This PDF file contains the front matter associated with SPIE Proceedings volume 7642, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Bionic technology involves the efficient integration of biology and electronics and is providing the basis for significant improvements in a number of medical treatments. The use of organic conducting polymers to provide a compatible multifunctional platform to interface the world of biology and electronics has attracted an increasing amount of attention over the past 15 years. This paper will discuss advances being made in the development of organic bionics and their application to improved health strategies.

Refreshable Braille can help visually impaired persons benefit from the growing advances in computer technology. The development of such displays in a full screen form is a great challenge due to the need to pack many actuators in small area without interferences. In recent years, various displays using actuators such as piezoelectric stacks have become available in commercial form but most of them are limited to one line Braille code. Researchers in the field of electroactive polymers (EAP) investigated methods of using these materials to form full screen displays. This manuscript reviews the state of the art of producing refreshable Braille displays using EAP-based actuators.

The authors present the worldwide need for electronic Braille displays to promote literacy among the blind. The use of of EAP's to produce Braille displays is encouraged and detailed descriptions of the technology of Braille are presented. Prior art is covered since the early 1950's through present day displays based mostly on piezoelectric technologies. EAP's offer the promise of the "Holy Braille", the ability to display a full page of Braille electronically. Details on "how not to make a Braille display" are covered in prior art.

Scavenging energy from human motion is a challenge to supply low consumption systems for sport or medical applications. A promising solution is to use electroactive polymers and especially dielectric polymers to scavenge mechanical energy during walk. In this paper, we present a tubular dielectric generator which is the first step toward an integration of these structures into textiles. For a 10cm length and under a strain of 100%, the structure is able to scavenge 1.5μJ for a poling voltage of 200V and up to 40μJ for a poling voltage of 1000V. A 30cm length structure is finally compared to our previous planar structure, and the power management module for those structures is discussed.

Structures demonstrating the viability of both the hydraulic and latching Braille dot, and the dielectric elastomer fiber Braille dot have been fabricated and characterized. A hydraulic proof-of-concept structure has achieved the necessary volumetric change required to lift a Braille dot over 0.5mm at voltages under 1000V and at speeds under 100ms. Long bimorphs have been fabricated that demonstrate large tip displacements over 2mm that could be used to mechanically latch the Braille rod in the 'up' position to achieve the force requirement. The addition of radial prestrain in dielectric elastomer tubes has reduced the wall thickness and directed the strain in the axial direction which has had a dramatic impact on their resulting characteristics. The required bias voltage for the dielectric elastomer fiber Braille dot has been reduced from 15.5kV to 8.75kV while the Braille head tip displacement of a fabricated prototype has almost tripled on average and now also exceeds the required displacement for a refreshable Braille display. Finally, potential solutions to the current shortcomings of both designs in meeting all of the requirements for such a display are discussed.

Piezoceramic actuators, presently used in commercial Braille displays, are limited by the material's relatively small strain and brittle nature. For this reason, it is a challenge to develop full page, compact, graphic Braille displays that are affordable. A newly developed material composed of P(VDF-TrFE-CFE) terpolymer blended with 5% P(VDF-CTFE) electrostrictive actuators exhibits large strains (~5% at 150V/μm), fast actuation (>5 mm/s), and has a relatively high elastic modulus (1.2 GPa). This material exhibits more than double the elastic energy density and a 50% higher modulus of the original electrostrictive terpolymer. Hence, the potential for viable actuators in compact, full page Braille displays is greater than ever, provided actuators can be manufactured reliably in quantity. This talk presents recent work in scaling production of such rolled actuators. Actuators extend .5 mm, are confined to the 2.5 mm grid spacing of conventional Braille text, generate >0.5 N force and operate at less than 200V, thus meeting the primary requirements for a commercialized Braille display. To manufacture these actuators, cast films are stretched using a roll-to-roll zone drawing machine that is capable of producing quantities of 2 μm thick film with high quality. What follows is a discussion of this machine, the roll-to-roll film stretching process and an assessment of the resulting stretched film for use as linear strain actuators, like those used in our Braille cell.

Reversible, large-strain, bistable actuation has been a lasting puzzle in the pursuit of smart materials and structures. Conducting polymers are bistable, but the achievable strain is small. Large deformations have been achieved in dielectric elastomers at the expense of mechanical strength. The gel or gel-like soft polymers generally have elastic moduli around or less than 10 MPa. The deformed polymer relaxes to its original shape once the applied electric field is removed. We report new, bistable electroactive polymers (BSEP) that are capable of electrically actuated strains as high as 335% area strain. The BSEP could be useful for constructing rigid structures. The structures can support high mechanical loads, and be actuated to large-strain deformations. We will present one unique application of the BSEP for Braille displays that can be quickly refreshed and maintain the displayed contents without a bias voltage.

Dielectric elastomer stack actuators (DESA) offer the possibility to build actuator arrays at very high density. The driving voltage can be defined by the film thickness, ranging from 80 μm down to 5 μm and driving field strength of 30 V/μm. In this paper we present the development of a vibrotactile display based on multilayer technology. The display is used to present several operating conditions of a machine in form of haptic information to a human finger. As an example the design of a mp3-player interface is introduced. To build up an intuitive and user friendly interface several aspects of human haptic perception have to be considered. Using the results of preliminary user tests the interface is designed and an appropriate actuator layout is derived. Controlling these actuators is important because there are many possibilities to present different information, e.g. by varying the driving parameters. A built demonstrator is used to verify the concept: a high recognition rate of more than 90% validates the concept. A characterization of mechanical and electrical parameters proofs the suitability of dielectric elastomer stack actuators for the use in mobile applications.

Hydrostatic coupling has been recently reported as a means to improve versatility and safety of dielectric elastomer (DE) actuators. Hydrostatically coupled DE actuators rely on an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load. In this paper, we present ongoing development of bubble-like versions of such transducers, made of silicone and oil. In particular, the paper describes millimeter-scale actuators, currently being developed as soft, light, acoustically silent and cheap devices for two types of applications: tactile displays and cutaneous stimulators. In both cases, the most significant advantages of the proposed technology are represented by high versatility for design (due to the fluid based transmission mechanism), tailorable stiffness perceived by the user (obtained by adjusting the internal fluid pressure), and suitable electrical safety (enabled by both a passive interface with the user and the insulating internal fluid). Millimeter-scale prototypes showed a resonance frequency of about 250 Hz, which represents the value at which Pacinian cutaneous mechanoreceptors exhibit maximum sensitivity; this provides an optimum condition to eventually code tactile information dynamically, either in combination or as an alternative to static driving.

Tactile information is prerequisite for dexterous manipulation of objects with robots. In this paper a novel tactile sensor using dielectric elastomer is presented. The sensor is a capacitive type and it can be easily covered onto any curved surface due to the intrinsic flexibility of the dielectric elastomer. The practical design and fabrication of a tactile sensor for the robot fingertip are described in details in this paper. Also,a fingertip shaped tactile sensor with twelve tactile cells is developed. The sensor is mounted on a multi-fingered robot hand, called "SKKU Hand III", and its effectiveness is validated with experimental results.

Mechanical stimuli are critical for the development and maintenance of most tissues such as muscles, cartilage, bones and blood vessels. The commercially available cell culture systems replicating the in vivo environment are typically based on simple membrane cell-stretching equipment, which can only measure the average response of large colonies of cells over areas of greater than one cm². We present here the conceptual design and the complete fabrication process of an array of 128 Electro-Active Polymer (EAP) micro-actuators which are uni-axially stretched and hence used to impose unidirectional strain on single cells, make it feasible to do experiments on the cytomechanics of individual cells. The Finite Element Method is employed to study the effect of different design parameters on achievable strain, leading to the optimized design. Compliant gold electrodes are deposited by low-energy ion implantation on both sides of a PDMS membrane, as this technique allows making electrodes that support large strain with minimal stiffening of the elastomer. The membrane is bonded to a rigid support, leading to an array of 100×100 μm² EAP actuators.

Electroactive Polymer Artificial Muscles (EPAM^TM) based on dielectric elastomers have the bandwidth and the energy density required to make haptic displays that are both responsive and compact. Recent work at Artificial Muscle Inc. has been directed toward the development of thin, high-fidelity haptic modules for mobile handsets. The modules provide the brief tactile "click" that confirms key press, and the steady state "bass" effects that enhance gaming and music. To design for these capabilities we developed a model of the physical system comprised of the actuator, handset, and user. Output of the physical system was passed through a transfer function to covert vibration into an estimate of the intensity of the user's haptic sensation. A model of fingertip impedance versus button press force is calibrated to data, as is impedance of the palm holding a handset. An energy-based model of actuator performance is derived and calibrated, and the actuator geometry is tuned for good haptic performance.

We discuss various approaches to increasing the dielectric constant of elastomer materials, for use in dielectric elastomer actuators. High permittivity metal-oxide nano-particles can show elevated impact compared to larger size particles, but suffer from water uptake. Composites with conducting particles lead to extremely high permittivity caused by percolation, but they often suffer early breakdown. We present experiments on approaches combining metal-oxides and metal particles, which compensate for the drawbacks, and may lead to useful DEA materials in which all relevant properties are technologically useful. The key seems to be to avoid percolation and achieve a constant nearest-neighbor separation.

Dielectric elastomer actuators (DEAs) have been demonstrated for meso- and macro-scale applications, but only a few devices have been shown at the micro-scale, the most common of which have been diaphragms that bulge out of the plane of the wafer. Microscale DEAs would be of value in a wide range of small devices, including micro-robots, micropumps, and micro-optical systems. An additional advantage of miniaturizing is a reduction in the required driving voltage from kilovolts to tens of volts because the layers are thinner. However, fabrication of micro-scale DEAs remains challenging, due in part to the fact that the vast majority of macro-scale materials and/or fabrication methods cannot be adapted to the micro-scale. On the micro-scale, the elastomers must be deposited as thin films, they must be patternable, and they must be compatible with the other materials used during fabrication, such as sacrificial layers. The realization of compliant electrodes must also be handled in a new way. To fully realize the potential of micro-DEAs, it would also be desirable to develop fabrication procedures for integrating the micro-scale DEAS with complementary metal-oxidesemiconductor (CMOS) driver circuits and other micro-electro-mechanical systems (MEMS). This article addresses the progress that has been made thus far in making microfabricated DEAs, as well as the challenges and the key areas in which additional research needs to be pursued.

The common approach for dielectric elastomer actuators (DEA) is based on the assumption that compliant electrodes are a fundamental design requirement. For tube-like applications compliant electrodes cause a change of the actuator diameter during actuation and would require additional support-structures. Focused on thinwalled actuator-tube geometries room consumption and radial stabilityr epresent crucial criteria. Following the ambition of maximum functional integration, the concept of using a rigid electrode structure arises. This structure realizes both, actuation and support characteristics. The intended rigid electrode structure is based on a stacked DEA with a non-compressible dielectric. Byactu ation, the displaced dielectric causes an overlap. This overlap serves as an indicator for geometrical limitations and has been used to extract design rules regarding the electrode size, electrode distance and maximum electrode travel. Bycons idering the strain in anydir ection, the mechanical efficiencyhas been used to define further design aspects. To verifyt he theoretic analysis, a test for determination of the compressive stress-strain-characteristics has been applied for different electrode setups. As result the geometrydep ending elastic pressure module has been formulated by implementation of a shape factor. The presented investigations consider exclusive the static behavior of a DEA-setup with rigid electrodes.

Dielectric elastomer actuators (DEAs) have attracted increasing attention over the last few years owing to their outstanding properties, e.g. their large actuation strains, high energy density, and pliability, which have opened up a wide spectrum of potential applications in fields ranging from microengineering to medical prosthetics. There is consequently a huge demand for new elastomer materials with improved properties to enhance the performance of DEAs and to overcome the limitations associated with currently available materials, such as the need for high activation voltages and the poor long-term stability. The electrostatic pressure that activates dielectric elastomers can be increased by higher permittivity of the elastomer and thus may lead to lower activation voltages. This has led us to consider composite elastomeric dielectrics based on thermoplastic elastomers or PDMS, and conductive polyaniline or ceramic (soft doped PZT) powder fillers. The potential of such materials and strategies to counter the adverse effects of increased conductivity and elastic modulus are discussed.

Previously, the dielectric elastomer based on Acrylonitrile Butadiene Rubber (NBR), called synthetic elastomer has been reported by our group. It has the advantages that its characteristics can be modified according to the requirements of performances, and thus, it is applicable to a wide variety of applications. In this paper, we address the effects of additives and vulcanization conditions on the overall performance of synthetic elastomer. In the present work, factors to have effects on the performances are extracted, e.g additives such as dioctyl phthalate (DOP), barium titanium dioxide (BaTiO₃) and vulcanization conditions such as dicumyl peroxide (DCP), cross-linking times. Also, it is described how the performances can be optimized by using DOE (Design of Experiments) technique and experimental results are analyzed by ANOVA (Analysis of variance).

Tubular actuators (push InLastor) fabricated from dielectric electro-active polymers (DEAP) have been developed and optimized with focus on high volume roll to roll automated manufacturing techniques and processes by Danfoss PolyPower®. This paper reports the dynamic mechanical behaviour from varying electrical stimulus of a PolyPower push InLastor. A simplified harmonic motion model of a spring load mass is shown to accurately predict the resonant frequency of push InLastors when working as displacement devices. The steady state frequency response results are presented for varying mechanical loads and drive voltage stimuli. The step function transient results are also present for different loading conditions. Methodology to extract parameters for the classic mass-spring-damper is also presented. Similarly, results are presented for the use of push Inlastors as force elements. The electrical to mechanical efficiency of PolyPower push InLastor is estimated.

Dielectric elastomer actuators (DEAs) offer numerous benefits as high displacement smart material actuators. The output of a DEA film is typically characterised by a large area expansion and a smaller transverse displacement. Consequently, their application is often limited by difficulties in resolving area expansion strain into a usable output. Certain DEAs also require pre-strain in order to achieve optimal performance. In this paper, Hoberman's radially expanding mechanism is used to form a novel DEA structure. The mechanism is composed of a number of repeating angulated scissor-links which resolve area expansion into a uniaxial displacement and have intrinsic pre-straining capabilities. This allows the Hoberman mechanism to be exploited as an actuator or as a pre-straining device. The stress distribution induced in the elastomer film when the mechanism is expanded was analysed using photoelasticity, which showed a 6 segment mechanism produces a significantly more uniform strain pattern compared to 4 segments. Prototype DEA mechanisms demonstrated that the Hoberman linkage does resolve area expansion strain into a uniaxial displacement (which can be linear or rotary) at the cost of mechanical friction losses. The 4 segment DEA prototype produced a maximum stroke of 3.13 mm (6.88% planar strain) with a tensile load of 1.46 N. The 6 segment DEA prototype demonstrated improved performance with a maximum stroke of 4.52 mm (7.51% planar strain) and a maximum rotation of 4.98°.

Dielectric elastomer actuators (DEAs) consist of an elastomer sandwiched between two electrodes, and they undergo a large in-plane expansion upon the application of an electric field. They therefore require compliant electrodes that can stretch tens of percent. The most commonly used electrode material is carbon grease, which smears easily and is difficult to pattern. This paper outlines the fabrication and performance of a novel polydimethylsiloxane (PDMS) composite having a 15 wt% loading of exfoliated graphite (EG). This new material has a Young's modulus of only 0.9 MPa and a conductivity of 0.15 S/cm. Unlike other composite electrode materials, the Young's modulus of the PDMS/EG increases only slightly, by a factor of two, upon addition of the EG. Furthermore, the PDMS/EG composite is patternable and will not rub off. DEAs were fabricated with 20:1 PDMS as the elastomer using this new electrode material. The actuation strains were equal to those of 10:1 PDMS DEAs with carbon grease electrodes under the same electric field. Elastomer/EG composites may also find applications in areas such as flexible electronics, robotics, strain gauges, and sensors.

Dielectric elastomers (DEs) are one particular type of electroactive polymers. Dielectric elastomers work as a variable capacitor. The effects of conductive particles on the actuating behavior of silicone rubber-based dielectric elastomer are studied in this work. Two different materials, which are carbon nanotube and carbon black, respectively, are used to increase the overall permittivity of the composites. Although the addition of these conductive particles increases the permittivity of the composite, they also produce a highly inhomogeneous electric field and reduced breakdown strength of the composite. This reduction in breakdown strength could be a serious drawback of nanocomposite approach. The main challenge, therefore, becomes how to enhance the permittivity of the composite while maintaining its high breakdown strength. These composites are characterized by dielectric spectroscopy, tensile mechanical analysis, and electromechanical transduction tests. The effect of variation in filler loadings on the complex and real parts of permittivity are distinctly visible, which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium. The phenomenon of percolation was discussed based on the measured changes in permittivity and morphology of composites at different concentrations of these particles.

Dielectric Elastomer Actuators (DEAs) are a promising actuation technology for mobile robotics due to their high forceto- weight ratio, their potential for high efficiencies, and their low cost. The preliminary design of such actuators requires a quick and precise assessment of actuator energy conversion performance. To do so, this paper proposes a simple thermodynamic model using experimentally acquired loss factors that predict actuator mechanical work, energy consumption, and efficiency when operating under constant voltage and constant charge modes. Mechanical and electrical loss factors for both VHB 4905 (acrylic) and Nusil's CF19-2186 (silicone) are obtained by mapping the performances of cone-shaped DEAs over a broad range of actuator speeds, capacitance ratios, and applied voltages. Extensive experimental results reveal the main performance trends to follow for preliminary actuator design, which are explained by the proposed model. For the tested conditions, the maximum experimental brake efficiencies are ~35% and ~25% for VHB and CF19-2186 respectively.

The current paper presents the latest advancements in manufacturing, modeling and applications of ionic polymer-metal composite (IPMC) materials at University of Nevada, Reno. The paper highlights the newest techniques used in making the novel IPMCs. This includes the dimension control and patterning the electrodes so that the multiaxial bending of the material can be achieved. The novel concept of strain sensing and also more energy efficient actuation is discussed. Moreover, we have been working on improving the modeling of IPMC. The focus has been creating a physical model for design purposes. This has lead to developing a first full scale 3-dimensional model of IPMC material. Additionally, electrode effect has been presented and new techniques have been explored to take the Finite Element (FE) modeling of IPMC to the next level.

This paper presents a realization of a self-sensing ionic polymer-metal composite (IPMC) device by patterning its surface electrodes and thus creating separate actuator and sensor parts. The sensor and actuator elements of such device are still electrically coupled through the capacitance and/or conductivity of the ionic polymer. By creating a separate grounded shielding electrode between the two parts, it is possible to suppress significantly the undesired cross-talk from the actuator to the sensor. The paper at hand compares three different methods for separating sensor and actuator parts: manual scraping, machine milling, and laser ablation. The basis of comparison of the methods is the electrical characteristics of the device after realizing the surface patterns and the convenience of manufacturing.

Environmental and electrical variables, as temperature, electrolyte concentration or driving current, influence oxidation and reduction oxidation rates of free-standing polypyrrole/DBSA/ClO₄- films. Under flow of a constant current for a constant time, decreasing electrical energies are consumed to oxidize or to reduce the film under increasing temperatures or rising electrolyte concentrations. By consuming the same charge under flow of rising constant currents, the consumed electrical energy increases. As conclusion the consumed electrical energy by flow of constant charges during oxidation, or reduction, of the film is a sensor of the electrochemical cell temperature, the electrolyte concentration or the flowing current. Those sensing capabilities seem to be a general property of the electrochemistry of conducting polymers. Any electrochemical based device, as actuators, polymeric batteries, smart membranes, smart drug delivery devices and others, are expected to sense environmental conditions while working. The sensing abilities of a complex actuator constituted by four polypyrrole films, two acting as electrodes (anodes or cathodes) and the other two as counter electrodes (cathodes or anodes, respectively) are presented. Experimental results are equivalent to sensing charge/discharge processes in all polymeric batteries.

Ionic polymer-metal composites (IPMC) are soft actuation materials with promising applications in robotics and biomedical devices. In this paper, a MEMS-based approach is presented for monolithic, batch fabrication of IPMC pectoral fin actuators that are capable of complex deformation. Such an actuator consists of multiple, individually controlled IPMC regions that are mechanically coupled through compliant, passive regions. Prototypes of artificial pectoral fins have been fabricated with the proposed method, and sophisticated deformation modes, including bending, twisting, and cupping, have been demonstrated, which shows the promise of the pectoral fin in robotic fish applications.

Ionic polymer metal composite (IPMC), an electrically activated polymer (EAP), has attracted great attention for the excellent properties such as large deformation, light weight, low noise, flexibility and low driving voltages, which makes the material a possible application as artificial muscle if the output force can be increased. To improve the property, we manufactured the Nafion membrane by casting from liquid solution, modified the surface by sandblasting or polishing, and obtained the isotropic and anisotropic surface texture respectively. The microstructure of the Nafion surface and metal electrode, effects of surface texture on the output force and displacement of IPMC were studied. Results show that the output force of IPMC with the anisotropic surface texture is 2~4 times higher than that with the isotropic surface texture without enormous sacrifice of the displacement. The output force may reach to 6.63gf (Sinusoidal 3.5V and 0.1Hz, length 20mm, width 5mm and thickness 0.66mm), which suggest an effective way to improve the mechanical properties of IPMC.

Ras Labs produces electroactive polymer (EAP) based materials and actuators that bend, swell, ripple, and now contract (new development) with low electric input. In addition, Ras Labs produces EAP materials that quickly contract and expand, repeatedly, by reversing the polarity of the electric input. These recent developments are important attributes in the field of electroactivity because of the ability of contraction and contraction-expansion to produce biomimetric motion. The mechanism of contraction is not well understood. Radionuclide-labeled experiments were conducted to determine the mechanisms during contraction of these EAPs.

Asymptotically accurate nonlinear analysis of electro elastomer membrane structures is carried out using Variational Asymptotic Method (VAM) with moderate strains and very small thickness-to-wavelength ratio as small parameters. Present work incorporates large deformations (displacements and rotations), material nonlinearity (hyper elasticity), and electrical effects. It begins with 3-D electro-elastic energy and mathematically splits the analysis into a 1-D through-the-thickness analysis and a 2-D membrane analysis. 1-D analysis provides asymptotically equivalent of 3-D energy which in turn 2-D constitutive law is input to membrane analysis and a set of recovery relations to approximately express the 3-D mechanical field variables in terms of two-dimensional variables determined from solving the equations of the membrane analysis. Numerical examples are presented to compare with existing analytical, semi-analytical and finite element solutions. Results based on this model will be demonstrated for specific inflatable structures of aerospace and bio-mechanics applications.

The focus of this paper is on the modeling of dielectric elastomer actuators and generators. One of the effects that is rarely considered in modeling of these systems is the influence of the materials' specific resistance on the performance. The non-ideal electrical properties of both elastomer and electrode material will cause undesired parasitic effects. Although for most laboratory scale prototypes these effects are hardly recognizable, they may however play an important role for larger structures and especially for dynamic applications. Therefore, an analytical model is developed and presented in this paper which can give helpful instructions for the design and fabrication process of EAP-systems. It is proven to be valid by means of the finite element method and subsequently extended for more complex systems.

In this paper, we study the electro-stress in dielectric elastomer (DE) undergoing large deformation subjected to a high voltage. The electrostriction is investigated and evaluated by the free-energy model when the dielectric permittivity does not remain constant in actuation. We investigate the nominal and true electric fields as the DE stretched with the electrostriction involved or not, and the stable domain for safe actuation is provided.

Dielectric breakdown often leads to catastrophic failure in Dielectric Elastomer Actuator(s) (DEA). The resultant damage to the dielectric membrane renders the DEA useless for future actuation, and in extreme cases the sudden discharge of energy during breakdown can present a serious fire risk. The breakdown strength of DEA however is heavily dependent on the presence of microscopic defects in the membrane giving its overall breakdown strength inherent variability. The practical consequence is that DEA normally have to be operated far below their maximum performance in order to achieve consistent reliability. Predicting when DEA are about to suffer breakdown based on feedback will enable significant increase in effective DEA performance without sacrificing reliability. It has been previously suggested that changes in the leakage current can be a harbinger of dielectric breakdown; leakage current exhibits a sharp increase during breakdown. In this paper the relationship between electric field and leakage current is investigated for simple VHB4905-based DEA. Particular emphasis is placed on the behaviour of leakage current leading up to and during breakdown conditions. For a sample size of nine expanding dot DEA, the DEA that failed at electric fields below the maximum tested exhibited noticeably higher nominal power dissipation and a higher frequency of partial discharge events than the DEA that did not breakdown during testing. This effect could easily be seen at electric fields well below that at which the worst performing DEA failed.

In this paper we discuss the electrical and mechanical modeling of dielectric elastomer stack actuators. The model is used to extract internal electrical parameters out of measurable values of the whole actuator system. Further parameters like the uniaxial Young's modulus, the assembly of the stack and the number of connected layers have to be considered. Using this data the static actuator performance for several driving conditions can be predicted. The final comparison of model based predicted deformation and real stack deformation show good accordance. Hence, the proven correlation of actuator layout parameters, fabrication parameters and driving conditions allow application dependent actuator design.

Metallic thin films, which are widely used for micro-electronics circuits, are seldom used as the electrodes for dielectric elastomer actuators (DEA). This is because metalized film restrains the lateral strain of soft dielectric elastomer. In this paper, we demonstrated utilizing metalized elastomeric layers to make a bimorph capable of a large bending. A compliant silver electrode is deposited on onto a VHB tape (F-9469 PC) using electroless deposition method, as for mirror silvering. The deposited silver is 200 nm thick and highly conductively though having an uneven surface. A silvered DEA bimorph is made of an active layer of silvered VHB elastomers and a passive layer of polydimethylsiloxane (PDMS). Experiments show that the silvered dielectric elastomer actuator is capable of producing a large bending, with a curvature of 32 mm for a 20 mm length at a driving voltage of 3000V. In addition, the electrolessly silvered elastomeric capacitor (130 μm thick VHB as dielectric) exhibits a breakdown voltage of 4kV, higher than 2kV of the silver-greased capacitor. In addition, the silvered VHB layer is found to be able to self clear after electrical breakdown. It remains functional at a lower voltage after surviving an electrical breakdown.

Dielectric Elastomer Generator(s) (DEG), are essentially variable capacitor power generators formed by hyper-elastic dielectric materials sandwiched between flexible electrodes. Electrical energy can be produced from a stretched, charged DEG by relaxing the mechanical deformation whilst maintaining the amount of charge on its electrodes. This increases the distance between opposite charges and packs likecharges more densely, increasing the amount of electrical energy. DEG show promise for harvesting energy from environmental sources such as wind and ocean waves. DEG can undergo large inhomogeneous deformations and electric fields during operation, meaning it can be difficult to experimentally determine optimal designs. Also, the circuit that is used for harnessing DEG energy influences the DEG output by controlling the amount of charge on the DEG. In this paper an integrated DEG model was developed where an ABAQUS finite element model is used to model the DEG and data from this model is input to a system level LT-Spice circuit simulation. As a case-study, the model was used as a design tool for analysing a diaphragm DEG connected to a self-priming circuit. That is, a circuit capable of overcoming electrical losses by using some of the DEG energy to boost the charge in the system. Our ABAQUS model was experimentally validated to predict the varying capacitance of a diaphragm DEG deformed inhomogeneously to within 6% error.

Energy harvesting using dielectric elastomers is an interesting possibility to convert ambient energy into electric energy. Different small scale prototypes of energy harvesting devices, like SRIs wind- and wave-power generators have been developed so far. Nevertheless, the theoretical limits and practical implementation still have to be considered. The contribution of this paper is related to the calculation of the achievable energy gain. Different harvesting cycles are investigated theoretically and compared to each other. Based on the derived equations, several design rules for the material development are quoted. To analyze the various properties of dielectric elastomer generators an electromechanical test bench is realized. The design of an appropriate HV power electronics for energy harvesting devices is presented in the last section.

Several generations of ionic polymer metal composite (IPMC) actuators have been developed since 1992. It has been discovered that the composite electrodes which are composed of electronic and ionic conductors, have great impact on performance of ionic polymer actuators by affecting strain level, efficiency and speed. One of important factors in composite electrodes is the shape and morphology of electronic conductor fillers. In this paper, RuO2 nanoparticles and vertically aligned carbon nanotube (Va-CNT) are used as conductor fillers. Making use of unique properties of Va-CNT forests with ultrahigh volume fraction in Nafion nanocomposite, an ionic polymer actuator is developed. Ion transport speed is greatly increased along CNT alignment direction. The high elastic anisotropy, arising from the high modulus and volume fraction of Va-CNTs, enhances actuation strain while reducing the undesirable direction strain. More than 8% actuation strain under 4 volts with less than one second response time has been achieved.

We investigate the influence of ionic liquids on the electromechanical performance of Ionic Polymer Conductor Network Composite (IPCNC) bending actuators. Two imidazolium ionic liquids (ILs) with one cation, which is 1-ethyl-3- methylimidazolium ([EMI+]), and two different anions, which are tetrafluoroborate ([BF4-]) and trifluoromethanesulfonate ([Tf-]), are chosen for the study. By combining the time domain electric and electromechanical responses, we developed a new model that describes the ion transports in IPCNC actuators. The time constant of excess cation and anion migration in various composite electrodes are deduced: 6s and 25s in RuO2/Nafion; 7.9s and 36.3s in RuO2/Aquivion; 4.8s and 53s in Au/PAH, respectively. NMR is also applied to provide quantitative measures of self-diffusion coefficients independently for IL anions and cations both in pure ILs and in ILs absorved into ionomers. All the results indicate that the motion of cation, in the studied pure ionic liquids, polymer matrix and conductor network composites, is faster than that of anion. Moreover, the CNC morphology is playing a crucial role in determining the ion transport in the porous electrodes.

Carbon nanotube (CNT) actuators have been extensively investigated from the perspective of materials, their composition, and system construction as well as from three main performance features, which are displacement, force and velocity. However, up till now none of the CNT actuators have reached the stage of implementation into products. It is due to the fact that even though from the point of view of performance each property can reach satisfactory values, their combination is much more difficult, as they are not proportional. This relation of properties motivated the work to test and investigate currently available CNT-polymer actuators to define their operation point. Under this term one should understand a performance of actuator where displacement, force and velocity do not affect each other. In other words, any change in one of the properties will adversely affect at least one of the remaining ones. The measurements are performed in out-of-plane mode on 2 cm diameter samples in low frequency range (0.01 - 1 Hz) under application of low voltage (2 V). Measurement curves of three main actuator properties are plotted together against the frequency resulting in operation point as the intersection point of those curves. Additionally the deviations in actuator performance are assessed to reflect the actuators' reproducibility and their production process stability by means of standard deviation. Knowledge about the relation between actuator properties and the value of operation point will facilitate evaluation of the existing CNT actuator against its potential applications.

Ionic Polymer Metal Composites (IPMCs) are soft electroactive polymer materials that bend in response to the voltage stimulus (1 - 4 V). They can be used as actuators or sensors. In this paper, we introduce two new highly-porous carbon materials for assembling high specific area electrodes for IPMC actuators and compare their electromechanical performance with recently reported IPMCs based on RuO₂ electrodes. We synthesize ionic liquid (Emi-Tf) actuators with either Carbide-Derived Carbon (CDC) (derived from TiC) or coconut shell based activated carbon electrodes. The carbon electrodes are applied onto ionic liquid-swollen Nafion membranes using the direct assembly process. Our results show that actuators assembled with CDC electrodes have the greatest peak-to-peak strain output, reaching up to 20.4 mε (equivalent to >2%) at a 2 V actuation signal, exceeding that of the RuO₂ electrodes by more than 100%. The electrodes synthesized from TiC-derived carbon also revealed significantly higher maximum strain rate. The differences between the materials are discussed in terms of molecular interactions and mechanisms upon actuation in the different electrodes.

Formation of controlled morphology of fillers in polymeric composites may be difficult to achieve by conventional methods such as mechanical shear or chemical methods. Tunable structure of filler and anisotropic properties in composites can be obtained by exploiting dielectrophoretic assembly of fillers in a polymer composite by using electric fields. In this study, different concentrations of Titanium Dioxide (TiO₂) particles in silicone rubber matrix were assembled in a chain-like structure by using an alternating electric field. Silicone rubber matrix was vulcanized to transform the liquid to solid and maintain the filler structure in the desired direction. Generation of chain structure of filler was verified by Scanning Electron Microscopy (SEM) and equilibrium swelling. It was shown that dielectric permittivity of the oriented composite is higher whereas its dielectric loss factor is lower in the orientation (thickness) direction than those for the composites with random distribution of filler. This phenomenon was in agreement with results of dynamic-mechanical loss factor for these composites, and can be utilized in more efficient dielectric elastomer actuators. Elastic modulus is higher for the structured samples, but presence of titania filler induced a softening effect at higher strains where the actuators are practically being pre-stretched. A critical concentration of filler was distinguished as the percolation point at which the change in dielectric behavior is amplified. Using a simple blocking-force measurement, potential advantages of structured composites over the ones with randomly-distributed filler was explained for potential dielectric elastomer actuator applications.

The synthesis of massive arrays of monodispersed carbon nanotubes that are self-assembled on hydrophilic polycarbonate membrane is reported. This approach involves individual carbon nanotube manufacturing by non-ionic surfactant to aid in dispersion and nanotubes self-assembled for three-dimensional orientation by high press filtration. The inherent capability of carbon nanotube and microstructure of well-packed arrays predominate excellent conductive properties of massive arrays. These potential applications of nanometer-sized sensor, probe and energy resistor have been characterized in this study. Furthermore, the route toward application of self-assembled regular arrays, as heat transmission intermedium, has been carried out by activating shape-memory polymer. The electrical conductivity of insulating polymer is significantly improved by assembled carbon nanotubes, resulting in shape recovery behavior of nanocomposite being driven by electrical resistive heating.

In the present study, multiwalled carbon nanotubes (MWCNTs) reinforced shape memory polymer (SMP) nanocomposites were prepared with a high shear mixing process. The shape memory effect and thermomechanical behaviors were characterized. A well dispersion of MWCNTs in SMP were reached with the current mixing process and brought in enhanced mechanical properties. The glass transition temperature of the nanocomposites does not vary with the MWCNT content. In the glass transition range, the addition of MWCNTs enhances the modulus of the SMP significantly, indicating the increased recovery force. The constrained recovery stress increased with the addition of carbon nanotubes.

Silicone rubber is a common dielectric elastomer material. Actuators made from it show excellent activate properties including very large strains (up to 380%), high elastic energy densities (up to 3.4 J/g), high efficiency, high responsive speed, good reliability and durability, etc. When voltage is applied on the compliant electrodes of the dielectric elastomers silicone rubber, the polymer shrinks along the electric field and expands in the transverse plane. In this paper, a theoretical analysis is performed on the coupling effects of the mechanical and electric fields. A nonlinear field theory of deformable dielectrics and hyperelastic theory are adopted to analyze the electromechanical field behavior of these actuators. Applied elastic strain energy function is obtained from the representative Yeoh model. The electric energy function involves invariant and variable dielectric constant respectively. Then deduce the constitutive relation for the dielectric elastomer film actuator based on the selected function. Also the mechanical behavior of the dielectric elastomer silicone rubber undergoing large free deformation is studied. The constitutive modules of dielectric elastomer composite under free deformation and restrained deformation are derived. The Barium Titanate (BaTiO3) with high permittivity was incorporated into the raw silicone to fabricate a new dielectric elastomer, the experimental results that the elastic modulus and dielectric constant were significantly improved. Finally the Yeoh model was developed to characterize the elastic behavior of the new dielectric elastomer. The constitutive modules of dielectric elastomer composite under free deformation and restrained deformation are derived. This is a promising analysis method for the study of the coupled fields and mechanical properties of the dielectric film actuator.

Rolled tubular dielectric elastomer-based actuators provide larger forces by making multiple thin layers of the dielectric elastomer apply their actuation forces in parallel. Such a rolled actuator is currently being marketed by Danfoss PolyPower A/S. This actuator is core-free has no pre-strain and is free-standing The dielectric elastomer (DE) material used to construct the actuator combines a silicon elastomer with compliant metal electrode technology that provides unidirectional motion. In this contribution the focus is on the three dimensional (3-D) modelling of this core-free tubular actuator. 3-D modelling is achieved by representing the actuator by two two-dimensional (2-D) models thus ensuring that the resulting 2-D models can be handled numerically by finite element simulation and analysis. Initially the Voltagestrain and Strain-blocking force characteristics of the actuators are investigated using only the modelled 'active' area, the electrode covered part of the actuator. The 'passive' area, which reduces the total force provided by the 'active' area, is modelled by approximating the steady-state characteristics of the passive area as a spring with a specified stiffness. The spring stiffness is related directly to the geometry and elastic modulus of the elastomer material in the 'passive' area. Using this simple model in conjunction with the force provided by the 3-D 'active' area model the 'effective force' of the actuator can be found. The use of this 'effective force' expression provides good agreement with the experimental forcestrain data obtained from a Danfoss PolyPower tubular actuator.

Ionic polymer transducers (IPTs) are soft sensors and actuators which operate through a coupling of micro-scale chemical, electrical, and mechanical interactions. The use of an ionic liquid as solvent for an IPT has been shown to dramatically increase transducer lifetime in free-air use, while also allowing for higher applied voltages without electrolysis. In this work we model charge transport in an ionic liquid IPT by considering both the cation and anion of the ionic liquid as mobile charge carriers, a phenomenon which is unique to ionic liquid IPTs compared to their water-based counterparts. The electrochemical behavior of the large ionic liquid ions is described through a modification of the Nernst-Planck equation given by Kornyshev which accounts for steric effects in double layer packing. The method of matched asymptotic expansions is applied to solve the resulting system of equations, and analytical expressions are derived for the nonlinear charge transferred and capacitance of the IPT as a function of the applied voltage. The influence of the fraction of mobile ionic liquid ions and steric effects on the capacitance of an ionic liquid IPT is shown and compared to water-based IPTs. These results show the fundamental charge transport differences between water-based and ionic liquid IPTs and give considerations for future transducer development.

Polyelectrolyte gels show adaptive viscoelastic characteristics. In water-based solutions they have enormous swelling capabilities under the influence of various possible stimulation types, such as chemical, electrical or thermal. In the present work a fully coupled 3-field formulation for polyelectrolyte gels using the Finite Element Method (FEM) is applied. This formulation consists of a chemical, electrical, and mechanical field equation. The mechanical field is coupled to the chemo-electrical field by a prescribed strain stemming from an osmotic pressure term. In experiments it has been proven that there is a large dependency between the applied temperature and the actual swelling degree of the gel. In the present research, the thermal stimulation is investigated. First, only the actual temperature is considered in the osmotic pressure term. Then, additionally, temperature-dependent material parameters obtained from experimental measurements are applied. The calibration of the numerical simulation is performed with experimental results available in literature.

Interpenetrating polymer network reinforced acrylic elastomers (IPN) offer outstanding performance in free-standing contractile dielectric elastomer actuators. This work presents the verification of a recently proposed material model for a VHB 4910 based IPN [1]. The 3D large strain material model was determined from extensive data of multiaxial mechanical experiments and allows to account for the variations in material composition of IPN-membranes. We employed inflation tests to membranes of different material composition to study the materials response in a stress state different from the one that was used to extract the material parameters. By applying the material model to finite element models we successfully validated the material model in a range of material compositions typically used for dielectric elastomer actuator applications. In combination with a characterization of electro-mechanical coupling, this 3D large strain model can be used to model IPN-based dielectric elastomer actuators.

In this paper, a finite element model is used to describe the inhomogeneous deformations of dielectric elastomers (DE). In our previous work, inhomogeneous deformations of the DE with simple boundary conditions represented by a system of highly nonlinear coupled differential equations (ordinary and partial) were solved using numerical approaches [1-3]. To solve for the electromechanical response for complex shapes (asymmetric), nonuniform loading, and complex boundary conditions a finite element scheme is required. This paper describes a finite element implementation of the DE material model proposed in our previous work in a commercial FE code (ABAQUS 6.8-1, PAWTUCKET, R.I, USA). The total stress is postulated as the summation of the elastic stress tensor and the Maxwell stress tensor, or more generally the electrostatic stress tensor. The finite element model is verified by analytical solutions and experimental results for planar membrane extensions subject to mechanical loads and an electric field: (i) equibiaxial extension and (ii) generalized biaxial extension. Specifically, the analytical solutions for equibiaxial extension of the DE is obtained by combining a modified large deformation membrane theory that accounts for the electromechanical coupling effect in actuation commonly referred to as the Maxwell stress [4]. A Mooney-Rivlin strain energy function is employed to describe the constitutive stress strain behavior of the DE. For the finite element implementation, the constitutive relationships from our previously proposed mathematical model [4] are implemented into the finite element code. Experimentally, a 250% equibiaxially prestretched DE sample is attached to a rigid joint frame and inhomogeneous deformations of the reconfigurable DE are observed with respect to mechanical loads and an applied electric field. The computational result for the reconfigurable DE is compared with the test result to validate the accuracy and robustness of the finite element model. The active membrane is being investigated to simulate the deformation response of the plagiopatagium of bat wing skins for a micro-aerial vehicle.

In nature, unidirectional fluid flows are often induced at micro-scales by cilia and related organelles. A controllable unidirectional flow is beneficial at these scales for a range of novel robotic and medical applications, whether the flow is used for propulsion (e.g. swimming robots) or mass transfer (e.g. prosthetic trachea). Ionic Polymer Metal Composites (IPMCs) are innovative smart materials that can be used directly as active propulsive surfaces rather than a traditional motor and propeller. IPMC actuators with two segmented electrodes that attempt to mimic the motion of cilia-like organelles have been realized. In this paper the optimization of these actuators towards producing unidirectional flows is described. A parametric study of the kinematic and hydrodynamic effect of modulating the drive signal has been conducted. As with eukaryotic cilia and flagella found in mammals, the segmented IPMC actuator can generate both flexural (asymmetric) and undulatory (symmetric) motions from the same physical structure. The motion is controlled by applying profiles of driving frequencies and phase differences. Kinematic analysis using a camera and laser displacement sensor has been used to measure and classify different motion types. The hydrodynamic forces produced by each motion type have been estimated using particle-tracking flow visualization. This allows drive signal profiles to be ranked in terms of fluid flow momentum transfer and directionality. Using the results of the parametric study, the IPMC motion is optimized towards producing unidirectional flow via repeatable cilia-inspired motion.

Most implantable chronic neural probes have fixed electrode sites on the shank of the probe. Neural probe shapes and insertion methods have been shown to have considerable effects on the resulting chronic reactive tissue response that encapsulates probes. We are developing probes with controllable articulated electrode projections, which are expected to provoke less reactive tissue response due to the projections being minimally sized, as well as to permit a degree of independence from the probe shank allowing the recording sites to "float" within the brain. The objective of this study was to predict and analyze the force-generating capability of conducting polymer bilayer actuators under physiological settings. Custom parylene beams 21 μm thick, 1 cm long, and of varying widths (200 - 1000 μm) were coated with Cr/Au. Electroplated weights were fabricated at the ends of the beams to apply known forces. Polypyrrole was potentiostatically polymerized to varying thicknesses onto the Au at 0.5 V in a solution of 0.1 M pyrrole and 0.1 M dodecylbenzenesulfonate (DBS). Using cyclic voltammetry, the bilayer beams were cycled in artificial cerebrospinal fluid (aCSF) at 37 °C, as well as in aqueous NaDBS as a control. Digital images and video were analyzed to quantify the deflections. The images and the cyclic voltammograms showed that divalent cations in the aCSF interfered with polymer reduction. By integrating polypyrrole-based conducting polymer actuators, we present a type novel neural probe. We demonstrate that actuating PPy(DBS) under physiological settings is possible, and that the technique of microfabricating weights onto the actuators is a useful tool for studying actuation forces.

This paper discusses a simple robust PID (proportional, integral and derivative) tuning method for force control of ionic polymer-metal composite actuators. The model is represented by a transfer function which consists of an electrical part and an electro-mechanical part. The uncertainty is represented by an interval polynomial set of the closed-loop characteristic equations. Using Kharitonov's theorem, we show that just one Kharitonov polynomial stability is necessary and sufficient for satisfying the robust stability of the system. The PID gain is determined by pole placement of the derived Kharitonov polynomial. Experimental results show the effectiveness of the PID force control achieved by the proposed method.

We present the preparation, characterization and electrical properties of a flexible electrically conducting nanocomposite polymer which has been prepared by high frequency ultrasonic agitation (42 kHz) of COOH functionalized multiwalled carbon nanotubes (MWCNTs) (outer diameter of 10nm and length of 30μm) in polydimethylsiloxane (PDMS) polymer matrix. We have characterized and compared the resistivity of films 3cm x 1 cm x 0.01cm in size as a function of weight percentage (ranging from 0.5 to 4.5) of COOH- functionalized MWCNT in the PDMS matrix, with a rest that percolation threshold of the prepared nanocomposite is achieved at 1.5 weight percentage (wt-%). The resistivity level achieved at 2 wt-% was approximately 62 Ω-cm. Microelectrodes were fabricated with a height of 30μm, width of 100μm, and lengths (l) ranging from 1mm to 10mm. We also demonstrate an improved micropatterning process than has not been previously reported: hybrid systems composed of micromolded combinations of both conductive nanocomposites with non-conductive PDMS. The fabricated microelectrodes maintain electrical continuity on being bent, flexed or twisted and can be used for electronic routing on a flexible MEMS.