Table of contents

Piezoelectric energy harvesting techniques have experienced increasing research effort during the last few years. Possible applications including wireless, fully autonomous electronic devices, such as sensors, have attracted great interest. The key aspect of harvesting techniques is the amount of converted and stored energy, because the energy source and the conversion rate is limited. In particular, switching techniques offer many parameters that can be optimized. It is therefore crucial to examine the influence of these parameters in a precise manner.

This paper addresses an accurate analytical modeling approach, facilitating the calculation of standard-DC and parallel SSHI-DC energy harvesting circuits. In particular the influence of the frequency ratio between the excitation and the electrical resonance of the switching LR-branch, and the voltage gaps across the rectifier diodes are studied in detail. Additionally a comparison with the SSDI damping network is performed. The relationship between energy harvesting and damping is indicated in this paper.

Dielectric elastomers are light weight, low-cost, highly deformable and fast response smart materials capable of converting electrical energy into mechanical work or vice versa. Silicone rubber is a well-known dielectric elastomer which is used as actuator, and in order to enhance the efficiency of this smart material, compounding of silicone rubber with various fillers can be carried out. The effect of organically modified montmorillonite (OMMT) nano-clay on improvement of dielectric properties, actuation stress and its relaxation response was considered in this study. OMMT was dispersed in room temperature vulcanized (RTV) silicone rubber, and a composite film was cast. Using an in-house actuation set-up, it was shown that the actuation stress for a given electric field intensity is higher for composites than that for pristine silicone rubber. Also, the time-dependent actuation response of the samples was evaluated, and it was shown that the characteristic relaxation time of the actuation stress for composites is less than for the pristine rubber as a result of OMMT addition.

Molecular techniques are transforming our understanding of cellular function and disease. However, accurate molecular analysis methods will be limited if the input DNA, RNA or protein is not derived from a pure population of cells or is contaminated by the wrong cells. The modeling and control of the piezoelectric actuator, with an objective application towards ultrasonic vibration cutting (UVC), is addressed in this paper. The piezoelectric actuator is used in realizing the fast and precise movements of the developed UVC so as to procure a pure population of targeted cells from tissue sections for subsequent pathology analysis with precision and without causing a large deformation. To address the nonlinearities and uncertainties of the piezoelectric actuator, an adaptive controller based on a hysteresis model is proposed to yield robust control performance. A multilayer piezoelectric actuator is used to actuate a sharp needle vibrating at high frequency and low amplitude to cut the tissue. Experimental results showed that the embedded tissue can be quickly and precisely cut with this ultrasonic vibration microdissection method.

This paper presents a simulation study on the downscaling of multiple electrodynamic proof mass actuators for the implementation of decentralized velocity feedback control loops on a thin panel. The system is conceived to reduce the panel response and sound radiation at low resonance frequencies. In the first part of the paper, the principal downscaling laws of a single proof mass actuator are revisited. In particular, the scaling laws are given for: (a) the fundamental natural frequency, (b) the damping factor, (c) the static displacement, (d) the maximum current that can be fed back to the actuator, (e) the maximum stroke of the proof mass and (f) the maximum control force that can be produced by the actuator. The second part of the paper presents a numerical study concerning the control performance produced by decentralized control systems with an increasing number of control units, which are scaled down in such a way as to keep the total base surface occupied by the actuators constant. This study shows that the control performance tends to rise as the number of control units is increased. However, this trend is reversed for large arrays of small scale actuators since the gain margin of the feedback loops tends to decrease with downscaling and incrementation of the actuators density.

Blind source separation using second-order blind identification (SOBI) has been successfully applied to the problem of output-only identification, popularly known as ambient system identification. In this paper, the basic principles of SOBI for the static mixtures case is extended using the stationary wavelet transform (SWT) in order to improve the separability of sources, thereby improving the quality of identification. Whereas SOBI operates on the covariance matrices constructed directly from measurements, the method presented in this paper, known as the wavelet-based modified cross-correlation method, operates on multiple covariance matrices constructed from the correlation of the responses. The SWT is selected because of its time-invariance property, which means that the transform of a time-shifted signal can be obtained as a shifted version of the transform of the original signal. This important property is exploited in the construction of several time-lagged covariance matrices. The issue of non-stationary sources is addressed through the formation of several time-shifted, windowed covariance matrices. Modal identification results are presented for the UCLA Factor building using ambient vibration data and for recorded responses from the Parkfield earthquake, and compared with published results for this building. Additionally, the effect of sensor density on the identification results is also investigated.

In PZT-induced acousto-ultrasound techniques, the adhesive layer between a PZT and a host structure significantly affects sensor signals. However, its effects have been barely studied so far. A numerical model is essential to fundamentally understand the role of the adhesive interface. Using the hybrid spectral element, the effects of the adhesive bond-line layer on the Lamb wave generation and reception were modeled and compared with available test data for validation of the hybrid spectral element. The validations were conducted with different adhesive layer thicknesses. The trends in simulation results agreed well with the experiments. Parametric studies are presented to understand the adhesive layer effects. In these studies, adhesive thickness and stiffness, and PZT diameter and thickness, are selected as parameters. The physics of the adhesive layer are then discussed.

Electrostatic micro-power generators (MPGs) are modeled and analyzed with particular emphasis on electromechanical coupling and its impact on the system dynamics. We identify two qualitatively different regimes in the MPG response, dubbed slow and fast. A linearized electromechanically coupled model of an electrostatic MPG and two simplified linear models are used to study the response of the MPG. Linear models are found adequate to represent the dynamic response of fast MPGs but inadequate to represent the response of slow and mixed domain MPGs. A nonlinear model is developed and validated to describe the response of those MPGs under moderately large excitations. On the basis of this analysis, we describe a method and provide design rules for realizing wideband electrostatic MPGs, and develop closed-form formulae for the extracted power for MPGs under moderately large excitations.

Shape memory alloys (SMAs) belong to the class of smart materials and have been used in numerous applications. Solid phase transformations induced either by stress or temperature are behind the remarkable properties of SMAs that motivate the concept of innovative smart actuators for different purposes. The SMA element used in these actuators can assume different forms and a spring is an element usually employed for this aim. This contribution deals with the modeling, simulation and experimental analysis of SMA helical springs. Basically, a one-dimensional constitutive model is assumed to describe the SMA thermomechanical shear behavior and, afterwards, helical springs are modeled by considering a classical approach for linear-elastic springs. A numerical method based on the operator split technique is developed. SMA helical spring thermomechanical behavior is investigated through experimental tests performed with different thermomechanical loadings. Shape memory and pseudoelastic effects are treated. Numerical simulations show that the model results are in close agreement with those obtained by experimental tests, revealing that the proposed model captures the general thermomechanical behavior of SMA springs.

In this paper, the asymmetric tensile–compressive behavior of shape memory alloys is modeled based on the mathematical framework of Raniecki and Mróz (2008 Acta Mech.195 81–102). The framework allows the definition of smooth, non-symmetric, pressure-insensitive yield functions that are used here to incorporate tensile–compressive modeling capabilities into the Zaki–Moumni (ZM) model for shape memory materials. It is found that, despite some increased complexity, the generalized model is capable of producing satisfactory results that agree with uniaxial experimental data taken from the literature.

To enhance the generality and flexibility of active constrained layer damped (ACLD) forms used in vibration control for circular cylindrical shells, the piezoelectric layer of the ACLD form is divided into several sub-blocks by thin insulated layers, and the sub-blocks are integrated on the viscoelastic layer continuously in the circumferential direction. In addition, on the basis of the authors' recent research on passive constrained layer damped (PCLD) circular cylindrical shells, the piezoelectric effects of the constrained layer (made of piezoelectric material) are further considered. Then, the integrated first-order differential equation for such an ACLD (partially treated in the axial direction) circular cylindrical shell is derived by reformulating the integrated first-order differential equation for the PCLD circular cylindrical shell. Next, employing the extended homogeneous capacity precision integration approach and the superposition principle, a high precision semi-analytical method is developed for solving the dynamic problem for such ACLD circular cylindrical shells. Subsequently, several kinds of circumferential modal control strategy are compared by the method presented. Furthermore, the concept of a circumferential dominant modal control strategy is proposed, which is different from the traditional modal control method. The numerical results show that, on applying the circumferential dominant modal control strategy, the ACLD cylindrical shell attenuates the vibration better. Lastly, some influence factors for the circumferential dominant modal control strategy affecting the damping effect of ACLD circular cylindrical shells are also investigated.

For many years there has been interest in using fiber-reinforced polymers (FRPs) as reinforcement in concrete structures. Unfortunately, due to their linear elastic behavior, FRP reinforcing bars are never considered for structural damping or dynamic applications. With the aim of improving the ductility and damping capability of concrete structures reinforced with FRP reinforcement, this paper studies the application of SMA–FRP, a relatively novel type of composite reinforced with superelastic shape memory alloy (SMA) wires. The cyclic tensile behavior of SMA–FRP composites are studied experimentally and analytically. Tests of SMA–FRP composite coupons are conducted to determine their constitutive behavior. The experimental results are used to develop and calibrate a uniaxial SMA–FRP analytical model. Parametric and case studies are performed to determine the efficacy of the SMA–FRP reinforcement in concrete structures and the key factors governing its behavior. The results show significant potential for SMA–FRP reinforcement to improve the ductility and damping of concrete structures while still maintaining its elastic characteristic, typical of FRP reinforcement.

Research on efficient shore bird morphology inspired the hyperelliptical cambered span (HECS) wing, a crescent-shaped, aft-swept wing with vertically oriented wingtips. The wing reduces vorticity-induced circulation loss and outperforms an elliptical baseline when planar. Designed initially as a rigid wing, the HECS wing makes use of morphing to transition from a planar to a furled configuration, similar to that of a continuously curved winglet, in flight. A morphing wing concept mechanism is presented, employing shape memory alloy actuators to create a discretized curvature approximation. The aerodynamics for continuous wing shapes is validated quasi-statically through wind tunnel testing, showing enhanced planar HECS wing lift-to-drag performance over an elliptical wing, with the furled HECS wing showing minimal enhancements beyond this point. Wind tunnel tests of the active morphing wing prove the mechanism capable of overcoming realistic loading, while further testing may be required to establish aerodynamic merits of the HECS wing morphing maneuver.

A beam-shape composite actuator using shape memory alloy (SMA) wires as the active component, termed a Bio-Inspired Shape Memory Alloy Composite (BISMAC), was designed to provide a large deformation profile. The BISMAC design was inspired by contraction of a jellyfish bell, utilizing the rowing mechanism for locomotion. Characterization of maximum deformation in underwater conditions was performed for different actuator configurations to analyze the effect of different design parameters, including silicone thickness, flexible steel thickness and distance between the SMA and flexible steel. A constant cross-section (CC)-BISMAC of length 16 cm was found to achieve deformation with a radius of curvature of 3.5 cm. Under equilibrium conditions, the CC-BISMAC was found to achieve 80% of maximum deformation, consuming 7.9  J/cycle driven at 16.2 V/0.98 A and a frequency of 0.25 Hz. A detailed analytical model was developed using the transfer matrix method and a 1D finite beam element (FE) model to simulate the behavior of the BISMAC incorporating gravity, buoyancy and SMA parameters. The FE and transfer matrix models had a maximum deformation error norm of 1.505 and 1.917 cm in comparison with experimentally observed beam deformation in the CC-BISMAC. The mean curvatures predicted by the FE and transfer matrix methods were 0.292  cm⁻¹ and 0.295 cm⁻¹ compared to a mean experimental curvature of 0.294  cm⁻¹, a percentage error of −5.4% and 2.77%, respectively. Using the developed analytical model, an actuator design was fabricated mimicking the maximum deformation profile of jellyfish of the species Aurelia aurita (AA). The designed AA-BISMAC achieved a maximum curvature of 0.428  cm⁻¹ as compared to 0.438 cm⁻¹ for A. aurita with an average square root error of 0.043  cm⁻¹, 10.2% of maximum A. aurita curvature.

Like most smart materials, such as piezoelectric materials and shape memory alloys, ion-exchange polymer–metal composite (IPMC), which is a kind of electroactive polymer material, exhibits the properties of hysteresis and creep. In this paper we explain the hysteresis and creep properties of IPMC, analyze the hysteresis using a discrete Prandtl–lshlinskii model, obtain a creep model of IPMC through modifying the creep model of piezoelectric material and present an inverse model of the hysteresis. For hysteresis and creep properties of IPMC changing with time at different rates, we applied the LMS (least mean square) algorithm to identify the hysteresis parameters online. An offline identification algorithm was used to obtain the creep parameters. An adaptive inverse strategy of control for IPMC actuators was set up on the basis of a superposition model of nonlinear hysteresis and linear creep, and we obtained good simulation and experiment results.

The pH response and mechanical properties of copolymer-based hydrogels such as poly(acrylonitrile-co-acrylic acid) are usually attributed to their chemical composition. In this study, it has been shown that the architecture of the polymer chains, i.e. the distribution of comonomers in the macromolecules, also plays a major role in controlling these properties. A series of four poly(acrylonitrile-co-acrylic acids) with fixed composition (i.e.  ∼30 mol% acrylic acid moieties) were synthesized, where the block lengths of both AN (acrylonitrile) and AAc (acrylic acid) moieties in the copolymers were varied by controlling the feeding pattern of the monomers during free radical copolymerization. These copolymers were then converted into fine fibers of the same dimensions. The monomer distribution in the four copolymers was estimated using quantitative carbon ¹³C nuclear magnetic resonance (NMR) and related to the mechanical and pH response properties of the resultant fibers. The pH response of the fibers with similar composition increased dramatically as the block length of the AAc moiety was increased, while the mechanical properties increased as a direct function of the block length of the AN moieties.

The fiber's response at pH 10 in terms of the change in length increased by ∼four times while its response rate increased by ∼50 times with the increase in block length of the AAc moiety. On the other hand, the tensile properties and retractive stress increased by ∼four times with the increase in the block length of the AN moiety.

This paper presents an analysis of the energy generating performance in a pressure-loaded system using piezoelectric transducer technology. The energy harvesting device in this study is a partially covered, simply supported piezoelectric unimorph circular plate to convert energy from fluctuating pressure into electrical energy. The analysis includes comprehensive modeling and a parametric study to provide a design primer for a specific application in which the frequency of fluctuating pressure is well below the natural frequency of the harvester. An expression for the total power output from the device for a given applied pressure is shown, and then used to determine optimal design parameters. It is shown that the device's deflection and stress under load are the limiting factors in the design. The analytical results indicate that the PMN–PT harvesters can generate over one order of magnitude more power than the PZT harvesters for any substrate material. Some possible factors that can degrade energy harvesting performance are also discussed.

Magneto-rheological (MR) dampers are semi-active control devices whose characteristics are varied under different current inputs in accordance with semi-active control laws to achieve optimized vibration control of a structural system. Experimental evaluation of the effectiveness of MR dampers for seismic hazard mitigation using selected control laws is necessary to enable performance-based design procedures to be developed and for these devices to become accepted by the practical design community. Real-time hybrid simulation provides an economical and efficient experimental technique which enables both the damper rate dependence and the damper–structure interaction to be accounted for. A successful real-time hybrid simulation requires accurate actuator control to achieve reliable experimental results. A time delay and actuator time lag (referred to hereafter as simply the delay) can be introduced into the actuator response due to state determination, communication, and servo-hydraulic dynamics. The variable current inputs and resulting variable forces induced by semi-active control laws pose additional challenges for actuator control by introducing variable delay in a real-time hybrid simulation. In this paper a newly developed adaptive inverse compensation technique is experimentally evaluated for application in real-time hybrid simulation involving an MR damper subjected to band-limited white noise-generated random displacements and variable current inputs. Actuator control is assessed using different evaluation criteria. The adaptive inverse compensation method is demonstrated to achieve good actuator control and therefore shows good potential for use in real-time hybrid simulation of structural systems with semi-active MR dampers.

Piezoelectric materials offer exceptional sensing and actuation properties; however, they are prone to breakage and difficult to apply on curved surfaces in their monolithic form. One method of alleviating these issues is through the use of 0–3 nanocomposites, which are formed by embedding piezoelectric particles into a polymer matrix. Material of this class offers certain advantages over monolithic materials; however, it has seen little use due to its low coupling. Here we develop micromechanics and finite element models to study the electroelastic properties of an active nanocomposite, as a function of the aspect ratio and alignment of the piezoelectric filler. Our results show that the aspect ratio is critical for achieving high electromechanical coupling, and with an increase from 1 to 10 at 30% volume fraction of piezoelectric filler the coupling can increase to 60 times its initial value and achieve a bulk composite coupling as high as 90% for a pure PZT-7A piezoelectric constituent.