Semi-active vibration control using piezoelectric actuators in smart structures

The piezoelectric materials, as the most widely used functional materials in smart structures, have many outstanding advantages for sensors and actuators, especially in vibration control, because of their excellent mechanical-electrical coupling characteristics and frequency response characteristics. Semi-active vibration control based on state switching and pulse switching has been receiving much attention over the past decade because of several advantages. Compared with standard passive piezoelectric damping, these new semi-passive techniques offer higher robustness. Compared with active damping systems, their implementation does not require any sophisticated signal processing systems or any bulky power amplifier. In this review article, the principles of the semi-active control methods based on switched shunt circuit, including state-switched method, synchronized switch damping techniques, and active control theorybased switching techniques, and their recent developments are introduced. Moreover, the future directions of research in semi-active control are also summarized.     

灵巧型电动底盘的设计与研究

灵巧型电动底盘采用四轮独立驱动和转向控制,主要由电动轮模块、平衡模块、控制模块组成。电动轮采用模块化设计理念,具有结构合理、行驶灵活、灵巧实用等特点。平衡模块使车辆无论在什么路况下行驶时始终保持底盘的水平平衡状态。同时,该底盘采用无刹车制动技术,可以通过调整各轮的转向角度控制驻停,使制动系统变得简单,安全性高。该底盘实现了四轮独立控制,简化了传动系统,减小了转弯半径,提高转弯速度,使底盘的机动灵活性更好,改善了操纵稳定性。     

柔性压电智能反射面的静态形状控制

建立了柔性压电智能反射面系统的有限元模型和优化控制模型,给出了结构力学建模和形状控制方法以及相应的优化算法。首先,将蜂窝夹层结构的压电智能反射面等效为多层复合板;基于Kirchhoff假设和经典层合板理论,根据虚功原理推导了柔性压电智能反射面的有限元方程;采用蜂窝等效理论计算了反射面蜂窝夹芯等效弹性模量,有限元模型中的单元为四节点四边形压电板单元,每个作动器单元中引入额外的电势自由度。然后,根据建立的有限元方程,推导了反射面变形均方根误差与作动器控制电压的关系式;以均方根误差最小为优化目标,建立了柔性压电智能发射面的静态形状控制优化模型;采用Lagrange乘子法处理了压电作动器工作电压的限制。最后,用提出的方法分析已有模型并验证建模方法。以600mm口径的平面柔性智能反射面为例,验证了采用压电陶瓷贴片对反射面静态形状控制的可行性及优化算法有效性。仿真结果表明:通过控制压电陶瓷贴片作动器,可以使反射面的静态形状误差减小97%以上,而且作动器的控制电压均在极限电压范围内。     

Natural convection between concentric spheres in electromagnetic fields

This study performs numerical analyses for two different working fluids. One is an analysis of natural convection using a model with air that is compared with the results of applied experiments. Then, it can be used to investigate the pattern of natural convection in concentric spheres. The other is an investigation for the relationship between velocity field, electromagnetic field, and temperature field in a model with molten metal. The subject of the analysis model is the natural convection between two concentric spherical shells. In particular, a process where induced magnetic fields intensify the imposed magnetic field can be called a dynamo process. This study uses a modified B method in order to investigate the role of this induced magnetic field. This method is also compared to a ϕ method that only considers imposed magnetic fields. In addition, this study examines the relationship between the velocity field and the electromagnetic field for the velocity field through applying Coriolis forces.     

Expression of picogram sensitive bending modes in piezoelectric cantilever sensors with nonuniform electric fields generated by asymmetric electrodes

Single-layer uniform cross-sectioned piezoelectric macro-cantilevers fabricated with an asymmetric electrode configuration enabled electrical measurement of picogram-sensitive resonant bending modes in liquids. Bending modes were otherwise not electrically measurable without excitation by a nonuniform electric field created by the geometric asymmetry in electrode design used. Electrode modification was confirmed by energy-dispersive X-ray spectroscopy (EDS). Mass-change sensitivity was tested using both bulk density changes and surface chemisorption experiments in a continuous flow apparatus. Significant response to density changes as small as 0.004 g/mL was measured. A sensitivity limit of ～1 picogram in liquid was determined from 1-dodecanethiol chemisorption experiments. The sensitivity decreased with chemisorbed mass and was log-linear over five orders of magnitude. The observed resonance responses were in agreement with previously reported models of resonating cantilever sensors. This work demonstrates experimentally for the first time that introducing electrode asymmetry enables measurement of bending modes in cantilevers containing only a single piezoelectric layer.     

Stress in piezoelectric hollow sphere with thermal gradient

The piezoelectric phenomenon has been exploited in science and engineering for decades. Recent advances in smart structures technology have led to a resurgence of interest in piezoelectricity, and in particular, in the solution of fundamental boundary value problems. In this paper, we develop an analytic solution to the axisymmetric problem of a radially polarized, spherically isotropic piezoelectric hollow sphere. The sphere is subjected to uniform internal pressure, or uniform external pressure, or both and thermal gradient. There is a constant thermal difference between its inner and outer surfaces. An analytic solution to the governing equilibrium equations (a coupled system of second-order ordinary differential equations) is obtained. On application of the boundary conditions, the problem is reduced to solving a system of linear algebraic equations. Finally, the stress distributions in the sphere are obtained numerically for two piezoceramics.     

压电智能悬臂梁结构振动主动控制仿真

为了提高LQR最优控制方法对压电类智能结构的振动控制效果,推导了表面离散分布压电元件的柔性悬臂梁结构的驱动和传感方程以及梁的弯曲振动方程,用模态分析方法对方程进行解耦和模型降阶,建立控制系统的状态空间方程。利用有限元分析方法来衡量压电元件对梁固有特性的影响,对状态空间方程的自振频率和振型函数进行修正,得到更为精确的数学模型。通过一悬臂梁的LQR最优控制仿真实例表明,经过模型修正后的最优振动控制效果更好。     

Local electric fields in ensembles of composite nanoparticles

Specific features of the formation of local fields in spherical composite nanoparticles containing metal cores surrounded by a silica shell with implanted dye molecules are studied. A system consisting of two closely located nanoparticles (dimers) is analyzed. It is shown that the field configuration in the dimer corresponds to a much more effective feedback than that in the case of individual spherical nanoparticles. The dynamics of the fluorescence field near a flat package of composite nanoparticles is studied numerically with due allowance for the enhancement of the dye fluorescence field, saturation of the energetic transition, and diffraction. It is found that close arrangement of nanoparticles leads under pumping conditions to the formation of high-intensity fields localized with time in the space of the nanoparticle package neighborhood.     

智能电动车控制系统设计

基于AT89C51研究的跷跷板上行进的智能电动车系统,其硬件主要由AT89C51单片机最小系统板、小车左右前轮驱动电路、小车行进轨迹探测电路、角度方向检测电路、显示电路及报警电路等组成.通过软件产生PWM波控制小车速度,利用插补运算调整小车行进轨迹.经过反复分析、比较和调测,证明本系统达到了设计的要求.     

The field emission in the alternative electric fields

We obtained a growth of the emitting points and a considerable increase in the emission current in the regime of alternative power supply for initially polished flat metal surfaces. Formed surfaces demonstrate sufficient field emission current stability in vacuum from 10(-4) to 10(-6)Torr and good tolerance and maintainability of field emission characteristics after series of explosive emission pulses. In an alternative power supply regime, using a grid as one of the electrodes enabled us to output the field emission electron current about 2 mA after accelerating grid.     

Vibration control of smart hull structure with optimally placed piezoelectric composite actuators

Active vibration control to suppress structural vibration of the smart hull structure was investigated based on optimized actuator configurations. Advanced anisotropic piezoelectric composite actuator, Macro-Fiber Composite (MFC), was used for the vibration control. Governing equations of motion of the smart hull structure including MFC actuators were obtained using the Donnell-Mushtari shell theory and Lagrange's equation. The Rayleigh-Ritz method was used to obtain the dynamic characteristics of the smart hull structure. Experimental modal tests were conducted to verify the proposed mathematical model. In order to achieve high control performance, optimal locations and directions of the MFC actuators were determined by genetic algorithm. Optimal control algorithm was then synthesized to suppress structural vibration of the proposed smart hull structure and experimentally implemented to the system. Active vibration control performances were evaluated under various modes excitations. Vibration tests revealed that optimal configurations of MFC actuators improved the control performance of the smart hull structure in case of the limited number of actuators available.     

Damage detection potential of a triangular piezoelectric configuration

In this work a problem of damage detection and localization was investigated. A new configuration of piezoelectric transducers was proposed. It consists of twelve transducers. It is in a form of an equilateral triangle that has a 2×2 transducer array in each vertex. Transducers of this configuration were used to excite and register guided waves in an aluminum alloy specimen. Due to known sensitivity of these waves to structural defects it was assumed that registered waves, in the form of voltage signals, carry information about the structure condition. A special algorithm was implemented to process these signals and extract features related to damage. This algorithm transfers information from the time domain to the spatial domain. Results are mapped into coordinate system assigned to monitored structure. In this way in the case of damage present outside or inside the configuration its coordinates are highlighted. In order to detect damage on the direct path between triangle vertices a damage index is defined that indicates whether there is damage present or not. Experimental investigation included three scenarios, one for outside and one for inside localization and one for direct path detection. Results showed that this method has a potential for Structural Health Monitoring of a structure made of an isotropic material.     

等静压压电常数测试中电荷信号的峰值检测

研究了压电换能器等静压压电常数测试系统的检测原理,阐述了等静压压电常数测试系统中电荷信号峰值检测的实现方法;应用PKD01设计了电荷信号峰值检测保持器,设计了峰值检测的实际应用电路,用实验数据进行了可行性验证.结果表明,该系统实际测试的等静压压电常数gh值与换能器的理论值相近,提高了其测量精确度.     

一种新型IC卡智能电表及其应用

设计了一种基于PIC16C57单片机的IC卡智能电表,阐述了SLM4442芯片的工作原理和硬件电路,给出了电表的核心控制部分及工作过程流程图.实际应用表明,该系统结构简单、计量精度高、抗干扰性好.     

外电场中Ba原子6pnk自电离态光谱的测量

介绍了一种可调谐激光三步孤立实激发方式测量外电场中原子自电离态光谱的技术.利用该技术结合适当的激光偏振组合方式,系统地测量了大量的Ba原子初态为M=0和|M|=1 Stark态的6pnk自电离态光谱,并且对这些实验光谱进行了初步的分析.分析结果得出这些自电离态光谱由于电场的作用,它们之间产生了强烈的混和从而导致了它们线形的变化.     

外场中Ba原子6pnk自电离态光谱的测量

介绍了一种可调谐激光三步孤立实激发方式测量外电场中原子自电离态光谱的技术.利用该技术结合适当的激光偏振组合方式,系统地测量了大量的Ba原子初态为M=0和|M|=1 Stark态的6pnk自电离态光谱,并且对这些实验光谱进行了初步的分析.分析结果得出这些自电离态光谱由于电场的作用,它们之间产生了强烈的混和从而导致了它们线形的变化.     

外电场中Ba原子6pnk自电离态光谱的测量

介绍了一种可调谐激光三步孤立实激发方式测量外电场中原子自电离态光谱的技术。利用该技术结合适当的激光偏振组合方式 ,系统地测量了大量的 Ba原子初态为 M=0和 |M|=1 Stark态的 6pnk自电离态光谱 ,并且对这些实验光谱进行了初步的分析。分析结果得出这些自电离态光谱由于电场的作用 ,它们之间产生了强烈的混和从而导致了它们线形的变化。