This PDF file contains the front matter associated with SPIE Proceedings Volume 9056, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Last year, nearly 160,000 industrial robots were shipped worldwide—into a total market valued at ~$26 Bn (including hardware, software, and peripherals).[1] Service robots for professional (e.g., defense, medical, agriculture) and personal (e.g., household, handicap assistance, toys, and education) use accounted for ~16,000 units, $3.4 Bn and ~3,000,000 units, $1.2 Bn respectively.[1] The vast majority of these robotic systems use fully actuated, rigid components that take little advantage of passive dynamics. Soft robotics is a field that is taking advantage of compliant actuators and passive dynamics to achieve several goals: reduced design, manufacturing and control complexity, improved energy efficiency, more sophisticated motions, and safe human-machine interactions to name a few. The potential for societal impact is immense. In some instances, soft actuators have achieved commercial success; however, large scale adoption will require improved methods of controlling non-linear systems, greater reliability in their function, and increased utility from faster and more forceful actuation. In my talk, I will describe efforts from my work in the Whitesides group at Harvard to prove sophisticated motions in these machines using simple controls, as well capabilities unique to soft machines. I will also describe the potential for combinations of different classes of soft actuators (e.g., electrically and pneumatically actuated systems) to improve the utility of soft robots. 1. World Robotics - Industrial Robots 2013, 2013, International Federation of Robotics.

Dielectric elastomer Generator(s) (DEG) are highly suited to harvesting from environmental sources because they are light weight, low cost, and can be coupled directly to rectilinear motions and harvest energy efficiently over a wide frequency range. Because of these benefits, simple and low cost generators could be enabled using DEG. Electrical energy is produced on relaxation of a stretched, charged DEG: like-charges are compressed together and opposite-charges are pushed apart, resulting in an increased voltage. The manner in which the DEG charge state is controlled greatly influences the amount of energy that is produced. For instance, the highest energy density ever demonstrated for DEG is 550 mJ/g, whereas the theoretical energy density of DEG has been reported as high as 1700 mJ/g if driven close to their failure limits. The discrepancy between realised and theoretical energy production highlights that large performance gains can be achieved through smarter charge control that drives the generator close to its failure limits. To do so safely, we need to be able to monitor the real-time electromechanical state of the DEG. This paper discusses the potential of self-sensing for providing feedback on the generator’s electromechanical state. Then we discuss our capacitive self-sensing method which we have demonstrated to track the displacement of a Danfoss Polypower generator as it was cyclically stretched and harvested energy.

This study investigates the effects of electrode surface structure on the mechanoelectrical transduction of IPMC sensors. A physics-based mechanoelectrical transduction model was developed that takes into account the electrode surface profile (shape) by describing the polymer-electrode interface as a Koch fractal structure. Based on the model, the electrode surface effects were experimentally investigated in case of IPMCs with Pd-Pt electrodes. IPMCs with different electrode surface structures were fabricated through electroless plating process by appropriately controlling the synthesis parameters and conditions. The changes in the electrode surface morphology and the corresponding effects on the IPMC mechanoelectrical transduction were examined. Our experimental results indicate that increasing the dispersion of Pd particles near the membrane surface, and thus the polymer-electrode interfacial area, leads to a higher peak mechanoelectrically induced voltage of IPMC. However, the overall effect of the electrode surface structure is relatively low compared to the electromechanical transduction, which is in good agreement with theoretical prediction.

This paper presents an experimentally verified static three-dimensional model for core free tubular dielectric elastomer actuators with anisotropic compliant metal electrodes. Due to the anisotropy of the electrodes, the performance (force versus voltage, force versus stroke, and stroke versus voltage) of the actuators depends strongly on their geometry. Based on the three-dimensional model, the performance of the actuators is optimized by means of the length of the axes of their inner elliptical cross section and their wall thickness.

Compliant electrodes of microstructures have been a research topic for many years because of the increasing interest in consumer electronics, robotics, and medical applications. This interest includes electrically activated polymers (EAP), mainly applied in robotics, lens systems, haptics and foreseen in a variety of medical devices. Here, the electrodes consist of metals such as gold, graphite, conductive polymers or certain composites. The common metal electrodes have been magnetron sputtered, thermally evaporated or prepared using ion implantation. In order to compare the functionality of planar metal electrodes in EAP microstructures, we have investigated the mechanical properties of magnetron sputtered and thermally evaporated electrodes taking advantage of cantilever bending of the asymmetric, rectangular microstructures. We demonstrate that the deflection of the sputtered electrodes is up to 39 % larger than that of thermally evaporated nanometer-thin film on a single silicone film. This difference has even more impact on nanometer-thin, multi-stack, low-voltage EAP actuators. The stiffening effect of many metallic electrode layers is expected to be one of the greatest drawbacks in the multi-stack approaches, which will be even more pronounced if the elastomer layer thickness will be in the sub-micrometer range. Additionally, an improvement in voltage and strain resolution is presented, which is as low as 2 V or 5 × 10^-5 above 10 V applied.

Dielectric elastomer actuator showed significant advantages at high energy density, large deformation with comparing to other artificial muscle. The robot actuated by dielectric elastomer will be more lightweight and have lower cost, which shows great potential in field of future planetary exploration based on a group of micro-robot. In this context, a quite simple structure for creeping was designed to make the robot more lightweight. The actuation unit of the robot is made of an ellipse frame which can expand and contract with membrane under electric field. After joining four actuation units, the robot can move forward in a cooperative manner. Fabrication and some preliminary experiments of the robot were presented and the proposed motion principle was demonstrated.

The expense and use of non-recyclable materials often requires the retrieval and recovery of exploratory robots. Therefore, conventional materials such as plastics and metals in robotics can be limiting. For applications such as environmental monitoring, a fully biodegradable or edible robot may provide the optimum solution. Materials that provide power and actuation as well as biodegradability provide a compelling dimension to future robotic systems. To highlight the potential of novel biodegradable and edible materials as artificial muscles, the actuation of a biodegradable hydrogel was investigated. The fabricated gelatine based polymer gel was inexpensive, easy to handle, biodegradable and edible. The electro-mechanical performance was assessed using two contactless, parallel stainless steel electrodes immersed in 0.1M NaOH solution and fixed 40 mm apart with the strip actuator pinned directly between the electrodes. The actuation displacement in response to a bias voltage was measured over hydration/de-hydration cycles. Long term (11 days) and short term (1 hour) investigations demonstrated the bending behaviour of the swollen material in response to an electric field. Actuation voltage was low (<10 V) resulting in a slow actuation response with large displacement angles (<55 degrees). The stability of the immersed material decreased within the first hour due to swelling, however, was recovered on de-hydrating between actuations. The controlled degradation of biodegradable and edible artificial muscles could help to drive the development of environmentally friendly robotics.

A new approach based on silicone interpenetrating networks with orthogonal chemistries has been investigated with focus on developing soft and flexible elastomers with high energy densities and small viscous losses. The interpenetrating networks are made as simple two pot mixtures as for the commercial available silylation based elastomers such as Elastosil RT625. The resulting interpenetrating networks are formulated to be softer than RT625 to increase the actuation caused when applying a voltage due to their softness combined with the significantly higher permittivity than the pure silicone elastomers.

In recent studies, stack based Dielectric Elastomer Actuators (DEAs) have been successfully used in haptic feedback and sensing applications. However, limitations in the fabrication method, and materials used to con- struct stack actuators constrain their force and displacement output per unit volume. This paper focuses on a fabrication process enabling a stacked elastomer actuator to withstand the high tensile forces needed for high power applications, such as mimetics for mammalian muscle contraction (i.e prostheses), whilst requiring low voltage for thickness-mode contractile actuation. Spun elastomer layers are bonded together in a pre-strained state using a conductive adhesive filler, forming a Laminated Inter-Penetrating Network (L-IPN) with repeatable and uniform electrode thickness. The resulting structure utilises the stored strain energy of the dielectric elas- tomer to compress the cured electrode composite material. The method is used to fabricate an L-IPN example, which demonstrated that the bonded L-IPN has high tensile strength normal to the lamination. Additionally, the uniformity and retained dielectric layer pre-strain of the L-IPN are confirmed. The described method is envisaged to be used in a semi-automated assembly of large-scale multi-layer stacks of pre-strained dielectric layers possessing a tensile strength in the range generated by mammalian muscle.

High-performance artificial muscles have been produced from fibers having highly anisotropic thermal expansion. Inserting twist into these precursor fibers enables thermally-driven torsional actuation and can cause the formation of helical coils. Such coiled structures provide giant-stroke tensile actuation exceeding the 20% in-vivo contraction of natural muscles. This contraction is highly reversible, with over one million cycles demonstrated, and can occur without the hysteresis that plagues competing shape-memory and piezoelectric muscles. Several materials and composites are investigated, including low-cost, commercially-available muscle precursors, potentially facilitating thermally-responsive textiles that change porosity to provide wearer comfort.

Electromechanically active polymers (EAP) are considered a good actuator candidate for a variety of reasons, e.g. they are soft, easy to miniaturize and operate without audible noise. The main structural component in EAPs is, as the name states, a type of deformable polymer. As polymers are known to exhibit a distinct mechanical response, the nature of polymer materials should never be neglected when characterizing and modeling the performance of EAP actuators. Bucky-gel actuators are a subtype of EAPs where ion-containing polymer membrane acts as an electronically insulating separator between two electrodes of carbon nanotubes and ionic liquid. In many occasions, the electrodes also contain polymer for the purpose of binding it together. Therefore, mechanically speaking, bucky-gel actuators are composite structures with layers of different mechanical nature. The viscoelastic response and the shape change property are perhaps the most characteristic effects in polymers. These effects are known to have high dependence on factors such as the type of polymer, the concentration of additives and the structural ratio of different layers. At the same time, most reports about optimization of EAP actuators describe the alteration of electromechanical performance dependent on the same factors. In this paper, the performance of bucky-gel actuators is measured as a function between the output force and bending deflection. It is observed that effective stiffness of these actuators depends on the input voltage. This finding is also supported by dynamic mechanical analysis which demonstrates that the viscoelastic response of bucky-gel laminate depends on both frequency and temperature. Moreover, the dynamic mechanical analysis reveals that in the range of standard operation temperatures, tested samples were in their glass transition region, which made it possible to alter their shape by using mechanical fixing. The mechanical fixity above 90% was obtained when high-frequency input signal was used to heat the bucky-gel sample.

Highly oriented nylon and polyethylene fibres shrink in length when heated and expand in diameter. By twisting and then coiling monofilaments of these materials to form helical springs, the anisotropic thermal expansion has recently been shown to enable tensile actuation of up to 49% upon heating. Joule heating, by passing a current through a conductive coating on the surface of the filament, is a convenient method of controlling actuation. In previously reported work this has been done using highly flexible carbon nanotube sheets or commercially available silver coated fibres. In this work silver paint is used as the Joule heating element at the surface of the muscle. Up to 29% linear actuation is observed with energy and power densities reaching 840 kJ m^-3 (528 J kg^-1) and 1.1 kW kg^-1 (operating at 0.1 Hz, 4% strain, 1.4 kg load). This simple coating method is readily accessible and can be applied to any polymer filament. Effective use of this technique relies on uniform coating to avoid temperature gradients.

Interest on Dielectric ElectroActive Polymer (DEAP) generators has aroused among scientists in recent years, due to the former ones’ documented advantages against competing electromagnetic and field-activated technologies. Yet, the need for bidirectional energy flow under high step-up and high step-down voltage conversion ratios, accompanied by low-average but relatively high-peak currents, imposes great challenges on the design of the employed power electronic converter. On top of that, the shortage of commercially-available, high-efficient, high-voltage, low-power semiconductor devices limits the effective operational range of the power electronic converter. In this paper, a bidirectional tapped-inductor buck-boost converter is proposed, addressing high- efficient high step-up and high step-down voltage conversion ratios, for energy harvesting applications based on DEAP generators. The effective operational range of the converter is extended, by replacing its high-side switch with a string of three serialized MOSFETs, to accommodate the need for high-efficient high-voltage operation. Experiments conducted on a single DEAP generator - part of a quadruple DEAP generator energy harvesting system with all elements installed sequentially in the same circular disk with a 90° phase shift - validate the applicability of the proposed converter, demonstrating energy harvesting of 0.26 J, at 0.5 Hz and 60% delta- strain; characterized by an energy density of 1.25 J per kg of active material.

In the last decade, ionic polymer–metal composites are emerged as viable intelligent materials working both as bending actuators and energy harvesting systems. Recently, the feasibility of actuation from mechanical buckling has been investigated. In the present research, we present relevant numerical experiments concerning the possible electromechanical transduction when different patterned electrodes are considered. The focus of this research is theoretical, numerical, and experimental. In particular, with reference to almost one–dimensional IPMC strips, we take into account the large influence of electrodes’ bending stiffness on the IPMC behavior. We consider an original continuous metal strip covering the ionic polymer, and the patterned electrodes with one or more gaps. The actuation response of the system to low and to high voltages is studied; a strong difference is evidenced in the two situations as, in presence of high voltage, the system shows a buckling in opposite direction which needs further investigations.

Throughout this paper, a small-signal model of the Dielectric Electro Active Polymer (DEAP) transducer is analyzed. The DEAP transducer have been proposed as an alternative to the electrodynamic transducer in sound reproduction systems. In order to understand how the DEAP transducer works, and provide guidelines for design optimization, accurate characterization of the transducer must be established. A small signal model of the DEAP transducer is derived and its validity is investigated using impedance measurements. Impedance measurements are shown for a push-pull DEAP based loudspeaker, and the dependency of the biasing voltage is explained. A measuring setup is proposed, which allows the impedance to be measured, while the DEAP transducer is connected to its biasing source.

The analytical formulas describing the behaviour of dielectric elastomer actuators (DEAs) are based on hyperelastic strain energy density functions. The analytical modelling of a DEA will only lead to meaningful results if the dielectric elastomer can be accurately represented by the chosen hyperelastic model and if its parameters are carefully matched to the elastomer. In the case of silicone elastomers, we show that the strain energy density of a thin elastomeric membrane depends on the maximum deformation the membrane was previously submitted to (Mullins effect). We also show that using model parameters coming from an uniaxial pull-test to predict the behaviour of the elastomer in an equi-biaxial configuration leads to erroneous results. We have therefore built a measurement setup, which allows testing thin elastomeric membranes under equi-biaxial stress by inflating them with a pressure source. When modelling a DEA under equi-biaxial stretch, the measurement data can be used directly, without the need of an hyperelastic model, leading to voltage-stretch prediction closer the the measured stress-stretch behaviour of the dielectric membrane.

Dielectric elastomer (DE) actuators can convert electrical energy to mechanical energy. However, actuating DE membranes requires applying high voltage. Continuously applying high voltage on DE actuator causes failures such as current leakage and electric breakdown. To overcome the high voltage actuation drawbacks of DE actuators, this paper raises a new actuation method using DE interacting with external elastic structures. The analysis is demonstrated based on continuum mechanics, and agrees very well with experiment measurements.

Dielectric elastomer generators (DEG) are suited for harvesting energy from low frequency and high strain natural sources including wind, wave and human movement. The stack configuration, for instance, in which a number of layers of DE membrane are placed one atop the other, offers a robust, compact and solid-state way for arranging the DE material for energy harvesting during heel strike. But the end conditions at top and bottom of a stack can substantially limit its ability to strain. Using an analytical model for compression of the stack, we have calculated thickness changes in capacitive membranes along the stack for several cylindrical shapes. DE generators that are short and fat will have approximately parabolic profiles with continuous reduction in layer thickness towards the middle. This will result in higher electrical fields at the middle with greater susceptibility to breakdown. For long, thin DEG stacks, the outward bulging will be confined to zones at the two ends with a more uniform cylindrical profile in between. The placing of inexpensive compliant end-caps between the DEG and a rigid structure will promote more homogeneous deformation across the active layers so that the efficacy of these layers for energy harvesting will improve.

Ionic Polymer Metal Composite (IPMC) is an Electo-Active Polymer (EAP) that is well-known for its actuation and sensing behavior. It has been shown that in charge sensing mode an IPMC generates one order of magnitude larger current as compared to piezoelectric materials. However the voltage generated is on the order of couple millivolts, making it less attractive as a sensor and energy harvester. Previous numerical work by the author, demonstrated that increasing the ionic concentration of the ionomer will increase the current and voltage generated by an IPMC. Conversely, the previous study showed that the electrode composition and architecture had minimal effects. This paper will present an experimental investigation of the effect of changing the composition of the ionomer, the membrane thickness, and electrode architecture on the sensing and energy harvesting behavior. The response of all IPMC transducers is analyzed and compared to numerical simulations.

Liquid silicone rubbers (LSRs) have been shown to possess very favorable properties as dielectric electroactive polymers due to their very high breakdown strengths (up to 170 V/μm) combined with their fast response, relatively high tear strength, acceptable Young’s modulus as well as they can be filled with permittivity enhancing fillers. However, LSRs possess large viscosity, especially when additional fillers are added. Therefore both mixing and coating of the required thin films become difficult. The solution so far has been to use solvent to dilute the reaction mixture in order both to ensure better particle dispersion as well as allowing for film formation properties. We show that the mechanical properties of the films as well as the electrical breakdown strength can be affected, and that the control of the amount of solvent throughout the coating process is essential for solvent borne processes. Another problem encountered when adding solvent to the highly filled reaction mixture is the loss of tension in the material upon large deformations. These losses are shown to be irreversible and happen within the first large-strain cycle.

Exploiting the molecular and nano-structure engineering, electroactive polymers (EAPs) with giant electromechanical responses have been developed at Penn State. For the field actuated EAPs, a class of defects modified polar-fluoropolymers have been demonstrated to exhibit a high electrostrictive strain, a high energy conversion efficiency, and high elastic energy density (< 1 J/cm3), which has been commercialized by Akema and commercial actuator products have been developed at Novesentis. This talk will briefly review these results. In contrast, the ionic EAPs such as ionic polymer metal composites whose actuation mechanism is based on the excess ion accumulation/depletion at the electrodes, suffer low actuation strain, elastic energy density, and efficiency. On the other hand, the very low operation voltage, often below 5 volts, of i-EAPs is very attractive, compared with very high operation voltage of the field actuated EAPs. In the past several years, we have been investigating approaches to significantly enhance the electromechanical response of i-EAPs. This talk will present the recent works on a class of nano-structure engineered graphene nano-composites that exhibit a high strain response (< 50% strain) with an exceptionally high elastic energy density < 1.5 J/cm3, induced under low voltage (< 5 V) with a high efficiency. These results point out the potential of EAPs in achieving high performance by exploiting nano-structure engineering and their promise for advanced solid state actuator applications. ACKNOWLEDGEMENT: The work was supported by NSF under Grant No. CMMI-1130437.

Poly(ethylene oxide) (PEO) has been widely studied as a solid-polymer electrolyte where both the cations and anions can move inside of it under an applied electric field. The motion of these charge carriers in the PEO results in the accumulation of ions close to the electrodes. The inherent size difference between the types of ions causes an unequal volume change between the two sides which translates to an observed mechanical bending. This is similar to electroactive polymers made from conducting polymers. Typically, PEO has a slow response. Some efforts have been given to develop PEO-based polymer blends to improve their performance. In this work, a fundamental study on the electromechanical response is conducted: the time dependence of the electromechanical response is characterized for PEO under different electric fields. Based on the results, a new methodology to monitor the electromechanical response is introduced. The method is based on the frequency dependence of the samples’ dielectric properties. To improve the electromechanical response, the PEO is embedded with piezoelectric nanocrystalline cellulose (NCC). NCC is a biomass derivative that is biodegradable, renewable, and inexpensive. The dielectric, mechanical, and electromechanical properties of the NCC-PEO composites are characterized. It is found that the mechanical and electromechanical properties of the PEO are significantly improved with adding NCC. For example, the composites with 1.5 vol.% of NCC exhibit an electromechanical strain and elastic modulus that is 33.4% and 20.1% higher, respectively, than for PEO without NCC. However, the electromechanical response decreases when the NCC content is high.

Stimuli-responsive hydrogels capable of performing work by converting an external stimulation into mechanical motion can be an effective framework for soft actuators. However, most conventional hydrogels are incapable of sustaining external loads. Here, a new approach to create a robust pH-responsive hydrogel is described. This hydrogel is employed to investigate the actuation performance and dynamics of pH-responsive hydrogel actuators under different external loads. The actuation results obtained are then analysed using two different approaches: a thermodynamics approach and a simple mechanical approach.

Though capable of generating a large strain, dielectric elastomer actuators (DEAs) generate only a moderate actuation stress not more than 200kPa, which seriously limits its use as artificial muscles for robotic arm. Enhancement of dielectric strength (greater than 500MV/m) by dielectric oil immersion could possibly enable it a larger force generation. Previously, the immersion was done in an oil bath, which limits portability together with DEAs. In this study, we developed portable capsules to enclose oil over the DEA substrate (VHB 4905). The capsules is made of a thinner soft acrylic membrane and they seals dielectric liquid oil (Dow Corning Fluid 200 50cSt). The DEA substrate is a graphiteclad VHB membrane, which is pre-stretched with pure-shear boundary condition for axial actuation. When activated under isotonic condition, the oil-capsule DEA can sustain a very high dielectric field up to 903 MV/m and does not fail; whereas, the dry DEA breaks down at a lower electric field at 570 MV/m. Furthermore, the oil-capsule DEA can produces higher isometric stress change up to 1.05MPa, which is 70% more than the maximum produced by the dry DEA. This study confirmed that oil capping helps DEA achieve very high dielectric strength and generate more stress change for work.

This study seeks to investigate the feasibility of energy harvesting from mechanical buckling of ionic polymer metal composites (IPMCs) induced by a steady fluid flow. In particular, we propose a harvesting device composed of a paddle wheel, a slider-crank mechanism, and two IPMCs clamped at both their ends. We test the system in a water tunnel to estimate the effects of the flow speed and the shunting resistance on power harvesting. The classical post-buckling theory of inextensible rods is utilized, in conjunction with a black-box model for IPMC sensing, to interpret experimental results.

The capability of Dielectric Elastomers to show large deformations under high voltage loads has been deeply investigated to develop a number of actuators concepts. From a space systems point of view, the advantages introduced by this class of smart materials are considerable and include high conversion efficiency, distributed actuation, self-sensing capability, light weight and low cost. This paper focuses on the design of a solid-state actuator capable of high positioning resolution. The use of Electroactive Polymers makes this device interesting for space mechanisms applications, such as antenna and sensor pointing, solar array orientation, attitude control, adaptive structures and robotic manipulators. In particular, such actuation suffers neither wear, nor fatigue issues and shows highly damped vibrations, thus requiring no maintenance and transferring low disturbance to the surrounding structures. The main weakness of this actuator is the relatively low force/torque values available. The proposed geometry allows two rotational degrees of freedom, and simulations are performed to measure the expected instant angular deflection at zero load and the stall torque of the actuator under a given high voltage load. Several geometric parameters are varied and their influence on the device behaviour is studied. Simplified relations are extrapolated from the numerical results and represent useful predicting tools for design purposes. Beside the expected static performances, the dynamic behaviour of the device is also assessed and the input/output transfer function is estimated. Finally, a prototype design for laboratory tests is presented; the experimental activity aims to validate the preliminary results obtained by numerical analysis.

Much research has been done on the development of tactile displays using Dielectric Elastomer Actuators (DEAs). It has been argued that they offer the potential to create low-cost full-page tactile displays — not achievable with conventional actuator technologies. All research to date has considered tactile elements moving perpendicular to the skin and thus applying a normal force distribution. In contrast to previous work, we have investigated the use of laterally moving tactile elements that apply shear forces to the skin. This allows for the areal expansion of the DEA to be exploited directly, and a tactile display could be made with no elements moving out of the plane. There is evidence that humans are very sensitive to shear force distributions, and that in some cases a shear stimulus is indistinguishable from a normal stimulus. We present a prototype shear tactile display actuated by a DEA, and demonstrate that the DEA can generate the necessary forces and displacements. We also present and discuss different display topologies.

An ideal plastic actuator for haptic applications should generate a relatively large displacement (minimum 0.2-0.6 mm, force (~50 mN/cm²) and a fast actuation response to the applied voltage. Although many different types of flexible, plastic actuators based on electroactive polymers (EAP) are currently under investigation, the ionic EAPs are the only ones that can be operated at low voltage. This property makes them suitable for applications that require inherently safe actuators. Among the ionic EAPs, bucky gel based actuators are very promising. Bucky gel is a physical gel made by grounding imidazolium ionic liquids with carbon nanotubes, which can then be incorporated in a polymeric composite matrix to prepare the active electrode layers of linear and bending actuators. Anyhow, many conflicting factors have to be balanced to obtain required performance. In order to produce high force a large stiffness is preferable but this limits the displacement. Moreover, the bigger the active electrode the larger the force. However the thicker an actuator is, the slower the charging process becomes (it is diffusion limited). In order to increase the charging speed a thin electrolyte would be desirable, but this increases the probability of pinholes and device failure. In this paper we will present how different approaches in electrolyte and electrode preparation influence actuator performance and properties taking particularly into account the device ionic conductivity (which influences the charging speed) and the electrode surface resistance (which influences both the recruitment of the whole actuator length and its speed).

In this paper, we propose the resistive type tactile sensor with a liquid pocket. The tactile sensor with polymer substrate has two components which are the sensing element and the structural part. The sensing part is surrounded by PDMS (Sylgard 184) which is relatively solid. To make the sensor more sensitive, we design the upper part of the sensing element in a shape of half-sphere filled with a liquid (silicone oil). When the force is applied to the sensor, the liquid pressure increases and evenly presses down the sensing element to deform. The size of sensor is 7 x 3 x 1 mm including the wiring part. The good sensitivity (0.012 S/kPa-1) of the fabricated sensor is experimentally verified.

Considering electromechanical transducers based on dielectric electroactive polymers (DEAP) beside a proper transducer design a feeding power supply is mandatory. In order to increase the energy efficiency these power electronics should provide a bidirectional energy flow. Therefore, in this contribution a bidirectional flyback-converter is investigated. Since the superimposed application-oriented control of the DEAP transducer requires an accurate control of the transducer voltage, in a first step a mathematical description of the flyback-converter for feeding capacitive loads is carried out. Based on this a sensor-based as well as a sensor-less current control is developed that is finally superimposed by a voltage control. The obtained results are experimentally validated by measurements of a realized prototype of the bidirectional flyback-converter feeding a DEAP transducer.

Beside their application in actuation and energy harvesting, dielectric elastomers (DE) have also strong capabilities for stretch-sensing based on capacitive measurements. However, for compression detection the simple state-of-the-art DE films are too insensitive. In order to close this gap, a novel class of DE sensors for compression measurements has been developed. The new sensor mats consist of two flexible elastomer profiles, between which an elastomer film is squeezed, converting the compression to a stretch load. With this mechanism, very high sensitivities of the capacitive measurement under compression load are achieved. Furthermore, various parameters which influence the characteristics of the sensor mat have been identified. Most relevant are the shape of the profiles, the number and design of the electrode layers as well as the hardness of the profiles and of the elastomer film. The high variability of the sensor mat design offers farreaching possibilities to tune the characteristics of the compressions sensor in terms of the dependence of capacitance on the load force. The basic principles of the design of the new compression sensor mats are outlined and various examples of such flexible sensors are introduced in this paper.

Dielectric elastomers are soft actuation materials with promising applications in robotics and biomedical de- vices. In this paper, a bio-inspired artificial muscle actuator with artificial tendons is developed for robotic arm applications. The actuator uses dielectric elastomer as artificial muscle and functionalized carbon fibers as artificial tendons. A VHB 4910 tape is used as the dielectric elastomer and PDMS is used as the bonding material to mechanically connect the carbon fibers to the elastomer. Carbon fibers are highly popular for their high electrical conductivities, mechanical strengths, and bio-compatibilities. After the acid treatments for the functionalization of carbon fibers (500 nm - 10 μm), one end of carbon fibers is spread into the PDMS material, which provides enough bonding strength with other dielectric elastomers, while the other end is connected to a DC power supply. To characterize the actuation capability of the dielectric elastomer and electrical conductivity of carbon fibers, a diaphragm actuator is fabricated, where the carbon fibers are connected to the actuator. To test the mechanical bonding between PDMS and carbon fibers, specimens of PDMS bonded with carbon fibers are fabricated. Experiments have been conducted to verify the actuation capability of the dielectric elastomer and mechanical bonding of PDMS with carbon fibers. The energy efficiency of the dielectric elastomer increases as the load increases, which can reach above 50%. The mechanical bonding is strong enough for robotic arm applications.

Sensing motion of the human body is a difficult task. From an engineers’ perspective people are soft highly mobile objects that move in and out of complex environments. As well as the technical challenge of sensing, concepts such as comfort, social intrusion, usability, and aesthetics are paramount in determining whether someone will adopt a sensing solution or not. At the same time the demands for human body motion sensing are growing fast. Athletes want feedback on posture and technique, consumers need new ways to interact with augmented reality devices, and healthcare providers wish to track recovery of a patient. Dielectric elastomer stretch sensors are ideal for bridging this gap. They are soft, flexible, and precise. They are low power, lightweight, and can be easily mounted on the body or embedded into clothing. From a commercialisation point of view stretch sensing is easier than actuation or generation - such sensors can be low voltage and integrated with conventional microelectronics. This paper takes a birds-eye view of the use of these sensors to measure human body motion. A holistic description of sensor operation and guidelines for sensor design will be presented to help technologists and developers in the space.

In this paper, we study the charge dynamics of ionic polymer metal composites (IPMCs) in response to an imposed time-varying flexural deformation. IPMC chemoelectromechanical behavior is described through the Poisson-Nernst-Planck framework, and the method of matched asymptotic expansions is utilized to establish a closed-form solution for the electric potential and counterion concentration in the IPMC. This solution is, in turn, leveraged to derive a mathematically tractable distributed circuit model of IPMC sensing.

Hand motion is one of our most expressive abilities. By measuring our interactions with everyday objects, we can create smarter artificial intelligence that can learn and adapt from our behaviours and patterns. One way to achieve this is to apply wearable dielectric elastomer strain sensors directly onto the hand. Applications such as this require fast, efficient and scalable sensing electronics. Most capacitive sensing methods use an analogue sensing signal and a backend processor to calculate capacitance. This not only reduces scalability and speed of feedback but also increases the complexity of the sensing circuitry. A capacitive sensing method that uses a DC sensing signal and continuous tracking of charge is presented. The method is simple and efficient, allowing large numbers of dielectric elastomer sensors to be measured simulatenously.

Besides actuator and generator applications, dielectric electroactive polymers (DEAP) are also predestined for sensor applications to monitor the actual mechanical state based on the deformation dependent electrical pa- rameters of the DEAP. In order to ensure a high sensitivity, accuracy and dynamic a suitable sensor concept is required. Within this contribution a summary of multiple sensor concepts is presented, which are designed for positioning-actuators. To investigate these concepts, an FEM simulation is used, considering electrical and mechanical constraints. Furthermore, identification algorithms are presented to evaluate such sensor concepts.

This work presents a dual purpose sensor for collecting proximity and tactile information by using a composite with dielectric elastomer (DE) and Carbon Micro Coils (CMC). CMC is a coil-like carbon microstructure with the size of several hundred micrometers, and its electrical characteristics change with the distance between the object or via physical contact. Especially, the impedance change of the composite depending on the distance can be used as the principle for proximity sensing. We present a method to process the materials by using dielectric materials and additives. A prototype of the sensor is fabricated and its feasibility is experimentally validated.

This work presents an integral approach to the power electronic challenges that are faced in DEAP-based energy conversion, such as wide converter operating ranges and high peak-to-average ratios. It is shown that for small strain cycles, the losses in the Power Electronic Converter (PEC) due to the cyclic charging and discharging are dominant. The efficiency profile of a realistic, high-voltage modular PEC was measured and fed into an optimization algorithm. The current amplitude, phase and shape are optimized, and different cycle types are compared. With optimization results for a wide strain range, it is demonstrated that with properly adapted harvesting cycles, the overall conversion efficiency is significantly improved, especially for small strain cycles.

Generators based on dielectric electroactive polymers (DEAP) convert mechanical strain energy into electrical field energy. In order to harvest renewable energy from ambient sources adequate generator setups have to be developed. Thus, in this contribution a DEAP generator is presented which uses periodic vortex induced vibration of a circular cylinder as excitation mechanism, by which e.g. Flow energy of a wind or water current can be converted. For this purpose a novel generator design consisting of a cylinder that is elastically mounted on DEAP material is presented. Since the effect of vortex induced vibrations depends on the stiffness and damping of the utilized generator's eigenmode, a method to adapt both via the electrostatic pressure and energy conversion is proposed. After the validation of the general functionality of the novel generator design, analyses concerning the control of the overall harvester are carried out.

Dielectric Elastomer Generators (DEGs) are devices that employ a cyclically variable membrane capacitor to produce electricity from oscillating sources of mechanical energy. Capacitance variation is obtained thanks to the use of dielectric and conductive layers that can undergo different states of deformation including: uniform or non-uniform and uni- or multi-axial stretching. Among them, uniform equi-biaxial stretching is reputed as being the most effective state of deformation that maximizes the amount of energy that can be extracted in a cycle by a unit volume of Dielectric Elastomer (DE) material. This paper presents a DEG concept, with linear input motion and tunable impedance, that is based on a mechanical loading system for inducing uniform equi-biaxial states of deformation. The presented system employs two circular DE membrane capacitors that are arranged in an agonist-antagonist configuration. An analytical model of the overall system is developed and used to find the optimal design parameters that make it possible to tune the elastic response of the generator over the range of motion of interest. An apparatus is developed for the equi-biaxial testing of DE membranes and used for the experimental verification of the employed numerical models.

Wave energy harvesting is one of the most promising applications for Dielectric Elastomer Generators. A simple and interesting concept of a Wave Energy Converter based on Dielectric Elastomers is the Polymeric Oscillating Water Column (Poly-OWC). In this paper, preliminary experimental results on the assessment of a small-scale Poly-OWC prototype are presented. The scale of the considered prototype is 1:50. Tests are conducted in a wave-flume by considering sea state conditions with different wave amplitudes and frequencies. The obtained experimental results confirm the viability of the Poly-OWC device.

Dielectric elastomer generators (DEGs) are light, compliant, silent energy scavengers. They can easily be incorporated into clothing where they could scavenge energy from the human kinetic movements for biomedical applications. Nevertheless, scavengers based on dielectric elastomers are soft electrostatic generators requiring a high voltage source to polarize them and high external strain, which constitutes the two major disadvantages of these transducers. We propose here a complete structure made up of a strain absorber, a DEG and a simple electronic power circuit. This new structure looks like a patch, can be attached on human’s wear and located on the chest, knee, elbow… Our original strain absorber, inspired from a sailing boat winch, is able to heighten the external available strain with a minimal factor of 2. The DEG is made of silicone Danfoss Polypower and it has a total area of 6cm per 2.5cm sustaining a maximal strain of 50% at 1Hz. A complete electromechanical analytical model was developed for the DEG associated to this strain absorber. With a poling voltage of 800V, a scavenged energy of 0.57mJ per cycle is achieved with our complete structure. The performance of the DEG can further be improved by enhancing the imposed strain, by designing a stack structure, by using a dielectric elastomer with high dielectric permittivity.

Recently, dielectric elastomer actuators (DEAs) have been adopted to tune liquid membrane lens, just like ciliary muscles do to the lens in human eye. However, it faces some challenges, such as high stress, membrane puncture, high driving voltage requirement, and limited focus distance (not more than 707cm), that limit its practical use. The design problem gets more complex as the liquid lens shares the same elastomeric membrane as the DEA. To address these challenges, we separate DEA from the lens membrane. Instead, a liquid-immersed DEA, which is safe from terminal failure, is used as a diaphragm pump to inflate or deflate the liquid lens by hydraulic pressure. This opens up the possibility that the DEA can be thinned down and stacked up to reduce the driving voltage, independent of the lens membrane thickness. Preliminary study showed that our 8-mm-diameter tunable lens can focus objects in the range of 15cm to 50cm with a small driving voltage of 1.8kV. Further miniaturization of DEA could achieve a driving voltage less than 1kV.

Gels are a new material having three-dimensional network structures of macromolecules. They possess excellent properties as swellability, high permeability and biocompatibility, and have been applied in various fields of daily life, food, medicine, architecture, and chemistry. In this study, we tried to prepare new multi-functional and high-strength gels by using Meso-Decoration (Meso-Deco), one new method of structure design at intermediate mesoscale. High-performance rigid-rod aromatic polymorphic crystals, and the functional groups of thermoreversible Diels-Alder reaction were introduced into soft gels as crosslinkable pendent chains. The functionalization and strengthening of gels can be realized by meso-decorating the gels’ structure using high-performance polymorphic crystals and thermoreversible pendent chains. New gels with good mechanical properties, novel optical properties and thermal properties are expected to be developed.

We experimentally and numerically probe the natural quasi-ordered complex structures in the transparent insect wings by a simple, non-invasive, real time optical diffraction technique using monochromatic cw lasers and broadband femtosecond laser pulses. A complex diffraction pattern in transmission unveils the signature of long range spatial correlation in structural arrangement (symmetry) at various length scales on the whole wing surface for a variety of insect wings. A quantitative analysis analysis of the Fast Fourier transform (FFT) angular spectrum reveals a direct link between the structural organization and optical transmitted diffraction patterns. Our findings directly demonstrate how the diffraction pattern through the transparent insect wings is spatially and functionally correlated with its structural origination at various length scales. The methodology of the studies developed in this paper is applicable to a wide class of disordered photonic structures.

Dielectric elastomer sensors are a recent type of mechanical sensors utilized to detect forces, pressures and deformations. The sensors have several advantages compared with traditional sensors including high elasticity, capacitive sensing and inexpensive fabrication. In this paper, a new sensing device for measuring small concentrated force is proposed. The device deploys the dielectric membrane on the surface of cantilever beam of constant strength. The dielectric membrane is a capacitance sensor built with dielectric polymer coated with soft electrodes. The change in strain arising from the cantilever beam with concentrated force at free end can be quickly transferred to the dielectric membrane. The strain variation of the dielectric membrane induces the change in the capacitance of the membrane. Tests on the device show that the concentrated force at the free end of the cantilever beam is approximately proportional to the change in the capacitance. According to the relation, the unknown concentrated force can be obtained accurately by measuring the change in the capacitance of the dielectric membrane. The new device is capable of monitoring small concentrated force with prominent sensitivity.

Dielectric electroactive polymer (DEAP) actuators are capacitive devices which provide mechanical motions when charged electrically. The charging characteristics of a DEAP actuator depends on its size, voltage applied to its electrodes, and its operating frequency. The main idea of this paper is to design and implement driving circuits for the DEAP actuators for their use in various applications. This paper presents implementation of parallel input, parallel output, high voltage (~2.5 kV) bi-directional DC-DC converters for driving the DEAP actuators. The topology is a bidirectional flyback DC-DC converter incorporating commercially available high voltage MOSFETs (4 kV) and high voltage diodes (5 kV). Although the average current of the aforementioned devices is limited to 300 mA and 150 mA, respectively, connecting the outputs of multiple converters in parallel can provide a scalable design. This enables operating the DEAP actuators in various static and dynamic applications e.g. positioning, vibration generation or damping, and pumps. The proposed idea is experimentally verified by connecting three high voltage converters in parallel to operate a single DEAP actuator. The experimental results with both film capacitive load and the DEAP actuator are shown for a maximum charging voltage of 2 kV.

Dielectric elastomers are useful for large-strain actuation and energy harvesting. Their application has been limited by their low dielectric constants and consequently high driving voltage. Various fillers with high dielectric constants have been incorporated into different elastomer systems to improve the actuation strain, force output and energy density of the compliant actuators and generators. However, agglomeration may happen in these nanocomposites, resulting in a decrease of dielectric strength, an increase of leakage current, and in many instances the degree of enhancement of the dielectric constant. In this work, we investigated aluminum nanoparticles as nanofillers for acrylate copolymers. This metallic nanoparticle was chosen because the availability of free electrons could potentially provide an infinite value of dielectric constant as opposed to dielectric materials including ferroelectric nanocrystals. Moreover, aluminum nanoparticles have a self-passivated oxide shell effectively preventing the formation of conductive path. The surfaces of the aluminum nanoparticles were functionalized with methacrylate groups to assist the uniform dispersion in organic solutions and additionally enable copolymerization with acrylate copolymer matrix during bulk polymerization, and thus to suppress large range drifting of the nanoparticles. The resulting Al nanoparticle-acrylate copolymer nanocomposites were found to exhibit higher dielectric constant and increased stiffness. The leakage current under high electric fields were significantly lower than nanocomposites synthesized without proper nanoparticle surface modification. The dielectric strengths of the composites were comparable with the pristine polymers. In dielectric actuation evaluation, the actuation force output and energy specific work density were enhanced in the nanocomposites compared to the pristine copolymer.

Subject to a voltage, dielectric elastomers deform by the effect of Maxwell stress which is depended directly on the dielectric constant of the material. The combination of large strain, soft elastic response and good dielectric properties has established VHB 4910 elastomer as the most used material for dielectric elastomer actuators. However, the effect of stretch on the dielectric constant for this elastomer is much debated topic while controversy results are demonstrated in the literature. The dielectric constant of this material is studied and demonstrated that it decreases slightly or hugely among the stretch but any pertinent response and any physic explications are validated by the scientific community. In this paper, we presented a detail study about dielectric behavior of VHB 4910 elastomer versus a broadband of stretch and temperature. We found that the dielectric constant of this material depends strongly on the stretch following a polynomial law. Among all the explanations of stretch dependence of the dielectric constant of VHB 4910 in the literature: the crystallization, the change of glass transition temperature, the decrease of dipole orientation, the electrostriction effect under stress; and based on our experimental result, we conclude that the decrease of dipole orientation seems the main reason to the drop of dielectric constant of VHB 4910 elastomer versus the stretch. We proposed also an accurate model describing the dielectric constant of this material for a large range of stretch and temperature.

We present a dielectric elastomer actuator (DEA) for in vitro analysis of mm² biological samples under periodic compressive stress. Understanding how mechanical stimuli affect cell functions could lead to significant advances in diseases diagnosis and drugs development. We previously reported an array of 72 micro-DEAs on a chip to apply a periodic stretch to cells. To diversify our cell mechanotransduction toolkit we have developed an actuator for periodic compression of small cell populations. The device is based on a novel design which exploits the effects of non-equibiaxial pre-stretch and takes advantage of the stress induced in passive regions of DEAs. The device consists of two active regions separated by a 2mm x 2mm passive area. When connected to an AC high-voltage source, the two active regions periodically compress the passive region. Due to the non-equibiaxial pre-stretch it induces uniaxial compressive strain greater than 10%. Cells adsorbed on top of this passive gap would experience the same uniaxial compressive stain. The electrodes configuration confines the electric field and prevents it from reaching the biological sample. A thin layer of silicone is casted on top of the device to ensure a biocompatible environment. This design provides several advantages over alternative technologies such as high optical transparency of the area of interest (passive region under compression) and its potential for miniaturization and parallelization.

Dielectric Elastomer Transducers (DETs) are deformable capacitors that can be used as sensors, actuators and generators. The design of effective and optimized DETs requires the knowledge of a set of relevant properties of the employed Dielectric Elastomer (DE) material, which make it possible to accurately predict their electromechanical dynamic behavior. In this context, an open-access database for DE materials has been created with the aim of providing the practicing engineer with the essential information for the design and optimization of new kinds of DET. Among the electrical properties, dielectric susceptibility, dielectric strength and conductivity are considered along with their dependence on mechanical strain. As regards mechanical behavior, experimental stress-strain curves are provided to predict hyperelasticity, plasticity, viscosity, Mullins effect and mechanical rupture. Properties of commercial elastomeric membranes have been entered in the database and made available to the research community. This paper describes the instrumentations, experimental setups and procedures that have been employed for the characterization of the considered DE materials. To provide an example, the experimental data acquired for a commercially available natural rubber membrane (OPPO Band Red 8012) are presented.

Polypyrrole (PPy) conducting polymers as one of the most well-known actuation materials have shown numerous applications in a variety of fields such as biomedical devices as well as biomimetic robotics. This study investigates the multiobjective optimization of a PPy/MWCNTs actuator through an electrochemomechanical model. The multilayer actuator is composed of a PVDF layer, as the core membrane and an electrolyte reservoir, as well as two one layer of a conjugated polymer and one layer of multiwalled carbon nanotubes deposited on each side of the PVDF layer. In order to obtain the optimum values for each decision variable (i.e., geometrical and electrochemical), the two main outputs of the bending actuator, the tip displacement and blocking force, have been mathematically modeled and formulated as the objective functions. A multiobjective optimization algorithm is applied to simultaneously maximize the blocking force and tip displacement generated by the actuator. Furthermore, a range for each design variable is defined within which none of the objective functions of the film-type actuator dominates the other one while they are both kept within an acceptable range. The results obtained from the mathematical model are experimentally verified. Moreover, in order to determine the performance of the fabricated actuator, its outputs are compared with their counterparts of a neat PPy actuator.

Polypyrrole-based actuators are of interest due to their biocompatibility, low operation voltage and relatively high strain and force. Modeling and simulation are very important to predict the behaviour of each actuator. To develop an accurate model, we need to know the electro-chemo-mechanical specifications of the Polypyrrole. In this paper, the non-linear time-variant model of Polypyrrole film is derived and proposed using a combination of an RC transmission line model and a state space representation. The model incorporates the potential dependent ionic conductivity. A function of ionic conductivity of Polypyrrole vs. local charge is proposed and implemented in the non-linear model. Matching of the measured and simulated electrical response suggests that ionic conductivity of Polypyrrole decreases significantly at negative potential vs. silver/silver chloride and leads to reduced current in the cyclic voltammetry (CV) tests. The next stage is to relate the distributed charging of the polymer to actuation via the strain to charge ratio. Further work is also needed to identify ionic and electronic conductivities as well as capacitance as a function of oxidation state so that a fully predictive model can be created.

Performance of the conducting polymer actuators (CPAs) are affected by material uncertainties, operating conditions and time of operation. The same size CPAs may have different actuation capabilities, which can also degrade over the course of operation. For accurate and repeatable position tracking, the uncertainties and variations in the actuator dynamics have to be carefully addressed to achieve a desirable control performance. This paper presents a systematic approach for the identification of parametric uncertainties and designing robust H_∞ control to achieve a guaranteed performance when the CPA is used for position tracking. We identify the uncertainties in actuator dynamics by performing series of experiments using two geometrically equivalent CPAs. A set of system models is obtained to determine the average actuation capability. The variations in the actuator dynamics are modeled as a parametric uncertainty. H_∞ controllers are designed and the robustness of the controllers is validated by experiments on two different but same sized CPAs. The performance of the H_∞ controller is also compared with a proportional-integralderivative (PID) controller. We demonstrate that the robust H_∞control strategy performs repeated acceptable performances on both samples.

Carbide–derived Carbon (CDC) material is applied for super capacitors due to their nanoporous structure and their high charging/discharging capability. In this work we report for the first time CDC linear actuators and CDC combined with polypyrrole (CDC-PPy) in ECMD (Electrochemomechanical deformation) under isotonic (constant force) and isometric (constant length) measurements in aqueous electrolyte. CDC-PPy actuators showing nearly double strain under cyclic voltammetric and square wave potential measurements in comparison to CDC linear actuators. The new material is investigated by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray analysis) to reveal how the conducting polymer layer and the CDC layer interfere together.

With smart materials and adaptive structures being nudged into mainstream technology progressively, the smart composites are donning a predominant role as indispensable structures. Among these, the Ionic Polymer Metal Composites (IPMC), with their large bending deformation and relaxation characteristics at very low voltages are attractive as transducers in many areas of application. The actuation and sensing properties of IPMC have been sought after for various engineering functions. The paper focuses on combining the ionic polymer with multi-walled carbon nanotube Bucky paper electrodes to create an enhanced IPMC, and comparatively analyzes the different methodologies briefly discussing the electrode morphology and also compares the uniformity of the electrode plating obtained from the different processes. This paper also concentrates on making use of different ionic solutions for comparison such as to determine the most suited ion content within the solid electrolyte for effective IPMC actuation. This new functionally graded material is tested for its bending deformation, blocking force and the current consumption to prove the electromechanical efficiency of the Bucky paper IPMC. By studying the electromechanical properties of this smart composite actuator based on its actuation under different electric excitations, we can draw conclusions subsequently from the results of the comparison.

In this paper, we analyze buckling of an ionic polymer metal composite (IPMC) shell subjected to uniaxial compression. A new technique is developed to fabricate tubular IPMCs using hot molding and a chemical reduction process. The short-circuit current and the mechanical deformation of the sample are recorded during the compression test. Experimental findings demonstrate that IPMC buckling can be accurately sensed via the short-circuit current, which is approximately zero during the loading phase, before exhibiting a sudden increase at the onset of the elastic instability.

To perform tasks such as hold an object with a constant force, the reliable control of an ionic electroactive polymer actuator is essential. The composite under research is an IPMC actuator with electrodes composed of nanoporous carbon and membrane made of ionic polymer. Compared to traditional platinum electrodes, these novel electrodes do not crack in clusters and have highly controllable properties which preserve even when the actuator is deformed. So far, there are no reports on the dynamic force response of this composite. We present the first attempts of testing the force dynamics of an IPMC with nanoporous carbon electrodes under open- and closed-loop controls. As many attempts have been focused on the sensorless force control of ionic electroactive polymers, we first investigate the uncompensated dynamics of the actuator, then use the direct inverse model to obtain the desired tracking performance. We also aim to identify the conditions, under which the actuator is suitable for sensorless control. Furthermore, we improve the tracking ability of the actuator using a feedback controller where the force sensor data is available and incorporate a feedforward controller into the feedback control system. Based on the experiments, the resulting effects on the tracking performance are observed.

Chromatophores are the colour changing organelles in the skins of animals including fish and cephalopods. The ability of cephalopods in particular to rapidly change their colouration in response to environmental changes, for example to camouflage against a new background, and in social situations, for example to attract a mate or repel a rival, is extremely attractive for engineering, medical, active clothing and biomimetic robotic applications. The rapid response of these chromatophores is possible by the direct coupling of fast acting muscle and pigmented saccules. In artificial chromatophores we are able to mimic this structure using electroactive polymer artificial muscles. In contrast to prior research which has demonstrated monochromatic artificial chromatophores, here we consider a novel multi-colour, multi-layer, artificial chromatophore structure inspired by the complex dermal chromatophore unit in nature and which exploits dielectric elastomer artificial muscles as the electroactive actuation mechanism. We investigate the optical properties of this chromatophore unit and explore the range of colours and effects that a single unit and a matrix of chromatophores can produce. The colour gamut of the multi-colour chromatophore is analysed and shows its suitability for practical display and camouflage applications. It is demonstrated how, by varying actuator strain and chromatophore base colour, the gamut can be shifted through colour space, thereby tuning the artificial chromatophore to a specific environment or application.

ABSTRACT: Bistable electroactive polymers (BSEP) amalgamating electrically induced large-strain actuation and shape memory effect present a unique opportunity for refreshable Braille displays. A new BSEP material with long-chain crosslinkers to achieve prolonged cycle lifetime of refreshable Braille displays is reported here. The modulus of the BSEP material decreases by more than three orders of magnitude from a rigid, plastic state to a rubbery state when heated above the polymer’s glass transition temperature. In its rubbery state, the polymer film can be electrically actuated to buckle convexly when a high voltage is applied across a circular active area. Modifying the concentration of long-chain crosslinkers in the polymer allows not only for fine-tuning of the polymer’s glass transition temperature and elasticity in the rubbery state, but also enhancement of the actuation stability. For a raised height of 0.4 mm by a Braille dot with a 1.3 mm diameter, actuation can be repeated over 2000 cycles at 70°C in the rubbery state. The actuated dome shape can be fixed by cooling the polymer below the glass transition temperature. This refreshable rigid-to-rigid actuation simultaneously provides large-strain actuation and large force support. Devices capable of displaying Braille characters over a page-size area consisting of 324 Braille cells have been fabricated.

Twisted carbon nanotube yarns have been shown to develop useful torsional and tensile actuation. Particularly useful are those hybrid yarns that incorporate a volume-changing guest material into the yarn pore space. Changing guest volume causes concomitant untwisting and shortening of the twisted yarn. Intriguingly, the magnitude of the tensile actuation can be increased by an order of magnitude by inserting such high twist into the fiber as to cause coiling. The mechanism of coil-induced stroke enhancement is investigated using ordinary spring mechanics and it is shown that tensile actuation can be adequately predicted from the coil and yarn geometries.

Many devices and processes produce low grade waste heat. Some of these include combustion engines, electrical circuits, biological processes and industrial processes. To harvest this heat energy thermoelectric devices, using the Seebeck effect, are commonly used. However, these devices have limitations in efficiency, and usable voltage. This paper investigates the viability of a Stirling engine coupled to an artificial muscle energy harvester to efficiently convert heat energy into electrical energy. The results present the testing of the prototype generator which produced 200 μW when operating at 75°C. Pathways for improved performance are discussed which include optimising the electronic control of the artificial muscle, adjusting the mechanical properties of the artificial muscle to work optimally with the remainder of the system, good sealing, and tuning the resonance of the displacer to minimise the power required to drive it.

Dielectric elastomers (DE) are thin polymer films belonging to the class of electroactive polymers (EAP), which are coated with compliant and conductive electrodes on each side. Due to the influence of an electrical field, dielectric elastomers perform a large amount of deformation. In this contribution a manufacturing process of automated fabricated stack-actuators based on dielectric electroactive polymers (DEAP) are presented. First of all the specific design of the considered stack-actuator is explained and afterwards the development, construction and realization of an automated manufacturing process is presented in detail. By applying this automated process, stack-actuators with reproducible and homogeneous properties can be manufactured. Finally, first DEAP actuator modules fabricated by the mentioned process are validated experimentally.

In this work we present a novel microfabrication process that is based on combined use of dielectrophoresis (DEP) to attract particles or cells to electrodes and to follow this step by an electrodeposition of polypyrrole (PPy) to entrap the particles or cells on electrode surface. This process can be used for mass-production of high surface area structures as well as to the creation of functionally graded materials. DEP was employed to pull the microparticles toward the surface of the electrodes and hold them in place while PPy was electrodeposited. Polystyrene microbeads with diameters ranging from 1 to 10 microns were employed in this study. Experimental results demonstrated that PPy can entrap the particles attracted to the electrode surface by the positive DEP. It was also demonstrated that hierarchical structures can be created where smaller microbeads are attached to, caught and secured on the surface of larger microbeads entrapped on the electrode surface. Furthermore, as DEP can be employed for manipulating of wide variety of polarizable materials, this process can also entrap inorganic and biological microparticles in the fabricated structure. Applications of this work include, but are not limited to, the development of biomedical, electrokinetic, and energy storage devices, electrochemical sensors, and scaffolds.

We present an analysis on the feasibility of the 3D printing technology known as Stereolithography for adaption to Dielectric Elastomer (DE) Production. We also present a method for 3D printing in two materials using Stereolithography, solving one of the main challenges identified in adapting this technology to DEs. Stereolithography is well suited to DE production because of similarities in the materials used and because of its high achievable resolution. However, DE production requires the use of two separate materials, and of soft materials, both of which are difficult with Stereolithography. Our method makes two material printing with Stereolithography possible by using multiple resin baths and an intermediary cleaning step. If the other challenges can be overcome, automatic 3D production of DEs will be possible.

Electroactive polymers, or EAPs, are polymers that exhibit a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. One promising technology is the elaboration of electronic conducting polymers based actuators with Interpenetrating Polymer Networks (IPNs) architecture. Their many advantageous properties as low working voltage, light weight and high lifetime make them very attractive for various applications including robotics. Conducting IPNs were fabricated by oxidative polymerization of 3,4-ethylenedioxythiophene within a flexible Solid Polymer Electrolytes (SPE) combining poly(ethylene oxide) and Nitrile Butadiene Rubber. SPE mechanical properties and ionic conductivities in the presence of 1-ethyl-3- methylimidazolium bis-(trifluoromethylsulfonyl)-imide (EMITFSI) have been characterized. The presence of the elastomer within the SPE greatly improves the actuator performances. The free strain as well as the blocking force was characterized as a function of the actuator length. The sensing properties of those conducting IPNs allow their integration into a biomimetic perception prototype: a system mimicking the tactile perception of rat vibrissae.

Comparative measurements of carbon-polymer composite micro-actuators based on room temperature ionic liquid electrolyte were carried out in situ (1) in vacuum using a state-of-the-art scanning electron microscope, (2) in an oxygen-free atmosphere under ambient pressure, and (3) under ambient environment. The fabricated micro-actuators sustained their actuation performance in all three environments, revealing important implications regarding their humidity-dependence. SEM observations demonstrate high stroke actuation of a device with submillimeter length, which is the typical size range of actuators desirable for medical or lab-on-chip applications.

Dielectric elastomer actuator (DEA) is a kind of soft actuators that can produce significantly large electric-field induced actuation strain and may be a basic unit of artificial muscles and robotic elements. Understanding strain development on a pre-stretched sample at different regimes of electrical field is essential for potential applications. In this paper, we report about ongoing work on determination of area strain using digital camera and image processing technique. The setup, developed in house consists of low cost digital camera, data acquisition and image processing algorithm. Samples have been prepared by biaxially stretched acrylic tape and supported between two cardboard frames. Carbon-grease has been pasted on the both sides of the sample, which will be compliant with electric field induced large deformation. Images have been grabbed before and after the application of high voltage. From incremental image area, strain has been calculated as a function of applied voltage on a pre-stretched dielectric elastomer (DE) sample. Area strain has been plotted with the applied voltage for different pre-stretched samples. Our study shows that the area strain exhibits nonlinear relationship with applied voltage. For same voltage higher area strain has been generated on a sample having higher pre-stretched value. Also our characterization matches well with previously published results which have been done with costly video extensometer. The study may be helpful for the designers to fabricate the biaxial pre-stretched planar actuator from similar kind of materials.

A soft robotic device inspired by the pumping action of a biological heart is presented in this study. Developing artificial heart to a humanoid robot enables us to make a better biomedical device for ultimate use in humans. As technology continues to become more advanced, the methods in which we implement high performance and biomimetic artificial organs is getting nearer each day. In this paper, we present the design and development of a soft artificial heart that can be used in a humanoid robot and simulate the functions of a human heart using shape memory alloy technology. The robotic heart is designed to pump a blood-like fluid to parts of the robot such as the face to simulate someone blushing or when someone is angry by the use of elastomeric substrates and certain features for the transport of fluids.

Dielectric Elastomer Actuators (DEAs) are an emerging actuation technology which are inherent lightweight and compliant in nature, enabling the development of unique and versatile devices, such as the Dielectric Elastomer Minimum Energy Structure (DEMES). We present the development of a multisegment DEMES actuator for use in a deployable microsatellite gripper. The satellite, called CleanSpace One, will demonstrate active debris removal (ADR) in space using a small cost effective system. The inherent flexibility and lightweight nature of the DEMES actuator enables space efficient storage (e.g. in a rolled configuration) of the gripper prior to deployment. Multisegment DEMES have multiple open sections and are an effective way of amplifying bending deformation. We present the evolution of our DEMES actuator design from initial concepts up until the final design, describing briefly the trade-offs associated with each method. We describe the optimization of our chosen design concept and characterize this design in terms on bending angle as a function of input voltage and gripping force. Prior to the characterization the actuator was stored and subsequently deployed from a rolled state, a capability made possible thanks to the fabrication methodology and materials used. A tip angle change of approximately 60° and a gripping force of 0.8 mN (for small deflections from the actuator tip) were achieved. The prototype actuators (approximately 10 cm in length) weigh a maximum of 0.65 g and are robust and mechanically resilient, demonstrating over 80,000 activation cycles.

In this paper, a humanoid robot is presented for ultimate use in the rehabilitation of children with mental disorders, such as autism. Creating affordable and efficient humanoids could assist the therapy in psychiatric disability by offering multimodal communication between the humanoid and humans. Yet, the humanoid development needs a seamless integration of artificial muscles, sensors, controllers and structures. We have designed a human-like robot that has 15 DOF, 580 mm tall and 925 mm arm span using a rapid prototyping system. The robot has a human-like appearance and movement. Flexible sensors around the arm and hands for safe human-robot interactions, and a two-wheel mobile platform for maneuverability are incorporated in the design. The robot has facial features for illustrating human-friendly behavior. The mechanical design of the robot and the characterization of the flexible sensors are presented. Comprehensive study on the upper body design, mobile base, actuators selection, electronics, and performance evaluation are included in this paper.

In this paper the concept of a PVDF based gesture controller is introduced and accompanied by a supporting model derived using Hamilton’s principle. The model incorporates strain contributions from two loading situations: beam subject to transverse loading and axial loading. The prototype gesture controller is comprised of a compression sleeve with a spatially shaded PVDF element situated above the extensor muscles of the right forearm. The goal of the gesture controller, at this stage, is to be able to measure and discern forearm muscle activity for three distinct hand gestures. In this study the system was modeled and simulated. Test data was then collected for each hand gesture and compared to simulations.

Ionic polymer-metal composite (IPMC) has been examined through simulation and experimental tests as a material for use in multi degree of freedom (DOF) sensor applications. Mechanoelectrical transduction, the ability to generate current from imposed mechanical deformation, enables IPMCs to be applied as sensor devices. This phenomenon has been reported and is reasonably well described by various models. In this study, a physics-based model is applied to predict performance of an IPMC sensor over a range of conditions. Configuration of our interest is cylindrical IPMC with 2-DOF mechanoelectrical sensor capabilities. The prototype of cylindrical IPMC has an outer diameter of 1 mm and a 25 mm length. Application of deformation induced voltage of the fabricated cylindrical IPMCs as a means of mechanoelectrical transduction have been simulated and experimentally verified. The performance of the prototype IPMC under several operating conditions was also analyzed, and experimental results have provided keen insight into the physical phenomenon of mechanoelectical IPMC transduction.

As our population ages, and trends in obesity continue to grow, joint degenerative diseases like osteoarthritis (OA) are becoming increasingly prevalent. With no cure currently in sight, the only effective treatments for OA are orthopaedic surgery and prolonged rehabilitation, neither of which is guaranteed to succeed. Gait retraining has tremendous potential to alter the contact forces in the joints due to walking, reducing the risk of one developing hip and knee OA. Dielectric Elastomer Actuators (DEAs) are being explored as a potential way of applying intuitive haptic feedback to alter a patient’s walking gait. The main challenge with the use of DEAs in this application is producing large enough forces and strains to induce sensation when coupled to a patient’s skin. A novel controller has been proposed to solve this issue. The controller uses simultaneous capacitive self-sensing and actuation which will optimally apply a haptic sensation to the patient’s skin independent of variability in DEAs and patient geometries.

Robotic devices typically utilize rigid components in order to produce precise and robust operation. Rigidity becomes a significant impediment, however, when navigating confined or constricted environments e.g. search-and-rescue, industrial pipe inspection. In such cases adaptively conformable soft structures become optimal. Dielectric elastomers (DEs) are well suited for developing such soft robots since they are inherently compliant and can produce large musclelike actuation strains. In this paper, a soft segmented inchworm robot is presented that utilizes pneumatically-coupled DE membranes to produce inchworm-like locomotion. The robot is constructed from repeated body segments, each with a simple control architecture, so that the total length can be readily adapted by adding or removing segments. Each segment consists of a soft inflatable shell (internal pressure in range of 1.0-15.9 mBar) and a pair of antagonistic DE membranes (VHB 4905). Experimental testing of a single body segment is presented and the relationship between drive voltage, pneumatic pressure and active displacement is characterized. This demonstrates that pneumatic coupling of DE membranes induces complex non-linear electro-mechanical behaviour as drive voltage and pneumatic pressure are altered. Locomotion of a two-segment inchworm robot prototype with a passive length of 80 mm is presented. Artificial setae are included on the body shell to generate anisotropic friction for locomotion. A maximum locomotion speed of 4.1 mm/s was recorded at a drive frequency of 1.5 Hz, which compares favourably to biological counterparts. Future development of the soft inchworm robot are discussed including reflexive low-level control of individual segments.

We present the successful operation of the first dielectric elastomer actuator (DEA) driven tunable millimeter-wave phase shifter. The development of dynamically reconfigurable microwave/millimeter-wave (MW/MMW) antenna devices is becoming a prime need in the field of telecommunications and sensing. The real time updating of antenna characteristics such as coverage or operation frequency is particularly desired. However, in many circumstances currently available technologies suffer from high EM losses, increased complexity and cost. Conversely, reconfigurable devices based on DEAs offer low complexity, low electromagnetic (EM) losses and analogue operation. Our tunable phase shifter consists of metallic strips suspended a fixed distance above a coplanar waveguide (CPW) by planar DEAs. The planar actuators displace the metallic strips (10 mm in length) in-plane by 500 μm, modifying the EM field distribution, resulting in the desired phase shift. The demanding spacing (50 ±5 μm between CPW and metallic strips) and parallel alignment criteria required for optimal device operation are successfully met in our device design and validated using bespoke methods. Our current device, approximately 60 mm x 60 mm in planar dimensions, meets the displacement requirements and we observe a considerable phase shift (~95° at 25 GHz) closely matching numerical simulations. Moreover, our device achieves state of the art performance in terms of phase shift per EM loss ~235°/dB (35 GHz), significantly out performing other phase shifter technologies, such as MMIC phase shifters.

A novel duct silencer was developed using dielectric elastomer absorbers (DEAs). Dielectric elastomer, a lightweight, high elastic energy density and large deformation under high DC/AC voltages smart material, was used to fabricate this new generation actuator. The acoustic performances of this duct silencer were experimentally investigated in a transmission loss (TL) measurement system using two-load method. It was found that the resonance peaks of this new duct silencer could be controlled by applying various DC voltages, a maximum resonance shift of 59.5Hz for the resonance peaks was achieved which indicated that this duct silencer could be adjusted to absorb broadband range noise without any addition mechanical part. Furthermore, the resonance shift and multiple resonances mechanisms using DEAs were proposed and discussed in the present paper which was aiming to achieve broadband noise reduction. The present results also provide insight into the appropriateness of the absorber for possible use as new acoustic treatment to replace the traditional acoustic treatment.

The article presents a working whisker structure based on dielectric elastomer actuators (DEAs). This preliminary work aims to exploit the features of the dielectric elastomer technology for use in an effective and reliable robotic application whilst accommodating the limitations of this emerging actuation technique. To this end, a modular design and structure have been conceived to simplify the building and repair process of the critical components such as the connectors, wiring, sensors and DEA membranes. This design represents the engineering and scaling of the concepts and techniques developed in previous work, and to overcome identified technical and methodological constraints that previously prohibited extensive real applications. The structure is realised as a trade-off between the unique characteristics of the DEA technology and the robotic development issues. Safety, robustness, production time and key aspects of robotic design are taken into account in the development of this prototype. The results presented show how this structure addresses the design requirement and technical constraints previously identified. The active whisking range achieved is ±14 degrees, measured using image processing of videos captured by both standard and high speed cameras. This metric will be used as one of the measures for planned improvements that are discussed in addition to the advantages and limitations of the structure and the design decisions made.

The most common approaches for the fabrication of poly(vinylidene fluoride)(PVDF)/ multi-walled carbon nanotubes(MWNTs) nanocomposites involve solution crystallization and melting crystallization methods. In this study, PVDF/ MWNTs nanocomposites with varied contents of MWCNTs (up to 0.3wt.%) were prepared via solution crystallized at 80 °C, solution crystallized at 120 °C and melting at 200 °C. The effect of processing conditions on the crystal structure, morphology, dielectric and ferroelectric properties of PVDF with the presence of MWNTs was investigated. It is seen that crystallization temperatures and the concentrations of MWNTs have a synergetic effect of on the crystal phase and crystallinity of PVDF. Higher crystallization temperatures appeared to be detrimental to the dispersion of MWNTs in PVDF matrix, however, it was advantage to the growth of crystals and leaded to a higher degree of crystallinity. Lower crystallization temperatures favored the dispersion of MWNTs in PVDF matrix, which can effectively promote the formation of polar crystalline β-phase of PVDF. In addition, MWNTs at relatively low content (<0.1 wt.%) can disperse well in PVDF matrix in different approaches, resulting in high content of -phase and enhancements in dielectric and ferroelectric properties.

The research on soft elastomers with high dielectric permittivity for the use as dielectric electroactive polymers (DEAP) has grown substantially within the last decade. The approaches to enhance the dielectric permittivity can be categorized into three main classes: 1) Mixing or blending in high permittivity fillers, 2) Grafting of high permittivity molecules onto the polymer backbone in the elastomer, and 3) Encapsulation of high permittivity fillers. The approach investigated here is a new type of encapsulation which does not interfere with the mechanical properties to the same content as for the traditionally applied thermoplastic encapsulation. The properties of the elastomers are investigated as function of the filler content and type. The dielectric permittivity, dielectric loss, conductivity, storage modulus as well as viscous loss are compared to elastomers with the same amounts of high permittivity fillers blended into the elastomer, and it is found that the encapsulation provides a technique to enhance some of these properties.

Due to the advantages of DEAP (Dielectric Electro Active Polymer) material, such as light weight, noise free operation, high energy and power density and fast response speed, it can be applied in a variety of applications to replace the conventional transducers or actuators. This paper introduces DEAP actuator to the heating valve system and conducts a case study to discuss the feasible solution in designing DEAP actuator and its driver for heating valve application. First of all, the heating valves under study are briefly introduced. Then the design and the development for DEAP actuator is illustrated in detail, and followed by the detailed investigation of the HV driver for DEAP actuator. In order to verify the implementation, the experimental measurements are carried out for DEAP actuator, its HV driver as well as the entire heating valve system.

Dielectric elastomers are being developed for use in actuators, sensors and generators to be used in various applications, such as artificial eye lids, pressure sensors and human motion energy generators. In order to obtain maximum efficiency, the devices are operated at high electrical fields. This increases the likelihood for electrical breakdown significantly. Hence, for many applications the performance of the dielectric elastomers is limited by this risk of failure, which is triggered by several factors. Amongst others thermal effects may strongly influence the electrical breakdown strength. In this study, we model the electrothermal breakdown in thin PDMS based dielectric elastomers in order to evaluate the thermal mechanisms behind the electrical failures. The objective is to predict the operation range of PDMS based dielectric elastomers with respect to the temperature at given electric field. We performed numerical analysis with a quasi-steady state approximation to predict thermal runaway of dielectric elastomer films. We also studied experimentally the effect of temperature on dielectric properties of different PDMS dielectric elastomers. Different films with different percentages of silica and permittivity enhancing filler were selected for the measurements. From the modeling based on the fitting of experimental data, it is found that the electrothermal breakdown of the materials is strongly influenced by the increase in both dielectric permittivity and conductivity.

A variety of possible configurations have been developed to exploit the capabilities of the dielectric elastomers. Circular dielectric actuator is a simple flexible structure that can be used in many areas, for example, it can be employed to adjust the properties of the optical elements. The configurations of circular dielectric actuators range from one active dielectric region to multiple active dielectric regions. When the active dielectric regions subjected to a voltage, they will expand and compress the electrode-less regions. The circular actuator in this work consists of two electrode regions and two electrode-less regions. One electrode-less region is an annular elastomer sandwiched between the inner dielectric circle and the middle dielectric annulus. The other electrode-less region is between the middle dielectric annulus and the rigid frame. We study the properties of the actuator based on the ideal dielectric model and obtain the relationship between the applied voltage and the deformation. Additionally, the inhomogeneous deformation of the circular actuator has been investigated both theoretically and experimentally and a good correlation is achieved. The strategy presented here is generic and can be applied to other circular configurations with multiple regions. The results may contribute to the use of circular dielectric actuators in advance.

The autofocus fluid lens device, as developed by Philips, is based on water/oil interfaces forming a spherical lens where the meniscus of the liquid can be switched by applying a high voltage to change from a convex to a concave divergent lens. In this work we construct a device to evaluate the performance of membrane actuators based on electro active polymers, in a design applicable for autofocus fluid lens applications. The membrane with a hole in the middle separates the oil phase from the electrolyte phase, forming a meniscus in the middle of the membrane between the oil and electrolyte. If the membrane actuator shows a certain force and displacement, the meniscus between oil and electrolyte changes form between concave and convex, applicable as a fluid lens. Ionic polymer metal composites (IPMCs) are applied in this work to investigate how the performance of the membrane actuator takes place in Milli-Q, certain electrolytes and in combination with an electrochemically deposited conducting polymer. The goal of this work is to investigate the extent of membrane displacement of IPMC actuators operating at a low voltage (±0.7 V), and the back relaxation phenomena of IPMC actuators.

An investigation is reported into the electrochemomechanical deformation (ECMD) of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS) in the form of freestanding films and deposited onto conductive substrates (chemically fixed poly-3,4-(ethylenedioxythiophene, PEDOT) based on PVdF (poly(vinylidenefluoride)). Linear actuation has been achieved starting from a trilayer bending actuator design with a stretchable middle layer. To allow evaluation of the proposed design, commercially available PVdF membranes were chosen as model material. For bending trilayer functionality, electronic separation of both electrode layers is essential, but in order to obtain linear actuation, the CP layers on either side are connected to form a single working electrode. The PPyDBS free standing films and PPyDBS deposited on PEDOT-PVdF-PEDOT were investigated by electrochemical methods (cyclic voltammetry, square wave potentials) in a 4-methyl-1,3-dioxolan-2-one (propylene carbonate, PC) solution of tetrabutylammonium trifluoromethanesulfonate (TBACF3SO3). This study also presents a novel method of utilizing scanning ion-conductance microscopy (SICM) to accurately examine the electrochemical redox behavior of the surface layer of the linear actuator using a micropipette tip.

The performance of a charge-controlled dielectric elastomer membrane is remarkably affected by the leakage current. Based on a charge-controlled dielectric elastomer configuration, this paper presents a theoretical study about the effect of leakage current on the performance of a dielectric elastomer membrane by spraying charge to the two surfaces of DE membrane. It is found that all of the stretch, the charge, and the electric displacement reduce gradually with the time because of the current leakage. The leakage current reduces gradually with the time, and has an abrupt drop in the initial period and becomes gently after a relatively long time. Based on the results of this paper, we have to keep spraying charge to make up the leaked one to maintain the charge-induced stretch.

In this paper, the emerging technology of energy harvesting based on dielectric elastomers (DE), a new type of functional materials belonging to the family of Electroactive Polymers (EAPs), is presented with emphasis on its performance characteristics and some key influencing factors. At first, on the basic principle of DE energy harvesting, the effects of some control parameters are theoretically analyzed under certain mechanical and electrical constraints. Then, a type of annular DE generator using the commercial elastomers of VHB 4910 (3M, USA), is specially designed and fabricated. A series of experimental tests for the device’s energy harvesting performance are implemented at different pre-stretch ratios, stretch amplitudes (displacements), and bias voltages in the constant charge (open-circuit) condition. The experiment results demonstrate the associated influence laws of the above control parameters on the performance of the DE generator, and have good consistent with those obtained from the theoretical analysis. This study is expected to provide a helpful guidance for the design and operation of practical DE energy harvesting devices/systems.

DE (dielectric elastomer) is one of the most promising artificial muscle materials for its large strain over 100% under driving voltage. However, to date, dielectric elastomer actuators (DEAs) are prone to failure due to the temperature-dependent electric breakdown. Previously studies had shown that the electrical breakdown strength was mainly related to the temperature-dependent elasticity modulus and the permittivity of dielectric substances. This paper investigated the influence of ambient temperature on the electric breakdown strength of DE membranes (VHB4910 3M). The electric breakdown experiment of the DE membrane was conducted at different ambient temperatures and pre-stretch levels. The real breakdown strength was obtained by measuring the deformation and the breakdown voltage simultaneously. Then, we found that with the increase of the environment temperature, the electric breakdown strength decreased obviously. Contrarily, the high pre-stretch level led to the large electric breakdown strength. What is more, we found that the deformations of DEs were strongly dependent on the ambient temperature.

As a new kind of ionic-driven smart materials, ionic polymer metal composite (IPMC ) is normally fabricated by depositing noble metal (gold, platinum, palladium etc.) on both sides of base membrane (Nafion, Flemion etc.) and shows large bending deflection under low voltage. In the process of fabricating IPMC, surface roughening of base membrane has a significant effect on the performance of IPMC. At present, there are many ways to roughen the base membrane, including physical and chemical ways. In this paper, we analyze the effects of different surface treatment time by plasma etching on surface resistance and mechanical properties of IPMCs fabricated by the treated base membranes. Experimental results show that the base membrane treated by plasma etching displays uniform surface roughness, consequently reducing IPMC’s surface resistance effectively and forming more uniform and homogeneous external and penetrative electrodes. However, due to the use of reactive gas, the plasma treatment leads to complex chemical reaction on Nafion surface, changing element composition and material properties and resulting in the performance degradation of IPMC. And sandblast way should be adopted and improved without any changes on element and material structure.

Ionic polymer-metal composite (IPMC) is one of the electro-active polymer materials which respond to electric stimuli with shape change. IPMC actuators can be activated with simple driving circuit and common control approach; however, dynamic characteristics change from environmental conditions such as the temperature or humidity. The output force of IPMC is very small, and the stress relaxation exists depending on the type of the counter-ions in the electrolyte. Therefore, it is desirable to construct robust controllers and connection of multiple actuator units to obtain stable and large output force. In this study, we apply a control method for cellular actuators to solve above problems. The cellular actuator is a concept of the actuators which consist of multiple actuator units. The actuator units connect in parallel or series, and each unit is controlled by distributed controllers, which are switched ON/OFF state stochastically depending on the broadcast error signal which is generated in the central controller. In this paper, we verify the control performance of the cellular actuator method through numerical simulations. In the simulations, we assume that the one hundred units of IPMC connected in parallel, the output force is controlled to the desired value. The control performance is investigated in the case of some mixed ratio of units whose counter-ions are Sodium (Na) ion or Tetraethylammonium (TEA). As a result of simulation, it was confirmed that the tracking performance is improved by combining the fast response actuator units of Na ions and the large output actuator units of TEA ions.

Dielectric elastomer generators (DEGs) produce electrical energy by converting mechanical into electrical energy. Efficient operation requires an optimal deformation of the DEG during the energy harvesting cycle. However, the deformation resulting from an external load has to be applied to the DEG. The deformation behavior of the DEG is dependent on the type of the mechanical interconnection between the elastic DEG and a stiff support area. The maximization of the capacitance of the DEG in the deformed state leads to the maximum absolute energy gain. Therefore several configurations of mechanical interconnections between a single DEG module as well as multiple stacked DEG modules and stiff supports are investigated in order to find the optimal mechanical interconnection. The investigation is done with numerical simulations using the FEM software ANSYS. A DEG module consists of 50 active dielectric layers with a single layer thickness of 50 μm. The elastomer material is silicone (PDMS) while the compliant electrodes are made of graphite powder. In the simulation the real material parameters of the PDMS and the graphite electrodes are included to compare simulation results to experimental investigations in the future. The numerical simulations of the several configurations are carried out as coupled electro-mechanical simulation for the first step in an energy harvesting cycle with constant external load strain. The simulation results are discussed and an optimal mechanical interconnection between DEG modules and stiff supports is derived.

A significant limitation of large-scale dielectric electroactive polymers (DEAP) actuators is their slow and rate dependent dynamic response. We develop a procedure to characterize, model and test DEAP planar actuators with integrated bi-stable mechanisms. We describe a procedure to design the bi-stable element, a post-buckled slender beam, so as to improve the quasi-static performance of the actuator. The impact of the bi-stable mechanism on the dynamic performance of the actuator is studied by measuring its maximum planar peak-topeak displacement upon dynamic excitation. Surprisingly, the dynamic performance is strongly enhanced by the bi-stable mechanism. The frequency response flattens and becomes almost frequency independent up to the resonant frequency of the actuator. Moreover, a four-fold increase in active displacement stroke is achieved. The margin for further improvements is large, commensurated with the aims of the present research: namely the fabrication of large-scale, planar oscillating surfaces for turbulent flow control purposes.

Dielectric elastomer is a kind of smart soft material that has many advantages such as large deformation, fast response, light weight and easy synthesis. Subject to a high voltage, dielectric elastomer film will deform sustainably. These features make dielectric elastomer a suitable material for actuators. This paper discussed a spring-roll bending actuator of dielectric elastomer. An actuator based on dielectric elastomer that could bend when applied a high voltage was fabricated. Based on thermodynamics theories, a theoretical model of dielectric elastomer bending actuator was established and the initial deformation and bending deformation of bending actuator was formulated. Most parameters used in formulas could be obtained from fabrication process or test data and theoretical prediction with these parameters explained the experimental phenomena well. Also, the allowable area of bending actuator is determined considering several failure models including electromechanical instability, electrical breakdown and tensile rupture.

Tactile stimulation enhances user experience and efficiency in human machine interaction by providing information via another sensory channel to the human brain. DEA as tactile interfaces have been in the focus of research in recent years. Examples are (vibro-) tactile keyboards or Braille displays. These applications of DEA focus mainly on interfacing with the user’s fingers or fingertips only – demonstrating the high spatial resolution achievable with DEA. Besides providing a high resolution, the flexibility of DEA also allows designing free form surfaces equipped with single actuators or actuator matrices which can be fitted to the surface of the human skin. The actuators can then be used to provide tactile stimuli to different areas of the body, not to the fingertips only. Utilizing and demonstrating this flexibility we designed a free form DEA pad shaped to fit into the inside of the human palm. This pad consists of four single actuators which can provide e.g. directional information such as left, right, up and down. To demonstrate the value of such free form actuators we manufactured a PC-mouse using 3d printing processes. The actuator pad is mounted on the back of the mouse, resting against the palm while operating it. Software on the PC allows control of the vibration patterns displayed by the actuators. This allows helping the user by raising attention to certain directions or by discriminating between different modes like “pick” or “manipulate”. Results of first tests of the device show an improved user experience while operating the PC mouse.

The use of dielectric elastomer (DE) for the realisation of new generation actuators has attracted the interest of many researchers in the last ten years due to their high efficiency, a very good electromechanical coupling and large achievable strains [1-3]. Although these properties constitute a very important advantage, the industrial exploitation of such systems is hindered by the high voltages required for the actuation [4] that could potentially constitute also a risk for the operators. In this work we present a DE based active layer that can be used in different macro-scaled parts of industrial equipment for roto-flexographic printing substituting traditional mechanical devices, reducing manufacturing costs and enhancing its reliability. Moreover, the specific configuration of the system requires the driving voltage to be applied only in the mounting/dismounting step thus lowering further the operative costs without posing any threat for the workers. Starting from the industrial requirements, a complete thermo-mechanical characterisation using DSC and DMA was undertaken on acrylic elastomer films in order to investigate their behaviour under the operative frequencies and solicitations. Validation of the active layer was experimentally evaluated by manufacturing a DE actuator controlling both prestrain and nature of the complaint electrodes, and measuring the electrically induced Maxwell’s strain using a laser vibrometer to evaluate the relative displacement along the z-axis.

This work presents a liquid-phase metal electrode to be used with poly(dimethylsiloxane) (PDMS) for a dielectric elastomer actuator (DEA). DEAs are favorable for soft-matter applications where high efficiency and response times are desirable. A consistent challenge faced during the fabrication of these devices is the selection and deposition of electrode material. While numerous designs have been demonstrated with a variety of conductive elastomers and greases, these materials have significant and often intrinsic shortcomings, e.g. low conductivity, hysteresis, incapability of large deformations, and complex fabrication requirements. The liquid metal alloy eutectic Gallium-Indium (EGaIn) is a promising alternative to existing compliant electrodes, having both high conductivity and complete soft-matter functionality. The liquid electrode shares almost the same electrical conductivity as conventional metal wiring and provides no mechanical resistance to bending or stretching of the DEA. This research establishes a straightforward and effective method for quickly depositing EGaIn electrodes, which can be adapted for batch fabrication, and demonstrates the successful actuation of sample curved cantilever elastomer actuators using these electrodes. As with the vast majority of electrostatically actuated elastomer devices, the voltage requirements for these curved DEAs are still quite significant, though modifications to the fabrication process show some improved electrical properties. The ease and speed with which this method can be implemented suggests that the development of a more electronically efficient device is realistic and worthwhile.

A polymer-based nanofiber composite actuator designed for contractile actuation was fabricated by electrospinning, stimulated by electrolysis, and characterized by electrochemical and mechanical testing to address performance limitations and understand the activation processing effects on actuation performance. Currently, Electroactive polymers (EAPs) have provided uses in sensory and actuation technology, but have either low force output or expand rather than contract, falling short in capturing the natural kinetics and mechanics of muscle needed to provide breakthroughs in the bio-medical and robotic fields. In this study, activated Polyacrylonitrile (PAN) fibers have demonstrated biomimetic functionalities similar to the sarcomere contraction responsible for muscle function. Activated PAN has also been shown to contract and expand by electrolysis when in close vicinity to the anode and cathode, respectively. PAN nanofibers (~500 nm) especially show faster response to changes in environmental pH and improved mechanical properties compared to larger diameter fibers. Tensile testing was conducted to examine changes in mechanical properties between annealing and hydrolysis processing. Voltage driven transient effects of localized pH were examined to address pHdefined actuation thresholds of PAN fibers. Electrochemical contraction rates of the PAN/Graphite composite actuator demonstrated up to 25%/min. Strains of 58.8%, ultimate stresses up to 77.1 MPa, and moduli of 0.21 MPa were achieved with pure PAN nanofiber mats, surpassing mechanical properties of natural muscles. Further improvements, however, to contraction rates and Young’s moduli were found essential to capture the function and performance of skeletal muscles appropriately.

Minimally Invasive Surgery (MIS) is receiving much attention for a number of reasons, including less trauma, faster recovery and enhanced precision. The traditional robotic actuators do not have the capabilities required to fulfill the demand for new applications in MIS. Ionic Polymer-Metal Composite (IPMC), one of the most promising smart materials, has extensive desirable characteristics such as low actuation voltage, large bending deformation and high functionality. Compared with traditional actuators, IPMCs can mimic biological muscle and are highly promising for actuation in robotic surgery. In this paper, a new approach which involves molding and integrating IPMC actuators into a soft silicone tube to create an active actuating tube capable of multi-degree-of-freedom motion is presented. First, according to the structure and performance requirements of the actuating tube, the biaxial bending IPMC actuators fabricated by using solution casting method have been implemented. The silicone was cured at a suitable temperature to form a flexible tube using molds fabricated by 3D Printing technology. Then an assembly based fabrication process was used to mold or integrate biaxial bending IPMC actuators into the soft silicone material to create an active control tube. The IPMC-embedded tube can generate multi-degree-of-freedom motions by controlling each IPMC actuator. Furthermore, the basic performance of the actuators was analyzed, including the displacement and the response speed. Experimental results indicate that IPMC-embedded tubes are promising for applications in MIS.

Electroactive polymers (EAPs) have emerged as viable materials in sensing and actuating applications, but the capability to mimic the structure and function of natural muscle is increased due to their ability to permit additional, sequential synthesis steps between stages of actuation. Current work is improving upon the mechanical performance in terms of achievable stresses, strains, and strain rates, but issues still remain with actuator lifetime and adaptability. This work seeks to create a bioinspired polymer actuation system that can be monitored using state estimation and adjusted in vivo during operation. The novel, time-saving process of sequential growth was applied to polymer actuator systems for the initial growth, as well as additional growth steps after actuation cycles. Synthesis of conducting polymers on a helical metal electrode directs polymer shape change during actuation, assists in charge distribution along the polymer for actuation, and as is described in this work, constructs a constant working electrode/polymer connection during operation which allows sequential polymer growth based on a performance need. The polymer system is monitored by means of a reduced-order, state estimation model that works between growth and actuation cycles. In this case, actuator stress is improved between growth cycles. The ability for additional synthesis of the polymer actuator not only creates an actuator system that can be optimized based on demand, but creates a dynamic actuator system that more closely mimics natural muscle capability.

We theoretically predict and experimentally investigate the electrical properties of the electrode of ionic polymer-metal composites (IPMCs). A microstructure model of the electrode and the model of the current in the polymer membrane were presented. By combining the physics of the polymer membrane and the electrode, the model of the surface electrical potential of the IPMC was proposed. Experiments were conducted to test the electrical characteristics of the electrode and validate the model. The results demonstrate that the theoretical model can appropriately predict the resistance, capacitance, and surface electrical potential of the IPMC electrode under external oscillation.

Unimorph deformable mirrors are attractive in adaptive optics system due to their advantages of simplicity, compact, low cost and large stroke. In this paper, a double drive modes unimorph deformable mirror is discussed, which comprises a 100 μm thick PZT layer and a 200 μm thick silicon layer. This deformable mirror (DM) can achieve two different directions deformation of concave and convex driven by only positive voltage. The dual direction maximum defocus deformations are -14.3 μm and 14.9 μm. The close-loop performance of this DM is also tested in an experimental adaptive optics system based on Hartman-Shack wavefront sensor. In experiments, the DM is controlled by the steepest descent algorithm (SD) to corrected the aberrations in a close-loop manner. The ability of this DM of correction for the system aberration and reconstruction for the low order Zernike mode aberration is tested. The root mean square (rms) value of the system aberration after close-loop correction is about 28 nm. The reconstruction results for most low order Zernike mode aberrations have a relative error less than 10%.