Table of contents

This paper describes the production of an adaptive composite by embedding thin pre-strained shape memory alloy actuators into a Kevlar-epoxy host material. In order to combine the activation and sensing capabilities, fibre Bragg grating sensors are also embedded into the specimens, and the strain measured in situ during activation. The effect of manufacturing conditions, and hence of the initial stress state in the composite before activation, on the magnitude of the measured strains is discussed. The results of stress and strain simulations are compared with experimental data, and guidelines are provided for the optimization of the composite. Finally, a pilot experiment is carried out to provide an example of how a strain-stabilizing feedback mechanism can be implemented in the smart structure.

Electroactive polymers undergo physical deformation in response to external voltage stimuli. These electrically activated polymers possess extraordinary features making them capable of use as lightweight sensors and actuators in manifold applications. The characteristics of applied voltage and environmental conditions, especially the moisture content surrounding the polymer, have a combined influence on the dynamical behavior of these polymers. In order to characterize these polymers under varying environmental conditions, this paper discusses the experimental procedure and modeling techniques used to derive a representative model. Validation of the model derived is provided by comparison tests of the simulated model results and those for experimental specimens. Ionic polymer–metal composites are used for this humidity and electrodynamical study. Insight into the numerous applications of electroactive polymers as actuators is given. The extended model allows for controller design for typical tracking problems. The control architecture presented includes a model reference adaptive scheme along with pole-placement control strategies for achieving the goal of tracking. A genetic algorithm approach is employed to carry out the optimization for the control action. The resulting tracking control of ionic polymer–metal composites, acting as actuators, is simulated. Simulations show that tracking results can be achieved with a correlation of 99% and a root mean square error of less than 30%.

The present paper demonstrates the effect of axial forces on smart columns that have adhesively bonded piezoelectric skins on substrates. Exact solutions for the piezolaminated columns have been presented. The solutions have been validated through experimental studies. The objectives of the present work are (1) to show the effect of axial force on sensing and actuation mechanisms of piezoelectric materials and (2) to demonstrate the active control of column type structures using these materials. In the experimental work, polyvinylidene fluoride (PVDF) films have been used as smart skins on a plastic substrate. PVDF films are shaped corresponding to the first mode shape of the cantilever column to ensure proportional sensing and actuation.

This paper is a study on the development of a tactile sensor system for reading Braille. The tactile sensor uses a PVDF (polyvinylidene fluoride) film as the sensory material. The sensor is attached to a slider driven by a DC servomotor and it is slid over a string of Braille with a constant speed to obtain the sensor output. A recognition system of Braille is proposed. In a recognition experiment, the sensor system is verified as to whether it has enough performance to recognize a string of letters appropriately. The obtained result shows that the proposed sensor and sensor system are effective to recognize Braille.

The necessity to reduce the size of actuators and at the same time increase the force and the air gap has placed severe constraints on the suitability of current microactuator technology for various applications. This has led to the development of new actuator technologies based on novel materials or modifying existing systems. As an effort in this direction, we are reporting on the design and fabrication of a hybrid actuator employing a combination of electromagnetic and piezoelectric actuation methods for the first time. This actuator was designed and optimized by using the piezoelectric and electromagnetic solvers of commercially available FEM software packages (CoventorWare and ANSYS). The device consists of a shaped piezoelectric composite cantilever on the top and a copper coil wound around a permalloy core assembled on a silicon substrate with a permanent magnet at the bottom. The composite cantilever consists of polarized piezoelectric polymer polyvinylidene fluoride (PVDF) with an electroplated permalloy layer on one side. Microstructures in the required shape are introduced using novel methodologies including laser micromachining and microembossing. The hybrid actuator has been fabricated and tested using standard testing procedures. The experimental data are compared with the simulation results from both the finite element methods and the analytical model. There is excellent agreement between the results obtained in simulation and by experiment. A maximum total deflection of 400 µm with a typical contact force of 200 µN has been achieved.

This paper describes the design and evaluation of biomimetic wing sections, where the trailing edges of the wing sections are actuated by the piezoceramic actuator LIPCA (lightweight piezo-composite actuator). Thermal analogy based on linear elasticity was used for the design and analysis of the wing sections. In the actuation test of the wing sections, the effective deflection angle of the trailing edge was approximately five degrees at 300 V input. The predicted and measured actuation displacements agreed very well up to an input of 150 V. However, the real actuation displacement became larger than the estimated value for higher input voltages due to the material non-linearity of the lead zirconate titanate (PZT) wafer in the LIPCA. The biomimetic wing sections can be used for control surfaces of small scale unmanned aerial vehicles (UAVs).

In this paper, design of a novel smart actuator with controllable characteristics based on a magnetorheological elastomer (MRE) is introduced. The actuator is composed of a piezoelectric layer bonded cantilever, whose free end is attached by an MRE layer. By adjusting the magnetic field applied to the MRE, the dynamic characteristics of the beam can be controlled due to the MRE's characteristics of field-dependent shear modulus. Thus, the characteristics of the actuator can be improved by adjusting the load curve and the resonant frequency of the actuator. Simulations on such field-controllable behavior of the actuator through introducing mass as the mechanical load are conducted. The variable load curves indicate that the driving force increases with the applied magnetic field under the same output velocity. The relative change of the resonant frequency of the actuator is found to be adjusted up to 30% by the applied magnetic field. This field-controlled resonant frequency opens the way to keep the actuator at high energy conversion rate through adjusting the applied magnetic field since the resonant state relates to the maximum energy conversion rate. This approach may lead to a novel design of a smart actuator which can work adaptively with the working condition.

This study investigated the possibility of using hydrogels as artificial muscle. Hydrogels fully swollen in a 0.9 wt% aqueous NaCl solution were inserted between a pair of platinum electrodes and an electric field was applied. The PAAc/PV SA copolymer hydrogels exhibited electrically induced contraction with concomitant deformation. The contractile behavior increased with increasing time and intensity of the electrical stimulus. These deformations were sensitive to the electric field and hydrogels, when placed in an electrochemical cell, may allow the electrical activation of artificial muscle. These results highlight the potential of developing an electrically activated hydrogel for use as artificial muscle and muscle actuators.

For the piezoelectric layer/substrate structure with slowly varying inhomogeneous initial stress in the layer, the influence of the initial stress on the properties of Love wave propagation is studied. The Wentzel–Kramers–Brillouin (WKB) approximate approach is adopted for analytical derivations. Numerical results obtained for the BaTiO₃ layer/borosilicate glass substrate combination system indicate that, under certain conditions, initial stress in the layer can markedly affect the propagation of the Love wave. The analysis is meaningful for the theoretical analysis and engineering applications of Love waves.

The general orientation dependence of the intrinsic converse longitudinal piezoelectric constant d_nn^f in an epitaxial rhombohedral film is calculated by taking into account the effect of substrate clamping. Theoretical predictions are made for d_nn^f of epitaxial 0.67Pb(Mg_1/3Nb_2/3)O₃–0.33PbTiO₃ rhombohedral films, which are compared with experimental results on pseudo-cubic (001), (110) and (111) orientations.

By using magnetorheological (MR) fluid in place of lubricating oil in a traditional squeeze film damper (SFD), one can build a variable-damping SFD, thereby controlling the vibration of a rotor by controlling the magnetic field. Assuming a Bingham model, the Reynolds equation for an MR fluid squeeze film is developed and solved to provide expressions for the velocity, the pressure distribution and the damping force. Electromagnetic theory is used to calculate the magnetic pull force between the magnetic poles in the damper. The mechanical properties of the squeeze film and the unbalance response characteristics of an MR fluid SFD–rigid rotor system are analyzed theoretically. An MR fluid SFD is designed and manufactured, and the unbalance response properties and control method of a flexible rotor supported on the damper are studied experimentally. The study shows that the magnetic pull force can decrease both the first critical speed and the critical amplitude; the film damping force can decrease the amplitude at the undamped critical speeds, but increase the amplitude in a speed range between two undamped critical speeds. The damper may have the best control effect to minimize the vibration within the range of all working speed by using the on–off control method.

Positive position feedback (PPF) control is widely used in active vibration control of flexible structures. To ensure quick vibration suppression, a large PPF scalar gain is often applied. However, PPF control with a large scalar gain causes initial overshoot, which is undesirable in many situations. In this paper, a fuzzy gain tuner is proposed to tune the gain in the positive position feedback control to reduce the initial overshoot while still maintaining quick vibration suppression. The fuzzy system is trained by a batch least squares algorithm based on desired input–output data so that the trained fuzzy system can behave like the training data. A 3.35 m long composite I-beam with piezoceramic patch sensors and actuators is used to demonstrate the fuzzy PPF control. For comparison purposes, three types of control methods are used in the experiment: a standard PPF control, a standard PPF control with traditional fuzzy gain tuning, and a PPF control with batch least squares fuzzy gain tuning. Experimental results clearly demonstrate that PPF control with batch least squares fuzzy gain tuning behaves much better than the other two control methods in terms of successfully reducing the initial overshoot and quickly suppressing vibration.

The success of the guided-wave damage inspection technology depends not only on the generation and measurement of desired waveforms but also on the signal processing of the measured waves, but less attention has been paid to the latter. This research aims to develop an efficient signal processing technique especially suitable for the current guided-wave technology. To achieve this objective, the use of a two-stage matching pursuit approach based on the Gabor dictionary is proposed. Instead of truncated sine pulses commonly used in waveguide inspection, Gabor pulses, the modulated Gaussian pulses, are chosen as the elastic energy carrier to facilitate the matching pursuit algorithm. To extract meaningful waves out of noisy signals, a two-stage matching pursuit strategy is developed, which consists of the following: rough approximations with a set of predetermined parameters characterizing the Gabor pulse, and fine adjustments of the parameters by optimization. The parameters estimated from measured longitudinal elastic waves can be then directly used to assess not only the location but also the size of a crack in a rod. For the estimation of the crack size, in particular, Love's theory is incorporated in the matching pursuit analysis. Several experiments were conducted to verify the validity of the proposed approach in damage assessment.

In-service strain monitoring of tyres of automobiles is quite effective for improving the reliability of tyres and anti-lock braking systems (ABS). Conventional strain gauges have high stiffness and require lead wires. Therefore, they are cumbersome for tyre strain measurements. In a previous study, the authors proposed a new wireless strain monitoring method that adopts the tyre itself as a sensor, with an oscillating circuit. This method is very simple and useful, but it requires a battery to activate the oscillating circuit. In the present study, the previous method for wireless tyre monitoring is improved to produce a passive wireless sensor. A specimen made from a commercially available tyre is connected to a tuning circuit comprising an inductance and a capacitance as a condenser. The capacitance change of the tyre alters the tuning frequency. This change of the tuned radio wave facilitates wireless measurement of the applied strain of the specimen without any power supply. This passive wireless method is applied to a specimen and the static applied strain is measured. Experiments demonstrate that the method is effective for passive wireless strain monitoring of tyres.

In this paper we demonstrate the operation of a dynamic serial-to-parallel shift register, with only four transistors per stage. A bootstrap capacitor is used to overcome the problem of transistor threshold voltage drop. We will refer to this new logic family as non-ratioed bootstrap logic (NRBL). Simulation results are presented showing the operation of the shift register along with Monte Carlo analysis to demonstrate the robustness of the circuit. A key application area for this novel shift register is in the addressing and read out of high-density smart sensor arrays.

Piezoelectric actuators have been traditionally driven by voltage amplifiers. When driven at large voltages these actuators exhibit a significant amount of distortion, known as hysteresis, which may reduce the stability robustness of the system in feedback control applications. Electric charge is known to reduce the effects of this nonlinearity. To date little research has been done on the coupling between piezoelectric actuators and highly resonant structures when charge is used to drive the actuator. This arrangement was used in a control feedback scheme to reject disturbance vibrations acting on a cantilevered beam. During the analysis it is shown that the dynamics for the coupled 'piezoelectric–beam' system differs depending on whether voltage or charge is used to drive the piezoelectric actuator. Experimental results demonstrating the effectiveness of using electrical charge are included.

The performance for the transmitted noise reduction of smart panels is experimentally tested. A smart panel is a plate on which piezoelectric patches are bonded with electrical shunt circuits so as to absorb the acoustic energy at the circuit. Four piezoelectric patches are bonded on the host panel along with resonant shunt circuits. The resonant shunt circuit is composed of a resistor and an inductor in series, and the optimal resistance and inductance are determined by maximizing the absorbed energy through the circuit. To be able to perform the transmitted noise reduction at low resonance frequencies, a multiple-shunt damping is investigated by using a tuning method based on the measured electrical impedance model. Three types of smart panels are tested: a bare smart panel, a single smart panel, and a double smart panel. It is found that the use of sound absorbing material and air gap can effectively absorb the sound transmitted at the mid-frequency region while the use of piezoelectric shunt damping can reduce the noise at low resonance frequencies of the panel structure. The transmitted noise of smart panels is tested in an acoustic tunnel. When the multiple-shunt damping is applied to panels, a remarkable transmitted noise reduction at the low frequency region is achieved. The double panel exhibits better noise reduction than the other panels do.

The vibration and the sound radiation of cylindrical shells are analyzed and controlled. Shunted piezoelectric rings are placed periodically along the shell length to act as sources of impedance mismatch. The resulting periodic structure features a behavior which is characterized by frequency bands, 'stop bands', where the vibrations are attenuated and wave propagation is impeded. The location and the width of the stop bands are controlled by the impedance mismatch introduced along the structure. In the considered configuration, the stop bands can be tuned by proper selection of the shunting circuit.

A finite element model is developed to predict the structural response and the acoustic radiation of the considered class of shells. The model accounts for the presence of the rings and for the effect of the shunting parameters on the behavior of the structure. The developed model is used to estimate the frequency response function of the shell and to formulate the transfer matrix for the considered periodic structure. The transfer matrix determines the nature of wave propagation and in particular can be used to estimate the stop bands. The presented results show the effectiveness of the proposed concept when the rings are shunted through a resistive–inductive circuit. The considered shunting strategy is able to generate an additional stop band at the tuning frequency. The location of the stop band is unaffected by the presence of the fluid loading, which demonstrates the robustness of the considered vibration control treatment with respect to significant structural modifications.

A semi-analytic method is proposed for analyzing layered, tubular piezoelectric cylinders under axisymmetric mechanical and electric loads. Discretization occurs in the radial direction, and axial and circumferential behaviors are obtained analytically. Mechanical loads include axial forces, torque, longitudinal and circumferential surface shears, and arbitrary pressure distributions. Electric loads include voltage and charge distributions along the axis of the cylinder that may be applied on any layer's surface. In the present approach, electro-mechanical loads are represented by power series in the axial coordinate. The veracity of this semi-analytic method and its implementation are demonstrated by comparing the solutions for various problems with those obtained via fully discrete finite element analyses. The analysis of a two-layered, tubular bimodal actuator that can simultaneously provide any desired pattern of axial displacement and twist at its tip-end is performed to demonstrate the utility of the present technique.

In this paper, the electromechanical displacements of curved actuators such as THUNDER are calculated by the finite-element method to design the optimal configuration of curved actuators. To predict the internal stress in the device due to the mismatch in coefficients of thermal expansion, the adhesive as well as metal and PZT ceramic is also numerically modeled by using hexahedral solid elements. Also, the nonlinear finite-element formulation is implemented to include the variation of material constants during the curing process and acquire more accurate actuating displacements. Because the modeling of these thin layers causes the numbers of degree of freedom to increase, large-scale structural analyses are performed in a cluster system in this study. The curved shape and internal stress in the actuator are obtained by the cured curvature analysis, and the displacement subject to the piezoelectric force by an applied voltage is also calculated to investigate the performance of curved actuators. The thickness of metals and adhesive, and the number of metal layers, are chosen as design variables.

Active vibration control is an important problem in structures. One of the ways to tackle this problem is to make the structure smart, adaptive and self-controlling. The main objective of active vibration control is to reduce the vibration of a system by automatic modification of the system's structural response. This work features the modeling and design of a robust decentralized controller for a smart flexible system using a periodic output feedback control technique when there is a failure of a system component to function (say, an actuator). The entire structure is modeled in state space form using the finite element method and Euler–Bernoulli theory principles by dividing the master structure into eight finite elements and placing the piezoelectric sensor/actuators as collocated pairs at finite element positions 2, 4, 6 and 8, thus giving rise to a multi-input multi-output plant. Robust decentralized periodic output feedback controllers are designed for the various models of the plant, retaining the first two vibratory modes and considering one actuator failure at a time. The effect of failure of one of the piezopatches on the system is observed. In this control law, the control input to each actuator of the multimodel flexible system is a function of the output of that corresponding sensor only and the gain matrix has all off-diagonal terms zero. The designed robust decentralized periodic output feedback controller provides satisfactory stabilization of the multimodel smart structure system.

This paper presents the theoretical foundation for an experimental method to investigate the host-to-fibre interaction based on the remote measurement, via the optical fibre path, of the displacement δ of the embedded fibre end relative to the surrounding host material under axial tension. It is shown that the measurement of δ as a function of the axial strain in the host ε₁ provides key representative information on the strain transfer mechanics and the integrity of the fibre/coating/host interfaces. Parameters are defined that are based on this measurement and are directly related to familiar descriptors of strain transfer mechanics, such as failure length and interfacial shear stress.

This paper describes the experimental approach and the experimental results of a new technique for the characterization of host-to-sensor interaction based on the measurement of the embedded fibre end face displacement. The method consists of monitoring the reflected signal from the Fabry–Perot cavity formed at the end of an embedded fibre while the test sample is under increasing axial load. The curve of displacement versus applied strain in the host is analysed to describe the quality of the strain transfer and the condition of the interfacial region. Results on a test configuration consisting of an optical fibre surrounded by epoxy in an aluminium matrix are presented. In this configuration, the epoxy acts as the fibre coating and the aluminium is the host material. The results show that for this configuration the mode of failure of the interfacial region is by plastic deformation of the epoxy material. The results also make evident the visco-elastic and visco-plastic response of the epoxy.

For the simultaneous measurement of strain and a damage signal, a fiber Bragg grating sensor system with a dual demodulator is proposed. The dual demodulator is composed of a demodulator with a tunable Fabry–Perot filter measuring the low-frequency signal with large magnitude such as strain and another with a passive Mach–Zehnder interferometer measuring the high-frequency signal with small amplitude such as a damage or impact signal. Using the proposed fiber Bragg grating sensor system, both the strain and the damage signal of a cross-ply laminated composite beam under tensile loading were simultaneously measured. The strain and the damage signal measured by the single fiber Bragg grating sensor showed that sudden strain shifts were accompanied with vibration at a maximum frequency of several hundred kilohertz at the instant of transverse crack propagation in the 90° layer of the composite beam.

Local scour is one of the major factors for bridge failure. Scour failures tend to occur suddenly and without prior warning or sign of distress to the structure. Two types of real-time monitoring systems for bridge scour, using fiber Bragg grating (FBG) sensors, have been developed and tested in the laboratory. These FBG scour-monitoring systems can measure both the processes of scouring/deposition and the variations of water level. Several experimental runs have been conducted in the flume to demonstrate the applicability of the FBG systems. The experimental results indicate that the real-time monitoring system has the potential for further applications in the field.

This paper presents a new approach for the non-destructive evaluation of concrete, covering both strength prediction and damage assessment, using the electro-mechanical impedance technique. A new empirical method is proposed to determine in situ concrete strength non-destructively using admittance signatures of surface-bonded piezo-impedance transducers. This is followed by the 'identification' of appropriate impedance parameters for concrete. The identified parameters are found to be sensitive to structural damages as well as to concrete strength gain during curing. Comprehensive tests were conducted on concrete specimens up to failure to empirically calibrate the 'identified' system parameters with damage severity. An empirical fuzzy probabilistic damage model is proposed to quantitatively predict damage severity in concrete based on variation in the identified equivalent stiffness.

The non-destructive detection of structural defects in multi-wire strands used as post-tensioned tendons and cable stays is a challenging, yet critical task. A promising method under investigation is based on the use of ultrasonic stress waves that propagate within the strand and interact with structural discontinuities. The waveguide-like geometry of the strands lends itself to the monitoring of long lengths at a time (long range).

The topic of this paper is the enhancement of ultrasonic monitoring of strands by a joint time–frequency analysis based on the discrete wavelet transform (DWT). The test set-up uses magnetostrictive sensors for the excitation and the detection of ultrasonic guided waves in the strands. The main advantage of the DWT is an unmatched de-noising performance. Effective de-noising becomes necessary for the detection of small defects located far away from the inspection probes as desirable in the field. When compared to the traditional signal averaging, the DWT can be used in real time owing to its computational efficiency.

The theory of the DWT filter bank decomposition is first revised. The effectiveness of the wavelet processing is then demonstrated for the detection of small notches of varying depths located in the free portion of the strands as well as in the critical anchored areas. The study also shows the importance of selecting the proper mother wavelet function for best performance. The DWT proves effective in eliminating the need for signal averaging and in reducing the power supply required by the monitoring system. Both outcomes make the guided wave inspection method for strands more suitable for field use.

An optical phase tracking technique for an extrinsic Fabry–Perot interferometer (EFPI) is proposed in order to overcome interferometric non-linearity. The basic idea is utilizing strain rate information, which cannot be easily obtained from the EFPI sensor itself. The proposed phase tracking system consists of a patch-type EFPI sensor and a simple on-line phase tracking logic. The patch-type EFPI sensor comprises an EFPI and a piezoelectric patch. An EFPI sensor itself has non-linear behavior due to the interferometric characteristics, and a piezoelectric material has hysteresis. However, the composed patch-type EFPI sensor system overcomes the problems that can arise when they are used individually. The proposed system can extract vibration information from severely distorted EFPI sensor signals. The dynamic characteristics of the proposed phase tracking system were investigated, and then the patch-type EFPI sensor system was applied to the active suppression of flutter, dynamic aeroelastic instability, of a swept-back composite plate structure. The real time neural predictive control algorithm effectively reduces the amplitude of the flutter mode, and 6.5% flutter speed enhancement for the aeroelastic system was obtained by integrating smart materials into advanced structures.

Magnetorheological (MR) dampers are one of the most promising control devices for civil engineering applications to earthquake hazard mitigation, because they have many advantages such as small power requirement, reliability, and low price to manufacture. To reduce the responses of the controlled structure by using MR dampers, a control system including a power supply, controller, and sensors is needed. However, when a lot of MR dampers are applied to large-scale civil structures, such as cable-stayed bridges and high-rise buildings, the control system becomes complex. Thus, it is not easy to install and to maintain the MR damper-based control system.

In this paper, to resolve the above difficulties, a smart passive system is proposed, which is based on an MR damper system. The smart passive system consists of an MR damper and an electromagnetic induction (EMI) system that uses a permanent magnet and a coil. According to the Faraday law of induction, the EMI system that is attached to the MR damper produces electric energy. The produced energy is applied to the MR damper to vary the damping characteristics of the damper. Thus, the smart passive system does not require any power at all. Furthermore, the output of electric energy is proportional to input loads such as earthquakes, which means the smart passive system has adaptability by itself without any controller or corresponding sensors. Therefore, it is easy to build up and maintain the proposed smart passive system.

To verify the effectiveness of the proposed smart passive system, the performance is compared with that of the normal MR damper-based control system. The numerical results show that the smart passive system has comparable performance to the normal MR damper-based control system.

The modeling of the nonlinear behavior of multiphase materials with ferroelectric phases is accomplished via an incremental micromechanical analysis that is based on the homogenization technique for composites with periodic microstructure. The representation of the monolithic ferroelectric material is based on recently developed nonlinear constitutive equations. The resulting nonlinear global constitutive relations that govern the hysteresis behavior of ferroelectric composites are implemented to study the response of a polymeric matrix with embedded piezoceramic fibers. The responses of this composite to a complete cycle of electric field which is acting in the fiber direction, in conjunction with constant normal tensile and compressive stresses that are applied in the axial and transverse directions, as well as applied transverse shear and axial shear stresses, are shown.

Various strategies are considered for the active control of a flexible beam, mounted on springs at either end. As the spring stiffness is decreased from an infinite value to zero, the boundary conditions of the beam change from being simply supported to being free–free, and a rich variety of behaviour is observed. Feedforward control of either the beam's kinetic energy or radiated sound power using a moment pair actuator is considered first. It is found that for small spring stiffness minimization of radiated sound power leads to significant increases in overall beam vibration.

The stability and performance of feedback controllers is then considered. It is found that using a moment pair actuator and a velocity sensor the feedback controller is only conditionally stable, particularly when the actuator and the sensor are close to the ends of the beam and the supporting stiffness is small. The reductions in sound and vibration are small under these conditions.

In order to fabricate ammonia sensors, thin films of zirconia (ZrO₂) nanoclusters and poly(sodium-4-styrenesulfonate) salt have been deposited on the cleaved ends of standard communications optical fibers using the electrostatic self-assembly method. These sensors can operate at room conditions, with no need of heaters, and have shown a high selectivity to ammonia with negligible cross-sensitivity to humidity and temperature. In addition, these sensors were submitted to the presence of volatile organic compounds such as acetone, ethanol and dichloromethane, showing insignificant changes on the optical response.

A Macro Fiber Composite (MFC) is a piezoelectric fiber composite which has an interdigitated electrode, rectangular cross-section and unidirectional polycrystalline piezoceramic (PZT) fibers embedded in the polymer matrix. A MFC actuator has much higher actuation performance and flexibility than a monolithic piezoceramic actuator. Moreover, the single crystal piezoelectric material exhibits much higher induced strain levels, energy density and coupling than those of polycrystalline piezoceramic materials. Thus, the performance of an MFC can be improved by using single crystal piezoelectric fiber instead of polycrystalline piezoceramic fiber. This study investigates the analytical modeling, material properties and actuation performance of an MFC using single crystal piezoelectric material (single crystal MFC). For single crystal MFC, the mechanical properties are calculated by the classical lamination theory, and the uniform fields model (UFM) is adopted to predict piezoelectric strain constants. In addition, the actuation performance of the single crystal MFC with the active twist rotor blade is studied. The material properties and actuation performance of single crystal MFC are compared with those of standard MFC.

This paper presents an analysis of the coupling effect on the behavior of piezoelectric wafers used for actuators and sensors. A fully coupled formulation for an eighteen-node assumed strain piezoelectric solid element is used to test the effect of full coupling stiffness on the electric potential distribution through the thickness of the actuator/sensor. Since the assumed strain solid element can alleviate locking, it can be used to analyze the behavior of very thin actuators without locking. In the formulation, the electric potential is regarded as a nodal degree of freedom in addition to three translations at each grid point. The electric potential is then prescribed for nodes at the top and bottom surfaces in the finite element model of a PZT wafer and is left unknown for the other nodes throughout the thickness. Consequently, the induced electric potential and actuation displacement can be computed for an input voltage. The effect of coupling stiffness on the through-the-thickness distribution of the electric potential is examined, considering parameters such as thickness and in-plane dimension. This research shows that full coupling stiffness only affects piezoelectric structures of specific thickness and shape. These new findings can be useful for precision sensor and actuator design.

The quality of life of patients who wear an orbital prosthesis would be vastly improved if their prostheses were also able to execute vertical and horizontal motion. This requires appropriate actuation and control systems to create an intelligent prosthesis. A method of actuation that meets the demanding design criteria is currently not available. The present work considers an activation system that follows a design philosophy of biomimicry, simplicity and space optimization. While several methods of actuation were considered, shape memory alloys were chosen for their high power density, high actuation forces and high displacements. The behaviour of specific shape memory alloys as an actuator was investigated to determine the force obtained, the transformation temperatures and details of the material processing. In addition, a large-scale prototype was constructed to validate the response of the proposed system.

We analyze the performance of a piezoelectric bimorph in the flexural mode for scavenging ambient vibration energy and evaluate the dependence of the performance upon the physical and geometrical parameters of the model bimorph. The analytical solution for the flexural motion of the piezoelectric bimorph shows that the output power density increases initially, reaches a maximum, and then decreases monotonically with increasing load impedance, which is normalized by a parameter that is a simple combination of the physical and geometrical parameters of the scavenging structure, the bimorph, and the frequency of the ambient vibration, underscoring the importance for the load circuit to have the impedance desirable by the scavenging structure. The numerical results illustrate the considerably enhanced performances achieved by adjusting the physical and geometrical parameters of the scavenging structure.

In this paper, a silicon on insulator based electrostatic micro-scanner with extremely low pull-in voltage and fast switching time is proposed. Two symmetric mirror plates are suspended by a cross suspension lever anchored on the substrate. A buried silicon dioxide (BOX) layer underneath the anchors separates the two actuation electrodes. The symmetric design can not only provide better balance of the mirror plates than cantilever design but also increase the dynamic range by scanning in two directions. The structural parameters of the micro-scanner are optimized for a combination of dynamic performance and actuation voltage according to finite element analysis (FEA). Squeeze film damping effects are addressed by a comparison of the theoretical analysis using FEA with experimental results. The testing results show that the pull-in voltage of the micro-scanner is as low as 2.7 V, making it compatible with off-the-shelf control logic circuits. The demonstrated tilt angle is approximately 0.5° and may be increased by adjusting the thickness of the pre-specified BOX layer.

The geometrically nonlinear behavior of piezo-laminated plates actuated with isotropic or anisotropic piezoelectric layers is analytically investigated. The analytical model is derived using the variational principle of virtual work along with the lamination and plate theories, the von Karman large displacement and moderate rotation kinematic relations, and the anisotropic piezoelectric constitutive laws. A solution strategy that combines the approach of the method of lines, the advantages of the finite element concept, and the variational formulation is developed. This approach yields a set of nonlinear ordinary differential equations with nonlinear boundary conditions, which are solved using the multiple-shooting method. Convergence and verification of the model are examined through comparison with linear and nonlinear results of other approximation methods. The nonlinear response of two active plate structures is investigated numerically. The first plate is actuated in bending using monolithic piezoceramic layers and the second one is actuated in twist using macro-fiber composites. The results quantitatively reveal the complicated in-plane stress state associated with the piezoelectric actuation and the geometrically nonlinear coupling of the in-plane and out-of-plane responses of the plate. The influence of the nonlinear effects ranges from significant stiffening in certain combinations of electrical loads and boundary conditions to amplifications of the induced deflections in others. The paper closes with a summary and conclusions.

For the first time a smart pixel that can function as a building block of an optical transceiver with circular dimensions is fabricated using an InP/InGaAs double-heterojunction bipolar transistor (DHBT) and an AlGaInAs/InP vertical cavity surface emitting laser (VCSEL). The DHBT showed a breakdown voltage of 12 V and a cut-off frequency of 42 GHz at I_c = 30 mA. Also a high performance 1550 nm VCSEL exhibited a threshold current of 3.5 mA with a maximum optical output of 4.8 mW at I_c = 20 mA and forward voltage of 1.8 V. The detector, comprised of the base-to-collector junction of the DHBT as a p–i–n PD, produced a photocurrent of 200 µA for a given input power of 0.3 mW.

The effect of barium doping on the superconducting and mechanical properties in the Bi₂Sr₂Ca₂Ba_xCu₅O_y (BSCCO) system has been investigated by thermoelectric power (TEP), Vickers microhardness (VHN), x-ray diffraction (XRD), and scanning electron microscope (SEM) analysis. Barium was incorporated with x ranging from 0.0 to 0.82. The temperature variation of the thermopower (Seebeck coefficient) S shows that the critical transition temperature T_c⁰ is enhanced (to 93 K) up to x = 0.45 and then disappears for x = 0.82. The results have also suggested an increased interaction of electrons and holes with phonons at low temperatures. The enhancement of T_c⁰ is ascribed to the improvement in electric connection between superconducting grains. XRD data show that the high-T_c (2:2:2:3) phase increases and the low-T_c (2:2:1:2) phase decreases as the barium concentration changes from x = 0.0 to 0.45. SEM analysis of a sample (x = 0.45) shows that plate-like grains (2223 phase) are formed. Also, an appropriate level of Ba dopant improves the microhardness and fracture toughness remarkably. The optimum dopant level of Ba from the point of view of mechanical properties is x = 0.45. The improvement of mechanical characteristics is due to the fact that Ba²⁺ can fill the intergrain spaces, and thereby reinforce the coupling between granules. From the above results, it is inferred that the added Ba has the positive effect of decomposing the structure of the low-T_c phase, leading to the production of BaBiO₃ and BaCuO₂ and enhancing the high-T_c phase creation.

The development of a powerful new magnetorheological fluid (MRF), together with recent progress in the understanding of the behavior of such fluids, has convinced researchers and engineers that MRF dampers are among the most promising devices for semi-active automotive suspension vibration control, because of their large force capacity and their inherent ability to provide a simple, fast and robust interface between electronic controls and mechanical components.

In this paper, theoretical and experimental studies are performed for the design, development and testing of a completely new MRF damper model that can be used for the semi-active control of automotive suspensions. The MR damper technology presented in this paper is based on a completely new approach where, in contrast to in the conventional solutions where the coil axis is usually superposed on the damper axis and where the inner cylindrical housing is part of the magnetic circuit, the coils are wound in a direction perpendicular to the damper axis. The paper investigates approaches to optimizing the dynamic response and provides experimental verification.

Both experimental and theoretical results have shown that, if this particular model is filled with an 'MRF 336AG' MR fluid, it can provide large controllable damping forces that require only a small amount of energy. For a magnetizing system with four coils, the damping coefficient could be increased by up to three times for an excitation current of only 2 A. Such current could be reduced to less than 1 A if the magnetizing system used eight small cores. In this case, the magnetic field will be more powerful and more regularly distributed. In the presence of harmonic excitation, such a design will allow the optimum compromise between comfort and stability to be reached over different intervals of the excitation frequencies.

Nonlinear dynamics of active piezolaminated plates are investigated considering snap-through thermopiezoelastic behaviors. For highly deformed structures with small strain, the incremental total Lagrangian formulation is presented based on Hamilton's variational principles. A multi-field layer-wise finite element is proposed to assure high accuracy and nonlinearity of displacement, electric and thermal fields. For dynamic consideration of thermopiezoelastic snap-through phenomena, the implicit Newmark-beta scheme with the Newton–Raphson iteration is implemented for the transient response of various piezolaminated models with symmetric or eccentric active layers. To validate the new finite element formulation and code, dynamic analyses of nonlinear elastic plates are compared with published data, resulting in good agreements and better solutions. The bifurcate buckling and sling-shot buckling of the symmetric and eccentric structural models are first investigated and the characteristics of piezoelectric active responses are studied to find snap-through piezoelectric potentials and the load-path tracking map. The thermoelastic stable and unstable postbuckling, thermopiezoelastic snap-through phenomena with several attractors are proved using the nonlinear time responses for initial conditions and damping loss factors. Present results show that the snap-through phenomena should be investigated with respect to nonlinear dynamics for shape control of piezolaminated buckled plates by using piezoelectric materials.

Bending behaviors of both a piezoelectric curved bi-morph actuator and a functional gradient piezoelectric curved actuator are studied and compared. The exact solutions of both mechanical and electrical fields of the actuators are obtained based fully on the theory of elasticity. It is found that non-zero normal stresses exist in the gradient piezoelectric curved actuator when the actuator is subjected to an external voltage, which is different from the results obtained in our previous works on the gradient piezoelectric flat actuator. It is also proved that the internal stresses are drastically reduced although the deflection of the gradient curved actuator is quite small. The present analytical solutions are compared with the FEM results and a good agreement is found.

In this paper, a nonlinear control scheme is presented to achieve small tracking errors in a flexible manipulator with two degrees of freedom. A secondary actuation mechanism using piezoelectric materials is added to the system for suppressing residual vibrations at the end point of the flexible link. A small piece of piezo-ceramic is also used, as a sensor, in order to obtain the modal states of the system. The effects of changing physical parameters such as relative thickness of the piezo-ceramic with respect to the flexible link, the optimum location and the length of the actuator are studied based on the singular value decomposition of the controllability Grammian of the system. A partial feedback linearization technique based on output redefinition is utilized to obtain an appropriate control output for each joint and the piezoelectric actuator. A model for friction is obtained and included in the control law. Experimental results show that applying the suggested control scheme results in smooth and precise motion of the flexible manipulator without exciting unwanted vibration modes. Comparisons are made when a linear control scheme is used for the tracking problem.

This paper aims to evaluate the modal frequencies, damping ratios and mode shapes of an asymmetric building, modeled as general torsionally coupled buildings using a modified random decrement method together with the Ibrahim time domain technique based only on few floor acceleration response records from earthquakes. It is not necessary to measure earthquake excitation input. The general relationship between the reduced random decrement signature and the true free vibration response is derived analytically. Because only partial floor response measurements are used, a mode shape interpolation technique is developed to estimate the mode shape values for the locations without measurement, such that all floor responses can be obtained. The results were obtained from simulation data from a five-story building under the 1940 El Centro earthquake and actual records from a seven-story RC school building in north-eastern Taiwan, due to an earthquake near the building site. The results show that the proposed system identification technique is capable of identifying structural dominant modal parameters and responses accurately even with highly coupled modes and high levels of noise contamination.

The present contribution is concerned with the active suppression of plane flexural vibrations of a slender, cantilever linear elastic beam. The vibrations of the beam are considered to be due to a prescribed large rigid-body motion of the beam support, as well as imposed forces. The rigid-body motion under consideration defines a floating reference configuration with respect to which the vibrations are studied. We assume these vibrations to take place in the moderately large strain regime. The beam is considered to be additionally equipped with distributed piezoelectric actuators, which are perfectly bonded to the beam. It is the scope of the present paper to derive a spatial shape of the latter actuators, such that the above vibrations can be completely suppressed by the piezoelectric actuation. This problem is also known as vibration compensation or shape control by piezoelectric actuation. In the present paper, an analytic solution for shape control is presented within the Bernoulli–Euler–von Karman theory of a slender cantilever beam, taking into account the so-called stress-stiffening effect. The presented solution for shape control makes the initial boundary value problem under consideration homogeneous, such that the vanishing of vibrations indeed represents a solution. Possible instabilities, such as parametrically excited vibrations, can be studied in the usual manner, this not being the content of the present paper. For the dynamically stable example of a rotating beam, the influence of the stress stiffening effect in the presence of a distributed piezoelectric actuation is studied in some detail. It turns out that the stress stiffening effect must indeed be taken into account for an adequate modelling. The corresponding analytic solution for shape control is validated by means of non-linear 3D finite element computations, showing excellent evidence of the appropriateness of the presented analytic beam-type solution for vibration compensation.

An optimization protocol for a high authority shape morphing plate is described. The shape morphing design incorporates an active back-plane comprising a Kagome truss, capable of changing the shape of a solid face, connected to the back-plane by means of a tetrahedral truss core. Several members of the Kagome truss are replaced by actuators, enabling the structure to deform. The trusses to be replaced depend on the desired deformation, subject to the load capacity of the individual actuators. A two-level scheme is used comprising a heuristic algorithm with a simplex based optimization providing the cost function. It is shown that methods capable of avoiding entrapment in local minima, such as simulated annealing and the genetic algorithm, give good results.

Actuators based on cellulose paper with conducting polymer (CP-EAPap) as an electrode material were constructed. The bilayer and trilayer types of actuators were fabricated by depositing conducting polypyrrole on one side and two sides of cellophane paper respectively, which was previously gold coated. By varying the deposition time, the electrode thickness was manipulated. The performance of these two types of actuators was compared with respect to humidity changes and thickness variation. The electrode thickness plays a key role in the displacement behavior of these types of actuators. The best performance at higher humidity is also characteristic of CP-EAPap actuators. The possible mechanism of actuation is addressed in this paper.

Thin films of poly(methyl methacrylate) (PMMA) were deposited on suitably prepared substrates by spinning the spreading solution in chloroform at 3000 rpm for atomic force microscopy and surface plasmon resonance studies. Four different types of PMMA were used within a range of molecular weight between 540 and 760 kg mol⁻¹. The film surface was found to be uniform. Values of refractive index for PMMA film were found to exist in the range of 1.50 ± 0.04 to 1.53 ± 0.02. All films exhibited fast response to the exposure of benzene vapour but the sensitivity of detection depended upon the molecular weight.

We have performed electro-spinning of poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS)/ethanol solution to produce uniform nanofibres. The optimum nanofibre morphologies were observed for a 6 wt% concentration solution, a 15 kV electric field, a 10 µl min⁻¹ feeding rate, and a 15 cm distance between the capillary tip and grounded collector. The average diameter of the electro-spun fibres was of order 60 nm. We have been able to produce uniform nanofibres by controlling the various parameters of electro-spinning: change of concentration, electric field, and feeding rate. The effect of these parameters on the electro-spun nanofibres was investigated using field emission scanning electron microscopy (FESEM).

Over-oxidative degradation of polythiophenes, which breaks the conjugation and destroys the electronic conductivity of the polymer, is well documented as a liability in these materials. We use this 'weakness', via controlled electrochemical over-oxidation, in a novel subtractive patterning technique compatible with high-speed reel-to-reel printing technology. We demonstrate the use of electrochemical over-oxidation to pattern PEDOT:PSS films via an x–y plotter, silk-screen and high-resolution photolithographic techniques, resulting in patterning down to a resolution of 2 µm and a conduction contrast between unpatterned and patterned areas of up to 10⁸.

We describe a new method for isolating embedded fiber Bragg gratings from strain. The strain isolated grating may serve as a pure temperature sensor in environments where both strain and temperature variations occur. The grating need not be at the end of the fiber, thus enabling multiplexing of several strain-isolated gratings along a single fiber.

A theoretical model for the prediction of interfacial behaviour is successfully developed for composites with pre-strained shape memory alloy (SMA) fiber. A two-cylinder model with a thin SMA fibre surrounding by epoxy matrix is employed for a pull-out test. The material constants and thermomechanical properties of the constituents were determined from a series of tensile tests, stress-recovery tests and strain-constrained tests. All this information is then substituted into the newly developed model so as to predict the debonding behaviour, initial debond stress and critical bonded fibre length. The maximum debond stresses at different activation temperatures are predicted and compared with the experimental results obtained from the fiber pull-out test. The good agreement between experimental findings and theoretical results warrants the application of this new developed theoretical model on the design of SMA-reinforced composites and structures.

Giant magnetostrictive alloy (GMA) actuators are tending to replace piezoelectric actuators in many applications owing to their giant magnetostrain and fast response. In an active vibration control system using GMA actuators, the investigation of dynamic magnetostrain can supply the basis for the optimization of actuator designs and control algorithms. Experiments have been carried out under varied operating conditions. The results show that there is a better dynamic output only at suitable prestress and magnetic bias values. For a fixed frequency, the output is basically proportional to the input amplitude but the inclination is slightly different for each input frequency. The natural frequency of the actuator is around 5 Hz and the output displacement decreases with frequency increase after 10 Hz. The dynamic magnetostrain at the natural frequency can be larger than the quasi-static value by up to 40%.

In our work, separation by implantation of oxygen and nitrogen (SIMON) wafers were fabricated with different nitrogen implantation doses and post-annealing. Secondary ion mass spectrometer (SIMS) analysis showed that for the samples with low nitrogen dose some nitrogen ions were distributed in the buried oxide layers and some others were collected at the Si/SiO₂ interface after annealing, and for the samples with large nitrogen dose distinct delamination appeared between the layer containing the nitrogen element and that containing the oxygen element. The results of the spreading resistance probe (SRP) suggested that a buried insulator was formed for wafers with large nitrogen implantation dose. The results of cross section transmission electron microscopy (XTEM) confirmed the analysis above. The results show that the quality of SIMON materials is closely related to nitrogen implantation parameters.