Smart Materials and Structures

Published by IOP Publishing
Online ISSN: 1361-665X
Print ISSN: 0964-1726
The effect of moisture absorption on the glass transition temperature (T(g)) and stress/strain behavior of network polyurethane shape memory polymer (SMP) foams has been investigated. With our ultimate goal of engineering polyurethane SMP foams for use in blood contacting environments, we have investigated the effects of moisture exposure on the physical properties of polyurethane foams. To our best knowledge, this study is the first to investigate the effects of moisture absorption at varying humidity levels (non-immersion and immersion) on the physical properties of polyurethane SMP foams. The SMP foams were exposed to differing humidity levels for varying lengths of time, and they exhibited a maximum water uptake of 8.0% (by mass) after exposure to 100% relative humidity for 96 h. Differential scanning calorimetry results demonstrated that water absorption significantly decreased the T(g) of the foam, with a maximum water uptake shifting the T(g) from 67 °C to 5 °C. Samples that were immersed in water for 96 h and immediately subjected to tensile testing exhibited 100% increases in failure strains and 500% decreases in failure stresses; however, in all cases of time and humidity exposure, the plasticization effect was reversible upon placing moisture-saturated samples in 40% humidity environments for 24 h.
This paper introduces an indirect intelligent sliding mode controller (IISMC) for shape memory alloy (SMA) actuators, specifically a flexible beam deflected by a single offset SMA tendon. The controller manipulates applied voltage, which alters SMA tendon temperature to track reference bending angles. A hysteretic recurrent neural network (HRNN) captures the nonlinear, hysteretic relationship between SMA temperature and bending angle. The variable structure control strategy provides robustness to model uncertainties and parameter variations, while effectively compensating for system nonlinearities, achieving superior tracking compared to an optimized PI controller.
In this work, tensile tests and one-dimensional constitutive modeling are performed on a high recovery force polyurethane shape memory polymer that is being considered for biomedical applications. The tensile tests investigate the free recovery (zero load) response as well as the constrained displacement recovery (stress recovery) response at extension values up to 25%, and two consecutive cycles are performed during each test. The material is observed to recover 100% of the applied deformation when heated at zero load in the second thermomechanical cycle, and a stress recovery of 1.5 MPa to 4.2 MPa is observed for the constrained displacement recovery experiments.After performing the experiments, the Chen and Lagoudas model is used to simulate and predict the experimental results. The material properties used in the constitutive model - namely the coefficients of thermal expansion, shear moduli, and frozen volume fraction - are calibrated from a single 10% extension free recovery experiment. The model is then used to predict the material response for the remaining free recovery and constrained displacement recovery experiments. The model predictions match well with the experimental data.
The cochlea is part of the inner ear and its mechanical response provides us with many aspects of our amazingly sensitive and selective hearing. The human cochlea is a coiled tube, with two main fluid chambers running along its length, separated by a 35 mm-long flexible partition that has its own internal dynamics. A dispersive wave can propagate along the cochlea due to the interaction between the inertia of the fluid and the dynamics of the partition. This partition includes about 12 000 outer hair cells, which have different structures, on a micrometre and a nanometre scale, and act both as motional sensors and as motional actuators. The local feedback action of all these cells amplifies the motion inside the inner ear by more than 40 dB at low sound pressure levels. The feedback loops become saturated at higher sound pressure levels, however, so that the feedback gain is reduced, leading to a compression of the dynamic range in the cochlear amplifier. This helps the sensory cells, with a dynamic range of only about 30 dB, to respond to sounds with a dynamic range of more than 120 dB. The active and nonlinear nature of the dynamics within the cochlea give rise to a number of other phenomena, such as otoacoustic emissions, which can be used as a diagnostic test for hearing problems in newborn children, for example. In this paper we view the mechanical action of the cochlea as a smart structure. In particular a simplified wave model of the cochlear dynamics is reviewed that represents its essential features. This can be used to predict the motion along the cochlea when the cochlea is passive, at high levels, and also the effect of the cochlear amplifier, at low levels.
A wireless, battery-less load cell was fabricated based on the resonant frequency shift of a vibrating magnetoelastic strip when exposed to an AC magnetic field. Since the vibration of the magnetoelastic strip generated a secondary field, the resonance was remotely detected with a coil. When a load was applied to a small area on the surface of the magnetoelastic strip via a circular rod applicator, the resonant frequency and amplitude decreased due to the damping on its vibration. The force sensitivity of the load cell was controlled by changing the size of the force applicator and placing the applicator at different locations on the strip's surface. Experimental results showed the force sensitivity increased with a larger applicator placing near the edge of the strip. The novelty of this load cell is not only its wireless passive nature, but also the controllability of the force sensitivity.
Smart materials such as piezoceramics and shape memory alloys (SMAs) exhibit significant hysteresis and in order to estimate the effect on open and closed loop control a suitable model is needed. One promising candidate is the Preisach independent domain hysteresis model that is characterized by the congruent minor loop and wiping out properties. Comparable minor loop and decaying oscillation test data for a multi-sheet piezoceramic actuator (made of lead zirconate titanate) attached to a flexible beam are presented and are seen to be very consistent with the two Preisach model properties. The commanded parameter is the sheet transverse electric field while the measured parameter is an approximately colocated strain induced in the beam. Equivalent data for a Nitinol SMA wire muscle, attached to the same beam, are also presented. The input and output parameters are the SMA current and a beam strain respectfully. The minor loop and wiping out evidence is less strong than that of the piezoceramic case, but encouraging. In all experiments the quasi-steady state responses were generated in order to avoid exciting beam flexible modes which would complicate the analysis
This paper presents a novel approach to continuously measure the mechanical deformations of a tire due to contact with asphalt, by embedding capacitive-resistive sensors on it. A strain monitoring method is proposed, that adopts the tire itself as a sensing element. In this way, the sensing area is pushed towards the tread interface (the part of the tire in direct contact with the asphalt) where the information concerning tire state is actually generated. Tire deformation causes a change of the spacing between the steel wires inside the tire carcass and this change is translated into an impedance change of that region of the tire. By measuring such an impedance change, our approach enables to determine the deformation of the tire. Experimental results supports the feasibility of our approach and are reported and discussed in this paper.
This paper proposes a neural network implementation of a model of fatigue damage dynamics which allows the damage information on critical plant components to be integrated with the plant dynamics for both online life prediction and off-line control synthesis. The aim is to alleviate the problem of slow computation via conventional numerical methods. The results of simulation experiments reveal that a neural network algorithm could be used as an intelligent instrument for online monitoring of fatigue damage and also as a tool for failure prognostics and service life prediction
The development and implementation of the optimized energy-delay sub-network routing (OEDSR) protocol for wireless sensor networks (WSN) is presented. This on-demand routing protocol minimizes a novel link cost factor which is defined using available energy, end-to-end (E2E) delay and distance from a node to the base station (BS), along with clustering, to effectively route information to the BS. Initially, the nodes are either in idle or sleep mode, but once an event is detected, the nodes near the event become active and start forming sub-networks. Formation of the inactive network into a sub-network saves energy because only a portion of the network is active in response to an event. Subsequently, the sub-networks organize themselves into clusters and elect cluster heads (CHs). The data from the CHs are sent to the BS via relay nodes (RNs) that are located outside the sub-networks in a multi-hop manner. This routing protocol improves the lifetime of the network and the scalability. This routing protocol is implemented over the medium access control (MAC) layer using UMR nodes. Experimental results illustrate that the protocol performs satisfactorily as expected
We present a programmable digital glove aimed to assist handicapped aphasiacs. Other than being mechanically simple, economic and robust, it is capable of fine-tuning the motion range and sensitivity to meet practical needs among patients through manipulating the optical flux and the topology of the glove. When further equipped with a letter input matrix system, it allows much faster letter keying. In fact, the developed glove can instantly bring great improvement to a patient's communications skill and thus reinstate his or her life anew, so long as he or she still possesses barely movable and bendable fingers. It is foreseeable that those hindered by speech problems, especially those further suffering from physical disabilities, may also be the extended beneficiaries of this evolving technology as it may likely become a new viable tool for communication, in addition to the traditional sign language.
Nanomanipulation in space-limited environments (e.g., inside a SEM (scanning electron microscope), and particularly in a TEM (transmission electron microscope)) requires small-sized nanomanipulators that are capable of producing sub-nanometer positioning resolutions and large output forces. This paper reports on a millimeter-sized MEMS (microelectromechanical systems) based nanomanipulator with a positioning resolution of 0.15 nm and a motion range of ± 2.55 µm. An amplification mechanism is employed to convert micrometer input displacements, generated by a conventional electrostatic comb-drive microactuator, into sub-nanometer output displacements. The device has a high load driving capability, driving a load as high as 98 µN without sacrificing positioning performance. Based on the pseudo-rigid-body approach, closed-form analytical models of the minification ratio and stiffness of the amplification mechanism are developed. Finite element simulation and testing results verify that the theoretical models are valid with an error smaller than 6.2% and that the mechanism has a high linearity (± 2.4%). The amplification mechanism and analytical models have general applicability to other MEMS transducer designs. A capacitive displacement sensor is integrated for detecting input displacements that are converted into output displacements via the minimization ratio, allowing closed-loop controlled nanomanipulation. The MEMS-based nanomanipulators are applicable to the characterization/manipulation of nanomaterials and construction of nanodevices. Corrections were made to this article on 29 August 2007 (in the Abstract and sections 3.2.3 and 5.2). The corrected electronic version is identical to the print version.
The electromechanical performance of planar dielectric elastomer (DE) actuators is predicted by applying a novel model for the mechanical behavior of visco-hyperelastic films such as VHB 4910 (manufactured by 3M). The electrostatic pressure was introduced in the film thickness direction to adapt the film model to DE actuators. Moreover, the actuator was embedded in an appropriate electrical supply circuit to account for the electrodynamic effects. The simulation of the active expansion of a biaxially prestrained, planar DE actuator configuration showed unstable deformation behavior under long-term activation. For activation voltages exceeding a critical level, the active expansion thus became uncontrolled after some time. The model was also applied to a DE strip actuator configuration under sinusoidal electromechanical excitation. The influence of selected parameters on the overall actuator performance was thereby investigated. While the specific energy density increases with increasing amplitudes of the activation voltage and the stretch ratio, the optimum efficiency is predicted to lie at moderate electromechanical excitations.
Comparison between different CNT-based structures a: randomly oriented CNT-mat, b: aligned CNT-mat, based on CNT-arrays. 
In-plain-Measuring facility.
Experimental investigations of highly vertically aligned carbon nanotubes (CNTs), also known as CNT-arrays, are the main focus of this paper. The free strain as result of an active material behavior is analyzed via a novel experimental setup. Previous test experiences of papers made of randomly oriented CNTs, also called Bucky-papers, reveal comparably low free strain. The anisotropy of aligned CNTs promises better performance. Via synthesis techniques like chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD), highly aligned arrays of multi-walled carbon nanotubes (MWCNTs) are synthesized. Two different types of CNT-arrays are analyzed, morphologically first, and optically tested for their active characteristics afterwards. One type of the analyzed arrays features tube lengths of 750–2000 μm with a large variety of diameters between 20 and 50 nm and a wave-like CNT-shape. The second type features a maximum, almost uniform, length of 12 μm and a constant diameter of 50 nm. Different CNT-lengths and array types are tested due to their active behavior. As result of the presented tests, it is reported that the quality of orientation is the most decisive property for excellent active behavior. Due to their alignment, CNT-arrays feature the opportunity to clarify the actuation mechanism of architectures made of CNTs.
We present a controlled mode of "topological" displacement of homogeneous piezo films that arises solely from an inhomogeneous in-plane strain due to an inhomogeneous polarization. For the rotationally symmetric case, we develop a theoretical model that analytically relates the shape of the displacement to the polarization for the cases of in-plane and out-of-plane polarization. This is verified for several examples, and we further demonstrate controlled asymmetric deformations.
Comparison of the properties of IPMC, SMA and EAC
This paper presents an introduction to ionic polymer-metal composites and some mathematical modeling pertaining to them. It further discusses a number of recent findings in connection with ion-exchange polymer-metal composites (IPMCS) as biomimetic sensors and actuators. Strips of these composites can undergo large bending and flapping displacement if an electric field is imposed across their thickness. Thus, in this sense they are large motion actuators. Conversely by bending the composite strip, either quasi-statically or dynamically, a voltage is produced across the thickness of the strip. Thus, they are also large motion sensors. The output voltage can be calibrated for a standard size sensor and correlated to the applied loads or stresses. They can be manufactured and cut in any size and shape. In this paper first the sensing capability of these materials is reported. The preliminary results show the existence of a linear relationship between the output voltage and the imposed displacement for almost all cases. Furthermore, the ability of these IPMCs as large motion actuators and robotic manipulators is presented. Several muscle configurations are constructed to demonstrate the capabilities of these IPMC actuators. This paper further identifies key parameters involving the vibrational and resonance characteristics of sensors and actuators made with IPMCS. When the applied signal frequency varies, so does the displacement up to a critical frequency called the resonant frequency where maximum deformation is observed, beyond which the actuator response is diminished. A data acquisition system was used to measure the parameters involved and record the results in real time basis. Also the load characterizations of the IPMCs were measured and it was shown that these actuators exhibit good force to weight characteristics in the presence of low applied voltages. Finally reported are the cryogenic properties of these muscles for potential utilization in an outer space environment of a few Torrs and temperatures of the order of - 140 degrees Celsius. These muscles are shown to work quite well in such harsh cryogenic environments and thus present a great potential as sensors and actuators that can operate at cryogenic temperatures.
We present a method to produce in-plane polarized piezo films with a freely adjustable ratio of the in-plane strain. They can be used in piezo bending actuators with a tunable curvature profile. The strains are obtained using a doubly interdigitated electrode structure that creates a polarization pattern with the appropriate mean strains and is demonstrated for several examples using PZT sheets. We further discuss how this tuning and the parameters of the electrode layout affect the overall magnitude of the displacement.
The problem of optimal placement of active members which are used for vibration control in adaptive truss structures is investigated. The control scheme is based on the method of eigenvalue assignment as a means of shaping the transient response of the controlled adaptive structures, and the minimization of required control action is considered as the optimization criterion. To this end, a performance index which measures the control strokes of active members is formulated in an efficient way. In order to reduce the computation burden, particularly for the case where the locations of active members have to be selected from a large set of available sites, several heuristic searching schemes are proposed for obtaining the near-optimal locations. The proposed schemes significantly reduce the computational complexity of placing multiple active members to the order of that when a single active member is placed.
Within the guide concept AROSYS (Adaptive Rotor Systems), the partners Eurocopter Deutschland (ECD), EADS München and Deutsches Zentrum für Luft- und Raumfahrt (DLR) developed active control technologies for helicopters. A trailing edge flap, direct twist and adaptive profile geometry system is investigated to reduce the rotor-induced vibrations and noise emissions and to expand the helicopter flight envelope. The advantageous effects of a profile geometry adaption in the form of a dynamical nose droop could be shown within the scope of unsteady Navier-Stokes simulations. Wind tunnel tests with the piezoelectric actuated trailing edge flap demonstrated the reliability and efficiency of the system. Its potential for vibration and noise reduction is compared with that of the direct twist concept and assessed on the basis of numerical rotor simulations.
This paper deals with different structuring methods for high temperature resistant nickel alloys. The ideal structured surface for a possible application on the blades of aeroengines combines high oxidation resistance with low drag in a hot gas flow. The effect of drag reduction due to riblet structured surfaces was originally inspired by shark scales, which have a drag reducing riblet structure. The necessary riblet sizes for effective drag reduction depend on the temperature, pressure and velocity of the flowing medium (gas or liquid). These riblet sizes were calculated for the different sections in an aeroengine. The riblets were successfully produced on a NiCoCrAlY coating by picosecond laser treatment. This method is suitable for larger structures within the range of some tens of micrometers. Furthermore, experiments were performed by depositing different materials through polymer and metal masks via electrodeposition and physical vapor deposition. All fabricated structures were oxidized at 900–1000 °C for up to 100 h to simulate the temperature conditions in an aeroengine. The resulting shape of the riblets was characterized using scanning electron microscopy. The most accurate structures were obtained by using photolithography with a subsequent electrodeposition of nickel. This method is suited for single digit micrometer structures. The reduction of the wall shear stress was measured in an oil channel. The riblet structures prior to oxidation showed a reduction of the wall shear stress of up to 4.9% compared to a normal smooth surface. This proves that the fabricated riblet design can be used as a drag reducing surface.
Activation ratio as a function of ply orientation.
Activation ratio with various substrate materials
DAP torque plate and fin geometry.
DAP torque fin mounted in wing tunnel undergoing ±22° Pitch deflections at 40 m S-1 airspeed.
Wind tunnel test data of aeroservoelastic DAP fin.
The development of an active aeroservoelastic missile fin using directionally attached piezoelectric (DAP) actuator elements is detailed. Several different types of actuator elements are examined, including piezoelectric polymers, piezoelectric fiber composites, and conventionally attached piezoelectric (CAP) and DAP elements. These actuator elements are bonded to the substrate of a torque plate. The root of the torque plate is attached to a fuselage hard point or folding pivot. The tip of the plate is bonded to an aerodynamic shell which undergoes a pitch change as the plate twists. The design procedures used on the plate are discussed. A comparison of the various actuator element shows that DAP elements provide the highest deflections with the highest torsional stiffness. A torque plate was constructed from 0.2032 mm thick DAP elements bonded to a 0.127 mm thick AISI 1010 steel substrate. The torque plate produced static twist deflections in excess of +/- 3 deg. An aerodynamic shell with a modified NACA 0012 profile was added to the torque plate. This fin was tested in a wind tunnel at speeds up to 50 ms/sec. The static deflection of the fin was predicted to within 6 percent of the experimental data.
The mathematical model of a flexible beam covered with shape memory alloy (SMA) layers is presented. The SMA layers are used as actuators, which are capable of changing their elastic modulus and recovery stress, thus changing the natural frequency of, and adjusting the excitation to, the vibrating beam. The frequency factor variation as a function of SMA Young's modulus, SMA layer thickness and beam thickness is discussed. Also control of the beam employing an optimal linear control law is evaluated. The control results indicate how the system reacts to various levels of excitation input through the non-homogeneous recovery shear term of the governing differential equation.
One field of work of the Institute of Flight Systems of the German Aerospace Center (DLR) is the investigation of flight characteristics of helicopters. For this task DLR operates the research helicopter FHS (Flying Helicopter Simulator/Type EC135) and a model helicopter wind tunnel test stand. The tail rotor of a helicopter has a significant impact on flight characteristics like vibration and noise. Sensors for the measurement of thrust, rotor speed, and pressure are already available. This paper presents a sensor for the acquisition of the flapping motion of the tail rotor. After an introduction and an explanation of the challenges of the measurement task, the mechanical and electrical integration of a smart and intelligent Hall sensor into the model test bed is described. Results from a wind tunnel test are discussed.
A linear ultrasonic motor was designed using a combination of the first longitudinal and the fourth bending mode. The motor consisted of a straight metal bar bonded with a piezo-ceramic element as a driving element. The resulting displacement was amplified by two teeth and transmitted by the frictional force between the motor and the rail in a linear motion. The basic design is discussed and simulations are compared with the experimental results.
Polycrystalline Bi1-xLaxFe1-xTixO3 (x = 0.000 – 0.250) ceramics were synthesized by the tartaric acid modified sol-gel technique. It was observed that the co-substitution of La & Ti at Bi & Fe sites in BiFeO3 suppresses the impurity phase formation which is a common problem in the bismuth ferrite ceramics. The quantitative crystallographic phase analysis of X-ray diffraction pattern by employing Rietveld technique was performed with the help of FULLPROF program which suggests the existence of compositional driven crystal structure transition from rhombohedral (space group R3c) to the orthorhombic (space group Pbnm) symmetry. The oxygen octahedral tilt angle was found to be ~13.82o for BiFeO3 (space group R3c) and decreases with the increase in co-substitution percentage. The structural transition breaks the spin cycloid structure in co-substituted BiFeO3 nanocrystallites and leads to canting of the antiferromagnetic spin structure. Hence, the remnant magnetization increases up to 10 % of co-substitution and becomes 22 times that of BiFeO3. However, it decreases for higher co-substitution percentage due to significant contribution from the collinear antiferromagnetic ordering in the orthorhombic crystal symmetry. The dielectric constant attains a maximum for 10% of co-substitution.
(Color in online) Schematic illustration of the composite bilayered magnetic elastomer in the form of a prism with 2-2 connectivity under an external magnetic field H 0 . 
(Color in online) Schematic presentation of the cross term R 1 ( H 2 ), which corresponds to the field lines generated by M 2 of layer 2 in the volume of layer 1 . 
(Color in online) Distribution of the magnetic poles at the prism boundaries. 
(Color in online) Geometrical illustration for the 4 different setups from Table 1. Upper row: Setups 1, 2, and 3; bottom row: Setup 4. 
Magnetic elastomers are appealing materials from an application point of view: they combine the mechanical softness and deformability of polymeric substances with the addressability by external magnetic fields. In this way, mechanical deformations can be reversibly induced and elastic moduli can be reversibly adjusted from outside. So far, mainly the behavior of single-component magnetic elastomers and ferrogels has been studied. Here, we go one step further and analyze the magnetoelastic response of a bilayered material composed of two different magnetic elastomers. It turns out that, under appropriate conditions, the bilayered magnetic elastomer can show a strongly amplified deformational response in comparison to a single-component material. Furthermore, a qualitatively opposite response can be obtained, i.e.\ a contraction along the magnetic field direction (as opposed to an elongation in the single-component case). We hope that our results will further stimulate experimental and theoretical investigations directly on bilayered magnetic elastomers, or, in a further hierarchical step, on bilayered units embedded in yet another polymeric matrix.
This paper introduces a new semi-flexible device able to turn thermal gradients into electricity by using a curved bimetal coupled to an electret-based converter. In fact, a two-steps conversion is carried out: (i) a curved bimetal turns the thermal gradient into a mechanical oscillation that is then (ii) converted into electricity thanks to an electrostatic converter using electrets in Teflon (r). The semi-flexible and low cost design of these new energy converters pave the way to mass production over large areas of thermal energy harvesters. Raw output powers up to 13.46uW per device were reached on a hot source at 60{\deg}C and forced convection. Then, a DC-to-DC flyback converter has been sized to turn the energy harvesters' raw output powers into a viable supply source for an electronic circuit (DC-3V). At the end, 10uW of directly usable output power were reached with 3 devices, which is compatible with Wireless Sensor Networks powering applications. Please cite as : S Boisseau et al 2013 Smart Mater. Struct. 22 025021 Available online at:
The feasibility of employing piezoceramic smart materials in active control of the higher harmonic vibration of hinged helicopter blades is investigated. The individual-blade-control concept is adopted to build feedback controllers that employ collocated smart sensors and actuators and are optimized to achieve damping augmentation for blade modes that significantly contribute to the airframe dynamic response. The results indicate that there is a parameter that will help the development of efficient smart rotors.
Integration of structures and functions allowed reducing electric consumptions of sensors, actuators and electronic devices. Therefore, it is now possible to imagine low-consumption devices able to harvest their energy in their surrounding environment. One way to proceed is to develop converters able to turn mechanical energy, such as vibrations, into electricity: this paper focuses on electrostatic converters using electrets. We develop an accurate analytical model of a simple but efficient cantilever-based electret energy harvester. Therefore, we prove that with vibrations of 0.1g (~1m/s^{2}), it is theoretically possible to harvest up to 30\muW per gram of mobile mass. This power corresponds to the maximum output power of a resonant energy harvester according to the model of William and Yates. Simulations results are validated by experimental measurements but the issues of parasitic capacitances get a large impact. Therefore, we 'only' managed to harvest 10\muW per gram of mobile mass, but according to our factor of merit, this puts us in the best results of the state of the art.
(a) Schematic of a cylindrical capacitor fiber preform featuring a spiralling multilayer comprising two conductive and two isolating films. The deep blue and light blue curves represent two conductive films, while red curves represent isolating LDPE films. (b) Schematic of a cylindrical capacitor fiber with two electrodes in the center. (c) Schematic of a rectangular preform prepared by encapsulating a zigzaging stack of two conductive and an isolating layer inside a rectangular PMMA tube. The deep blue and light blue curves represent conductive films, while the red curves represent isolating polycarbonate (PC) films.
A novel, highly flexible, conductive polymer-based fiber with high electric capacitance is reported. In its crossection the fiber features a periodic sequence of hundreds of conductive and isolating plastic layers positioned around metallic electrodes. The fiber is fabricated using fiber drawing method, where a multi-material macroscopic preform is drawn into a sub-millimeter capacitor fiber in a single fabrication step. Several kilometres of fibers can be obtained from a single preform with fiber diameters ranging between 500um -1000um. A typical measured capacitance of our fibers is 60-100 nF/m and it is independent of the fiber diameter. For comparison, a coaxial cable of the comparable dimensions would have only ~0.06nF/m capacitance. Analysis of the fiber frequency response shows that in its simplest interrogation mode the capacitor fiber has a transverse resistance of 5 kOhm/L, which is inversely proportional to the fiber length L and is independent of the fiber diameter. Softness of the fiber materials, absence of liquid electrolyte in the fiber structure, ease of scalability to large production volumes, and high capacitance of our fibers make them interesting for various smart textile applications ranging from distributed sensing to energy storage.
Fiber-optic balanced double-polarization Michelson interferometers with fringe-counting read-out using passive-quadrature demodulation are employed for remote sensing of the surface strain of plates made from carbon-fiber composites, which are screwed to the main wing spar of a Cessna C207A. Two series of flight tests have been performed with three different sensors. During parabolic flight maneuvers, quasistatic strain variations of up to 500 mu in are measured along with superimposed engine- and aerodynamically induced vibrations with strain amplitudes of 5 mu in at (sub-) harmonics of the engine speed (40 Hz), and compared with the read-out of a conventional resistive strain gauge.
The micromechanical generalized method of cells model is employed for the prediction of the effective moduli of electro-magneto-thermo-elastic composites. These include the effective elastic, piezoelectric, piezomagnetic, dielectric, magnetic permeability, electromagnetic coupling moduli, as well as the effective thermal expansion coefficients and the associated pyroelectric and pyromagnetic constants. Results are given for fibrous and periodically bilaminated composites.
Analysed boundary-value problems for a layered composite actuator in the conditions sketched in figure 1. 'Bvp A' is not reported.  
Performance of a bi-layered, charge-controlled layered actuator ('bvp A'), as a function of the layering angle and the contrast ratios r = m between the two phases ( ¯ ω 0 = ω 0 / µ b b , λ: longitudinal stretch). (a) θ 0 = 20 @BULLET , (b) θ 0 = 30 @BULLET ; in part (b) an electromechanical instability is induced for loading paths at high values of parameter r.  
Performance of a charge-controlled layered actuator with vanishing normal and shear tractions ('bvp B') for different stiffness and permittivity ratios.  
Thickening effect displayed by a charge-actuated layered composite ('bvp A'). For the parameters reported in the figure this effect is displayed for an initial layer inclination in the range 12.5 @BULLET < θ 0 < 42 @BULLET .  
Performance of a layered actuator with vanishing normal and shear tractions ('bvp B'). (a) λ–γ plot for different angles θ 0 , all deformation paths are valid for both types of actuation. (b) Undeformed and deformed configurations for a geometry with θ 0 = 65 @BULLET .  
This paper contains a thorough investigation of the performance of electrically activated layered soft dielectric composite actuators under plane deformation. Noting that the activation can be induced controlling either the voltage or the surface charge, the overall behaviour of the system is obtained via homogenization at large strains taking either the macroscopic electric field or the macroscopic electric displacement field as independent electrical variable. The performance of a two-phase composite actuator compared to that of the homogeneous case is highlighted for few boundary-value problems and for different values of stiffness and permittivity ratios between constituents being significant for applications, where the soft matrix is reinforced by a relatively small volume fraction of a stiff and high-permittivity phase. For charge-controlled devices, it is shown that some composite layouts admit, on one hand, the occurrence of pull-in/snap-through instabilities that can be exploited to design release-actuated systems, on the other, the possibility of thickening at increasing surface charge density.
The deflection characteristics of structures using directionally attached piezoelectric (DAP) and enhanced DAP (EDAP) elements are investigated analytically and experimentally. It is shown that directional attachment can be achieved by partial attachment, transverse shear lag, and differential stiffness bonding. The effective stiffnesses of DAP elements can be accurately modeled by an active element area estimation of partial attachment with a shear lag modification. Methods of integrating DAP and EDAP elements in missile wings and ways of alleviating such difficulties as control power degradation and adverse coupling are discussed.
Thanks to miniaturisation, it is today possible to imagine self-powered systems that use vibrations to produce their own electrical energy. Many energy-harvesting systems already exist. Some of them are based on the use of electrets: electrically charged dielectrics that can keep charges for years. This paper presents an optimisation of an existing system and proves that electret-based electrostatic energy scavengers can be excellent solutions to power microsystems even with low-level ambient vibrations. Thereby, it is possible to harvest up to 200\muW with vibrations lower than 1G of acceleration (typically 50\mumpp at 50Hz) using thin SiO2 electrets with an active surface of 1 cm^{2} and a mobile mass of 1g. This paper optimises such a system (geometric, electrostatic and mechanical parameters), using FEM (Finite Element Method) software (Comsol Multiphysics) and Matlab to compute the parameters and proves the importance of such an optimisation to build efficient systems. Finally, it shows that the use of electrets with high surface potential is not always the best way to maximise output power.
So far proposed quantum computers use fragile and environmentally sensitive natural quantum systems. Here we explore the notion that synthetic quantum systems suitable for quantum computation may be fabricated from smart nanostructures using topological excitations of a neural-type network that can mimic natural quantum systems. These developments are a technological application of process physics which is a semantic information theory of reality in which space and quantum phenomena are emergent.
The problem of vibration reduction of rotary wings in forward flight is studied using the concept of individual blade control. Smart structures are used as a means to construct geometric modal filters able to perform independent modal control of the critical modes in the rotating frame. A real time controller that could circumvent the inherent nonlinearities of the system and is intrinsically robust is devised.
With embedded sensors, the structures are capable of monitoring parameters at such critical locations not accessible to ordinary sensors. Recently, fiber optic sensor emerges as one promising technology to be integrated with structures. Embedding of fiber optic sensors into composites and some metals, especially those with low melting points, have been reported. However, all reported embedding techniques so far are either complicated or difficult to achieve coherent bonding with low residue stresses. Thus, it is of strong interest to pursue some economical ways to embed fiber optic sensors into metallic structures with low residue stresses. In this work, a new technique is proposed for embedding fiber optic sensor into metallic structures, such as nickel, with minimized residue stress. Fiber Bragg Grating (FBG) sensors have been embedded into nickel structures. Thermal performance of such embedded FBG sensor is studied. Higher temperature sensitivity is demonstrated for the embedded FBG sensors. For temperature measurements, the embedded FBG sensor yields an accuracy of about 2 C. Under rapid temperature changes, it is found that thermal stresses due to the temperature gradient in the metallic structures would be the main cause for errors.
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.
Ionic polymer-metal composites (IPMCs) form an important category of electroactive polymers and have many potential applications in biomedical, robotic and micro/nanomanipulation systems. In this paper, a nonlinear, control-oriented model is proposed for IPMC actuators. A key component in the proposed model is the nonlinear capacitance of the IPMC. A nonlinear partial differential equation (PDE), which can capture the fundamental physics in the IPMC, is fully considered in the derivation of nonlinear capacitance. A systems perspective is taken to get the nonlinear mapping from the voltage to the induced charge by analytically solving the nonlinear PDE at the steady state when a step voltage is applied. The nonlinear capacitance is incorporated into a circuit model, which includes additionally the pseudocapacitance due to the electrochemical adsorption process, the ion diffusion resistance, and the nonlinear DC resistance of the polymer, to capture electrical dynamics of the IPMC. With electromechanical coupling, the curvature output is derived based on the circuit model. The proposed model is formulated in the state space, which will be the starting point for nonlinear controller design. Experimental verification shows that the proposed model can capture the major nonlinearities in the electrical response of the IPMC.
This study analytically investigates the behavior of a coupled, unloaded/loaded actuator–mechanism system, which is the main element of a modern adaptive structure. The analysis is performed from an energy transfer perspective. It couples the actuator to a compliant mechanism and takes into account interactions between this mechanized system and an applied load. Analytical relationships are developed that describe energy transfer between the actuator and the mechanized structure. The methodology is general and can be applied to a myriad of loaded, adaptive structure systems. Results are consistent with existing energy based techniques and provide a fundamental insight into the behavior of adaptive structure systems. It is shown that the design of such a structure must consider the interaction between these basic elements. This body of work extends existing research by developing a methodology that can be used to optimize a mechanized structure based on interactions between its driving actuator and its external load.
(1 − x)(Ni0.8Zn0.1Cu0.1)Fe2O4/x0.48Pb(Ni1/3Nb2/3)O3–0.02Pb(Zn1/3Nb2/3)O3–0.05Pb(Ni1/2W1/2)O3–0.45PbTiO3 ((1 − x)NZCF/xPNZNWT) magnetoelectric particulate ceramic composites were prepared by the conventional solid-state reaction method via a low-temperature sintering process. X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) observation confirm that ferrite and piezoelectric phases coexist in the sintered particulate composites. With the addition of sintering aids, densified ceramic composites can be prepared by the low-temperature sintering technique, which can improve the dielectric properties of the synthesized (1 − x)NZCF/xPNZNWT composites. The (1 − x)NZCF/xPNZNWT composites exhibit typical P–E hysteresis loops, where remnant polarization Pr decreases and coercive field Ec increases accompanied by the decrease of piezoelectric constant d33 with the increase of the ferrite phase incorporated into the composites. Although a magnetoelectric (ME) voltage coefficient of just 7.34 mV (cm Oe) − 1 is obtained in the 0.2NZCF/0.8PNZNWT composite, it is expected to be comparable to that of the reported bulk composites when the magnitude of the ac magnetic field increases and the frequency of the ac magnetic field increases to the resonant frequency of the piezoelectric phase.
This paper reports on direct thermal to electrical energy conversion by performing the Olsen (or Ericsson) cycle on [001]-poled 0.945PbZn1/3Nb2/3O3–0.055PbTiO3 (PZN-5.5PT) single crystals. The cycle consists of two isothermal and two constant electric field processes. The energy density was found to decrease with increasing cycle frequency while the power density increased. The maximum energy density obtained was 150 J/l/cycle for temperatures between 100 and 190 °C and electric field between 0 and 1.2 MV m−1 at frequency 0.034 Hz. The maximum power density reached 11.7 W l−1 at 0.1 Hz for temperatures between 100 and 190 °C and electric fields between 0.2 and 1.5 MV m−1. Moreover, the dielectric constant and saturation polarization of PZN-5.5PT are reported for the first time at 0.1 Hz for temperatures between 100 and 190 °C. Finally, the experimental results agree relatively well with predictions by a recently developed temperature-dependent property model already validated with PMN-32PT. Inter-sample variability and sample durability are also discussed.
The magnetoelectric composites (1 − x){Ba0.92(Bi0.5Na0.5)0.08TiO3}−xNi0.65Zn0.35Fe2O4 (BNBT−NZF) for x = 0, 0.1, 0.2, 0.3 and 0.4 were synthesized by solid state reaction methods to study their structural, dielectric and magnetic properties. Powder x-ray diffraction (XRD) indicates a mixed phase of composites with a spinel phase for NZF and a perovskite phase for BNBT. The microstructural analysis shows dense structure with some porosity. The dielectric and magnetic properties of the composite ceramics were enhanced with an increase in ferrite (NZF) content. In the ferroelectric study, the values of remnant polarization, 2Pr, decrease with an increase in NZF content. The presence of a magnetodielectric property depicts the magnetoelectric coupling at room temperature; the highest value of magnetodielectric was found to be 2.89% for a 40% addition of NZF. The optical band gap of the composites was calculated using diffuse reflectance spectroscopy. The band gap was found to decrease with the addition of NZF, which makes these materials promising candidates for photocatalysis.
The general orientation dependence of the intrinsic converse longitudinal piezoelectric constant dnnf in an epitaxial rhombohedral film is calculated by taking into account the effect of substrate clamping. Theoretical predictions are made for dnnf of epitaxial 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 rhombohedral films, which are compared with experimental results on pseudo-cubic (001), (110) and (111) orientations.
A comparative study on the effective piezoelectric properties and hydrostatic piezoelectric response is first carried out for advanced 2–2 composites based on single crystals of relaxor-ferroelectric solid solutions. Different orientations of domains and different poling directions of components are taken into consideration in the analysis of the effective longitudinal piezoelectric coefficients d33*, e33*, g33* and hydrostatic piezoelectric coefficients dh*, eh* and gh*. The important role of the polarization orientation effect and the effect of combination of the electromechanical properties in attaining the large effective parameters is shown for the parallel-connected 2–2 single-domain 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3/polyvinylidene fluoride composite. In particular, near extremum points of the effective parameters, this composite is characterized by the piezoelectric coefficients g33*≈500 mV m N−1, |dh*|≈400 pC N−1, |eh*|≈40 C m−2, and gh*≈400 mV m N−1. Three piezo-sums are first found to describe major contributions of the piezoelectric coefficients dij*, eij* and gij* to dh*, eh* and gh*, respectively, in the vicinity of absolute maxima (minima) of the aforementioned hydrostatic parameters. Advantages concerned with the presence of the single crystal (either single-domain or polydomain) in the studied 2–2 composites are discussed in connection with their piezoelectric activity, sensitivity and hydrostatic response.
This study reports the various physical properties of (1 − x)(0.3CoFe2O4-0.7BiFeO3)-xBaTiO3 composites (equivalently denoted as 0.3CFO-0.7BFO/BT) with the compositions x = 0, 0.30, 0.35, 0.40 and 1.0. The composites are synthesized through a hybrid processing technique in which 0.3CFO–0.7BFO is prepared through a sol-gel process, and BT is processed through a solid state reaction method. Subsequently, the effects of the addition of BT on the structural, dielectric, magnetic and magneto-dielectric properties of 0.3CFO–0.7BFO have been investigated for various BT concentrations. The Rietveld refinement analysis of x-ray diffraction patterns reveals the structural distortion in the BFO phase with the addition of BT, while no such distortion has been observed for the CFO phase. Energy dispersive spectroscopy confirms the presence of two types of grains that correspond to the 0.3CFO–0.7BFO and BT phases in field emission scanning electron micrographs of the composites. Improved dielectric properties have been observed, which are associated with the improved density of composites with the addition of BT. Measurements of the magnetic and ferroelectric hysteresis loops at room temperature indicate that the composites exhibit ferroelectricity and ferromagnetism simultaneously at room temperature. An increase of the electric polarization has been observed due to structural distortion arising with the addition of BT. The significant dependence of the dielectric constant on the magnetic field has been observed in the prepared composites. The highest value of the magneto-dielectric response (3.2%) has been observed for a 40 mol% addition of BT.
A modelling framework that incorporates the peculiarities of microstructural features, such as the spatial correlation of crystallographic orientations and morphological texture in piezoelectrics, is established. The mathematical homogenization theory of a piezoelectric medium is implemented using the finite element method by solving the coupled equilibrium electrical and mechanical fields. The dependence of the domain orientation on the macroscopic electromechanical properties of crystalline as well as polycrystalline ceramic relaxor ferroelectric 0.58Pb(Mg1/3Nb2/3)O3–0.42PbTiO3 (PMN–42% PT) is studied based on this model. The material shows large anisotropy in the piezoelectric coefficient ejK in its crystalline form. The homogenized electromechanical moduli of polycrystalline ceramic also exhibit significantly anisotropic behaviours. An optimum texture at which the piezoceramic exhibits its maximum longitudinal piezoelectric response is identified.
The magnetoelectric (ME) effect in magnetoelectric composites is an induced electric polarization in response to an applied magnetic field and magnetization in response to an applied electric field. The individual phases NiFe2O4 (NFO), Pb(Mg1/3Nb2/3)0.67Ti0.33O3 (PMN-PT) and composites of (x) NFO+(1−x) PMN-PT with x = 0.15, 0.30 and 0.45 were prepared using a solid-state reaction technique. The presence of NFO and PMN-PT was confirmed using x-ray diffraction. Scanning electron microscopy (SEM) images were used to study the microstructure of the composites. The connectivity scheme present in the ME composites was investigated from the microscope images. The connectivity scheme changes with change in the NFO content in the composites. A ferroelectric hysteresis loop (at 50 Hz) was obtained and studied at room temperature. Variation of the dielectric constant with temperature for all the composites was studied in the range 300–925 K. Here we report the effect of NFO mole fraction on connectivity schemes between NFO and PMN-PT grains, % porosity, magnetoelectric and magneto-dielectric effects in NFO/PMN-PT composites. The maximum value of the magnetoelectric voltage coefficient, 10.43 mV cm−1 Oe−1, was obtained for 0.15 NFO+0.85 PMN-PT composites. The maximum value of the magneto-dielectric coefficient, 4.54, was obtained for 0.15 NFO+0.85 PMN-PT composites.
The shape-memory effect (SME) is demonstrated to occur for the solid solution of lead magnesium niobate with lead titanate for the molar ratio 70:30. Since the material is an insulator, it was possible to apply an electric field to influence and investigate the SME. It is shown that electric field can be used for enhancing the shape strain produced by the bending load, although some fraction of the shape strain becomes irrecoverable on repeated SME cycling under the combined effects of mechanical and electric loads. An explanation is offered for this and other observations, invoking the relaxor-ferroelectric nature of the ceramic. Such materials have potential for use as 'actuators with a memory' in smart structures.
Surface-energy-induced selective grain growth has been used to increase the presence of preferred planes in polycrystalline ternary Fe–Ga based alloys and thereby maximize the magnetostrictive performance of these alloys. In this study, alloys were either doped with elemental sulfur or annealed under sulfur atmospheres to control the sulfur concentration on the surface of samples during annealing. We show that the segregation of sulfur, which is known to play an important role in controlling surface energy, can be correlated to the selective growth of {001} grains and an increase in the saturation magnetostriction of the samples. The results show that sulfur atoms are adsorbed (diffused) from the sulfur atmosphere (bulk interior) and segregate on the sample surface. The correlation between surface chemistry, texture development and magnetostriction is presented. The formation of {001} grains occurred under slight surface segregation of sulfur, i.e. at levels of concentration of surface sulfur between 0.5 and 1.35 at.%, for alloys of (Fe0.813Ga0.187)99B1 and (Fe0.813Ga0.187)99.5B0.5 doped with 50 ppm S. In the case of (Fe0.81Ga0.19)99(NbC)1 alloy annealed under a H2S atmosphere, abnormal growth of (001) grains resulted in 88.3% of the sample area being covered with a (001) grain.
Top-cited authors
Fabrizio Scarpa
  • University of Bristol
Wieslaw Jerzy Staszewski
  • AGH University of Science and Technology in Kraków
Gyuhae Park
  • Chonnam National University
Charles Farrar
  • Los Alamos National Laboratory
Jinlian Hu
  • The Hong Kong Polytechnic University