Table of contents

Volume 16

Number 6, December 2007

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TOPICAL REVIEW

R23

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A wide range of microelectromechanical systems (MEMSs) and devices are actuated using electrostatic forces. Multiphysics modeling is required, since coupling among different fields such as solid and fluid mechanics, thermomechanics and electromagnetism is involved. This work presents an overview of models for electrostatically actuated MEMSs. Three-dimensional nonlinear formulations for the coupled electromechanical fluid–structure interaction problem are outlined. Simplified reduced-order models are illustrated along with assumptions that define their range of applicability. Theoretical, numerical and experimental works are classified according to the mechanical model used in the analysis.

PAPERS

1989

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The experimental fact that the acoustic emission (AE) of a shape memory alloy (SMA) is confined well in the temperature range of the martensitic transformation hysteresis suggests the possibility of there being an SMA that is suitable for use as a temperature-sensing device sending AE signals out. This study has proposed a method to measure the temperature at the point of a small SMA particle in a solid body by detecting the AE signals from the particle. Moreover, a two-sensor method, which is the technique for locating the source of AE signals by measurement with two AE sensors, has been applied. It allows us to monitor the temperatures at many points in the solid body with many SMA particles in it. The proposed method was examined using a model composite material that was composed of five SMA particles lying in an array in an aluminum plate. It is shown that the method could locate the positions of the particles having emitted AE signals by martensite transformation. It has also been proposed that the AE during deformation of the SMA can be used for sensing stress. When a point load was applied at various positions on the surface of an epoxy–SMA particle composite plate, the AE method located the point load correctly.

1997

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Based on a curvature model for van der Waals (vdW) pressure between the interlayer of a double-walled carbon nanotube (DWNT), explicit expressions are derived for the critical buckling load of a DWNT which is modeled as a double-elastic shell under combined axial compression and lateral pressure. The critical load is calculated for various radii, length-to-radius ratios and load combinations. New results show that the curvature effects play a significant role in buckling problems for DWNTs of small radii. Neglecting the curvature effect usually leads to an under-estimate of the critical load for DWNTs when lateral pressure dominates. In addition, unlike Wang et al (2003b Int. J. Solids Struct.40 3893) and Qian et al (2005 Int. J. Solids Struct.42 5426), the buckling mode corresponding to the minimum axial buckling strain is unique, even when the lateral pressure is very small. For the DWNTs under combined axial compression and lateral pressure, the critical axial strain is reduced due to the external pressure.

2006

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This paper presents a study of the effectiveness of using actively controlled panels to block the transmission of sound. Ideally, the acoustical pressure behind the panel is driven to zero by actuators mounted on the panel surface. Microphones are used as the sensors to detect the acoustical pressure, with the adaptive FXLMS algorithm being used for feedforward control. It is found experimentally that major limitations of this approach are non-uniform cancellation of noise across the panel at high frequencies, harmonic nonlinear behavior at very low frequencies and actuator saturation at high sound levels. These limitations restrict the controllable frequency range and noise level, and in some cases can lead to instability. Approaches are suggested to overcome these limitations. Non-uniformity can be lowered by using multiple or distributed actuators, harmonic nonlinearities can be reduced by using back-to-back panels and instability from saturation can be avoided by using a proposed half-power FXLMS algorithm.

2015

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An analytical model is developed for an asymmetric piezoelectric bending actuator consisting of a slender beam and a piezoelectric actuator patch that is bonded to one side of this beam. For the kinematical model of the laminate section of this actuator, the piezoelectric patch and the substrate beam are assumed to undergo bending as well as longitudinal deformation, while the bonding layer is modeled as purely shear elastic. In addition, this model accounts for the dielectric properties of the bonding layer. The boundaries of the actuator are described with dynamic stiffness matrices, which are given here for the two special cases of a free beam and for an ideally damped beam. The actuator losses are accounted for by using complex material parameters. Both special cases are verified experimentally for a free beam and for an ideally damped beam. The input electrical impedance of the actuator as well as the beam deflection are in excellent agreement with the model. The model is further used to optimize the geometrical dimensions of the piezoelectric patch in terms of a maximum power flux into the substrate beam.

2026

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This paper presents a higher-order shear-flexible piezolaminated C1 QUAD-8 multi-layer smart composite plate finite element with 48 elastic degrees of freedom and 9 electric degrees of freedom per piezoelectric layer in the element. The electric potential is assumed to vary quadratically over the thickness, representing the potential induced due to bending deformation more accurately, by interpolating using nodal mid-plane electric potentials and one electric degree of freedom representing the potential difference between the top and bottom surfaces of the piezoelectric layer. The higher-order plate theory used satisfies the stress and displacement continuity at the interface of the composite laminates and has zero shear stress on the top and bottom surfaces. The transverse shear deformation is of a higher order represented by the trigonometric functions, allowing us to avoid the shear correction factors. In order to maintain the field consistency, the in-plane displacements u and v and rotations θx and θy are interpolated using quadratic interpolation functions while the transverse displacement w is interpolated using a Hermite cubic interpolation function. The element is developed to include stiffness and the electromechanical coupling of the piezoelectric sensor/actuator layers. The active vibration control performance of the piezolaminated smart composite plates have been studied by modelling them with the above element and applying LQR optimal control.

2040

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In this paper, an analysis of a Gunn loaded stacked annular ring microstrip antenna is presented using a circuit concept. Consequently, various parameters such as input impedance, voltage standing wave ratio, return loss, band width, radiation pattern, and beam width of the antenna are evaluated as a function of bias voltage for different threshold values. It is found that the operating frequency of the Gunn loaded stacked patch is controllable with the bias voltage. The band width of the Gunn loaded stacked patch is improved to 11.61% as compared to the 9.16% band width of the stacked patch in addition to there being better matching and wider tunability. The radiated power and beam width of the stacked patch are also enhanced by loading a Gunn diode with it.

2046

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In this paper, we propose a coilless backlight inverter for LCD TVs. To simplify the manufacturing procedures of the inverter, a single-layer piezoelectric transformer was used as the basis for the development. Traditionally, the input capacitance of a single-layer piezoelectric transformer prevents us from identifying a proper inductor to achieve LC resonance. Without the presence of LC resonance, high-frequency noise within the output signal can be found. The zero-voltage switching technique can be used to adjust the rectified input voltage to become a trapezoidal voltage waveform and thus reduce some of the high-frequency voltage signals amplified from the input voltage waveform. As the presence of this high-frequency voltage waveform will influence the vibration of the Rosen-type piezoelectric transformer, which can lead to a lower energy transfer efficiency and higher temperature rise on the MOSFET, a solution is needed to further enhance the performance of the piezoelectric transformer-based inverter. It can be shown that the above problems can be solved using a quasi-modal surface electrode adopted onto the surface of a piezoelectric transformer. More specifically, modal filtering provided by the surface electrode of the piezoelectric transformer can be shown to facilitate the removal of the inductor and to eliminate the high-frequency noise that cannot be eliminated by a soft switching technique. In addition, the temperature rise of the MOSFET within the driving circuitry can be shown to be improved significantly. The experimental results were found to match well with the theoretical predictions.

2056

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This paper designs an innovative reinforced concrete (RC) beam strengthened with carbon fiber reinforced concrete (CFRC) composites. Six groups of test beams, five with different degrees of strengthening, achieved by changing the location and the thickness of the CFRC layer, and one virgin RC beam, were tested in four-point bending over a span of 3000 mm. We investigate the effect of the CFRC layer on the flexural performance and the electrical properties of the designed beams. The test results indicate that the CFRC strengthened RC beam exhibits improved electrical properties as well as better mechanical performance. Also, the location and the thickness of the CFRC layer affect the initial electrical resistance and other electrical properties of the beam. Relationships between electrical resistance, loading, deflection and cracks show that the increase in the electrical resistance can be used to monitor the extent of damage to the designed beam. Based on this discovery, a new health monitoring technique for RC structures is produced by means of electrical resistance measurements.

2063

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A novel magnetostrictive rotary motor using Terfenol-D (Tb0.3Dy0.7Fe1.9) material as the driving element is developed. The motor is constructed of three giant magnetostrictive actuators connected to a stator frame and a rotor is placed in the center of the stator. The small movement of the magnetostrictive actuator is scaled to three times by using flexible flexure hinges and a specially designed mechanism is used to combine three such actuators to form a pure rotation movement and this movement is used to drive the rotor of the motor. A prototype of this research motor is made and a common three-phase alternating current is used to drive it. Preliminary experiments are also carried out in the laboratory of School of Mechanical Engineering of Hangzhou Dianzi University.

2067

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Multi-damage causes much more complex scattering phenomena in captured signals than mono-damage does. Examination of an individual signal may fail to provide sufficient information to identify all instances of damage. Upon comparative evaluation of the performance of forward and inverse inferences for damage identification, a data fusion scheme was developed for predicting multi-damage in a structure with the aid of a sensor network. The approach, conducted hierarchically by activating different sensors in a sensor network, fused an extracted signal feature, time-of-flight (ToF), at different levels, to provide an overall consensus as to all possible instances of damage. This consensus was presented in an intuitional contour map indicating the probability of damage occurrence. Benefiting from the sensor network, the dependence of identification processes on a specific sensor was minimized, and the need for interpreting complex signal scattering by multi-damage was avoided as much as possible. To facilitate the extraction of ToF from raw signals, a signal processing approach, scale-averaged wavelet power (SAP) analysis, was introduced. As validation, the proposed identification scheme was employed to gauge dual delamination in a CF/EP woven laminate with a built-in active piezoelectric sensor network. The results have demonstrated the excellent capability of the approach in evaluating multiple structural damage sites.

2080

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A new thermomechanical hysteresis model for a high-temperature shape memory alloy (HTSMA) actuator material is presented. The proposed Brinson–Preisach model is capable of predicting the strain output of a tensile-loaded HTSMA when excited by arbitrary temperature–stress inputs for the purpose of actuator and control design. Quasistatic generalized Preisach hysteresis models available in the literature require large sets of experimental data for model identification at a particular operating point, and substantially more data for multiple operating points. The minor loop algorithm is an alternate approach to common Preisach methods that is better suited for research-stage alloys, such as recently developed HTSMAs, for which a complete identification database is not yet available. A detailed description of the minor loop hysteresis algorithm is presented in this paper and a methodology for determination of model parameters is introduced. The algorithm is assembled together with a modified form of the one-dimensional Brinson constitutive equation to provide a continuous thermomechanical response even within the characteristically wide detwinning region of the HTSMA. The computationally efficient algorithm is shown to demonstrate each of the unique characteristics of Preisach minor loop hysteresis over the usable actuation range in high-stress, high-temperature applications.

2091

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A one-dimensional coupled thermomechanical model is presented for shape memory alloys (SMAs) under non quasi-static loading by defining a Helmholtz free-energy function consisting of strain energy, thermal energy, and the energy of phase transformation. The first law of thermodynamics is used to address the thermomechanical coupling due to the influence of strain rate on the SMA temperature. The convective heat transfer coefficient of an SMA wire is calculated by using temperature-dependent empirical relations, and it is shown that no single empirical formula for the heat transfer coefficient can be applied to obtain experimentally consistent results under different loading conditions. The martensite fraction is decomposed into stress-induced and temperature-induced fractions so that the model is capable of predicting both the shape memory effect and the pseudoelasticity. Cyclic loading, the effect of wire diameter and the variation of dissipated energy with strain rate are studied, and the general features of the responses are found to be in agreement with the experimental observations.

2102

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A physically based one-dimensional shape memory alloy (SMA) model is implemented into the finite element software ABAQUS via a user interface. Linearization of the SMA constitutive law together with complete transformation kinetics is performed and tabulated for implementation. Robust rules for transformation zones of the phase diagram are implemented and a new strategy for overlapping transformation zones is developed. The iteration algorithm, switching point updates and solution strategies are developed and are presented in detail. The code is validated via baseline simulations including the shape memory effect and pseudoelasticity and then further tested with complex loading paths. A hybrid composite with self-healing function is then simulated using the developed code. The example demonstrates the usefulness of the methods for the design and simulation of materials or structures actuated by SMA wires or ribbons.

2116

This paper presents a technique for the analysis of full wavefield data in the wavenumber/frequency domain as an effective tool for damage detection, visualization and characterization. Full wavefield data contain a wealth of information regarding the space and time variation of propagating waves in damaged structural components. Such information can be used to evaluate the response spectrum in the frequency/wavenumber domain, which effectively separates incident waves from reflections caused by discontinuities encountered along the wave paths. This allows removing the injected wave from the overall response through simple filtering strategies, thus highlighting the presence of reflections associated with damage. The concept is first illustrated on analytical and numerically simulated data, and then tested on experimental results. In the experiments, full wavefield measurements are conveniently obtained using a scanning laser Doppler vibrometer, which allows the detection of displacements and/or velocities over a user-defined grid, and it is able to provide the required spatial and time information in a timely manner. Tests performed on a simple aluminum plate with artificially seeded slits simulating longitudinal cracks, and on a disbonded tongue and groove joint, show the effectiveness of the technique and its potentials for the inspection of a variety of structural components.

2130
The following article is Free article

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The electromechanical conversion capacity of a piezoelectric power generator is investigated by considering a quasi-static work cycle. How the maximum energy can be harvested from a piezoelectric element limited by its maximum parameters such as the maximum strain, maximum field, maximum surface charge density and maximum stress is detailed in this paper. The work cycle in which the electric field and the stress are controlled in a way designed to get the most energy is illustrated. A contrast has been made between synchronized switching harvesting with an inductor (SSHI) and the methods introduced here, and it is pointed out theoretically that the proposed method yields more power than SSHI.

2137

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This paper presents the development and application of a miniaturized impedance sensor node for structural health monitoring (SHM). A large amount of research has been focused on utilizing the impedance method for structural health monitoring. The vast majority of this research, however, has required the use of expensive and bulky impedance analyzers that are not suitable for field deployment. In this study, we developed a wireless impedance sensor node equipped with a low-cost integrated circuit chip that can measure and record the electrical impedance of a piezoelectric transducer, a microcontroller that performs local computing and a wireless telemetry module that transmits the structural information to a base station. The performance of this miniaturized and portable device has been compared to results obtained with a conventional impedance analyzer and its effectiveness has been demonstrated in an experiment to detect loss of preload in a bolted joint.

Furthermore, for the first time, we also consider the problem of wireless powering of such SHM sensor nodes, where we use radio-frequency wireless energy transmission to deliver electrical energy to power the sensor node. In this way, the sensor node does not have to rely on an on-board power source, and the required energy can be wirelessly delivered as needed by human or a remotely controlled robotic device.

2146

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The objective of this paper is to present an integrated feedback control concept for adaptive landing gears (ALG) and its experimental validation. Aeroplanes are subjected to high dynamic loads as a result of the impact during each landing. Classical landing gears, which are in common use, are designed in accordance with official regulations in a way that ensures the optimal energy dissipation for the critical (maximum) sink speed. The regulations were formulated in order to ensure the functional capability of the landing gears during an emergency landing. However, the landing gears, whose characteristics are optimized for these critical conditions, do not perform well under normal impact conditions. For that situation it is reasonable to introduce a system that would adapt the characteristics of the landing gears according to the sink speed of landing. The considered system assumes adaptation of the damping force generated by the landing gear, which would perform optimally in an emergency situation and would adapt itself for regular landings as well. This research covers the formulation and design of the control algorithms for an adaptive landing gear based on MR fluid, implementation of the algorithms on an FPGA platform and experimental verification on a lab-scale landing gear device. The main challenge of the research was to develop a control methodology that could operate effectively within 50 ms, which is assumed to be the total duration of the phenomenon. The control algorithm proposed in this research was able to control the energy dissipation process on the experimental stand.

2159

Several active–passive damping treatments using viscoelastic and piezoelectric materials have been studied in the last decade. The main motivation of such hybrid damping mechanisms is that they combine the reliability, low cost and robustness of viscoelastic damping treatments with high-performance, modal selective and adaptive piezoelectric active control. However, active–passive damping performance is highly dependent on the relative positions of viscoelastic and piezoelectric materials. This work presents a geometric and topological optimization of active–passive damping treatments, consisting of a viscoelastic layer, a constraining layer, a spacer layer and a set of piezoelectric actuators. The modelling is performed using a piezoelectric sandwich/multilayer beam finite element model in which the viscoelastic material's frequency dependence is accounted for using the anelastic displacement fields model. The resulting model is then reduced using a two-step modal reduction and applied to a limited-input optimal control strategy to evaluate the resulting active–passive modal damping factors. A genetic algorithm based optimization technique combined with an aggregated weighted minimum–maximum approach for a multiobjective optimization is used, aiming for the maximization of active–passive damping and minimization of weight added to the structure. Results show that a considerable improvement of damping performance is achievable with a controlled increase in the mass of the structure.

2169

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Silica-poly(acrylic acid) (PAAc) core–shell nanoparticles (NPs) were successfully prepared via graft copolymerization of acrylic acid (AAc) onto vinyl-bond-modified silica NPs. Transmission electron microscopy (TEM) results indicated that the obtained micropheres have a core–shell morphology. Fourier transform infrared (FTIR) analysis and x-ray photoelectron spectroscopy (XPS) measurements confirmed that the surface of the nanoparticles was polymer-rich, consistent with the core–shell morphology. The influence of the synthetic conditions, such as reaction time and AAc concentration on the graft yield of PAAc grafted on the silica NPs was investigated. Dynamic light scattering (DLS) analysis showed that the silica-PAAc core–shell nanoparticles possessed excellent response to pH and ion strength. Because of their pH-responsive behavior and small feature size, nanostructure devices designed from the smart silica nanoparticles have potential applications including sensors and membranes.

2175

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A novel temperature-sensitive hydrogel with fast deswelling and swelling rates was prepared from an N-isopropylacrylamide monomer mixture with poly(vinylpyrrolidone) (PVP) and its lightly crosslinked counterpart (so-called polyvinyl-polypyrrolidone, PVPP). The PVP worked as a porogen for the polymerization-induced phase separation of the hydrogel while the PVPP microgels were used as a pore-structure modifier. The hydrogel, in the form of a layer, was laminated with an acrylic resin layer to make a temperature-sensitive flap which can work as a bimetallic-like actuator with fast responses. Owing to the different deswelling/swelling ratios of the two layers, the smart flap bent in opposite directions in water at different temperatures. The switching temperature, at which the flap changed its bending direction, was adjusted by applying different ratios of PVP/PVPP in the hydrogel precursors. Dynamic results show that the flap with a hydrogel layer modified by PVP/PVPP required only several seconds to bend to its equilibrium states in both directions. No obvious performance loss was found after numerous heating–cooling cycles and the processes of drying and recovery.

2183

and

Electrorheological (ER) fluids are a class of smart materials in which their rheological properties can be changed reversibly under the influence of an applied electric field. In recent years, many industrial applications of these smart fluids have been introduced by researchers, especially in the damping control of systems. In the present work, the applicability of squeeze-mode ER dampers in suppressing the vibration of a cantilever beam is investigated. The dynamic response of the beam for an impulse exciting force is obtained using a direct integration method based on a finite-element model for the structure. The nonlinear displacement and velocity-dependent characteristics of the squeeze-mode ER damper are considered in each of the iterations. Although the proposed ER damper has been found to have a significant influence on the dynamic response of the structure, adding a closed-loop control system could improve the damping behavior of the structure considerably. While the strength of the electric field depends on the gap between the electrodes, the control system uses displacement feedback for producing a controlling voltage to prevent the electric field exceeding its allowable bounds.

2190

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Vibration suppression of laminated composite beams using the smart structures concept is presented in the present work. The smart system consists of a laminated composite beam as the host structure and piezoceramic and PVDF patches as the actuation and sensing elements. To treat the material and geometric inhomogeneities through the thickness of the laminated smart structure, a finite element model based on the layerwise displacement theory which incorporates the electro-mechanical coupling effects has been developed. The state space model of the active laminated beam is then used to design the control system. A linear quadratic regulator (LQR) controller is designed to achieve vibration suppression of the laminated smart beam. The effects of the laminate configuration and locations of sensors/actuators on controlled response are investigated. An experimental set-up has been developed to determine the natural frequency and damping factor of the smart laminated beam. The experimental measurements are then used to design a control mechanism with LQR to suppress the vibration response of the system. Open-loop and closed-loop responses of the system have been obtained experimentally and compared with the corresponding simulation results to demonstrate the accuracy and efficiency of the present approach in the vibration control of laminated smart structures.

2202

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This paper addresses the vibration mitigation of stay cables by using superelastic shape memory alloy (SMA) dampers. A closed form solution of the additional equivalent modal damping ratio of a combined stay cable/SMA damper system is formulated when the combined stay cable/SMA damper system vibrates with a single mode. The responses of a stay cable model on a cable-stayed bridge model with/without one SMA damper subjected to sweeping sinusoidal excitations are numerically investigated. An experimental investigation on the stay cable model incorporated with superelastic SMA spring dampers is finally carried out to verify the effectiveness of the proposed approach and the computational results.

2214

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Transparent chips with regular micrometer posts were fabricated from glass slides, glass wafers and silicon wafers via the available photolithography and pattern transfer techniques. The fabrication conditions, e.g. the substrate type, the photomask type, the etchant composition and the etching time, have been adjusted to pattern chips with post height of 6–70 µm. On the other hand, colloidal Au particles with size of 12 nm were synthesized by the reduction of tetrachloroauric acid and further modified by mercaptoundecanoic acid into nano-optical tags. The functionalization of transparent chips with 3-aminopropyltrimethoxysilane brings about the attachment of modified Au nanoparticles onto the surface, which shows characteristic UV–vis absorbance and indicates the feasibility as a new type of biosensor based on a specially patterned chip with high sensitivity.

2222

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Control over protein adsorption is a key issue for numerous biomedical applications ranging from diagnostic microarrays to tissue-engineered medical devices. Here, we describe a method for creating surfaces that prevent non-specific protein adsorption, which upon application of an external trigger can be transformed into surfaces showing high protein adsorption on demand. Silicon wafers were used as substrate materials upon which thin functional coatings were constructed by the deposition of an allylamine plasma polymer followed by high-density grafting of poly(ethylene oxide) aldehyde, resulting in a low-fouling surface. When the underlying highly doped silicon substrate was used as an electrode, the resulting electrostatic attraction between the electrode and charged proteins in solution induced protein deposition at the low-fouling interface. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to characterize the surface modifications. Controlled protein adsorption experiments were carried out using horseradish peroxidase. The amount of protein deposited at the surface was then investigated by means of a colorimetric assay. It is expected that the concept described here will find use in a variety of biotechnological and biomedical applications, particularly in the area of biochips.

2229

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Lower-order shear deformation theories are adequate to predict the global behavior of a smart plate. They cannot, however, predict accurate deformation and stress distributions through the thickness of laminated smart plates. Thus higher-order zigzag theories have been proposed to accurately calculate them. In most cases, a simplified higher-order zigzag theory requires C1 shape functions in finite-element implementation that are not so common for plate and shell analysis in commercial FE software. This presents the practical limitation of simplified zigzag theories to the commercial FE package. In fact, an iso-parametric C0 plate model is standard for the analysis and design of composite laminated plates and shells. In this paper, an enhanced lower-order shear deformation theory (ELSDT) is developed to provide a simple yet accurate tool for the analysis of smart structures under combined loads (including thermal and electrical loads as well as mechanical loads). It is systematically derived by minimizing the least-square errors between the first-order theory and the higher-order theory. This makes it possible to transform the strain energy of a higher-order zigzag theory to that of a lower-order zigzag theory. The resulting lower-order theory, which is referred to as the ELSDT, requires the C0 shape function only, and it is applicable to fully coupled mechanical, electric, and thermal problems. First a higher-order zigzag theory is established, which includes both a linear zigzag function and a cubic polynomial for in-plane displacements, a quadratic polynomial in the out-of-plane displacement, and a layerwise function for the electric potential. The ELSDT is then constructed via the aforementioned procedure. The accuracy and robustness of the present theory are demonstrated through numerical examples.

2242

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This paper presents the geometric optimal design of magnetorheological (MR) valves in order to improve valve performance, such as pressure drop. The optimization problem is to find the optimal geometric dimensions of MR valves constrained in a specific volume. After describing the configuration of MR valves, their pressure drops are investigated on the basis of the Bingham model of an MR fluid. Then, the valve ratio, which is an objective function, is derived by considering the field-dependent (controllable) and viscous (uncontrollable) pressure drops of the MR valves. Subsequently, the optimization procedure using a golden-section algorithm and a local quadratic fitting technique is constructed via a commercial finite element method (FEM) parametric design language. From the constructed optimization tool, optimal solutions of the MR valves, which are constrained in a specific cylindrical volume defined by its radius and height, are calculated and compared with analytical ones. In addition, several different types of MR valves are optimized in the same specific volume and results are presented.

2253
The following article is Free article

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This paper provides an analysis for the performance evaluation of a piezoelectric energy harvesting system using the synchronized switch harvesting on inductor (SSHI) electronic interface. In contrast with estimates based on a variety of approximations in the literature, an analytic expression of harvested power is derived explicitly and validated numerically for the SSHI system. It is shown that the electrical response using an ideal SSHI interface is similar to that using the standard interface in a strongly coupled electromechanical system operated at short circuit resonance. On the other hand, if the SSHI circuit is not ideal, the performance degradation is evaluated and classified according to the relative strength of coupling. It is found that the best use of the SSHI harvesting circuit is for systems in the mid-range of electromechanical coupling. The degradation in harvested power due to the non-perfect voltage inversion is not pronounced in this case, and a new finding shows that the reduction in power is much less sensitive to frequency deviations than that using the standard technique.

2265

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In this work a geometrically nonlinear finite shell element is presented, incorporating piezoelectric layers. The finite element is implemented in a total Lagrangian approach, which requires special attention to be given to the proper definition of the mechanical and electrical quantities. The strain–displacement relations are based on the assumption of small strains and moderate rotations. The transverse displacement field and the transverse electric potential are assumed to vary linearly through the thickness. With the presented finite element, static as well as dynamic examples are calculated. The differences between the results obtained with linear and nonlinear theory are emphasized.

2275

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A resonant trailing-edge flap actuation system for helicopter rotors is developed and evaluated experimentally. The concept involves deflecting each individual trailing-edge flap using a compact resonant piezoelectric actuation system. Each resonant actuation system yields high authority, while operating at a single frequency. By tailoring the natural frequencies of the actuation system (including the piezoelectric actuator and the related mechanical and electrical elements) to the required operating frequencies, one can increase the output authority. The robustness of the device can be enhanced by increasing the high authority bandwidth through electric circuitry design. Such a resonant actuation system (RAS) is analyzed for a full-scale piezoelectric induced-shear tube actuator, and bench-top testing is conducted to validate the concept. An adaptive feed-forward controller is developed to realize the electric network dynamics and adapt to phase variation. The control strategy is then implemented via a digital signal processor (DSP) system. Analysis is also performed to examine the rotor system dynamics in forward flight with piezoelectric resonant actuators, using a perturbation method to evaluate the system's time-varying characteristics. Numerical simulations reveal that the resonant actuator concept can be applied to forward flights as well as to hover conditions.

2286

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In this study, we geometrically modeled an electroless-plated platinum electrode of the IPMC and performed parametric studies to estimate the electrical properties (resistance and capacitance) of the electrode. We conducted experiments to control the change of the electrode characteristics (electrode thickness, particle size, particle gap, etc.). We measured the electrical properties of the electrodes in an aqueous environment and compared these findings with the modeling results to verify the model. The model's estimations of the effects of the parameters were well conceived; however, it was also found that there were limits of the estimations of the curved electrode's properties.

2296

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This paper describes the results of our numerical and experimental studies of the nonlinear electromechanical response in functionally graded piezoelectric actuators under alternating current (AC) electric fields. A nonlinear finite-element method is employed to simulate the dynamic bending of clamped–clamped functionally graded piezoelectric bimorphs. A phenomenological model of domain wall motion is used in the computation, and the effects of AC electric field amplitude and frequency, number of layers and property gradation on the sound pressure level, deflection and internal stresses of the actuators are examined. The sound pressure level is also measured to validate the numerical predictions, and comparison is made between numerical results and experimental data.

2302

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A microactuator made from poly(vinylidene fluoride) (PVDF), a piezoelectric polymer, was fabricated to control the gas flow rate through a glass micronozzle. The actuator was formed by gluing together two PVDF sheets with opposite polarization directions. The sheets were covered with thin conducting films on one side, that were then used as electrodes to apply an electric field to move the valve. The actuator has a rectangular shape, 3 mm × 6 mm. The device was incorporated with a micronozzle fabricated by a powder blasting technique. Upon applying a DC voltage across the actuator electrodes, one sheet expands while the other contracts, generating an opening motion. A voltage of +300 V DC was used to open the device by moving the actuator 30 µm, and a voltage of −200 V DC was used to close the device by moving the actuator 20 µm lower than the relaxed position. Flow measurements were performed in a low-pressure vacuum system, maintaining the microvalve inlet pressure constant at 266 Pa. Tests carried out with the actuator in the open position and with a pressure ratio (inlet pressure divided by outlet pressure) of 0.5, indicated a flow rate of 0.36 sccm. In the closed position, and with a pressure ratio of 0.2, a flow rate of 0.32 sccm was measured.

2308

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This paper presents the development of a dual-axis convective microaccelerometer, whose working principle is based on the convective heat transfer and thermoresistive effect of lightly doped silicon. In contrast to the developed convective accelerometer, the sensor utilizes new structures of the sensing element which can reduce at least 90% of the thermally induced stress. By using a numerical method, the dimensions of the sensing chip and of the package are optimized. The sensitivity of the sensor is simulated; other characteristics such as frequency response, shock resistance and the noise problem were investigated. The sensor has been fabricated by a microelectrical mechanical systems (MEMS) process and characterized by experiments.

2315

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The paper investigates the use of Macro Fiber Composite (MFC) actuators to actively control thermally induced deformations in composite structures. Numerical and experimental results are presented. A finite-element model is developed using the commercial software ABAQUS. The model includes structural, thermal and piezoelectric fields. A control algorithm is implemented to control the response of the structure in a closed loop actively. The control scheme is based on the measure of the out-of-plane displacement of the structure. A few experiments are conducted to check the validity of the predictions and to test the feasibility of using MFC actuators for active control. To generate thermal distortion easily a laminated structure with an unsymmetric lay-up was placed in an oven. The oven temperature was varied to create thermal loading. The experimental and theoretical results correlate very well and demonstrate that the proposed method can be used to perform active shape control of a structure subjected to thermal distortion.

2323

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The feasibility of a newly developed smart passive control system equipped electromagnetic induction device is experimentally investigated. An electromagnetic induction device consists of a permanent magnet and a solenoid, which produces electrical energy (i.e. induced current) according to Faraday's law of electromagnetic induction. The produced energy is applied to the magnetorheological (i.e. MR) damper to change the damping characteristics by itself without any controller or corresponding sensors for reducing structural responses. Recently, the smart passive control system was conceptually and numerically introduced without consideration of its practical applicability. This paper describes the design of an electromagnetic inductive device which is composed of a permanent magnet and a solenoid, and experiments with the MR damper-based smart passive control system on a shaking table which produces various sinusoidal and random excitations. The experimental results demonstrate that it is feasible to apply the smart passive control system equipped electromagnetic induction device for changing the damping characteristics of an MR damper.

2330

, , , , and

Shape memory polymer foams have significant potential in biomedical and aerospace applications, but their thermo-mechanical behavior under relevant deformation conditions is not well understood. In this paper we examine the thermo-mechanical behavior of epoxy shape memory polymer foams with an average relative density of nearly 20%. These foams are deformed under conditions of varying stress, strain, and temperature. The glass transition temperature of the foam was measured to be approximately 90 °C and compression and tensile tests were performed at temperatures ranging from 25 to 125 °C. Various shape recovery tests were used to measure recovery properties under different thermo-mechanical conditions. Tensile strain to failure was measured as a function of temperature to probe the maximum recovery limits of the foam in both temperature and strain space. Compression tests were performed to examine compressibility of the material as a function of temperature; these foams can be compacted as much as 80% and still experience full strain recovery over multiple cycles. Furthermore, both tensile strain to failure tests and cyclic compression recovery tests revealed that deforming at a temperature of 80 °C maximizes macroscopic strain recovery. Deformation temperatures above or below this optimal value lead to lower failure strains in tension and the accumulation of non-recoverable strains in cyclic compression. Micro-computed tomography (micro-CT) scans of the foam at various compressed states were used to understand foam deformation mechanisms. The micro-CT studies revealed the bending, buckling, and collapse of cells with increasing compression, consistent with results from published numerical simulations.

2341

and

Particle swarm optimization (PSO), which is a new robust stochastic evolutionary computational algorithm based on the movement and intelligence of swarms, is proposed to estimate parameters of the Bouc–Wen hysteresis model. The performance of the PSO method is compared with the more common genetic algorithms (GAs) in terms of parameter accuracy. Simulation results of the Bouc–Wen model with all the unknown parameters are illustrated to show that a higher quality solution with better computational efficiency than the GA method can be achieved by means of the PSO method. Furthermore, parameter estimation of the Bouc–Wen model with noisy data is considered. The results show that the proposed method is still effective even if the simulated data are corrupted by noise.

2350

, , , , , , , , and

In this paper, we report on a method to fabricate selenium (Se) nanospheres and lead selenide (PbSe) nanoshells in aqueous solution at 100 °C under refluxing and vigorous magnetic stirring. The PbSe nanoshells (the average diameter is 2.0 µm and average shell-thickness is 250 nm) were synthesized by using ascorbic acid as the reducing agent with the assistance of a template of synthesized Se nanospheres (the average diameter is 1.5 µm). The synthesized selenium nanospheres and PbSe nanoshells were further characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Finally, the growth mechanism of Se nanospheres and PbSe nanoshells is also discussed.

2354

, and

This paper presents the design, analysis and fabrication of a piezoelectric multi-axis stage based on a new stick-and-clamping actuation technology for miniaturized machine tool systems, referred to as meso-scale machine tool (mMT) systems. In the stick-and-clamping actuation system, shearing/expanding piezoelectric actuators, an inertial mass and an advanced preload system are configured innovatively to generate the motion of an inertial mass. There are two operating modes in the stick-and-clamping actuation technology: (1) stick mode and (2) clamp mode. In stick mode, the 'slow' deformation of the shearing piezoelectric actuators drives an inertial mass, which is located on the tips of the shearing piezoelectric actuators, by means of the friction force at their contact interface. On the other hand, in clamp mode, the expanding piezoelectric actuators provide the clamping force to an inertial mass when the rapid backward deformation of the shearing piezoelectric actuators occurs. The stick-and-clamping actuation technology also enables two-degrees-of-freedom (DOF) motion of an inertial mass in a single plane by perpendicularly stacking two shearing piezoelectric actuators. The 2-DOF piezoelectric multi-axis stage is developed on the basis of the stick-and-clamping actuation technology, and the dynamic and static performance analyses are conducted. The LuGre friction model for the contact interfaces is introduced, and their dynamic behaviours are characterized. In the open-loop static performance test, linear, diagonal and circular motions of the developed piezoelectric multi-axis stage are generated, and their performances are evaluated. The dynamic characteristics and static performances of the developed 2-DOF piezoelectric multi-axis stage show its applicability and effectiveness for the precision positioning system.

2368

, , and

At present much attention is being devoted to the study of self-monitoring materials, which simultaneously offer good structural and sensing properties. In the present study self-sensing carbon–glass hybrid structural composites, behaving as 'guard' sensors (i.e. they give a warning when fixed loads are reached) were designed, manufactured and tested. In particular, samples containing different carbon fibre/glass fibre ratios were prepared and tested, by performing both mechanical (monotonic and cycle tensile tests) and electrical measurements. The results showed the efficiency of the proposed system and the possibility to design such materials to suit any specific application need. The advantages of these materials, compared to other more sophisticated monitoring systems, are the ease of fabrication and use, low production costs and versatility, so such materials are suitable for widespread low-cost applications.

2375

and

A new methodology of guided-wave-based nondestructive testing (NDT) is developed to detect crack damage in a thin metal structure without using prior baseline data or a predetermined decision boundary. In conventional guided-wave-based techniques, damage is often identified by comparing the 'current' data obtained from a potentially damaged condition of a structure with the 'past' baseline data collected at the pristine condition of the structure. However, it has been reported that this type of pattern comparison with the baseline data can lead to increased false alarms due to its susceptibility to varying operational and environmental conditions of the structure. To develop a more robust damage diagnosis technique, a new concept of NDT is conceived so that cracks can be detected even when the system being monitored is subjected to changing operational and environmental conditions. The proposed NDT technique utilizes the polarization characteristics of the piezoelectric wafers attached on both sides of the thin metal structure. Crack formation creates Lamb wave mode conversion due to a sudden change in the thickness of the structure. Then, the proposed technique instantly detects the appearance of the crack by extracting this mode conversion from the measured Lamb waves, and the threshold value from damage classification is also obtained only from the current dataset. Numerical and experimental results are presented to demonstrate the applicability of the proposed technique to instantaneous crack detection.

2388

, and

In this paper the use of actuators utilizing the magnetic shape memory effect for force vibration control of beam-like structures is discussed. In order to model the shape memory effect in magnetic shape memory alloys, a modified phenomenological one-dimensional model based on the Liang and Rogers classical shape memory alloy behaviour model is developed and presented. The model developed has been implemented for use by the finite element method. Then the effectiveness of the use of magnetic shape memory actuators for the case of a beam with two actuators has been investigated. The influence of various actuation parameters for the magnetic shape memory actuators for control and tuning of transverse vibration of the beam has also been successfully shown.

2398

Membrane mirrors and apertures pose exciting alternatives to traditional technologies in the reconnaissance field. The ultra-flexibility of membrane structures translates into an order of magnitude reduction in weight and mission cost savings while improving the aperture size on-orbit by an order of magnitude. However, the flexibility of these structures wreaks havoc with on-orbit stability as membranes demonstrate adverse dynamics at low frequencies. To counter these adverse dynamics, novel means of vibration control must be pursued. Currently, a Kapton membrane strip augmented with a piezoelectric bimorph is modeled using Euler–Bernoulli beam theory, experimentally validated, and then controlled through numerical simulation using linear quadratic regulator theory. In formulating the linear quadratic regulator (LQR) problem, the functional gains of the active membrane strip are also numerically computed. The functional gains are used to intelligently select regions within the structure's domain to place strain gages and to take velocity measurements. The 1D membrane sample provides a building block for more complex models, and illustrates the concept of functional gain analysis.

2408

, and

Recently, the functionally graded material (FGM) concept has been explored in piezoelectric materials to improve properties and to increase the lifetime of bimorph piezoelectric actuators. For instance, elastic, piezoelectric, and/or dielectric properties may be graded along the thickness of a piezoceramic. Thus, the gradation of piezoceramic properties influences the performance of piezoactuators. The usual FGM modelling using traditional finite element formulation and discretization into layers gives a highly discontinuous stress distribution, which is undesirable. In this work, we focus on nonhomogeneous piezoelectric materials using a generalized isoparametric formulation based on the graded finite element concept, in which the properties change smoothly inside the element. This approach provides a continuum material distribution, which is appropriate to model FGMs. Both four-node quadrilaterals and eight-node quadrilaterals for piezoelectric FGMs were implemented using the graded finite element concept. A closed form two-dimensional analytical model of piezoelectric FGMs is also developed to check the accuracy of these finite elements and to assess the influence of material property gradation on the behavior of piezoelectric FGMs. The paper discusses and compares the behavior of piezoelectric graded elements under four loading conditions with respect to the analytical solutions (derived in this work) considering exponential variation of elastic, piezoelectric, and dielectric properties separately. The analytical solutions provide benchmark problems to verify numerical procedures (such as the finite element method and the boundary element method).

2429

, , and

Aircraft landing gears are subjected to a wide range of excitation conditions, which result in conflicting damping requirements. A novel solution to this problem is to implement semi-active damping using magnetorheological (MR) fluids. This paper presents a design methodology that enables an MR landing gear to be optimized, both in terms of its damping and magnetic circuit performance, whilst adhering to stringent packaging constraints. Such constraints are vital in landing gear, if MR technology is to be considered as feasible in commercial applications.

The design approach focuses on the impact or landing phase of an aircraft's flight, where large variations in sink speed, angle of attack and aircraft mass makes an MR device potentially very attractive. In this study, an equivalent MR model of an existing aircraft landing gear is developed. This includes a dynamic model of an MR shock strut, which accounts for the effects of fluid compressibility. This is important in impulsive loading applications such as landing gear, as fluid compression will reduce device controllability. Using the model, numerical impact simulations are performed to illustrate the performance of the optimized MR shock strut, and hence the effectiveness of the proposed design methodology. Part 2 of this contribution focuses on experimental validation.

2441

, , and

Aircraft landing gears are subjected to a wide range of excitation conditions with conflicting damping requirements. A novel solution to this problem is to implement semi-active damping using magnetorheological (MR) fluids. In part 1 of this contribution, a methodology was developed that enables the geometry of a flow mode MR valve to be optimized within the constraints of an existing passive landing gear. The device was designed to be optimal in terms of its impact performance, which was demonstrated using numerical simulations of the complete landing gear system. To perform the simulations, assumptions were made regarding some of the parameters used in the MR shock strut model. In particular, the MR fluid's yield stress, viscosity, and bulk modulus properties were not known accurately. Therefore, the present contribution aims to validate these parameters experimentally, via the manufacture and testing of an MR shock strut. The gas exponent, which is used to model the shock strut's nonlinear stiffness, is also investigated. In general, it is shown that MR fluid property data at high shear rates are required in order to accurately predict performance prior to device manufacture. Furthermore, the study illustrates how fluid compressibility can have a significant influence on the device time constant, and hence on potential control strategies.

2453

and

Spider silks have great potential in many fields due to their high strength and superb toughness. In this work, fluorescent spider silks were fabricated by consecutively assembling CdTe nanocrystals and polyelectrolyte (PE) macromolecules onto spider dragline silks. Scanning electron microscopy and fluorescence microscopy images showed that a large number of CdTe nanocrystals and PE molecules were successfully deposited on the surface of the spider silks, and the silk composites obtained exhibited core–shell structure characteristics. The energy dispersion x-ray spectrum (EDS) showed that the silk composites contained about 2.68% (w/w) of CdTe nanocrystals when the spider silks were coated with just one layer of PE/CdTe/PE. The resulting fluorescent spider silks exhibited very bright fluorescence, and their emission spectrum was located in the near-infrared (NIR) band. The mechanical properties of these modified spider silks, such as the maximum pull force and the elastic limit elongation when a single spider silk strand breaks, showed a slight decrease after coating with CdTe nanocrystals and PE. This fluorescent spider silk is envisioned to have applications in materials science, microelectronics, and even biology.

2457

, , , and

Ionic polymer–metal composites (IPMCs) have been considered for various applications due to their light weight, large bending, and low actuation voltage requirements. However, their response can be slow and vary widely, depending on various factors such as fabrication processes, water content, and contact conditions with the electrodes. In order to utilize their capability in various high-performance microelectromechanical systems, controllers need to address this uncertainty and non-repeatability while improving the response speed. In this work, we identified an empirical model for the dynamic relationship between the applied voltage and the IPMC beam deflection, which includes the uncertainties and variations of the response. Then, four types of controller were designed, and their performances were compared: a proportional–integral–derivative (PID) controller with optimized gains using a co-evolutionary algorithm, and three types of robust controller based on , with loop shaping, and μ-synthesis, respectively. Our results show that the robust control techniques can significantly improve the IPMC performance against non-repeatability or parametric uncertainties, in terms of the faster response and lower overshoot than the PID control, using lower actuation voltage.

2464

, , , , and

The objective of this paper is to examine experimentally the applicability of a structural health monitoring system employing TRIP (transformation induced plasticity) steels. The capability of TRIP steels in the assessment of structural performance degradation was evaluated through material tests. The magnetic characteristics of TRIP steels under tensile and compressive uniaxial loadings were investigated through the measurement of induced voltage. The stress–strain hysteresis and the associated magnetic alternation of TRIP steels were identified. Furthermore, plate-bending tests and beam-bending tests were carried out in order to study the damage-detection characteristics. As the conclusion, the dual function of TRIP steels, serving as both a high ductility load-carrying member and a sensor to monitor damage accumulation, was confirmed.

2477

and

A micro–macro model is formulated for the magnetomechanical behavior of magnetorheological fluids (MRFs) based on micromechanics and a statistical approach. It includes two stages: (1) the analysis of the aggregation of the particles in an MRF into chains of dipoles aligning in the direction of the applied magnetic field and its contribution to resistance against shear deformation, and (2) the attainment of solid-like mechanical properties of the MRF by assuming numerous chains inclining with the angles arranged in a normal distribution. This model takes into account the effect of each of the main influencing factors, such as the intensity of magnetic induction, the size and the volume fraction of particles, shear strain rate and saturation magnetization, etc, on the critical shear stress of MRFs. The effect of typical governing parameters on the behavior of MRFs is investigated individually, which shows the capability of the proposed model in the description of the magnetorheological behavior of MRFs. The common Bingham's model of viscoplasticity and the dual-viscosity model can be obtained from the proposed model as special cases. The model is comprehensive, simple, and can easily be used for the initial design and optimization of high-performance MRFs.

2486

, , and

Polyurethane flexible foam having shape memory effects has been synthesized from polyester polyol and 4,4'-diphenylmethane diisocyanate (MDI) following the quasi-prepolymer method in the presence of water as the blowing agent, and the effect of the organometallic catalyst and the molecular weight of polyol has been studied. It was found that the closed cell content, foam density, rubbery modulus, compression set, and shape fixability increased with increasing amounts of organometallic catalyst and decreasing molecular weight of polyol, whereas the cell size showed the opposite tendency. On the other hand, the shape recoverability of the foam was over 99% regardless of the catalyst content and molecular weight of polyol.

2492

, , and

Piezoelectric materials exhibit high electromechanical coupling that allows them to both generate an electrical signal when strained and, conversely, to produce a strain under an applied electric field. This coupling has led to the use of these materials for a variety of sensing and actuation purposes. One unique application of these materials is their use as self-sensing actuators where both the sensing and actuation functions are performed by a single patch of material. Since the actuation and sensing voltages both exist simultaneously in the piezoelectric material, a specially designed electric circuit, referred to as a bridge circuit, is required to realize the concept. Configuration of the material in this manner is advantageous for control systems due to the enhanced stability associated when collocated control is applied. While certain advantages result from this type of system, precise equilibrium of the bridge circuit is required to achieve stability. This equilibrium is easy to achieve in theory, but difficult in practice due to the thermal dependence of the piezoelectric material's dielectric constant. This study will investigate a novel method of accounting for these changes through the use of thermal switches to passively adjust the bridge circuit and maintain a balanced state. The proposed concept will be theoretically modeled and simulated in a vibration control application to identify the thermal range for stability with and without the array of switches. It will be shown that, through the use of nine thermal switches, the stable operating range can be increased by 95 °C while maintaining vibration control performance.

2501

, , and

The magnetoelectric (ME) coupling from 20 Hz to 100 kHz and the hydrogen effect on Ni–PZT–Ni trilayer composites made by electrodeposition have been investigated. The results show that the magnetoelectric voltage coefficient, αE,31, increases with increased Ni layer thickness, up to αE,31 = 16 V cm−1 Oe−1. The ME voltage coefficient decreases with the increase of hydrogen concentration. To prevent the degradation of ME coupling, the plating solution and process parameters of electrodeposition should be chosen suitably. Moreover, an additional outgassing process after electrodeposition can reduce the hydrogen concentration and effectively promote ME coupling.

2505

, and

Long-range, torsional guided waves generated in pipes using magnetostrictive sensors (MsSs) have great potential for applications to the structural health monitoring (SHM) of hard-to-inspect pipes. This paper reports an improved MsS technique (when compared to related techniques currently used for the NDT of pipes) that uses polymeric magnetic tape material that is suitable for use in a variety of industries as an SHM tool for pipes. Improvements include increased efficiency, reduced cost and increased long-term survivability of the sensor system. Transduction efficiency was increased by reducing the sensor eddy current losses and by using a field concentrator strip. For long-term monitoring, a low-cost magnetic oxide based MsS material (video recording tape) having the required magnetic properties was used. The MsS strips were oriented to generate non-dispersive torsional guided ultrasonic waves that propagate long distances with minimal mode conversion. Further, considering both safety and long-term survivability of the sensor, low-power ultrasonic instrumentation was developed and tested. Measurements reported here demonstrate the sensitivity of this sensor to both radial notches (saw cuts) and drilled holes. Results also show that magnetic anisotropy of the strip plays a role in generating torsional waves. It is envisioned that results obtained from the present study will significantly enhance the ability to monitor the long-term structural health of piping systems.

2516

and

In this paper, models of adaptive composite panels with surface-mounted/embedded piezoelectric patches are analytically built using the Lagrange–Rayleigh–Ritz method (LRRM), verified through experiments and finite element method (FEM), and used in piezoelectric actuator placement optimization and vibration control. Two panels are considered: a cantilevered adaptive composite beam (ACB) and an adaptive circular composite plate (ACCP) with complex boundaries. The inertia and stiffness of the surface-mounted/embedded piezoelectric patches are included in the developed models. To obtain the mode shapes of the ACCP, which are essential to the LRRM modeling, the method of separation of variables is employed and Bessel series and modified Bessel series are introduced. The built models are verified by experiments for the ACB and by the FEM for the ACCP. The actuation configurations of the piezoelectric patches in the panels are optimized based on the introduced analytical model. Finally, with the optimal locations of the piezoelectric patches, the vibration suppression of the ACB and the ACCP is experimentally and numerically carried out, and excellent vibration suppressions for both adaptive panels are obtained.

2526

and

Placement and sizing of piezo actuators is normally based on control effectiveness. However, retrofitting of piezoelectric actuators alters the inherent stiffness/mass properties of the parent structure. In rotating structures, the additional mass due to piezo patches contributes to the centrifugal stiffening force. The parent structure is originally designed to have a certain natural frequency spectrum in relation to the disturbance excitation. In the event of failure of the active system, the dynamics of the structure with piezos (now rendered passive) will therefore become significant. Thus it will be helpful to determine locations for mounting piezo patches based on minimal natural frequency change yet with good control authority. In this study, a finite element based procedure for plate structures is presented. Favorable locations for mounting piezos based on minimal natural frequency changes are iteratively evolved from an initial configuration wherein the whole plate is covered with piezos. A modal controllability approach has been used for finding piezo mounting locations from a good controllability perspective. The procedure is demonstrated for simply supported square, swept-back, circular and rotating rectangular plates considering the first four modes.

2543

and

The creation of an effective two-way shape memory alloy (TWSMA) requires appropriate heat treatment and optimal training considerations. In particular, the training method used plays a key role. This work investigates different training methods for producing NiTi TWSMA wires with the hot shape of an arc and the cold shape of a straight line. These methods are shape memory cycling, constrained cycling of deformed martensite, pseudoelastic cycling and combined shape memory and pseudoelastic cycling. In order to give a meaningful evaluation of their performance that is relevant to training TWSMA for practical applications, these training methods are assessed in terms of maximum two-way strain, changes in the original hot shape together with the transformation temperatures after the training process, and the effective production of the cold shape. It was found that only the combined shape memory and pseudoelastic cycling provides an effective training method for creating NiTi TWSMA with a non-uniaxial two-way shape change. The undesirable side effects of training are that the NiTi TWSMA wire loses partial memory of the original hot shape and its transformation temperatures shift to lower values. There also exists an optimal number of training cycles, and possibly an optimal training load for obtaining the best cold shape memory and the greatest two-way recoverable strain. These findings give future directions to advance the training technology for TWSMA.

2550

, and

It has been proven that carbon-fiber-reinforced polymer (CFRP) sheets or plates are capable of improving the strength of reinforced concrete (RC) structures. However, residual deformation of RC structures in service reduces the effect of CFRP strengthening. SMA can be applied to potentially decrease residual deformation and even close concrete cracks because of its recovery forces imposed on the concrete when heated. Therefore, a method of a RC structure strengthened by CFRP plates in combination with SMA wires is proposed in this paper. The strengthening effect of this method is investigated through experiments and numerical study based on the nonlinear finite element software ABAQUS in simple RC beams. Parametric analysis and assessment of damage by defining a damage index are carried out. The results indicate that recovery forces of SMA wires can decrease deflections and even close cracks in the concrete. The recovery rate of deflection of the beam increases with increasing the ratio of SMA wires. The specimen strengthened with CFRP plates has a relatively large stiffness and smaller damage index value when the residual deformation of the beam is first reduced by activation of the SMA wires. The effectiveness of this strengthening method for RC beams is verified by experimental and numerical results.

2560

, , , and

The present work deals with the stress generation capability of nickel–titanium shape memory alloys (SMAs) under constrained conditions for two well-defined loading modes: recurrent crystalline transformation (transformation fatigue) and a one-step continuous activation (generated stress relaxation). The data acquired will be very useful during the design process of an SMA Ni–Ti element as a functional part of an assembly. Differential scanning calorimetry (DSC) was employed in order to investigate the transformation characteristics of the alloy before and after the tests. Transformation fatigue tests revealed that the parameter that affects more the rate of the functional degradation is the number of crystalline transitions the wire undergoes. Thus, the service life limit of this material as a stress generator can be reduced to a few thousand working cycles. For stress relaxation, the main factor that affects the ability for stress generation is the working temperature: the higher the temperature above the austenite finish (TAf) limit the higher the relaxation effect. Thermomechanical treatment of the alloy during the tests reveals the 'hidden' transformation from the cubic structure (B2) of austenite to the rhombohedral structure of the R-phase. It is believed that the gradual loss of the stress generation capability of the material under constrained conditions must be associated to a gradual slipping relaxation mechanism. Scanning electron microscopy (SEM) observations on as-received, re-trained, fatigued and stress-relaxed specimens in the martensitic state provide further support for this hypothesis.

2571

, , , and

Piezoceramic materials are used today in a variety of applications. By combining a piezoceramic powder with paint resin it is possible to fabricate a new type of piezomaterial, which can easily be applied to almost any surface. This paper describes the development of such a paint. The thermal stability and sensitivity as a function of frequency were investigated. Furthermore, a sensor based on an optimized epoxy piezopaint having a thickness of 80 µm was fixed on a steel beam of a footbridge to study the performance of the sensor and its long-term stability. It was demonstrated that the sensor could detect signals easily both from bridge movement and from pedestrian traffic on the bridge. The signal remained constant for a period of over thirteen months of monitoring.

2577

and

This paper presents an integrated model of a one dimensional periodic structure with distributed piezoelectric actuators and sensors for complete active or passive wave propagation control. The periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called 'pass bands' and wave propagation is completely blocked within other frequency bands called 'stop bands'. This basic property of periodic structures is enhanced by the application of distributed piezoelectric actuators and sensors, to actively control the wave propagation over the frequency range of interest.

The finite element model, based on the transfer matrix approach, is developed to study the flexural wave propagation of the uniform beams resting on periodically spaced, rigid simple supports with distributed piezoelectric actuators and sensors. The model is used to predict pass and stop frequency bands for different proportional and derivative control gains. The results indicate that the location and width of the stop bands as well as the attenuation characteristics in the beam can be modified by proper choice of the control gains. The numerical predictions demonstrate that the attenuation characteristics can be maximized within different frequency bands by proper tuning of the control gains. Also, the finite element method is used to find the response of the active periodic beams to a convected harmonic pressure field. Computed results show that the response amplitudes at coincidence frequency can be actively controlled by proper selection of control gains.

The tunable characteristics of the piezoelectric inserts are also used to introduce irregularities in the periodic structure. The source of disorder is the variance in the control gains of the inserts. Disorder in the periodicity typically extends the stop bands into adjacent propagation zones. More importantly, it produces localization of the vibration energy near the excitation source. The results obtained demonstrate the localization phenomenon and its control through appropriate tuning of the level of disorder in the control gains.

2595

, and

This paper presents a new subspace-based 2D direction of arrival (DOA) estimation algorithm for narrow-band sources with high-resolution localization capabilities. DOA estimation is achieved by using the noise-subspace eigenvectors of a new extended correlation matrix (ECM). A 2-L-shape antenna array is proposed. Unlike common planar and circular arrays, the novel antenna array with this special geometry requires no pair matching between the azimuth and elevation angle estimation. The performance of the proposed approach is examined by a simulation study in the presence of multiple wave fields. The simulation results show a good estimated performance of the proposed method.

2600

, and

Based on the synthesis of the copolymer of N-isopropylacrylamide and acrylic acid copolymeric microgel P(NIPAM-co-AAc), a new kind of complex of Tb(III) and P(NIPAM-co-AAc) with novel fluorescent properties was successfully prepared and characterized with different techniques. The UV and FT-IR spectrum showed that terbium coordinated with the carbonyl group of the microgel. The fluorescence spectrum indicated that the complex had good fluorescence properties and obtained the strongest fluorescence emission at 1.0 wt% ratio. This novel thermosensitive and fluorescence characterization of the P(NIPAM-co-AAc)-Tb(III) complex may be useful in fluorescence systems and the biomedical field.

2605

, and

The concept of a functionally graded material (FGM) is useful for engineering advanced piezoelectric actuators. For instance, it can lead to locally improved properties, and to increased lifetime of bimorph piezoelectric actuators. By selectively grading the elastic, piezoelectric, and/or dielectric properties along the thickness of a piezoceramic, the resulting gradation of electromechanical properties influences the behavior and performance of piezoactuators. In this work, topology optimization is applied to find the optimum gradation and polarization sign variation in piezoceramic domains in order to improve actuator performance measured in terms of selected output displacements. A bimorph-type actuator is emphasized, which is designed by maximizing the output displacement or output force at selected location(s) (e.g. the tip of the actuator). The numerical discretization is based on the graded finite element concept such that a continuum approximation of material distribution, which is appropriate to model FGMs, is achieved. The present results consider two-dimensional models with a plane-strain assumption. The material gradation plays an important role in improving the actuator performance when distributing piezoelectric (PZT5A) and non-piezoelectric (gold) materials in the design domain; however, the performance is not improved when distributing two types of similar piezoelectric material. In both cases, the polarization sign change did not play a significant role in the results. However, the optimizer always finds a solution with opposite polarization (as expected).

2621

, , and

In this study we investigated the electrochromic properties and electrochromic device application of poly(5,12-dihydrothieno[3',4':2,3][1,4]dioxocino[6,7-b]quinoxaline (DDQ)-co-2,2'-bithiophene (BT)). Copolymerization was successfully achieved electrochemically in acetonitrile containing 0.1 M tetrabutylammonium tetrafluoroborate as the supporting electrolyte by direct anodic oxidation on platinum and indium tin oxide coated glass electrodes. The structure and morphology of the copolymer were investigated by infrared spectroscopy and scanning electron microscopy (SEM). Spectroelectrochemical analysis of the resulting copolymer reflected electronic transitions at 504 nm and ∼800 nm revealing a π–π* transition and polaron formation, respectively. Dual-type polymer electrochromic devices (ECDs) based on P(DDQ-co-BT) were constructed with poly(3,4-ethylenedioxythiophene) (PEDOT). Spectroelectrochemistry, switching ability and stability experiments showed that the copolymer concerned can be a good anode material for electrochromic devices.

2627

, , , , , , , and

In this study we implemented manufacturing process and strain monitoring of a composite structure by optical fiber sensors for vacuum-assisted resin transfer molding (VaRTM). Optical fibers with fiber Bragg gratings were embedded into a glass fiber reinforced plastic specimen made by VaRTM and the applicability of structural health monitoring with fiber Bragg grating (FBG) sensors based on optical frequency domain reflectometry (OFDR) was investigated. In this study, long-gage FBGs which are 10 times longer than ordinary FBGs (which are about 10 mm long) were employed for distributed sensing. We can easily map the strain or temperature profile along gratings by OFDR and the spatial resolution of this sensing technique is about 1 mm. The resin flow process in VaRTM could be monitored by measuring the difference in temperature between the resin and preform. Then, the shrinkage of resin could be also monitored during the curing process. The specimen was then subjected to a bending load in a three-point bending test and the strain distributions along the FBGs were measured. From these results we could show the applicability of distributed sensors to quality assurance of a composite structure made by VaRTM and assessment of the structural integrity of in-service composite structures.

2636

This paper presents a piezoelectric dome-shaped-diaphragm transducer (DSDT) designed to harvest vibration energy for microgenerator applications. An equivalent circuit of the DSDT microgenerator is constructed and is used to investigate its efficiency in converting input mechanical vibration energy into output electrical power. The results show that DSDT-based microgenerators have a constant energy conversion efficiency of approximately 50%. The respective effects on the generated power output of the piezoelectric layer material (i.e. ZnO, PVDF or PZT), the piezoelectric layer thickness, the insulating layer thickness, the mass loading layer thickness, and the dome curvature radius are systematically examined. The results enable the optimal DSDT design parameter values to be specified for a given output power and piezoelectric material.

2645

, and

The microstructures and viscoelastic properties of anisotropic magnetorheological elastomers are investigated. The measurement results show that their mechanical properties are greatly dependent on the magnetic flux density applied during preparation. A finite-column model is proposed to describe the relationships between the microstructures and the viscoelastic properties. The simulation results agree well with the experimental results.

2651

, , , , , and

Ti50Ni47Cu3 films were prepared using magnetron sputtering deposition, and their martensitic transformation and mechanical properties were characterized. Free-standing TiNiCu films showed an intrinsic two-way shape memory effect which is attributed to a composition gradient through the film thickness. Different types of TiNiCu microactuators, including microtweezers and microcages, have been successfully fabricated which employ this two-way shape memory effect for operation. Upon heating/cooling, the microtweezers showed both horizontal and vertical displacement due to combined shape memory and thermal effects. The microcage actuators could be opened/closed through substrate heating with a maximum temperature of 90 °C, or by electrical heating with a power less than 5 mW and a maximum frequency of 100–300 Hz. Issues related to the fabrication and applications, such as stability and beam bending after release, have been addressed.

2658

and

Setting up a health monitoring system for large-scale civil engineering structures requires a large number of sensors and the placement of these sensors is of great significance for such spatially separated large structures. In this paper, we present an optimal sensor placement (OSP) algorithm by treating OSP as a combinatorial optimization problem which is solved using a swarm intelligence technique called particle swarm optimization (PSO). We propose a new hybrid PSO algorithm by combining a self-configurable PSO with the Nelder–Mead algorithm to solve this rather difficult combinatorial problem of OSP. The proposed algorithm aims precisely to achieve the best identification of modal frequencies and mode shapes. Numerical experiments have been carried out by considering civil engineering structures to evaluate the performance of the proposed swarm-intelligence-based OSP algorithm. Numerical studies indicate that the proposed hybrid PSO algorithm generates sensor configurations superior to the conventional iterative information-based approaches which have been popularly used for large structures. Further, the proposed hybrid PSO algorithm exhibits superior convergence characteristics when compared to other PSO counterparts.

2673

, , , , and

ZnO thin films with c-axis orientation have been prepared by a sol–gel method on glass substrates. An ethanol solution mixed with zinc acetate dihydrate and monoethanolamine was used as the precursor for spin-coating. Preferentially oriented ZnO thin films were prepared by preheating the as-deposited films at 300 °C and sintering from 350 to 600 °C. Thermogravimetry–differential thermal analysis (TG–DTA), x-ray diffraction (XRD) and scanning tunneling microscopy (STM) were employed to investigate the growth and morphology of the films. The results reveal that the thin films consist of stacked, nearly spherical, nanocrystalline particles, and that 500 °C is optimal temperature for the crystallization of ZnO thin films. It is argued that the extremely preferential c-axis orientation is a result of self-assembly induced by dipole–dipole interaction between polar nanograins. Moreover, the orientation and continuity of ZnO thin film are affected by the number and kind of the hydroxyl groups of the complexing agent.

2680

and

This paper considers the optimal placement of collocated piezoelectric actuator–sensor pairs on a thin plate using a model-based linear quadratic regulator (LQR) controller. LQR performance is taken as objective for finding the optimal location of sensor–actuator pairs. The problem is formulated using the finite element method (FEM) as multi-input–multi-output (MIMO) model control. The discrete optimal sensor and actuator location problem is formulated in the framework of a zero–one optimization problem. A genetic algorithm (GA) is used to solve the zero–one optimization problem. Different classical control strategies like direct proportional feedback, constant-gain negative velocity feedback and the LQR optimal control scheme are applied to study the control effectiveness.

TECHNICAL NOTES

N47

, , , and

We demonstrate a generic approach for producing different shaped and sized protrusive features using shape-memory polymer (SMP). Utilizing the large recoverable strain in the SMP, and depending on the pre-straining of the SMP, shape of the indenter, temperature during indenting and the depth of polishing, we show that a variety of features of different sizes can be easily obtained.

N51

and

In this paper, shape memory alloy (SMA) wire actuators are used to control the flap movement of a model airplane wing. Conventionally, the flap of an aircraft wing is driven by electric motors or hydraulic actuators. The use of SMA actuators has the advantage of significant weight reduction. Two SMA actuators are used: one to move the flap up and the other to move the flap down. A sliding mode based nonlinear robust controller is designed and implemented on a real-time data acquisition and control platform to control the position of the flap. Feedback control experiments of both position regulation and tracking control are conducted. To demonstrate the controller's robustness to uncertainties and disturbances, experiments are conducted with additional mass on the flap, changing thermodynamic conditions and time varying aerodynamic loads. Experiments in all cases show that the actual position of the flap closely follows the desired command during experiments. In conclusion, this paper shows the feasibility of using SMA wire actuators for aircraft flap control.