Showing papers on "Smart material published in 2011"

Magnetorheological fluids: a review

Abstract: Magnetorheological (MR) materials are a kind of smart materials whose mechanical properties can be altered in a controlled fashion by an external magnetic field. They traditionally include fluids, elastomers and foams. In this review paper we revisit the most outstanding advances on the rheological performance of MR fluids. Special emphasis is paid to the understanding of their yielding, flow and viscoelastic behaviour under shearing flows.

Colorimetric biosensing using smart materials.

Abstract: In recent years, colorimetric biosensing has attracted much attention because of its low cost, simplicity, and practicality. Since color changes can be read out by the naked eye, colorimetric biosensing does not require expensive or sophisticated instrumentation and may be applied to field analysis and point-of-care diagnosis. For transformation of the detection events into color changes, a number of smart materials have been developed, including gold nanoparticles, magnetic nanoparticles, cerium oxide nanoparticles, carbon nanotubes, graphene oxide, and conjugated polymers. Here, we focus on recent developments in colorimetric biosensing using these smart materials. Along with introducing the mechanisms of color changes based on different smart materials, we concentrate on the design of biosensing assays and their potential applications in biomedical diagnosis and environmental monitoring.

Bioinspired Tunable Lens with Muscle-Like Electroactive Elastomers

Abstract: Optical lenses with tunable focus are needed in several fields of application, such as consumer electronics, medical diagnostics and optical communications. To address this need, lenses made of smart materials able to respond to mechanical, magnetic, optical, thermal, chemical, electrical or electrochemical stimuli are intensively studied. Here, we report on an electrically tunable lens made of dielectric elastomers, an emerging class of “artificial muscle” materials for actuation. The optical device is inspired by the architecture of the crystalline lens and ciliary muscle of the human eye. It consists of a fluid-filled elastomeric lens integrated with an annular elastomeric actuator working as an artificial muscle. Upon electrical activation, the artificial muscle deforms the lens, so that a relative variation of focal length comparable to that of the human lens is demonstrated. The device combined optical performance with compact size, low weight, fast and silent operation, shock tolerance, no overheating, low power consumption, and possibility of implementation with inexpensive off-the-shelf elastomers. Results show that combing bioinspired design with the unique properties of dielectric elastomers as artificial muscle transducers has the potential to open new perspectives on tunable optics.

Hierarchical Mesoporous Films: From Self-Assembly to Porosity with Different Length Scales

Abstract: Hierarchical porous films are formed by interconnected pores of different dimensions, and are particularly attractive for the development of smart materials with multiple functions and enhanced transport properties. We have focused this review on hierarchical porous films whose synthesis, at least at one scale of porosity, is based on self-assembly. Several strategies have been proposed for the preparation of hierarchical porous films which for bulks and monoliths are more difficult to obtain. These materials represent a step further in the fabrication of complex materials through self-assembly, and achieving order through templating routes at different length scales is the ultimate goal.

Electrically Adjustable, Super Adhesive Force of a Superhydrophobic Aligned MnO2 Nanotube Membrane

Abstract: A superhydrophobic membrane of MnO2 nanotube arrays on which a water droplet can be immobilized by application of a small DC bias, despite a large contact angle, is reported. For a 3 mu L water droplet, the measured adhesive force increases monotonically with increasing negative voltage, reaching a maximum of 130 mu N at 22 V, 25 times the original value. It follows that the nearly spherical water droplet can be controllably pinned on the substrate, even if the substrate is turned upside down. Moreover, the electrically adjustable adhesion is strongly polarity-dependent: only a five-fold increase is found when a positive bias of 22 V is applied. This remarkable electrically-controlled adhesive property is ascribed to the change in contact geometry between the water droplet and MnO2 nanotube array, on which water droplets exhibit the different continuities of three-phase contact line. As the modulation in this manner is in situ, fast, efficient and environmentally-friendly, this kind of smart material with electrically adjustable adhesive properties has a wide variety of applications in biotechnology and in lab-on-chip devices.

A novel technique for optimal placement of piezoelectric actuators on smart structures

Abstract: The problem of positioning of actuators and sensors on smart materials has been a point of interest in recent years. This is due to the fact that in many practical applications there are limitations in space, weight, etc. of the smart structures, which make the problem of positioning more complex. In addition, it is required that the actuators/sensors have the best possible performance. The development of smart structures technology in recent years has provided numerous opportunities for vibration control applications. The use of piezoelectric ceramics or polymers has shown great promise in the development of this technology. The employment of piezoelectric material as actuators in vibration control is beneficial because these actuators only excite the elastic modes of the structures without exciting the rigid-body modes. This is important since very often only elastic motions of the structures are needed to be controlled. The purpose of this paper is to introduce a novel approach developed for optimizing the location of piezoelectric actuators for vibration suppression of flexible structures. A flexible fin with bonded piezoelectric actuators is considered in this study. The frequency response function (FRF) of the system is then recorded and maximization of the FRF peaks is considered as the objective function of the optimization algorithm to find the optimal placement of the piezoelectric actuators on the smart fin. Three multi-layer perceptron neural networks are employed to perform surface fitting to the discrete data generated by the finite element method (FEM). Invasive weed optimization (IWO), a novel numerical stochastic optimization algorithm, is then employed to maximize the weighted summation of FRF peaks. Results indicate an accurate surface fitting for the FRF peak data and an optimal placement of the piezoelectric actuators for vibration suppression is achieved.

Seismic Performance Analysis of A Smart Base-isolation System Considering Dynamics of MR Elastomers

Abstract: This article investigates a smart base-isolation system using magnetorheological (MR) elastomers, which are a new class of smart materials whose elastic modulus or stiffness can be adjusted dependi...

Smart materials in dentistry

Abstract: Most dental materials are designed to have a relatively 'neutral' existence in the mouth. It is considered that if they are 'passive' and do not react with the oral environment they will be more stable and have a greater durability. At the same time, it is hoped that our materials will be well accepted and will cause neither harm nor injury. This is an entirely negative approach to material tolerance and biocompatibility and hides the possibility that some positive gains can be achieved by using materials which behave in a more dynamic fashion in the environment in which they are placed. An example of materials which have potential for 'dynamic' behaviour exists with structures which are partly water-based or have phases or zones with significant water content and for which the water within the material can react to changes in the ambient conditions. Such materials may even be said to have the potential for 'smart' behaviour, i.e. they can react to changes in the environment to bring about advantageous changes in properties, either within the material itself or in the material-tooth complex. The controlled movement of water or aqueous media through the material may cause changes in dimensions, may be the carrier for various dissolved species, and may influence the potential for the formation of biofilms at the surface. Some of these issues may be closely interrelated. Clearly, materials which do not have the capacity for water transport or storage do not have the potential for this sort of behaviour. Some materials which are normally resistant to the healthy oral environment can undergo controlled degradation at low pH in order to release ions which may prove beneficial or protective. It is doubtful whether such behaviour should be classified as 'smart' because the material cannot readily return to its original condition when the stimulus is removed. Other materials, such as certain alloys, having no means of transporting water through their structure, can display smart behaviour by undergoing predictable changes in structure in response to applied mechanical or thermal stimuli. It has been difficult to harness such behaviour to the benefit of patients but progress in this area is slowly being made.

Physically responsive field-effect transistors with giant electromechanical coupling induced by nanocomposite gate dielectrics.

Abstract: Physically responsive field-effect transistors (physi-FETs) that are sensitive to physical stimuli have been studied for decades. The important issue for separating the responses of sensing materials from interference by other subcomponents in a FET transducer under global physical stimuli has not been completely resolved. In addition, challenges remain with regard to the design and employment of smart materials for flexible physi-FETs with a large electro-physical coupling effect. In this article, we propose the direct integration of nanocomposite (NC) gate dielectrics of barium titanate (BT) nanoparticles (NPs) and highly crystalline poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) into flexible organic FETs to achieve a large electro-physical coupling effect. Additionally, a new alternating current biasing method is proposed for precise extraction and quantification of tiny variations in the remnant polarization of NCs caused by mechanical stimuli. An investigation of physi-FETs under static mechanical stimuli revealed the first ever reported giant, positive piezoelectric coefficients of d(33) up to 960 pC/N in the NCs. The large coefficients are presumably due to the significant contributions of the intrinsic positive piezoelectricity of the BT NPs and P(VDF-TrFE) crystallites.

Equivalent electro-elastic properties of Macro Fiber Composite (MFC) transducers using asymptotic expansion approach

Abstract: This paper aims to model and compute the effective electro-mechanical properties of Macro Fiber Composite (MFC) transducers using the Asymptotic Expansion Homogenization (AEH) method. The AEH method is commonly used to solve problems involving physical phenomena on continuous media with periodic micro-structures. In particular, the AEH is a useful technique to study the behaviour of structural components built with composite materials. The obtained results are satisfactory when compared with those obtained using the Periodic Homogenization Method (PHM) as well as with the experimental results available from the literature.

Composition-Dependent Basics of Smart Heusler Materials from First- Principles Calculations

Abstract: The structural and magnetic order are the decisive elements which vastly determine the properties of smart ternary intermetallics such as X2YZ Heusler alloys. Here, X and Y are transition metal elements and Z is an element from the III-V group. In order to give a precise prescription of the possibilities to optimize the magnetic shape memory and magnetocaloric effects of these alloys, we use density functional theory calculations. In particular, we outline how one may find new intermetallics which show higher Curie and martensite transformation temperatures when compared with the prototypical magnetic shape-memory alloy Ni2MnGa. Higher operation temperatures are needed for technological applications at elevated temperatures.

Membrane-based biomolecular smart materials

Abstract: Membrane-based biomolecular materials are a new class of smart material that feature networks of artificial lipid bilayers contained within durable synthetic substrates. Bilayers contained within this modular material platform provide an environment that can be tailored to host an enormous diversity of functional biomolecules, where the functionality of the global material system depends on the type(s) and organization(s) of the biomolecules that are chosen. In this paper, we review a series of biomolecular material platforms developed recently within the Leo Group at Virginia Tech and we discuss several novel coupling mechanisms provided by these hybrid material systems. The platforms developed demonstrate that the functions of biomolecules and the properties of synthetic materials can be combined to operate in concert, and the examples provided demonstrate how the formation and properties of a lipid bilayer can respond to a variety of stimuli including mechanical forces and electric fields.

Control of torsional rotor vibrations using an electrorheological fluid dynamic absorber

Abstract: Torsional rotor vibrations are undesirable phenomena which are very difficult to control in rotating systems. A common method for reducing vibrations involves the use of dynamic absorbers. However, if their physical parameters are constant, the frequency range of efficiency of dynamic absorbers is tight, making them unsuitable for systems with variable speeds. The use of smart materials, due to their variable and controllable mechanical properties, may be a powerful tool for increasing the frequency range. Electrorheological (ER) fluids are attractive materials that undergo very fast reversible changes in their rheological properties upon the application of an electric field. In this study, an electrorheological dynamic torsional absorber, called the Smart ER Dynamic Absorber, has been designed in order to reduce torsional rotor vibrations. Under shear mode, the ER absorber can exhibit various torsional damping and stiffness characteristics when an electric field is applied. A nonlinear empirical model of...

A Novel Concept for Strain Sensing Based on the Ferromagnetic Shape Memory Alloy NiMnGa

Abstract: This paper reports on a novel approach of using magnetic shape memory (MSM) alloys as smart materials in mechanical sensing. The presented concept enables the measurement of tensile strain. The underlying sensor mechanism is based on the reorientation of the martensite variants of the tetragonal unit cell of the MSM alloy (MSMA) which can be induced by either a magnetic field or a mechanical stress. In the novel concept, a magnetic bias field exerts a restoring force opposing the externally applied mechanical stress. The magnetic stray field at the rim of an MSMA sample, measured using a conventional Hall sensor, is used as the sensor signal. The operating principle was experimentally verified using a custom-made tensile test setup. A linear dependence of the magnetic flux density of the stray field on the mechanical strain was observed.

Nonlinear strain–electric field relationship of carbon nanotube buckypaper/Nafion actuators

Abstract: Due to their large electric field-induced strains and flexibility, carbon nanotube thin film or buckypaper/Nafion actuators can be used in various applications, such as lightweight, low power consuming electroactive materials for morphing structures. However, this material is very new, and only limited studies have been devoted to characterizing and understanding their electromechanical couplings. This paper reports on the study of the conversion mechanism and determination of the current flowing through buckypaper/Nafion actuators driven by electric fields. Experimental results revealed that the saturation of the electrically induced strains of the actuator were due to nonlinear characteristics between the electric field and electric charge behaviours. Moreover, by modeling the electric charge changes versus electric fields, we are able to calculate the strain and current versus electric fields of the actuators. The predicted values were in good agreement with the experimental data. The efficiency of the conversion was calculated and demonstrated to determine the potential of CNT buckypaper/Nafion actuators for smart structure applications.

Non-linear response of dipolar colloidal gels to external fields

Abstract: Dipolar colloids can be made to gel by forming a reversible but persistent network of chain-like aggregates at very low volume fractions. Using the model of charged soft dumbbells in molecular dynamics simulations, we find that, under the effect of an external electric field, this gel displays a highly non-linear dielectrical susceptibility. We show that the latter is caused by a switch from a network to a structure of bundling chains when the field is strong enough. Such dramatic structural transformation upon applying external fields could allow to control the mechanical and dielectric response of these complex fluids, pointing to new applications of dipolar colloids as smart materials.

Digital fabrication of smart structures and mechanism: Creative applications in art and design

Abstract: A peer-reviewed conference paper given at the Digital Fabrication: methods, tooling and processes panel at the Digital Fabrication 2011 Conference, NIP 27, 27th International Conference on Digital Printing Technologies. This paper describes the design and fabrication of novel “soft” structures and mechanisms employing “smart” shape-changing materials. These structures and mechanisms incorporate shape memory alloy (SMA) micro-actuators, enabling them to exhibit lifelike movement when stimulated by the application of electric current. Fabricated by 3D printing in a soft elastomer material, their design includes internal channels into which the SMA actuators are easily mounted. Other design features allow flexibility of movement and facilitate cooling of the SMA actuators. A tentacle-like active structure is described, which incorporates an antagonistic pair of SMA microactuators, allowing it to exhibit two-way motion. Results are presented for the speed and range of motion of the tentacle-like structure. The paper goes on to describe a creative arts application for smart active structures and mechanisms which exploits the technologies under investigation: an interactive puppet which exhibits lifelike, expressive movement. This research in digital fabrication and smart materials has implications for the fields of interactive and robotic art and design, soft robotics and physical computing.

Highly piezoresistive textiles based on a soft conducting charge transfer salt

Abstract: The integration of smart materials into human wearable interfaces is a current topic of interest. This paper reports the integration into a polyester textile of a bi-layer (BL) film based on a polymeric matrix containing a top-layer of a microcrystalline network of an organic conductor. The resulting textiles, in addition to be conducting, exhibit the excellent strain sensing properties of BL films maintaining at the same time their flexibility.

Smart Control Systems for Smart Materials

Abstract: Shape memory alloys (SMAs) are thermally activated smart materials. Due to their ability to change into a previously imprinted shape by the means of thermal activation, they are suitable as actuators for microsystems and, within certain limitations for macroscopic systems. Most commonly used SMAs for actuators are binary nickel-titanium alloys (NiTi). The shape memory effect relies on the martensitic phase transformation. On heating the material from the low temperature phase (martensite) the material starts to transform into the high temperature phase (austenite) at the austenite start temperature (A s). The reverse transformation starts at the martensite start temperature after passing a hysteresis cycle. To apply these materials to a wide range of industrial applications, a simple method for controlling the actuator effect is required. Today’s control concepts for shape memory actuators, in applications as well as in test stands, are time-based. This often leads to overheating after transformation into the high temperature phase which results in early fatigue. Besides, the dynamic behavior of such systems is influenced by unnecessary heating, resulting in a poor time performance. To minimize these effects, a controller system with resistance feedback is required to hold the energy input on specific keypoints. These two key points are directly before transformation (A s) and shortly before retransformation (M s). This allows triggering of fast and energy-efficient transformation cycles. Both experimental results and a mechatronical demonstrator system, exhibit the advantages of systems concerning efficiency, dynamics, and reliability.

Experimentally validated improvement of IPMC performance through alternation of pretreatment and electroless plating processes

Abstract: It has been known for years that polymers can be stimulated to change shapes and sizes. Electro-active polymers (EAPs) have recently been spotlighted in biomimetic applications due to the properties of energy transduction from the electrical to the mechanical form for actuation. Ionic polymer metal composites (IPMCs) are a type of ionic EAP and considered to be one of the most promising smart materials. IPMCs are light in weight, chemically stable, fast responding and can make large bending deformations under low driving voltages. This study focuses on the fabrication method and performance of IPMCs by using Nafion? films. Tip force optimization is determined by using the Taguchi design of experiment technique.

A review of mechanically reconfigurable antennas using smart material actuators

Abstract: Mechanically reconfigurable antennas have the potential to provide a large range of antenna reconfiguration and to have a lower cost than other reconfigurable technologies. Solid state devices in the RF signal path can cause distortion and power limiting, but such issues can be averted by keeping them out of the direct RF signal path. In this paper, new smart material technologies, namely electro-active polymers and shape memory alloy actuators, are presented as potential candidates to implement mechanically reconfigurable antennas. A review of some proof-of-concept reconfigurable antenna prototypes using these technologies is presented, including the advantages and disadvantages for the antenna applications.

Smart Composites With Short Ferromagnetic Microwires for Microwave Applications

Abstract: Smart composites with short-cut Co68.7Fe4Ni1B13Si11Mo2.3 microwires were prepared and studied in terms of their microwave tunable properties. It is shown that the frequency dependence of effective permittivity relaxes with the application of magnetic field till around the anisotropy field of the microwire due to the increase of internal losses. There exists a significant field tunable effect in the transmission and reflection spectra, featured as a resonance-relaxation transformation; a step-like shift of reflection phase was also observed with increasing applied magnetic field, which can be exploited especially for the sensing applications such as field/stress monitoring. Notably, with increasing microwire concentration from 0.06 cm-2 to 0.24 cm-2 , the microwave absorption is more than doubled; the reflection phase shift corresponding to the magnetic field change from 500 to 1000 A/m is also increased from 1.2 to 1.3. These results indicate that the developed short-wire composites have the potential for microwave absorption and remote sensing applications.

Towards programmable smart materials: Dynamical reconfiguration of emergent transport networks

Abstract: Smart materials promise adaptive morphology and functionality of materials, however, controlling the desired pattern formation using simple and local bottom-up interactions is a difficult task, but one which living organisms appear to manage effortlessly. We have previously demonstrated a virtual material inspired by the slime mould Physarum polycephalum which, from simple interactions within a swarm based particle collective, forms complex emergent transport networks. One desired characteristic of smart materials is that they should be programmable, adapting their structure in response to external stimuli. As a step towards this aim we suggest a prototype method to dynamically reconfigure emergent transport networks, based on real-time network analysis of the current configuration and feedback via dynamic adjustment of network node weights. The analysis method utilises a novel collective memory of previous network history which is used to provide connectivity information to control a feedback method to the network nodes. Although simple in operation, the feedback method utilises complex neural network-like control including excitation, inhibition and refractory dynamics. The transitions of the reconfiguration method are analysed and high level motifs and transitions are described. We suggest how the dynamical reconfiguration method may be used as a spatially represented unconventional computing method for combinatorial optimisation problems including the Euclidean Travelling Salesman Problem. We conclude by discussing limitations and possible improvements to the dynamical reconfiguration method and exploring the potential advantages of exploring low-level and indirect methods of influence on smart materials.

Numerical Simulation of Hybrid Composite Shape-Memory Alloy Wire-Embedded Structures

Abstract: The large recovery force and non-linear deformation behaviour resulting from a change in the temperature in shape-memory alloys (SMAs) make them attractive materials for applications in smart materials and structures, as well as actuators. However, SMAs are limited in their application because they cannot support general loads such as bending or compression. SMA wire-embedded composite materials, where materials such as glass fibre reinforced plastics (GFRPs) are combined with SMAs, are proposed to overcome these limitations. However, the increased stiffness of GFRPs limits the deformation that can be achieved. The inclusion of more compliant materials, such as silicon rubber, into the matrix can improve the achievable deformation, and the characteristics of the resulting hybrid composite can be controlled by varying the conformation of the material. In this study, a numerical simulation method was developed to predict the deformation behaviour of SMA wire-embedded hybrid composites. To verify the simulat...

Optimization of surface-actuated piezocomposite variable-camber morphing wings: ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2011

Abstract: A theoretical, two-dimensional, static-aeroelastic design, modeling and optimization of a variable-camber morphing airfoil that employs surface-induced forces via smart material actuators is presented. The structural parameters of the airfoil, mainly the substrate features, are determined using a Genetic Algorithm optimization technique. A coupled treatment of the fluid-structure interaction is employed which allows the realization of a design that is not only feasible in a bench top experiment, but that can also sustain aerodynamic loads in the wind tunnel. The substrate is assumed to be a carbon nanotube reinforced composite whose constitutive response is obtained by means of a homogenization-based multi-scale finite element model. A separate parametric study on different geometric configurations of representative volume elements is carried out for the description of the substrate material. The analyzed representative volume elements consist of a single wall carbon nanotube embedded in a soft polymer matrix.Copyright © 2011 by ASME