Compact piezoelectric stacked actuators for high power applications

Small, hollow, multilayer actuators with a diameter of 3 mm were fabricated by the stacking method from piezoelectric hard lead zirconate titanate (PZT) ceramics. Langevin vibrators were also constructed with the hollow multilayer actuators. The performance capabilities of the actuator and Langevin vibrator samples were examined under high-power conditions. The high-power vibration level at a given sinusoidal drive voltage was significantly enhanced by using a multilayer structure under either a nonresonance or resonance condition. A maximum vibration velocity of 0.17 m/sec was obtained for the 9-layer actuator sample under nonresonance conditions. The vibration velocity was further improved with the Langevin vibrator driven at the resonance frequency. The temperature rise due to heat generation under high-power conditions was the immediate limitation on the maximum accessible vibration velocity for the stacked actuators.     

Electromechanical coupling and output efficiency of piezoelectric bending actuators

Electromechanical coupling mechanisms in piezoelectric bending actuators are discussed in this paper based on the constitutive equations of cantilever bimorph and unimorph actuators. Three actuator characteristic parameters, (e.g., electromechanical coupling coefficient, maximum energy transmission coefficient, and maximum mechanical output energy) are discussed for cantilever bimorph and unimorph actuators. In the case of the bimorph actuator, if the effect of the bonding layer is negligible, these parameters are directly related to the transverse coupling factor lest. In the case of the unimorph actuator, these parameters also depend on the Young's modulus and the thickness of the elastic layer. Maximum values for these parameters can be obtained by choosing proper thickness ratio and Young's modulus ratio of elastic and piezoelectric layers. Calculation results on four unimorph actuators indicate that the use of stiffer elastic material is preferred to increase electromechanical coupling and output mechanical energy in unimorph actuators.     

Real-time calibration of open-loop piezoelectric actuators for interferometric applications

In the present paper a piezoelectric actuator realized for interferometric applications is described, together with a numerical model to simulate its electro-mechanical behavior. The actuator is an open-loop device made up of three piezoelectric ceramics glued into a stainless steel case and connected directly to the parallel port of a personal computer by control electronics developed on purpose. It consists of a 16 bit digital-to-analog converter whose voltage is fixed by the parallel port, a charge amplifier which provides the voltage to the piezoelectric ceramics and a current divider for the control of the voltage on each channel. The layout based on three active elements has allowed to obtain a device which is able to perform a straight expansion with a negligible tilting, a desirable feature for an actuator used for interferometric applications. The hysteretic behavior, a typical characteristic of this kind of actuator, was simulated by a numerical model, based on the Prandtl–Ishlinskii hysteresis operator, which shows a high capability to predict the input–output response at any level of the input signal, and it is efficient enough for use in real-time applications.     

Developments of piezoelectric ultrasonic actuators operating under bending hybrid vibration modes

The exciting methods for the sandwich type piezoelectric ultrasonic actuators used bending hybrid modes are investigated. Five exciting methods are discussed and compared in detail, in which the polarizations and the partitions of the ceramic rings are different. Harmonic analyses are developed to obtain the effects of the exciting methods on the electromechanical coupling factors and the vibration amplitudes. At last, five prototypes are manufactured to verify their differences. Both the simulation and experiment results prove that the exciting method using ceramic rings with four separated partitions achieves great improvements on the efficiency, velocity and force, synchronously.     

Design and performance testing of an ultrasonic linear motor with dual piezoelectric actuators

In this work, design and performance testing of an ultrasonic linear motor with dual piezoelectric actuator patches are studied. The motor system consists of a linear stator, a pre-load weight, and two piezoelectric actuator patches. The piezoelectric actuators are bonded with the linear elastic stator at specific locations. The stator generates propagating waves when the piezoelectric actuators are subjected to harmonic excitations. Vibration characteristics of the linear stator are analyzed and compared with finite element and experimental results. The analytical, finite element, and experimental results show agreement. In the experiments, performance of the ultrasonic linear motor is tested. Relationships between velocity and pre-load weight, velocity and applied voltage, driving force and applied voltage, and velocity and driving force are reported. The design of the dual piezoelectric actuators yields a simpler structure with a smaller number of actuators and lower stator stiffness compared with a conventional design of an ultrasonic linear motor with fully laminated piezoelectric actuators.     

Analysis of the bending fracture process for piezoelectric composite actuators using dominant frequency bands by acoustic emission

We examined the fracture process of a thin monolithic PZT and a plate-type piezoelectric composite actuator (PCA) subjected to a three-point bending load with the aid of an acoustic emission (AE) monitoring. Fracture surface observations were conducted using a scanning electron microscope (SEM) and optical microscope. AE signals were analyzed during the bending fracture process of a PCA in terms of the dominant frequency band which was processed by a fast Fourier transform (FFT) along with the behavior of AE amplitude. Three dimensional finite element simulations were performed to investigate the stress state in each layer of PCAs. It was concluded that the damage of a PCA under a bending load was initiated in the brittle PZT layer, which induced the interlaminar delamination between PZT layer and adjacent fiber composite layers. As a bending load approached maximum, fiber breakages hindering the main crack propagation in the glass–epoxy bottom layer together with macro-delamination between the PZT and fiber composite layers led to the final failure of PCAs. The fracture process and mechanisms of PCAs were successfully identified by AE characteristics based on the analysis of dominant frequency bands.     

Design of piezoelectric actuators for measurement technology instruments

Engineering methods are presented for calculating mechanical stresses and deformations in homogeneous piezoceramic plates having a nonuniform polarization across their thickness. A detailed examination is made of the design of a piezoceramic modulator for a pyroelectric temperature transducer. The results of numerical calculations are compared with experimental data. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 48–52, July, 1998.     

Petri-net based applications for supply chain management: an overview

Supply networks are discrete event dynamic systems consisting of suppliers, manufacturers, distributors, and customers. It is a difficult and challenging task to model such a complex system. Recently, characterised as being capable of model parallelism and synchronisation, Petri nets (PNs) have attracted great attention for modelling and studying a supply network. Since each type of Petri net has its unique properties to model specific applications, this paper reviews and classifies Petri net applications for supply chain management (SCM). According to the decision problems facing SCM, we have the Petri net applications classified into three areas: competitive strategy, firm focused tactics, and operational efficiency. Categorising the Petri net applications will provide a guideline to industry practitioners and research academics to choose the appropriate Petri net for the problem. In addition, the paper attempts to offer future directions in applying the Petri net to SCM including: (1) modelling with uncertainty elements; (2) addressing the scalability issue of Petri nets; (3) integrating Petri nets with other tools; and (4) extending Petri nets to emerging applications.     

Large-area fabrication of superhydrophobic surfaces for practical applications: an overview

This review summarizes the key topics in the field of large-area fabrication of superhydrophobic surfaces, concentrating on substrates that have been used in commercial applications. Practical approaches to superhydrophobic surface construction and hydrophobization are discussed. Applications of superhydrophobic surfaces are described and future trends in superhydrophobic surfaces are predicted.     

Large-area fabrication of superhydrophobic surfaces for practical applications: an overview

Abstract

This review summarizes the key topics in the field of large-area fabrication of superhydrophobic surfaces, concentrating on substrates that have been used in commercial applications. Practical approaches to superhydrophobic surface construction and hydrophobization are discussed. Applications of superhydrophobic surfaces are described and future trends in superhydrophobic surfaces are predicted.     

Design and fabrication of a high performance multilayer piezoelectric actuator with bending deformation

A new bending mode multimorph actuator was designed and fabricated successfully by a multiple screen printing process. Unlike the conventional bimorph actuator in which the bend occurs in the thickness direction, the bend in the multimorph actuator occurs in the widthwise direction because of synchronistical deformation of each single monolithic layer in the multilayer structure. The theoretical analysis and experimental measurements were conducted to study the performance of this type of actuator, and a comparison was made with the conventional bimorph actuator. Larger displacement, higher resonance frequency, and much larger blocking force could be achieved with the multimorph actuator than with a bimorph actuator of similar dimensions. The multimorph actuator presented in this paper provides a valuable alternative for actuator applications beyond those available with the popular bimorph and longitudinal multilayer actuators.     

振动控制中压电作动器非线性的补偿方法研究

在周期振动的自适应控制中,压电作动器的非线性特性会产生高次谐波,激发高阶模态振动。为抑制压电作动器的高次谐波激励,同时结合自适应振动控制的特点,提出一种新的作动器非线性补偿方法。该方法将作动器的非线性与结构的动态特性部分融合,用正交多项式从输入输出信号中拟合静态非线性及其逆变换,计算过程简单,数值稳定性高。在控制通道中,通过逆变换对控制信号进行预处理,使得补偿后的输入输出具有线性系统的特征,而输入输出之间的相位差完全由自适应算法进行补偿。实验结果表明,所给出的补偿方法能够抑制高次谐波,并改善了振动控制效果。     

Study of elastic wave propagation induced by piezoelectric actuators for crack identification

The current paper provides a theoretical study of elastic wave propagation in a cracked elastic medium induced by an embedded piezoelectric actuator. The formulation of the problem is based on a newly developed actuator model and the solution of coupled crack and actuator problems. The interaction between an actuator and a crack is studied to develop basic understanding of the effect of the crack upon the wave field generated. The resulting wave field is used to simulate 'sensor signals'. Scattered wave from the crack is then regenerated by solving a reverse elastodynamic problem and used in an imaging technique to identify the crack.     

Models for lifetime estimation: an overview with focus on applications to wind turbines

This paper provides an overview of models and methods for estimation of lifetime of technical components. Although the focus in this paper is on wind turbine applications, the major content of the paper is of general nature. Thus, most of the paper content is also valid for lifetime models applied to other technical systems. The models presented and discussed in this paper are classified in different types of model classes. The main classification used in this paper divides the models in the following classes: physical models, stochastic models, data-driven models and artificial intelligence, and combined models. The paper provides an overview of different models for the different classes. Furthermore, advantages and disadvantages of the models are discussed, and the estimation of model parameters is briefly described. Finally, a number of literature examples are given in this paper, providing an overview of applications of different models on wind turbines.     

Factors affecting the performance of metakaolin geopolymers exposed to elevated temperatures

The effects of geopolymer binder systems exposed to elevated temperatures are examined. Geopolymers investigated were synthesized from metakaolin, activated by combinations of sodium/potassium silicate and sodium/potassium hydroxide. The specimens were then exposed to temperatures of 800 °C. The factors studied were: (1) calcining temperatures of kaolin; (2) Si/Al ratio of the geopolymer; (3) activator/metakaolin ratio; (4) curing temperature; and (5) alkali cation type. Altogether 30 geopolymer formulations were studied. The samples were subjected to compressive strength, thermogravimetry, and scanning electron microscopy tests. Results showed that Si/Al ratio has a significant influence on elevated temperature exposure deterioration. Lesser strength loss due to elevated temperature exposures were observed in geopolymer with high Si/Al ratios (>1.5). The geopolymer binders activated by potassium-based activators showed an enhanced post-elevated temperature exposure performance compared to sodium-based systems. The optimum calcining temperature of kaolin and curing temperatures for improved temperature performance are also reported.     

On the elastic wave propagation induced by a network of piezoelectric actuators

Summary.  This paper provides a comprehensive analysis of the two-dimensional wave propagation in an elastic medium induced by embedded multiple piezoceramic actuators. Based on a new actuator model, which involves the deformation in both the transverse and longitudinal directions of the actuator, the actuation process and the dynamic load transfer between multiple actuators and the host medium is studied. The formulation of the problem is established using the analytical solution of the single actuator problem and a pseudo-incident wave method. Detailed numerical simulation is conducted to study the electroelastic behavior of this composite system. Attention is focussed on the properties of generated waveforms for different actuator arrangements. Received March 5, 2002; revised July 24, 2002 Published online: January 16, 2003     

Diamond-like carbon coatings for orthopaedic applications: an evaluation of tribological performance

A detailed investigation of the tribological behaviour of vacuum arc diamond-like carbon coated Ti–6Al–4V against a medical grade ultra-high molecular weight polyethylene is conducted in this work in order to investigate the potential use of diamond-like carbon coatings for orthopaedic appplications. Lubricated and non-lubricated wear experiments are performed using a standard pin-on-disc wear tester. The coefficient of friction is monitored continuously during testing and wear rate calculations are performed using surface profilometry measurements of worn disc surfaces. Sliding wear tests show the existence of two distinct friction and wear regimes distinguished by physically different mechanisms. In the first stages of wear, adhesion and abrasion are the dominant mechanisms of wear while fatigue processes are activated later in the tests. The effects of diamond-like carbon coating structure, surface roughness and lubrication on tribological behaviour are presented. Optimal process–structure–property design for vacuum arc plasma deposition is utilized in order to obtain strong adhesion to the titanium alloy substrate. Diamond-like carbon coatings significantly improve the friction and wear performance of the orthopaedic bearing pair and show exceptional promise for biomedical applications. © 1999 Kluwer Academic Publishers     

An overview of fatigue and fracture for design and certification of advanced high performance ships

Reliability of structures is an overriding consideration in the design of surface ships, submarines and aircraft, particularly for high performance, weight-critical vehicles which require design with new materials having high strength-to-weight ratios. These high strength materials can be susceptible to catastrophic failure in the presence of small flaws, such that the initiation and propagation of cracks by cyclic loading of the structure is of the utmost concern. Techniques for dealing with these problems, as they relate to structural reliability are discussed, and the close relationship between problems of high performance ships and aircraft are examined. The current need to rely on large scale validation testing of vehicle structure and structural details is examined, with particular attention to the requirements for high-performance ship structures.     

New bibliometric tools for the assessment of national research performance: Database description,overview of indicators and first applications

This paper gives an outline of a new bibliometric database based upon all articles published by authors from the Netherlands, and processed during the time period 1980–1993 by the Institute for Scientific Information (ISI) for theScience Citation Index (SCI),Social Science Citation Index (SSCI) andArts & Humanities Citation Index (A&HCI). The paper describes various types of information added to the database: data on articles citing the Dutch publications; detailed citation data on ISI journals and subfields; and a classification system of publishing main organizations, appearing in the addresses. Moreover, an overview is given of the types of bibliometric indicators that were constructed. Their relationship to indicators developed by other researchers in the field is discussed. Finally, two applications are given in order to illustrate the potentials of the database and of the bibliometric indicators derived from it. The first represents a synthesis of ‘classical’ macro indicator studies at the one hand, and bibliometric analyses of research groups or institutes at the other. The second application gives for the first time a detailed analysis of a country's publication output per institutional sector.