scispace - formally typeset
Search or ask a question

Showing papers in "Smart Materials and Structures in 2007"


Journal ArticleDOI
TL;DR: The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans as mentioned in this paper, and the use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement.
Abstract: The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. Current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of a disposable nature to allow the device to function over extended periods of time. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. A number of sources of harvestable ambient energy exist, including waste heat, vibration, electromagnetic waves, wind, flowing water, and solar energy. While each of these sources of energy can be effectively used to power remote sensors, the structural and biological communities have placed an emphasis on scavenging vibrational energy with piezoelectric materials. This article will review recent literature in the field of power harvesting and present the current state of power harvesting in its drive to create completely self-powered devices.

2,438 citations


Journal ArticleDOI
TL;DR: In this article, an ultrasonic guided wave structural health monitoring (SHM) system was developed for aircraft wing inspection, where small, low-cost and light-weight piezoelectric (PZT) discs were bonded to various parts of the aircraft wing, in a form of relatively sparse arrays, for simulated cracks and corrosion monitoring.
Abstract: This work focuses on an ultrasonic guided wave structural health monitoring (SHM) system development for aircraft wing inspection. In part I of the study, a detailed description of a real aluminum wing specimen and some preliminary wave propagation tests on the wing panel are presented. Unfortunately, strong attenuation and scattering impede guided waves for large-area inspection. Nevertheless, small, low-cost and light-weight piezoelectric (PZT) discs were bonded to various parts of the aircraft wing, in a form of relatively sparse arrays, for simulated cracks and corrosion monitoring. The PZT discs take turns generating and receiving ultrasonic guided waves. Pair-wise through-transmission waveforms collected at normal conditions served as baselines, and subsequent signals collected at defected conditions such as rivet cracks or corrosion detected the presence of a defect and its location with a novel correlation analysis based technique called RAPID (reconstruction algorithm for probabilistic inspection of defects). The effectiveness of the algorithm was tested with several case studies in a laboratory environment. It showed good performance for defect detection, size estimation and localization in complex aircraft wing structures.

670 citations


Journal ArticleDOI
Gangbing Song1, Haichang Gu1, Yi-Lung Mo1, T T C Hsu1, Hemant B. Dhonde1 
TL;DR: In this article, the authors used piezoceramic transducers for damage detection of a 61 m long reinforced concrete bridge bent-cap in order to identify the existence and severity of cracks inside the concrete structure.
Abstract: Health monitoring of reinforced concrete bridges and other large-scale civil infrastructures has received considerable attention in recent years However, traditional inspection methods (x-ray, C-scan, etc) are expensive and sometimes ineffective for large-scale structures Piezoceramic transducers have emerged as new tools for the health monitoring of large-scale structures due to their advantages of active sensing, low cost, quick response, availability in different shapes, and simplicity for implementation In this research, piezoceramic transducers are used for damage detection of a 61 m long reinforced concrete bridge bent-cap Piezoceramic transducers are embedded in the concrete structure at pre-determined spatial locations prior to casting This research can be considered as a continuation of an earlier work, where four piezoceramic transducers were embedded in planar locations near one end of the bent-cap This research involves ten piezoceramic patches embedded at spatial locations in four different cross-sections To induce cracks in the bent-cap, the structure is subjected to loads from four hydraulic actuators with capacities of 80 and 100 ton In addition to the piezoceramic sensors, strain gages, LVDTs, and microscopes are used in the experiment to provide reference data During the experiment, one embedded piezoceramic patch is used as an actuator to generate high frequency waves, and the other piezoceramic patches are used as sensors to detect the propagating waves With the increasing number and severity of cracks, the magnitude of the sensor output decreases Wavelet packet analysis is used to analyze the recorded sensor signals A damage index is formed on the basis of the wavelet packet analysis The experimental results show that the proposed methods of using piezoceramic transducers along with the damage index based on wavelet packet analysis are effective in identifying the existence and severity of cracks inside the concrete structure The experimental results demonstrate that the proposed method has the ability to predict the failure of a concrete structure as verified by results from conventional microscopes (MSs) and LVDTs

413 citations


Journal ArticleDOI
TL;DR: In this paper, an analytical expression of harvested power is derived explicitly and validated numerically for the synchronized switch harvesting on inductor (SSHI) electronic interface for a piezoelectric energy harvesting system.
Abstract: 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.

332 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a novel energy harvesting backpack that can generate electrical energy from the differential forces between the wearer and the pack by replacing the traditional strap of the backpack with one made of the piezoelectric polymer polyvinylidene fluoride (PVDF).
Abstract: Over the past few decades the use of portable and wearable electronics has grown steadily These devices are becoming increasingly more powerful However, the gains that have been made in the device performance have resulted in the need for significantly higher power to operate the electronics This issue has been further complicated due to the stagnant growth of battery technology over the past decade In order to increase the life of these electronics, researchers have begun investigating methods of generating energy from ambient sources such that the life of the electronics can be prolonged Recent developments in the field have led to the design of a number of mechanisms that can be used to generate electrical energy, from a variety of sources including thermal, solar, strain, inertia, etc Many of these energy sources are available for use with humans, but their use must be carefully considered such that parasitic effects that could disrupt the user's gait or endurance are avoided These issues have arisen from previous attempts to integrate power harvesting mechanisms into a shoe such that the energy released during a heal strike could be harvested This study develops a novel energy harvesting backpack that can generate electrical energy from the differential forces between the wearer and the pack The goal of this system is to make the energy harvesting device transparent to the wearer such that his or her endurance and dexterity is not compromised This will be accomplished by replacing the traditional strap of the backpack with one made of the piezoelectric polymer polyvinylidene fluoride (PVDF) Piezoelectric materials have a structure such that an applied electrical potential results in a mechanical strain Conversely, an applied stress results in the generation of an electrical charge, which makes the material useful for power harvesting applications PVDF is highly flexible and has a high strength, allowing it to effectively act as the load bearing member In order to preserve the performance of the backpack and user, the design of the pack will be held as close to existing systems as possible This paper develops a theoretical model of the piezoelectric strap and uses experimental testing to identify its performance in this application

324 citations


Journal ArticleDOI
TL;DR: In this article, a carbon nanotube and polyelectrolyte composite multilayer thin film fabricated by a layer-by-layer (LbL) method is proposed to develop a multifunctional material for measuring strain and corrosion processes.
Abstract: Since the discovery of carbon nanotubes, researchers have been fascinated by their mechanical and electrical properties, as well as their versatility for a wide array of applications. In this study, a carbon nanotube–polyelectrolyte composite multilayer thin film fabricated by a layer-by-layer (LbL) method is proposed to develop a multifunctional material for measuring strain and corrosion processes. LbL fabrication of carbon nanotube composites yields mechanically strong thin films in which multiple sensing transduction mechanisms can be encoded. For example, judicious selection of carbon nanotube concentrations and polyelectrolyte matrices can yield thin films that exhibit changes in their electrical properties to strain and pH. In this study, experimental results suggest a consistent trend between carbon nanotube concentrations and strain sensor sensitivity. Furthermore, by simply altering the type of polyelectrolyte used, pH sensors of high sensitivity can be developed to potentially monitor environmental factors suggesting corrosion of metallic structural materials (e.g. steel, aluminum). (Some figures in this article are in colour only in the electronic version)

295 citations


Journal ArticleDOI
TL;DR: In this article, an overview of models for electrostatically actuated microelectromechanical systems (MEMSs) is presented, along with simplified reduced-order models along with assumptions that define their range of applicability.
Abstract: 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.

277 citations


Journal ArticleDOI
TL;DR: In this paper, an analytical approach based on Euler-Bernoulli beam theory and Timoshenko beam equations for the voltage and power generation of a PZT bender is presented.
Abstract: Piezoelectric materials (PZT) have shown the ability to convert mechanical forces into an electric field in response to the application of mechanical stresses or vice versa. This property of the materials has found extensive applications in a vast array of areas including sensors and actuators. The study presented in this paper targets the modeling of a PZT bender for voltage and power generation by transforming ambient vibrations into electrical energy. This device can potentially replace the battery that supplies the power in a microwatt range necessary for operating sensors and data transmission. One of the advantages is that it is maintenance-free over a long time span. The feasibility of this application has been repeatedly demonstrated in the literature, but a real demonstration of a working device is partially successful because of the various design parameters necessary for a construction of the PZT bender. According to a literature survey, the device can be modeled using various approaches. This paper focuses on the analytical approach based on Euler–Bernoulli beam theory and Timoshenko beam equations for the voltage and power generation, which is then compared with two previously described models in the literature: the electrical equivalent circuit and energy method. The three models are then implemented in a Matlab/Simulink/Simpower environment and simulated with an AC/DC power conversion circuit. The results of the simulation and the experiment have been compared and discussed.

270 citations


Journal ArticleDOI
TL;DR: In this article, a nonlinear dynamic model of motion actuators based on ionic polymer metal composites (IPMCs) working in air is presented, where significant quantities ruling the acting properties of IPMC-based actuators are taken into account.
Abstract: This paper introduces a comprehensive nonlinear dynamic model of motion actuators based on ionic polymer metal composites (IPMCs) working in air. Significant quantities ruling the acting properties of IPMC-based actuators are taken into account. The model is organized as follows. As a first step, the dependence of the IPMC absorbed current on the voltage applied across its thickness is taken into account; a nonlinear circuit model is proposed to describe this relationship. In a second step the transduction of the absorbed current into the IPMC mechanical reaction is modelled. The model resulting from the cascade of both the electrical and the electromechanical stages represents a novel contribution in the field of IPMCs, capable of describing the electromechanical behaviour of these materials and predicting relevant quantities in a large range of applied signals. The effect of actuator scaling is also investigated, giving interesting support to the activities involved in the design of actuating devices based on these novel materials. Evidence of the excellent agreement between the estimations obtained by using the proposed model and experimental signals is given.

256 citations


Journal ArticleDOI
TL;DR: 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, and its potentials for the inspection of a variety of structural components.
Abstract: 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

238 citations


Journal ArticleDOI
TL;DR: In this article, a new configuration of a contractile actuator made of a silicone elastomer is described, which consists of a monolithic structure made of an electroded sheet, which is folded up and compacted.
Abstract: Polymer-based linear actuators with contractile ability are currently demanded for several types of applications. Within the class of dielectric elastomer actuators, two basic configurations are available today for such a purpose: the multi-layer stack and the helical structure. The first consists of several layers of elementary planar actuators stacked in series mechanically and parallel electrically. The second configuration relies on a couple of helical compliant electrodes alternated with a couple of helical dielectrics. The fabrication of both these configurations presents some specific drawbacks today, arising from the peculiarity of each structure. Accordingly, the availability of simpler solutions may boost the short-term use of contractile actuators in practical applications. For this purpose, a new configuration is here described. It consists of a monolithic structure made of an electroded sheet, which is folded up and compacted. The resulting device is functionally equivalent to a multi-layer stack with interdigitated electrodes. However, with respect to a stack the new configuration is advantageously not discontinuous and can be manufactured in one single phase, avoiding layer-by-layer multi-step procedures. The development and preliminary testing of prototype samples of this new actuator made of a silicone elastomer are presented here.

Journal ArticleDOI
TL;DR: In this article, the microstructures and viscoelastic properties of anisotropic magnetorheological elastomers are investigated and it is shown that their mechanical properties are greatly dependent on the magnetic flux density applied during preparation.
Abstract: 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.

Journal ArticleDOI
TL;DR: The first arm wrestling match between a human arm and a robotic arm driven by electroactive polymers (EAP) was held at the EAPAD conference in 2005 as mentioned in this paper.
Abstract: The first arm wrestling match between a human arm and a robotic arm driven by electroactive polymers (EAP) was held at the EAPAD conference in 2005. The primary objective was to demonstrate the potential of the EAP actuator technology for applications in the field of robotics and bioengineering. The Swiss Federal Laboratories for Materials Testing and Research (Empa) was one of the three organizations participating in this competition. The robot presented by Empa was driven by a system of rolled dielectric elastomer (DE) actuators. Based on the calculated stress condition in the rolled actuator, a low number of pre-strained DE film wrappings were found to be preferential for achieving the best actuator performance. Because of the limited space inside the robot body, more than 250 rolled actuators with small diameters were arranged in two groups according to the human agonist–antagonist muscle configuration in order to achieve an arm-like bidirectional rotation movement. The robot was powered by a computer-controlled high voltage amplifier. The rotary motion of the arm was activated and deactivated electrically by corresponding actuator groups. The entire development process of the robot is presented in this paper where the design of the DE actuators is of primary interest. Although the robot lost the arm wrestling contest against the human opponent, the DE actuators have demonstrated very promising performance as artificial muscles. The scientific knowledge gained during the development process of the robot has pointed out the challenges to be addressed for future improvement in the performance of rolled dielectric elastomer actuators.

Journal ArticleDOI
TL;DR: This paper 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the authors introduce integral resonant control (IRC), a simple, robust and well-performing technique for vibration control in smart structures with collocated sensors and actuators.
Abstract: This paper introduces integral resonant control, IRC, a simple, robust and well-performing technique for vibration control in smart structures with collocated sensors and actuators. By adding a direct feed-through to a collocated system, the transfer function can be modified from containing resonant poles followed by interlaced zeros, to zeros followed by interlaced poles. It is shown that this modification permits the direct application of integral feedback and results in good performance and stability margins. By slightly increasing the controller complexity from first to second order, low-frequency gain can be curtailed, alleviating problems due to unnecessarily high controller gain below the first mode. Experimental application to a piezoelectric laminate cantilever beam demonstrates up to 24 dB modal amplitude reduction over the first eight modes.

Journal ArticleDOI
TL;DR: In this article, the geometric optimal design of magnetorheological (MR) valves in order to improve valve performance, such as pressure drop, is presented, where the optimization problem is to find the optimal geometric dimensions of MR valves constrained in a specific volume.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this paper, the applicability of the proposed nonlocal elastic shell theory is explored and analyzed based on the differences between the wave solutions from local and nonlocal theories in numerical simulations.
Abstract: Wave propagation in carbon nanotubes (CNTs) is studied based on the proposed nonlocal elastic shell theory. Both theoretical analyses and numerical simulations have explicitly revealed the small-scale effect on wave dispersion relations for different CNT wavenumbers in the longitudinal and circumferential directions and for different wavelengths in the circumferential direction. The applicability of the proposed nonlocal elastic shell theory is especially explored and analyzed based on the differences between the wave solutions from local and nonlocal theories in numerical simulations. It is found that the newly proposed nonlocal shell theory is indispensable in predicting CNT phonon dispersion relations at larger longitudinal and circumferential wavenumbers and smaller wavelength in the circumferential direction when the small-scale effect becomes dominant and hence noteworthy. In addition, the asymptotic frequency, phase velocities and cut-off frequencies are also derived from the nonlocal shell theory. Moreover, an estimation of the scale coefficient is provided based on the derived asymptotic frequency. The research findings not only demonstrate great potential of the proposed nonlocal shell theory in studying vibration and phonon dispersion relations of CNTs but also signify limitations of local continuum mechanics in analysis of small-scale effects, and thus are of significance in promoting the development of nonlocal continuum mechanics in the design of nanostructures.

Journal ArticleDOI
TL;DR: In this paper, a dynamic physics-based model for ionic polymer-metal composite (IPMC) sensors is presented, which is an infinite-dimensional transfer function relating the short-circuit sensing current to the applied deformation.
Abstract: A dynamic, physics-based model is presented for ionic polymer–metal composite (IPMC) sensors. The model is an infinite-dimensional transfer function relating the short-circuit sensing current to the applied deformation. It is obtained by deriving the exact solution to the governing partial differential equation (PDE) for the sensing dynamics, where the effect of distributed surface resistance is incorporated. The PDE is solved in the Laplace domain, subject to the condition that the charge density at the boundary is proportional to the applied stress. The physical model is expressed in terms of fundamental material parameters and sensor dimensions and is thus scalable. It can be easily reduced to low-order models for real-time conditioning of sensor signals in targeted applications of IPMC sensors. Experimental results are provided to validate the proposed model.

Journal ArticleDOI
TL;DR: An approach based upon the employment of piezoelectric transducer rosettes is proposed for passive damage or impact location in anisotropic or geometrically complex structures as discussed by the authors.
Abstract: An approach based upon the employment of piezoelectric transducer rosettes is proposed for passive damage or impact location in anisotropic or geometrically complex structures. The rosettes are comprised of rectangular macro-fiber composite (MFC) transducers which exhibit a highly directive response to ultrasonic guided waves. The MFC response to flexural (A0) motion is decomposed into axial and transverse sensitivity factors, which allow extraction of the direction of an incoming wave using rosette principles. The wave source location in a plane is then simply determined by intersecting the wave directions detected by two rosettes. The rosette approach is applicable to anisotropic or geometrically complex structures where the conventional time-of-flight source location is challenging due to the direction-dependent wave velocity. The performance of the rosettes for source location is validated through pencil-lead breaks performed on an aluminum plate, an anisotropic CFRP laminate and a complex CFRP-honeycomb sandwich panel.

Journal ArticleDOI
TL;DR: In this paper, the magnetic properties of aligned and isotropic magnetorheological elastomer composites were tested in cyclic compression passively and with increasing magnetic flux density.
Abstract: Magnetorheological elastomers (MRE) are interesting candidates for active vibration control of structural systems. In this study, spring elements consisting of magnetorheological elastomer were prepared and tested in dynamic compression to study the changes in their stiffness and vibration damping characteristics under the influence of a magnetic field. Aligned and isotropic magnetorheological elastomer composites were prepared using room temperature vulcanizing silicone elastomer as the matrix material and carbonyl iron as the magnetizable filler. Aligned MREs were prepared by curing the material under an external magnetic field. Aligned MREs were tested and the results were compared with isotropic composites with no preferred orientation. The mechanical properties of the MREs were tested in cyclic compression passively and with increasing magnetic flux density. The influence of the testing frequency and strain amplitude on the dynamic stiffness and damping properties was studied. It was noted that when measured in a magnetic field both the dynamic spring constants and the loss factor values of aligned MREs were increased compared to the zero-field values. The dynamic stiffness of aligned MREs increased with increasing testing frequency and it was tunable with magnetic flux density in the studied frequency range. The loss factor of aligned MREs was also tunable with the magnetic flux density but the absolute values also depend on the testing frequency. The dynamic stiffness of the aligned MREs measured in compression decreased with increasing strain amplitude, but the damping properties were not affected similarly. On the basis of these results, MREs are applicable as tunable spring elements for active vibration control.

Journal ArticleDOI
TL;DR: In this paper, the one-stage and two-stage energy harvesting schemes were compared and the results showed that the one stage energy harvesting scheme can achieve higher efficiency than the two stage scheme towards a range of energy storage voltages.
Abstract: Using piezoelectric elements to harvest energy from ambient vibrations has been of great interest over the past few years. Due to the relatively low power output of piezoelectric materials, energy storage devices are used to accumulate harvested energy for intermittent use. Piezoelectric energy harvesting circuits have two schemes: one-stage and two-stage energy harvesting. A one-stage energy harvesting scheme includes a conventional diode bridge rectifier and an energy storage device. In recent years, two-stage energy harvesting circuits have been explored. While the results shown in previous research and development are promising, there are still some issues that need to be studied. Energy storage devices such as rechargeable batteries and supercapacitors have different cell voltages. Moreover, the storage cells can be connected in series to increase the voltage range. The storage device voltage is an important factor that influences the energy harvesting efficiency. This paper will study the efficiencies of the energy harvesting circuits considering the storage device voltages. For one-stage energy harvesting, expressions are derived to calculate the efficiencies towards different storage device voltages and verified by experiments. For two-stage energy harvesting circuits, theoretical efficiency expressions are derived and verified by PSPICE simulations. These two energy harvesting schemes are also compared. The results show that a one-stage energy harvesting scheme can achieve higher efficiency than the two-stage scheme towards a range of energy storage voltages.

Journal ArticleDOI
TL;DR: In this article, a vascular sandwich structure that appears as a conventional sandwich composite has been developed and tested, where the vascular network is used to deliver a healing agent from a remote reservoir to a region of damage via a vascular network.
Abstract: Impact damage can degrade the flexural strength of composite sandwich structures by over 50% due to a loss of skin support inducing localized skin buckling. Various self-healing methodologies have been applied to laminated composites but the concept of delivering a healing agent from a remote reservoir to a region of damage via a vascular network offers the potential for a robust and replenishable system housed in the core of a sandwich structure. In this pilot study a vascular sandwich structure that appears as a conventional sandwich composite has been developed and tested. The network has been shown to have negligible influence on the innate static mechanical properties of the host panel. Infiltration of the vascular network with a pre-mixed epoxy resin system after impact damage demonstrated a complete recovery of flexural failure mode and load. Infiltration with the same resin system from separate unmixed networks, where self-healing is initiated autonomously via mixing within the damage, has also been shown to fully recover undamaged failure load when both networks are successfully breached.

Journal ArticleDOI
TL;DR: In this article, 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the static bending, free vibration, and dynamic response of monomorph, bimorph, and multimorph actuators made of functionally graded piezoelectric materials (FGPMs) under a combined thermal-electro-mechanical load by using the Timoshenko beam theory was investigated.
Abstract: This paper investigates the static bending, free vibration, and dynamic response of monomorph, bimorph, and multimorph actuators made of functionally graded piezoelectric materials (FGPMs) under a combined thermal-electro-mechanical load by using the Timoshenko beam theory. It is assumed that all of the material properties of the actuator, except for Poisson's ratio, are position dependent due to a continuous variation in material composition through the thickness direction. Theoretical formulations are derived by employing Hamilton's principle and include the effect of transverse shear deformation and axial and rotary inertias. The governing differential equations are then solved using the differential quadrature method to determine the important performance indices, such as deflection, reaction force, natural frequencies, and dynamic response of various FGPM actuators. A comprehensive parametric study is conducted to show the influence of shear deformation, temperature rise, material composition, slenderness ratio, end support, and total number of layers on the thermo-electro-mechanical characteristics. It is found that FGPM monomorph actuators exhibit the so-called 'non-intermediate' behavior under an applied electric field.

Journal ArticleDOI
TL;DR: In this article, the axial preloading of a piezoelectric bimorph vibrating in the flexural mode was studied for a power harvester to effectively scavenge energy from ambient mechanical vibrations/noise with varying frequency spectra.
Abstract: We study the technique to adjust the performance of a piezoelectric bimorph vibrating in the flexural mode through axial preloads, which is useful for a power harvester to effectively scavenge energy from ambient mechanical vibrations/noise with varying-frequency spectra. The external circuit connected to the bimorph is simplified as an impedance in the analysis. Analytical solutions are derived. The analyses show that resonance happens when the natural frequency of the bimorph is adjusted adjacent to the external driving frequency by preloading, and the output power density can be raised many more times in that case. The mechanism for an axial preload to improve the bimorph performance at varying-frequency vibrations is examined in detail.

Journal ArticleDOI
TL;DR: In this article, a new algorithm employing chirplet matching pursuit was proposed to isolate individual reflections from defects in the structure, if any, which could be overlapping and multimodal.
Abstract: Signal processing algorithms for guided wave pulse echo-based structural health monitoring (SHM) must be capable of isolating individual reflections from defects in the structure, if any, which could be overlapping and multimodal. In addition, they should be able to estimate the time–frequency centers, the modes and individual energies of the reflections, which would be used to locate and characterize defects. Finally, they should be computationally efficient and amenable to automated processing. This work addresses these issues with a new algorithm employing chirplet matching pursuits followed by a mode correlation check for single point sensors. Its theoretical advantages over conventional time–frequency representations for SHM are elaborated. Results from numerical simulations and experiments in isotropic plate structures are presented, which show the capability of the proposed algorithm. Finally, the issue of in-plane triangulation is discussed and experimental work done to explore this issue is presented.

Journal ArticleDOI
TL;DR: Zhao et al. as discussed by the authors developed a wireless ultrasonic structural health monitoring (SHM) system for aircraft wing inspection, which can effectively deliver at least 100?mW of DC power continuously from a transmitter at a range of 1?m.
Abstract: The objective of this study is to develop a wireless ultrasonic structural health monitoring (SHM) system for aircraft wing inspection. In part I of the study (Zhao et al 2007 Smart?Mater.?Struct. 16 1208?17), small, low cost and light weight piezoelectric (PZT) disc transducers were bonded to various parts of an aircraft wing for detection, localization and growth monitoring of defects. In this part, two approaches for wirelessly interrogating the sensor/actuator network were developed and tested. The first one utilizes a pair of reactive coupling monopoles to deliver 350?kHz RF tone-burst interrogation pulses directly to the PZT transducers for generating ultrasonic guided waves and to receive the response signals from the PZTs. It couples enough energy to and from the PZT transducers for the wing panel inspection, but the signal is quite noisy and the monopoles need to be in close proximity to each other for efficient coupling. In the second approach, a small local diagnostic device was developed that can be embedded into the wing and transmit the digital signals FM-modulated on a 915?MHz carrier. The device has an ultrasonic pulser that can generate 350?kHz, 70?V tone-burst signals, a multiplexed A/D board with a programmable gain amplifier for multi-channel data acquisition, a microprocessor for circuit control and data processing, and a wireless module for data transmission. Power to the electronics is delivered wirelessly at X-band with an antenna?rectifier (rectenna) array conformed to the aircraft body, eliminating the need for batteries and their replacement. It can effectively deliver at least 100?mW of DC power continuously from a transmitter at a range of 1?m. The wireless system was tested with the PZT sensor array on the wing panel and compared well with the wire connection case.

Journal ArticleDOI
TL;DR: In this article, a reusable hysteretic damper (RHD) is proposed for passive seismic response control of civil engineering structures in a three-story steel frame building with and without an RHD.
Abstract: This paper presents a special shape memory alloy-based hysteretic damper with distinctive features such as tunable hysteretic behavior and ability to withstand several design level earthquakes. Superelastic nitinol stranded wires are used for energy dissipation in this damping device, termed a reusable hysteretic damper (RHD). By adjusting its design parameters, the hysteretic behavior of the RHD can be modified to best fit the needs for passive structural control applications. Adjustable design parameters of the RHD include the inclination angle of the nitinol wires, pretension level, and friction effect. A simulation-based parametric study was carried out to examine the effects of these design parameters of the RHD on its energy dissipating performance. The effectiveness of the RHD in passive seismic response control of civil engineering structures is examined through a nonlinear dynamic analysis of a three-story steel frame building with and without an RHD. The simulation results suggest that it can effectively reduce the structural response of building structures subjected to strong earthquakes. With proper design, an RHD can be reused for several strong earthquakes without the need for repair, due to the high fatigue life of nitinol wires.

Journal ArticleDOI
TL;DR: In this paper, an over-height collision detection and evaluation system for concrete bridge girders using piezoelectric transducers was developed for highway bridges, where an electric circuit is designed to detect the impact and activate a digital camera to take photos of the offending truck.
Abstract: With increasing traffic volume follows an increase in the number of overheight truck collisions with highway bridges. The detection of collision impact and evaluation of the impact level is a critical issue in the maintenance of a concrete bridge. In this paper, an overheight collision detection and evaluation system is developed for concrete bridge girders using piezoelectric transducers. An electric circuit is designed to detect the impact and to activate a digital camera to take photos of the offending truck. Impact tests and a health monitoring test were conducted on a model concrete bridge girder by using three piezoelectric transducers embedded before casting. From the experimental data of the impact test, it can be seen that there is a linear relation between the output of sensor energy and the impact energy. The health monitoring results show that the proposed damage index indicates the level of damage inside the model concrete bridge girder. The proposed overheight truck–bridge collision detection and evaluation system has the potential to be applied to the safety monitoring of highway bridges.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the actuation of yarns of twist-spun multi-wall carbon nanotubes in response to voltage ramps and potentiostatic pulses.
Abstract: We report on actuation in high tensile strength yarns of twist-spun multi-wall carbon nanotubes. Actuation in response to voltage ramps and potentiostatic pulses is studied to quantify the dependence of the actuation strain on the applied voltage. Strains of up to 0.5% are obtained in response to applied potentials of 2.5 V. The dependence of strain on applied voltage and charge is found to be quadratic, in agreement with previous results on the actuation of single-wall carbon nanotubes, with the magnitude of strain also being very similar. The specific capacitance reaches 26 F g−1. The modulus of the yarns was found to be independent of applied load and voltage within experimental uncertainty.