悬臂梁、圆柱绕流体和磁铁组成;首先基于Euler-Bernoulli梁理论,推导了流致振动附磁压电俘能器的能量函数,利用Hamilton原理建立了流致振动附磁压电俘能器的机电耦合方程;利用数值方法研究详细分析了流速、圆柱绕流体直径和长度、磁间距、磁极和外接电阻等系统参数对压电俘能器振动特性和输出电压的影响.分析结果表明, 该型压电俘能器的振动幅值在低流速条件下产生涡激振动,并产生最大的输出电压;磁力可以降低压电俘能器的共振频率并能够拓宽压电俘能器频带带宽,因此,附磁压电俘能器具有相比没有附磁的压电俘能器更适用于低速层流环境;实验结果与数值结果吻合较好,验证了附磁压电悬臂梁流致振动俘能器的理论分析的正确性.      

层叠式PVDF压电作动器及圆柱壳的振动主动控制

设计了一个层叠式PVDF压电作动器用于壳结构的振动控制。考虑压电层、粘接层、壳体耦合关系,推导了表面局部粘贴层叠式PVDF压电作动器的圆柱壳的振动控制方程,给出了作动力与压电层和粘接层层数、厚度之间的关系以及作动力与作动器粘贴位置之间的关系。针对一端固定、另一端自由的圆柱壳,进行了振动控制仿真。结果表明层叠式PVDF压电作动器作动力与作动器层数近似成线性关系,增大作动器层数能有效增大作动力,在低控制电压下能显著抑制圆柱壳振动,作动器周向不完全粘贴时,在径向产生的径向作动力对壳体横向振动控制非常有利。说明了层叠式PVDF压电作动器是一种可用于壳体结构振动并具有良好作动效果的作动器。     

压电智能复合材料层合梁的力电耦合模型及层间应力分析

由于非凡的物理性能,石墨烯纳米片(GPL)被认为是最有吸引力的复合材料增强材料之一.GPL增强材料可以明显提高聚偏氟乙烯(PVDF)压电性能和力学性能.在力电载荷作用下,对含均匀石墨烯薄片增强(GSR)智能压电复合材料层合梁层间应力预测至关重要.若对受到力电耦合作用且层与层之间材料性能突变的压电层合梁层间剪切变形预测有误,则其层间应力过大可能导致层间失效.因此,论文提出一种适于分析此类问题且满足层与层之间相容性条件的有效力电耦合模型,用于含GSR致动器的复合材料层合梁层间应力分析.应用Reissner混合变分原理(RMVT),可以提高考虑力电耦合效应的横向剪应力预测精度.三维(3D)弹性理论和所选模型计算结果将用于评估所提梁模型性能.此外,还从力电载荷、压电层厚度、石墨烯体积分数和长厚比等方面对含GSR致动器复合材料层合梁力学响应特性进行了系统的研究.     

Development, modeling and deflection analysis of hybrid micro actuator with integrated thermal and piezoelectric actuation

Micro actuators are irreplaceable part of motion control in minimized systems. The current study presents an analytical model for a new Hybrid Thermo Piezoelectric micro actuator based on the combination of piezoelectric and thermal actuation mechanisms. The micro actuator structure is a double PZT cantilever beam consisting of two arms with different lengths. The presented micro actuator uses the structure of electrothermal micro actuator in which polysilicon material is replaced by PZT. Also the voltage and poling directions are considered in the lengthwise of PZT beams. As a result, the piezoelectric actuation mechanism is based on d ₃₃ strain coefficient. The tip deflection of micro actuator is obtained using Timoshenko beam theory. Analytical results are compared with FEM results along with other reported results in the literature. The effects of geometrical parameters and PZT material constants on actuator tip deflection are studied to provide an efficient optimization of HTP micro actuator.     

EXPERIMENTAL AND NUMERICAL STUDIES ON PERFORMANCE OF MACRO FIBER COMPOSITES FOR BEAM TWISTING APPLICATIONS

This paper presents the use of macro-fiber composites (MFC) as actuators for twisting control of pre-twisted beams, which is one efficient method of vibration suppression techniques of helicopter rotors. An MFC is a piezoelectric fiber composite which has an interdigitated electrode, rectangular cross-section and unidirectional piezoceramic (PZT) fibers embedded in the polymer matrix. An MFC actuator has much higher actuation performance, flexibility and durability than a traditional piezoceramic (PZT) actuator. This study showed that an MFC could be used as an actuator to change the displacement and twist tip-angle of a pre-twisted beam. In the test, an MFC patch was pasted on the beam’s upper surface to twist the pre-twisted beam actively. Different twist tip-angle changes of the pre-twisted beam were measured under a series of actuation voltages, and a good agreement was observed when experimental results were compared with numerical results. In addition, the actuation performance of MFC was compared with those of PZT4 and PVDF and the influence of anisotropic property of the MFC on its actuation performance was also studied. The experimental and numerical results presented in this paper show the potential of MFC for use in the vibration control of helicopter rotors.     

A Motion Amplifier Using an Axially Driven Buckling Beam: I. Design and Experiments

For active materials such as piezoelectric stacks, which produce large force and small displacement, motion amplification mechanisms are often necessary – not simply to trade force for displacement, but to increase the output work transferred through a compliant structure. Here, a new concept for obtaining large rotations from small linear displacements produced by a piezoelectric stack is proposed and analyzed. The concept uses elastic (buckling) and dynamic instabilities of an axially driven buckling beam. The optimal design of the buckling beam end conditions was determined from a static analysis of the system using Euler's elastica theory. This analysis was verified experimentally. A stack-driven, buckling beam prototype actuator consisting of a pre-compressed PZT stack (140 mm long, 10 mm diameter) and a thin steel beam (60 mm× 12 mm× 0.508 mm) was constructed. The buckling beam served as the motion amplifier, while the PZT stack provided the actuation. The experimental setup, measuring instrumentation and method, the beam pre-loading condition, and the excitation are fully described in the paper. Frequency responses of the system for three pre-loading levels and three stack driving amplitudes were obtained. A maximum 16^∘ peak-to-peak rotation was measured when the stack was driven at an amplitude of 325 V and frequency of 39 Hz. The effects of beam pre-load were also studied.     

Electro-mechanical properties and electrostriction response of a rubbery polymer for EAP applications

The mechanical response of a widely used electro-active polymer (EAP) material, and the sensitivity of this response to imposed strain rate, are measured by performing tension and compression tests at constant strain rate as well as relaxation experiments. Simple actuators are constructed and used to determine the sensitivity of the material’s relative dielectric permittivity to excitation frequency and imposed equibiaxial strain. Actuators are subjected to both a monotonic, slowly increasing electrical excitation and to a more rapid oscillating electric field; the differences in the resulting actuation strains reveal the importance of the material’s viscosity in its performance as an actuator.     

A mathematical model for cylindrical,fiber reinforced electro-pneumatic actuators

In recent years, dielectric elastomers have received increasing attention due to their unparalleled large strain actuation response (>100%). The force output, however, has remained a major limiting factor for many applications. To address this limitation, a model for a fiber reinforced dielectric elastomer actuator based on the deformation mechanism of McKibben actuators is presented. In this novel configuration, the outer cylindrical surface of a dielectric elastomer is enclosed by a network of helical fibers that are thin, flexible and inextensible. This configuration yields an axially contractile actuator, in contrast to unreinforced actuators which extend. The role of the fiber network is twofold: (i) to serve as reinforcement to improve the load-bearing capability of dielectric elastomers, and (ii) to render the actuator inextensible in the axial direction such that the only free deformation path is simultaneous radial expansion and axial contraction. In this paper, a mathematical model of the electromechanical response of fiber reinforced dielectric elastomers is derived. The model is developed within a continuum mechanics framework for large deformations. The cylindrical electro-pneumatic actuator is modeled by adapting Green and Adkins’ theory of reinforced cylinders to account for the applied electric field. Using this approach, numerical solutions are obtained assuming a Mooney–Rivlin material model. The results indicate that the relationship between the contractile force and axial shortening is bilinear within the voltage range considered. The characteristic response as a function of various system parameters such as the fiber angle, inflation pressure, and the applied voltage are reported. In this paper, the elastic portion of the modeling approach is validated using experimental data for McKibben actuators.     

Experimental damping of boundary-layer oscillations using DBD plasma actuators

In the present work artificially excited Tollmien–Schlichting waves were cancelled using plasma actuators operated both in continuous and pulsed modes. To achieve this a vibrating surface, driven by an electromagnetic turbulator, was flush-mounted in a flat plate to excite the TS waves. These were amplified by an adverse pressure gradient induced by an insert on the upper wall of the test section. Control plasma actuators positioned downstream of the excitation actuator attenuate the waves by imparting a steady or unsteady force into the boundary-layer. In the case with steady actuation the two actuators change the velocity profile of the laminar boundary-layer, which then attenuates the waves by itself. In the case of pulsed actuation the actuator creates an unsteady body force to counteract directly the oscillation. As a result the amplitude of the velocity fluctuations at the excitation frequency is reduced significantly in both cases. The principles and the results of the two sets of experiments are presented and discussed.     

正弦交流介质阻挡放电等离子体激励器诱导流场研究的进展与展望

正弦交流介质阻挡放电等离子体流动控制技术是基于等离子体激励的主动流动控制技术,具有响应时间短、结构简单、能耗低、不需要额外气源装置等优点,在飞行器增升减阻、抑振降噪、助燃防冰等方面具有广阔的应用前景.针对“激励器消耗的大部分能量尚未被挖掘利用、诱导流场的完整演化过程尚未完全掌握、诱导流场的演化机制尚不明确”这三方面问题,本文首先从激励器诱导流场的空间结构、时空演化过程、演化机制三个方面回顾总结了激励器诱导流场的研究进展.在诱导流场空间结构方面,发现了高电压激励下诱导射流的湍流特性,辨析了壁面拟序结构与无量纲激励参数之间的关联机制;从激励器诱导声能方面挖掘出了激励器潜在的能量,发现了“等离子体诱导超声波与诱导声流”的新现象,提出了声激励机制;在时空演化过程方面,阐明了激励器诱导流场从薄型壁射流发展为“拱形”射流、再演变为启动涡,最终形成准定常射流的完整演化过程;在演化机制方面,结合声学特性提出了以“升推”为主的诱导流场演化机制.其次,围绕激励器诱导流场,进一步凝练出下一步研究重点,为突破等离子体流动控制技术瓶颈,打通“概念创新—技术突破—演示验证”的创新链路,实现工程应用提供支撑.     

Nonlinear vibration analysis of piezoelectric bending actuators: Theoretical and experimental studies

Piezoelectric bimorph actuators are used in a variety of applications, including micro positioning, vibration control, and micro robotics. The nature of the aforementioned applications calls for the dynamic characteristics identification of actuator at the embodiment design stage. For decades, many linear models have been presented to describe the dynamic behavior of this type of actuators; however, in many situations, such as resonant actuation, the piezoelectric actuators exhibit a softening nonlinear behavior; hence, an accurate dynamic model is demanded to properly predict the nonlinearity. In this study, first, the nonlinear stress–strain relationship of a piezoelectric material at high frequencies is modified. Then, based on the obtained constitutive equations and Euler–Bernoulli beam theory, a continuous nonlinear dynamic model for a piezoelectric bending actuator is presented. Next, the method of multiple scales is used to solve the discretized nonlinear differential equations. Finally, the results are compared with the ones obtained experimentally and nonlinear parameters are identified considering frequency response and phase response simultaneously. Also, in order to evaluate the accuracy of the proposed model, it is tested out of the identification range as well.     

Experimental investigation of side force control on cone-cylinder slender bodies with flexible micro balloon actuators

Side forces on slender bodies of revolution at medium to high angles of attack (AOA > 30°) has been known from a large number of investigations. Asymmetric vortex pairs over a slender body are believed to be the principle cause of the side forces. Under some flight conditions, this side force may be as large as the normal force acting on the slender body. In this paper, experimental results are presented for side force control on a cone-cylinder slender body by using microfabricated balloon actuators. The micro balloon actuators are made of polydimethylsiloxane (PDMS) elastomer by using micro molding techniques. They can be packaged on curve surfaces of a cone-cylinder slender body. As actuator is actuated, the micro balloon actuator inflates about 1.2 mm vertically, which is about 2.4% of the cylinder diameter D (=50 mm) of the cone-cylinder slender body. Micro balloon actuators are actuated at different roll angles of a cone-cylinder slender body. Aerodynamic force measurement results indicate the effects of micro balloon actuators vary at different actuation locations on the cone-cylinder slender body. The side forces can be significantly reduced if the actuators are actuated in the weak vortex side (the side corresponding to the asymmetric vortex which is far from the surface) and actuation angles are located at about 50–60° (the actuation angle here is measured from stagnation line of the incidence plane toward weak vortex side direction). Significant changes are noticed from the surface pressure, as well as leeside vortex flow field, measurement. Micro balloon actuators change nose shapes of the slender body which decide adverse-pressure-gradient values and directly influence the origin of the separation lines and characteristics of the separated vortices over the leeside surface.