Artificial muscles based on carbon derivative molecular structures are chemical (electro-chemo-mechanical) actuators. The electrochemical reaction drives the film volume variation and the actuation. The applied current controls the movement rate and the charge controls the amplitude of the displacement (Faraday’ motors). Any working or surrounding variable influencing the reaction rate will be sensed by the muscle potential, or by the consumed electrical energy, evolution during actuation. Experimental results and full theoretical description of the basic reactive material and of any dual electrochemical sensing-actuator will be presented. During current flow the muscle potential and the consumed electrical energy evolution are influenced by the working variables: temperature, electrolyte concentration, driving current, film volume variation (external pressure, applied strain, hanged masses, obstacles in its way). The working muscle becomes an electrochemical sensor. Only two connecting wires contain actuating (current) and sensing (potential) signals read and controlled, at any time from the computer-generator. One device integrates several sensing and actuating tools working simultaneously mimicking muscles/brain feedback communication.

In comparison to other ionic electromechanically active polymers (ionic EAP), carbon-polymer composite (CPC) actuators are considered especially attractive due to possibility of producing completely metal-free devices. However, mechanical response of ionic EAP-s is, in addition to voltage and frequency, dependent on environmental variables such as humidity and temperature. Therefore, similarly to other EAPs, one of the major challenges lies in achieving controlled actuation of the CPC sample. Due to their size and added complexity, external feedback devices (e.g. laser displacement sensors and video cameras) tend to inhibit the application of micro-scale actuators. Hence, self-sensing EAP actuators – capable for simultaneous actuation and sensing – are often desired. A thin polyvinylidene fluoride-cohexafluoropropylene film with ionic liquid (EMIMBF₄) was prepared and masked coincidently on opposite surfaces prior to spray painting carbide-derived carbon electrodes. The purpose of masking was to create different electrically insulated electrodes on the same surface of polymer in order to achieve separate sections for actuator and sensor on one piece of CPC material. Solution of electrode paint consisting of carbide-derived carbon, EMIMBF₄ and dimethylacetamide was applied to the polymer film. After removing the masking tape, a completely metal-free CPC actuator with sophisticated electrode geometry was achieved to foster simultaneous sensing and actuation, i.e. self-sensing carbon-polymer actuator was created.

Ionic polymer-metal composites (IPMCs) have inherent sensing and actuation properties. An IPMC sensor typically consists of a thin ion-exchange membrane, chemically plated with electrodes on both surfaces. Such IPMC sensors respond to deflections in the beam-bending directions only and thus are considered one-dimensional. In this paper, a novel IPMC sensor capable of two-dimensional sensing is proposed by plating two pairs of electrodes on orthogonal surfaces of a Nafion beam that has comparable thickness and width. The fabrication method is reported along with the characterization of the fabricated sensor. Experimental results show that the proposed IPMC sensor can be used for 2D flow sensing with promising applications in artificial lateral line systems. In the fabrication process Nafion solution is first cast and solidified, and the resulting structure is then cut to form beams with square cross-sections. In particular, the sample we fabricated has cross section of 1mm by 1mm and length of 15mm. Platinum electrodes are then plated on four side surfaces of the Nafion beam, insulated from each other. The fabricated IPMC sensor is shown to respond to 2D mechanical stimuli, and separate sensor signals are collected from the two pairs of electrodes. The responses (short-circuit currents) of the fabricated IPMC sensor are characterized both in air and in water, to verify the 2D sensing capability and examine the correlation between the two sensor signals.

Conducting polymers are soft, wet and reactive gels capable of mimicking biological functions. They are the electrochemomechanical actuators having the ability to sense the surrounding variables simultaneously. The sensing and actuating signals are sent/received back through the same two connecting wires in these materials. The sensing ability is a general property of all conducting polymers arises from the unique electrochemical reaction taking place in them. This sensing ability is verified for two different conducting polymers here – for an electrochemically generated polypyrrole triple layer bending actuator exchanging cations and for a chemically generated polytoluidine linear actuator exchanging anions. The configuration of the polypyrrole actuator device corresponds to polypyrrole-dodecyl benzene sulfonate (pPy-DBS) film/tape/ pPy-DBS film in which the film on one side of the triple layer is acted as anode and the film on the other side acted as cathode simultaneously, and the films interchanged their role when move in the opposite direction. The polytoluidine linear actuator was fabricated using a hydrgel microfiber through in situ chemical polymerization. The sensing characteristics of these two actuators were studied as a function of their working conditions: applied current, electrolyte concentration and temperature in aqueous electrolytes. The chronopotentiometric responses were studied by applying square electrical currents for a specified time. For the pPy actuator it was set to produce angular movement of ± 45° by the free end of the actuator, consuming constant charges of 60 mC. In both the actuators the evolution of the muscle potential along the electrical current cycle was found to be a function of chemical and physical variables acting on the polymer reaction rates: electrolyte concentration, temperature or driving electrical current. The muscle potential evolved decreases with increasing electrolyte concentrations, increasing temperatures or decreasing driving electrical currents. The electrical energy consumed during reaction was a linear function of the working temperature or of the driving electrical current and a double logarithmic function of the electrolyte concentration. Thus, the conducting polymer based actuators exchanging cations or anions during electrical current flow is a sensor of the working physical and chemical conditions which is a general property of all conducting polymers.

There is a strong need to replicate natural muscles with artificial materials as the structure and function of natural muscle is optimum for articulation. Particularly, the cylindrical shape of natural muscle fiber and its interconnected structure promote the critical investigation of artificial muscles geometry and implementation in the design phase of certain platforms. Biomimetic robots and Humanoid Robot heads with Facial Expressions (HRwFE) are some of the typical platforms that can be used to study the geometrical effects of artificial muscles. It has been shown that electroactive polymer and shape memory alloy artificial muscles and their composites are some of the candidate materials that may replicate natural muscles and showed great promise for biomimetics and humanoid robots. The application of these materials to these systems reveals the challenges and associated technologies that need to be developed in parallel. This paper will focus on the computer aided design (CAD) models of conductive polymer and shape memory alloys in various biomimetic systems and Humanoid Robot with Facial Expressions (HRwFE). The design of these systems will be presented in a comparative manner primarily focusing on three critical parameters: the stress, the strain and the geometry of the artificial muscle.

Ionomeric polymer-metal composites (IPMCs) are a class of electroactive polymers (EAPs) that silently bend and exert force in response to an applied voltage. In this work, a unique design is presented where IPMCs are used to accomplish rotary motion. A novel feature is that EAP actuation is used in conjunction with gravity to cause rotation. This idea could be used to create a self-driven roller device. Such a roller could resemble a wheel with a circular or cylindrical geometry, or a sphere capable of rolling in all directions. Numerical simulations were performed that show a two dimensional roller device can accomplish rolling motion as a result of IPMC actuation. Experimental data on the deformation performance of fabricated IPMCs was used to drive the numerical simulations of the device. A possible application of this mechanism could be a mobility device on the centimeter scale that can transport a payload silently to a target destination.

Compared to single layer electroactive polymer (EAP) actuators, stack actuators exhibit advantageous properties such as large displacements at acceptably low operating voltages. Therefore, EAP stack actuators seem to be a promising option for the successful use in commercial applications. For an energy-efficient operation of EAP stack actuators or EAP actuators in general an adequate power electronics with high voltage capability is indispensable. Depending on the specific application, the use of different converter topologies combined with suitable control concepts has to be considered. In this contribution different possible converter concepts for driving EAP stack actuators are presented. For each fundamental converter concept, different converter topologies are proposed. A flyback converter combined with an active discharging circuit is analyzed in detail and suitable control designs are developed. Finally, simulation and experimental results of the prototype flyback converter are presented.

Dielectric elastomers (DEs) can theoretically operate at efficiencies greater than that of electromagnetics. This is due to their unique mode of operation which involves charging and discharging a capacitive load at a few kilovolts (typically 1kV-4kV). Efficient recovery of the electrical energy stored in the capacitance of the DE is essential in achieving favourable efficiencies as actuators or generators. This is not a trivial problem because the DE acts as a voltage source with a low capacity and a large output resistance. These properties are not ideal for a power source, and will reduce the performance of any power conditioning circuit utilizing inductors or transformers. This paper briefly explores how circuit parameters affect the performance of a simple inductor circuit used to transfer energy from a DE to another capacitor. These parameters must be taken into account when designing the driving circuitry to maximize performance.

Social robotics and artificial intelligence have progressed steadily in recent years, appearing in a variety of useful applications and products as well as breakthrough research. However, limitations in conventional motors continue to limit the possibilities of bio-inspired robotics. Such motors are needed for locomotion, grasping and manipulation, and social expressions and gestures. EAP actuators, being more like biological muscle in key regards, could revolutionize the hardware for such robots, if made robust, powerful, and manufacturable at reasonable prices. The author presents a survey of the progress and opportunities for EAP actuators in these fields, and discusses the latest work of his team in developing and manufacturing social robots that could benefit from EAP actuators.

Ionic Polymer Metal Composite (IPMC) is an Electro-Active Polymer (EAP) that is used as an electro-mechanical sensor and being investigated as an energy harvester. The IPMC transducer is proved to be inefficient as an energy harvester due to the small amount of voltage it generates when deformed. This study explores this problem by developing a fully-coupled 2D mechano-chemo-electrical finite element model that predicts the sensing behaviour in IPMC. The electrochemical element is modelled based on the Nernst-Planck and Poisson’s equations. The chemo-mechanical coupling is due to the change in the concentration of ions upon deforming the sensor. This paper is focused on developing methods to control the amount of voltage and current the IPMC sensor can generate. The developed FEM model is used to assess the effects of increasing the thickness of the transducer and of manipulating the architecture of the high surface area electrodes. The IPMC transducer is simulated and experimentally tested using two electrical boundary conditions: the open circuit voltage or the short circuit current. All numerical results are supported by experimental data. The results are shown to be in good agreement with model predictions.

Dielectric elastomers can work as a variable capacitor to convert mechanical energy such as human motion into electrical energy. Nevertheless, scavengers based on dielectric elastomers require a high voltage source to polarize them, which constitutes the major disadvantage of these transducers. We propose here to combine dielectric elastomer with an electret, providing a quasi-permanent potential, thus replacing the high voltage supply. Our new scavenger is fully autonomous, soft, lightweight and low cost. Our structure is made of a dielectric elastomer (Polypower from Danfoss) and an electret developing a potential of -1000V (Teflon from Dupont). The transducer is designed specifically to scavenge energy from human motion. Thus, it works on pure-shear mode with maximum strain of about 50% and it is textured in 3D form because electret is not deformable. The shape of the hybrid structure is critical to insure huge capacitance variation and thus higher scavenged energy. We present in this paper our process for the optimization of the 3D shape that leads us to the developpment and characterization of our first prototype. From an appropriate electromechanical analytical model, an energy density of about 1.48mJ.g^-1 is expected on an optimal electrical load. Our new autonomous dielectric generator can produce about 0.55mJ.g^-1 on a resistive load, and can further be improved by enhancing the performance of dielectric elastomer such as dielectric permittivity or by increasing the electret potential.

Dielectric Elastomers (DE) have been largely studied as actuators and sensors. Fewer researches have addressed their application in the field of energy harvesting. Their light weightiness, low cost, high corrosion resistance, and their intrinsic high-voltage and cyclical-way of operation make DE suited for harvesting mechanical energy from sea waves. To date, the development of cost-effective Wave Energy Converters (WECs) is hindered by inherent limitations of available material technologies. State of the art WECs are indeed based on traditional mechanical components, hydraulic transmissions and electromagnetic generators, which are all made by stiff, bulky, heavy and costly metallic materials. As a consequence, existing WECs result in being expensive, difficult to assemble, sensitive to corrosion and hard to maintain in the marine environment. DE generators could be an enabling technology for overcoming the intrinsic limitations of current WEC technologies. In this context, this paper focuses on Polymer-based Oscillating-Water-Column (Poly-OWC) type WECs, and analyzes the viability of using DE generators as power-take-off systems. Regarding paper structure, the first sections introduce the working principle of OWC devices and discuss possible layouts for their DE-based power-take-off system. Then, a simplified hydraulic-electro-hyperelastic model of a two-dimensional Poly-OWC is described. Finally, preliminary simulation results are shown which provide insights on the potential capabilities of Poly-OWC.

Dielectric elastomer generators (DEG) provide an opportunity to harvest energy from low frequency and aperiodic sources. Because DEG are soft, deformable, high energy density generators, they can be coupled to complex structures such as the human body to harvest excess mechanical energy. However, DEG are typically constrained by a rigid frame and manufactured in a simple planar structure. This planar arrangement is unlikely to be optimal for harvesting from compliant and/or complex structures. In this paper we present a soft generator which is fabricated into a 3 Dimensional geometry. This capability will enable the 3-dimensional structure of a dielectric elastomer to be customised to the energy source, allowing efficient and/or non-invasive coupling. This paper demonstrates our first 3 dimensional generator which includes a diaphragm with a soft elastomer frame. When the generator was connected to a self-priming circuit and cyclically inflated, energy was accumulated in the system, demonstrated by an increased voltage. Our 3D generator promises a bright future for dielectric elastomers that will be customised for integration with complex and soft structures. In addition to customisable geometries, the 3D printing process may lend itself to fabricating large arrays of small generator units and for fabricating truly soft generators with excellent impedance matching to biological tissue. Thus comfortable, wearable energy harvesters are one step closer to reality.

Target of this article will be the energy harvesting with dielectric elastomers for wave energy conversion. The main goal of this article is to introduce a new developed material profile enabling a specific amount of energy, making the harvesting process competitive against other existing offshore generation technologies. Electroactive polymers offer the chance to start with small wave energy converters to gain experiences and carry out a similar development as wind energy. Meanwhile there is a consortium being formed in Germany to develop such materials and processes for future products in this new business area. In order to demonstrate the applicability of the technological advancements, a scale demonstrator of a wave energy generator will be developed as well.

Electroactive Polymer (EAP) has gained increasing focus, in research communities, in last two decades. Research within the field of EAP has, so far, been mainly focused on material improvements, characterization, modeling and developing demonstrators. As the EAP technology matures, the need for a new area of research namely product development emerges. Product development can be based on an isolated design and production for a single product or platform design where a product family is developed. In platform design the families of products exploits commonality of platform modules while satisfying a variety of different market segments. Platform based approach has the primary benefit of being cost efficient and short lead time to market when new products emerges. Products development based on EAP technology is challenging both technologically as well as from production and processing point of view. Both the technological and processing challenges need to be addressed before a successful implementation of EAP technology into products. Based on this need Danfoss PolyPower A/S has, in 2011, launched a EAP platform project in collaboration with three Danish universities and three commercial organizations. The aim of the project is to develop platform based designs and product family for the EAP components to be used in variety of applications. This paper presents the structure of the platform project as a whole and specifically the platform based designs of EAP transducers. The underlying technologies, essential for EAP transducers, are also presented. Conceptual design and solution for the concepts are presented as well.

Applied to voltage, a dielectric elastomer membrane may deform into a mixture of two states under certain conditions. One of which is the flat state and the other is the wrinkled state. In the flat state, the membrane is relatively thick with a small area, while on the contrary, in the wrinkled state, the membrane is relatively thin with a large area. The coexistence of these two states may cause the electromechanical phase transition of dielectric elastomer. The phase diagram of idea dielectric elastomer membrane under unidirectional stress and voltage inspired us to think about the liquid-to-vapor phase transition of pure substance. The practical working cycle of a steam engine includes the thermodynamical process of liquid-to-vapor phase transition, the fact is that the steam engine will do the maximum work if undergoing the phase transition process. In this paper, in order to consider the influence of coexistent state of dielectric elastomer, we investigate the homogeneous deformation of the dielectric elastomer tube. The theoretical model is built and the relationship between external loads and stretch are got, we can see that the elastomer tube experiences the coexistent state before reaching the stretching limit from the diagram. We think these results can guide the design and manufacture of energy harvesting equipments.

Electroactive polymers are soft capacitors made of thin elastic and electrically insulating films coated with compliant electrodes offering a large amount of deformation. They can either be used as actuators by applying an electric charge or they can be used as energy converters based on the electrostatic principle. These unique properties enable the industrial development of highly efficient and environmentally sustainable energy converters, which opens up the possibility to further exploit large renewable and inexhaustible energy sources like wind and water that are widely unused otherwise. Compared to other electroactive polymer materials, polyurethanes, whose formulations have been systematically modified and optimized for energy harvesting applications, have certain advantages over silicones and acrylates. The inherently higher dipole content results in a significantly increased permittivity and the dielectric breakdown strength is higher, too, whereby the overall specific energy, a measure for the energy gain, is better by at least factor ten, i.e. more than ten times the energy can be gained out of the same amount of material. In order to reduce conduction losses on the electrode during charging and discharging, a highly conductive bidirectional stretchable electrode has been developed. Other important material parameters like stiffness and bulk resistivity have been optimized to fit the requirements. To realize high power energy harvesting systems, substantial amounts of electroactive polymer material are necessary as well as a smart mechanical and electrical design of the generator. In here we report on different measures to evaluate and improve electroactive polymer materials for energy harvesting by e.g. reducing the defect occurrence and improving the electrode behavior.

The Dielectric ElectroActive Polymer (DEAP) generator energy harvesting cycles have been in the spotlight of the scientific interest for the past few years. Indeed, several articles have demonstrated thorough and comprehensive comparisons of the generator fundamental energy harvesting cycles, namely Constant Charge (CC), Constant Voltage (CV) and Constant E-field (CE), based on average theoretical models. Yet, it has not been possible until present to validate the outcome of those comparisons via respective experimental results. In this paper, all three primary energy harvesting cycles are experimentally compared, based upon the coupling of a DEAP generator with a bidirectional non-isolated power electronic converter, by means of energy gain, energy harvesting efficiency and energy conversion efficiency.

Energy harvesting with EAPs requires an energy-efficient power electronics providing a bidirectional energy transfer and operating voltages of up to several kilovolts. A possibility to achieve a high energy-efficiency for high voltage conversion is the use of a modular converter system consisting of several bidirectional converter modules, which are connected in series on the converter output side and in parallel at the input side. Since each converter stage provides only a part of the overall converter output voltage, the converter module output voltages can effectively be reduced by choosing the number of cascaded converter modules appropriately. This allows the use of standard semiconductor switches with superior electrical characteristics compared to high voltage semiconductors, enabling a high energy-efficiency and smaller passive components. Since EAP devices exhibit a mainly capacitive behavior and a limitation of the operating current is required for electrode protection, the utilized converter structure/topology has to be operated as a controllable current source on the lowest control level, which is achieved by operating the converter modules of the modular converter system with a subordinate closed-looped current control scheme. In order to avoid voltage unbalances among the single converter modules, a method for voltage balancing is presented. For validation, experimental results of a realized bidirectional flyback converter prototype are presented and discussed.

Dielectric elastomer generators (DEGs) are attractive candidates for harvesting electrical energy from mechanical work since they comprise relatively few moving parts and large elastomer sheets can be mass produced. Successfully demonstrations of the DEG prototypes have been reported from a diverse of energy sources, including ocean waves, wind, flowing water and human movement. The energy densities achieved, however, are still small compared with theoretical predictions. We show that significant improvements in energy density (550 J/kg with an efficiency of 22.1%), can be achieved using an equi-biaxial mechanical loading configuration, one that produces uniform deformation and maximizes the capacitance changes. Analysis of the energy dissipations indicates that mechanical losses, which are caused by the viscous losses both within the acrylic elastomer and within the thread materials used for the load transfer assembly, limits the energy conversion efficiency of the DEG. Addressing these losses is suggested to increase the energy conversion efficiency of the DEG.

In the recent times, cellulose-based Electro-Active Paper (EAPap) has been investigated to have electro-mechanical coupling and piezoelectric effects which are promising characteristics for a smart material. In this paper, the effects of electrodes of EAPap are investigated for vibration energy harvesting. Although piezopolymers have smaller value of electro-mechanical coupling constants as compared to the piezoceramics, but are very flexible, which motivates to use these materials as potential media for flexible energy harvesting. Cellulose based Electro-active papers are deposited with different metal electrodes like aluminum, gold and silver. The fabricated samples are tested with aluminum cantilever beam under an input excitation. The effects of area of electrodes are also investigated by comparing the output voltage at the different area of electrodes ranging from 400mm² to 1200mm². EAPap cantilever are tested at lowest resonant frequency and under varying acceleration amplitude to maximize the output voltage. From the experimental results, it is concluded that the potential of EAPap as a flexible energy harvester are very promising.

To our knowledge no known technologies or processes are commercially available for embossing microstructures and sub-micron structures on elastomers like silicones in large scale production of films. The predominantly used technologies to make micro-scale components for micro-fluidic devices and microstructures on PDMS elastomer are 1) reaction injection molding 2) UV lithography and 3) photolithography, which all are time-consuming and not suitable for large scale productions. A hot-embossing process to impart micro-scale corrugations on an addition curing vinyl terminated PDMS (polydimethyl siloxane) film, which is thermosetting elastomer, was established based on the existing and widely applied technology for thermoplasts. We focus on hot-embossing as it is one of the simplest, most costeffective and time saving methods for replicating structures for thermoplasts. Addition curing silicones are shown to possess the ability to capture and retain an imprint made on it 10-15 minutes after the gel-point at room temperature. This property is exploited in the hot-embossing technology.

Dielectric elastomer stack actuators are a promising configuration of electroactive polymer actuators due to their favourable balance of output force and stroke capabilities. These performance characteristics are highly dependent on many factors including layer geometry, mechanical and electrical material properties, etc. Thus, the specification of an optimal actuator design remains a challenging task. This study aims to assess the relationship of these factors on actuator performance by the application of evolutionary optimization algorithms in conjunction with a coupled multi-physics finite element simulation. This approach rapidly identifies the optimal actuator performance without the computational expense of simulating the entire design space.

The output strain of a dielectric elastomer actuator is directly proportional to the square of its applied electric field. However, since the likelihood of electric breakdown is elevated with an increased applied field, the maximum operating electric field of the dielectric elastomer is significantly derated in systems employing these actuators so that failure due to breakdown remains unlikely even as the material ages. In an effort to ascertain the dielectric strength so that stronger electric fields can be applied, partial discharge testing is used to assess the health of the actuator by detecting the charge that is released when localized instances of breakdown partially bridge the insulator. Pre-stretched and unstretched samples of VHB4910 tape were submerged in dielectric oil to remove external sources of partial discharges during testing, and the partial discharge patterns were recorded just before failure of the dielectric sample.

Ionic conducting polymer-metal composites (IPMC) are flexible actuators that can act as artificial muscles in many robotic and microelectromechanical systems. The authors have already investigated the possibility of kinematically stable bipedal locomotion using these actuators. Fabrication parameters of actuators including minimum lengths, installation angles, plating thicknesses and maximum required voltages were found in previous studies for a stable bipedal gait with maximum speed of 0.1093 m/s. Extending the FEA solution of the governing partial differential equation of the behavior of IPMCs to 2D, actuator limits were found. Considering these limits, joint path trajectories were generated to achieve a fast and smooth motion on a seven-degree of freedom biped robot. This study utilizes the same biped model, and focuses on the kinetics of the proposed gait in order to complement the evaluation of using IPMCs as biomimetic actuators for bipedal locomotion. The dynamic equations of motion of the previously designed bipedal gait are solved here to find the maximum required joint torques. Blocking force of a flap of IPMC is found by plugging results of the FEA into a model based on beam theories. This force adequately predicts the maximum deliverable torque of a piece of IPMC with certain length. Feasibility of using IPMCs as joint actuators is then evaluated by comparing the required and achievable torques. This study concludes the previous work to cover feasibility, stability and design of a biped robot actuated with IPMC flaps.

It is generally understood that increasing the specific surface area of the electrodes of IPMC leads to improved electromechanical performance of the material. Most physics based models compensate the effect of high surface area of the electrodes by increasing both diffusion constant and dielectric permittivity values, while using flat electrode approximation in calculations. Herein, a model was developed to take into account the shape and area of the electrodes. High surface area of the electrodes in the model was achieved by designing 2D polymer-electrode interface as a Koch fractal structure – different generation depths and both unidirectional and random directional generations were studied. The calculations indicate that increasing the generation depth of fractals, thus surface area of the electrodes results in more overall transported charge during the actuation process. Based on the model, the effect of the specific surface area of the electrodes on the electromechanical performance was experimentally investigated. IPMCs with different Pd-Pt electrode structures were prepared and their electromechanical and electrochemical properties were examined and discussed. The methods to manipulate the surface structure of Pd-Pt electrodes were proposed.

IPMC actuation is described with a system of partial differential equations – the Poisson’s equation, the Nernst- Planck equation, and the Navier’s equations for the displacement field. In such systems, one physical field can be very smooth while others are not. This can possibly result in very large problem size in terms of number of degrees of freedom (nDOF) when implemented with the finite element method (FEM). Furthermore, finding an optimal mesh is challenging due to the fact that the physical fields are time dependent. In order to overcome these deficiencies, hp-FEM was used to solve the system of equations. The hp-FEM is a modern version of the FEM that is capable of exponential convergence (the approximation error drops exponentially as new degrees of freedom are added during adaptivity). It is shown how the multi-meshing allows reducing the problem size in terms of nDOF; also, how the solution domain that describes IPMC can be scaled without a significant increase in the nDOFs and solution time. The model was implemented in Hermes that is a free hp-FEM solver.

This paper describes the development of an active isolation mat for cancelation of vibrations on sensitive devices with a mass of up to 500 gram. Vertical disturbing vibrations are attenuated actively while horizontal vibrations are damped passively. The dimensions of the investigated mat are 140 × 140 × 20 mm. The mat contains 5 dielectric elastomer stack actuators (DESA). The design and the optimization of active isolation mat are realized by ANSYS FEM software. The best performance shows a DESA with air cushion mounted on its circumference. Within the mounting encased air increases static and reduces dynamic stiffness. Experimental results show that vibrations with amplitudes up to 200 μm can be actively eliminated.

The electrostrictive terpolymer poly(vinylidene fluoride-trifluoroethylene-1,1-chlorofluoroethylene) – P(VDF-TrFECFE) – exhibits higher field-induced strain and larger dielectric constant (> 30) than most materials. In this paper we show that the strain of this terpolymer can be increased even more by mixing it with BaTiO₃ nanoparticles of high dielectric constant. For our investigation, actuator-like stacks on basis of terpolymer / nanoparticles blend thin films were prepared. Measurements of electric-field induced strain in the blend thin films, carried out with a Michelson interferometric set-up, show that indeed that the electrostrictive strain increases with increasing the nanoparticle content in the blend. Structural characterization by means of X-ray diffraction and phase transitions analysis with differential scanning calorimetry (DSC) indicate that the crystalline phase in the terpolymer host has been altered by the presence of nanoparticles. Additional measurements reveal that the dielectric permittivity of the obtained blend thin films is larger than that of the terpolymer. For the blend containing 1 wt% nanoparticles a dielectric permittivity of about 40 and an electrostriction coefficient of about 4 times larger than that of terpolymer were determined. Besides we show that by employing optimum annealing temperatures, the film quality with respect to its surface roughness can be improved.

EAP technology has the potential to be used in a wide range of applications. This poses the challenge to the EAP component manufacturers to develop components for a wide variety of products. Danfoss Polypower A/S is developing an EAP technology platform, which can form the basis for a variety of EAP technology products while keeping complexity under control. High level product architecture has been developed for the mechanical part of EAP transducers, as the foundation for platform development. A generic description of an EAP transducer forms the core of the high level product architecture. This description breaks down the EAP transducer into organs that perform the functions that may be present in an EAP transducer. A physical instance of an EAP transducer contains a combination of the organs needed to fulfill the task of actuator, sensor, and generation. Alternative principles for each organ allow the function of the EAP transducers to be changed, by basing the EAP transducers on a different combination of organ alternatives. A model providing an overview of the high level product architecture has been developed to support daily development and cooperation across development teams. The platform approach has resulted in the first version of an EAP technology platform, on which multiple EAP products can be based. The contents of the platform have been the result of multi-disciplinary development work at Danfoss PolyPower, as well as collaboration with potential customers and research institutions. Initial results from applying the platform on demonstrator design for potential applications are promising. The scope of the article does not include technical details.

Dielectric elastomer generators (DEG) produce electrical energy by converting mechanical into electrical energy. Efficient operation requires homogeneous deformation of each single layer. However, by different internal and external influences like supports or the shape of a DEG the deformation will be inhomogeneous and hence negatively affect the amount of the generated electrical energy. Optimization of the deformation behavior leads to improved efficiency of the DEG and consequently to higher energy gain. In this work a numerical simulation model of a multilayer dielectric elastomer generator is developed using the FEM software ANSYS. The analyzed multilayer DEG consists of 49 active dielectric layers with layer thicknesses of 50 μm. The elastomer 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 need to be included. Therefore, the mechanical and electrical material parameters of the PDMS are determined by experimental investigations of test samples while the electrode parameters are determined by numerical simulations of test samples. The numerical simulation of the DEG is carried out as coupled electro-mechanical simulation for the constant voltage energy harvesting cycle. Finally, the derived numerical simulation model is validated by comparison with analytical calculations and further simulated DEG configurations. The comparison of the determined results show good accordance with regard to the deformation of the DEG. Based on the validated model it is now possible to optimize the DEG layout for improved deformation behavior with further simulations.

Ionic polymer-metal composites (IPMCs) have been and still are one of the best candidates with great potential to be used as actuators and sensors particularly in bioengineering where the environmental conditions are in an aqueous medium. Each component of an IPMC is important. However, the ion exchange membrane should be more emphasized because it is where ions migrate when electrical stimulation is applied and eventually it produces deformation of the IPMC. So far, the most commonly used ion exchange membrane is Nafion and many studies have been conducted with it for IPMC applications. There are a number of other commercially available ion exchange membranes now, but only a few studies have been done on those membranes to be used in IPMC applications. In this study, four commercially available membranes, (1) Nafion N115 (DuPont), (2) CMI7000S (Membranes International Inc.), (3) F-14100 (fumatech), (4) GEFC-700 (Golden Energy Fuel Cell) were selected and fabricated in IPMCs and their potentials as actuators were examined by conducting various characterizations such as water uptake, ion exchange capacity, SEM, DSC, blocking force and bending displacement.

Research was carried out on a foamed ionic polymer metal composite (IPMC) to improve actuation performance. Foamed IPMC is manufactured from a foamed membrane with micro-sized cells formed via a microcellular foaming process, which is a technology used to form and control micro-sized cells in plastics. We measured the changes in the blocked force and free bending displacement of foamed IPMC as the applied voltage increased. The maximum change in displacement was caused by a foaming rate of 20%. Finally, thick Nafion was fabricated via casting and foaming processes, and then tested.

Dielectric elastomers are thin polymer films belonging to the class of electroactive polymers, which are coated with compliant and conductive electrodes on each side. Under the influence of an electrical field, dielectric elastomers perform a large amount of deformation. Depending on the mechanical setup, stack and roll actuators can be realized. In this contribution the mechanical properties of stack actuators are modeled by a holistic electromechanical approach of a single actuator film, by which the model of a stack actuator without constraints can be derived. Due to the mechanical connection between the stack actuator and the application, bulges occur at the free surfaces of the EAP material, which are calculated, experimentally validated and considered in the model of the stack actuator. Finally, the analytic actuator film model as well as the stack actuator model are validated by comparison to numerical FEM-models in ANSYS.

Performance of dielectric elastomer transducers (DEST) depends on mechanical and electrical parameters. For designing DEST it is therefore necessary to know the influences of these parameters on the overall performance. We show an electrical equivalent circuit valid for a transducer consisting of multiple layers and derive the electrical parameters of the circuit depending on transducers geometry and surface resistivity of the electrodes. This allows describing the DESTs dynamic behavior as a function of fabrication (layout, sheet and interconnection resistance), material (breakdown strength, permittivity) and driving (voltage) parameters. Using this electrical model transfer function and cut-off frequency are calculated, describing the influence of transducer capacitance, resistance and driving frequency on the achievable actuation deflection. Furthermore non ideal boundary effects influencing the capacitance value of the transducer are investigated by an electrostatic simulation and limits for presuming a simple plate capacitor model for calculating the transducer capacitance are derived. Results provide the plate capacitor model is a valid assumption for typical transducer configurations but for certain aspect ratios of electrode dimensions to dielectric thickness -- arising e.g. in the application of tactile interfaces -- the influence of boundary effects is to be considered.

This contribution presents a theoretically investigation of dielectric elastomer loudspeakers similar in design to the loudspeakers studied at SRI International more than 10 years ago. The main emphasis of the contribution is on the effect of dissipative effects, specifically radiative losses (acoustic losses). The starting point of the theoretical model is a free-energy description and include hyper-elastic contributions. In the designs considered in this work the dielectric elastomer material is subject to a pre-strain which has been applied either by subjecting the membrane to an applied back pressure, or simply applying a biaxial mechanical pre-strain. The membrane is then actuated relative to this pre-strain by the application of an applied ac voltage. The nonlinear equations are linearized around the given pre-strain in order to perform relatively fast calculations of the mechanical frequency response of the structure.

Actuators based on electroactive polymers use the electrostatic pressure to convert electrical energy into strain energy. Depending on the setup, stack- and roll-actuators can be realized. Here the authors introduce a completely new roll-actuator design, in which bi-axially prestretched electroactive material is winded up around a compressed polymer core. The modeling of this actuator yields to an electromechanically coupled dynamic model, which consists of a non-linear mechanical model to describe the hyperelastic properties of the polymer and an electrical model to describe the electrostatic behavior. Based on this model, the authors discuss the influence of some of the actuators design parameters and present a realized prototype of the polymer core roll-actuator.

Dielectric elastomer actuators are considered as promising candidates for robotic elements. To this end, planar dielectric elastomer actuators (p-DEAs) and dielectric elastomer minimum energy structures (DEMES) are applicable. However, the knowledge of their electrical and mechanical characteristics is of major importance for engineering tasks. Therefore we study p-DEAs and DEMES by impedance spectroscopy (IS) and dynamic capacitive extensometry (DCE). We vary the boundary conditions with regard to p-DEAs (free and fixed boundaries) and fabricate various DEMES with one angular degree of freedom. A mixture of carbon black particles and silicone oil serves as compliant electrodes. We present equivalent circuit models of the actuators based on impedance spectroscopy data, the frequency ranges in which they are applicable and effects of aging on the equivalent circuit models. By DCE the electrical characteristics of dielectric elastomer actuators are monitored in situ during dynamic high voltage actuation. These electrical characteristics of the dielectric elastomer actuators such as p-DEAs and DEMES can be related to their transient stretch in response to high voltage driving signals. We study the viscoelastic response of the actuators to square driving signals of different magnitudes; furthermore we monitor the state of the compliant electrodes. By means of the DCE measurement data and the impedance spectra the p-DEAs and DEMES can be compared.

Polydimethylsiloxane (PDMS) elastomers are excellent materials for dielectric electroactive polymers (DEAPs) due to their high efficiency and fast response. PDMS suffers, however, from low dielectric permittivity and high voltages are therefore required when the material is used for DEAP actuators. In order to improve the dielectric properties of PDMS a novel system is developed where push-pull dipoles are grafted to a new silicone compatible cross-linker. The grafted cross-linkers are prepared by reaction of two different push-pull dipole alkynes as well as a fluorescent alkyne with the new azide-functional cross-linker by click chemistry. The dipole cross-linkers are used to prepare PDMS elastomers of various chains lengths providing different network densities. The functionalized cross-linkers are incorporated successfully into the networks and are well distributed as determined by the fluorescent functional cross-linker and fluorescence microscopy. The thermal, mechanical and electro-mechanical properties of PDMS elastomers of 0 wt% to 3.6 wt% of push-pull dipole cross-linker are investigated. An increase in the dielectric permittivity of 19 % at only 0.46 wt% of pure push-pull dipole is observed. Furthermore, the dielectric losses are found to be very low while the electrical breakdown strengths are high and adequate for DEAP applications.

We demonstrate that the force output and work density of polydimethylsiloxane (PDMS) based dielectric elastomer transducers can be significantly enhanced by the addition of high permittivity titanium dioxide nanoparticles which was also shown by Stoyanov et al[1] for pre-stretched elastomers and by Carpi et al for RTV silicones[2]. Furthermore the elastomer matrix is optimized to give very high breakdown strengths. We obtain an increase in the dielectric permittivity of a factor of approximately 2 with a loading of 12% TiO₂ particles compared to the pure modified silicone elastomer with breakdown strengths remaining more or less unaffected by the loading of TiO₂ particles. Breakdown strengths were measured in the range from approximately 80-150 V/μm with averages of the order of 120-130 V/μm for the modified silicone elastomer with loadings ranging from 0 to 12%.

Preferred structuring of filler particles in a polymer matrix by using dielectrophoretic assembly process can enhance anisotropic dielectric properties. For this purpose, precipitated silica (SiO₂) was structured in silicone rubber using an alternating electric field. This filler structure was stabilized by vulcanizing rubber during electric field application. Filler particle orientation and resulted anisotropy was verified by equilibrium swelling. Structuring filler in the rubber matrix led to increased dielectric permittivity and loss in the thickness direction. Filler surface modification by (vinyl-tris-(2- diethoxy/methoxy) silane) improved structure formation and anisotropic properties. It was shown that applying silane modifier and orientation of silica particles by dielectrophoretic assembly process increased dielectric permittivity of silicone rubber in the thickness direction while dielectric loss had either minor changes or increased less than permittivity in this direction. Although elastic modulus of composite, which was measured by dynamic-mechanical analysis, increased to some extent, enhancement in dielectric permittivity was much higher. This introduced the structured composite as a potential for dielectric elastomeric actuator with higher efficiency than the original silicone rubber with no filler addition.

The best performing dielectric elastomer materials reported thus far are commercial products manufactured for applications unrelated to electro-mechanical transduction. Prestretching is commonly employed to obtain high actuation strain and energy density. The limited knowledge of the polymers’ chemical structure makes it difficult to re-formulate the polymers for significantly improved overall material performance. We report the synthesis of new acrylate-based dielectric elastomers that exhibit high actuation strain without prestretching. Mixtures of commercial acrylate monomers and other additives are copolymerized by UV-initiated radical polymerization to form thin dielectric elastomer membranes. This processing can readily be scaled up to fabricate multi-layer stacked actuators with 11% linear actuation strain.

Dielectric Electroactive Polymers belong to a new class of smart materials, whose functional principle is based on electrostatic forces. They can either be used as actuators to provide considerable stretch ratios or as generators to convert mechanical strain energy into electrical energy by use of an initial amount of energy. Since the polymer material and also the covering compliant electrodes show non-ideal electrical properties, like finite resistivity and conductivity respectively, design rules have to be derived, in order to optimize the transducer. The electrode conductivity in connection with the polymer resistivity causes a voltage drop along the electrode surface, resulting in a reduced actuation strain or energy conversion. To minimize its parasitic effects, the influence of this effect is studied by the field-distribution based on a model obtained with the equivalent network method. It is shown that the proposed model provides accurate results that can be used to study the effect of contacting electrodes with diagonal-edge contacts in combination with alternating contacts in between.

Material parameter uncertainty is a key aspect of model development. Here we quantify parameter uncertainty of a viscoelastic model through validation on rate dependent deformation of a dielectric elastomer that undergoes finite deformation. These materials are known for there large field induced deformation and applications in smart structures, although the rate dependent viscoelastic effects are not well understood. To address this issue, we first quantify hyperelastic and viscoelastic model uncertainty using Bayesian statistics by comparing a linear viscoelastic model to uniaxial rate dependent experiments. The probability densities, obtained from the Bayesian statistics, are then used to formulate a refined model that incorporates the probability densities directly within the model using homogenization methods. We focus on the uncertainty of the viscoelastic aspect of the model to show under what regimes does the stochastic homogenization framework provides improvements in predicting viscoelastic constitutive behavior. It is show that VHB has a relatively narrow probability distribution on the viscoelastic time constants. This supports use of a discrete viscoelastic model over the homogenized model.

Silicone based dielectric elastomer actuators are preferred for reliable and fast actuation due to their negligible viscoelastic behavior. However, it is more challenging to achieve large deformation actuation using this class of polymers compared to the traditionally used VHB films. In this paper, we present theoretical guidelines for improving actuation strain of silicone based dielectric elastomer actuators. The electromechanical behavior of two different silicones is compared and it is demonstrated that the softest elastomer is not necessarily the best choice to achieve large deformation. Lastly, we have experimentally shown that uniaxially prestretching the elastomer with an optimum prestretch ratio enhances the actuation strain up to 10 times. Actuation strain of up to 80% on 100 × 100 μm² microactuators is generated.

Dielectric elastomer actuators (DEAs) are prone to failure by pull-in instability. However, this work showed that DEAs, which were immersed in a silicone oil bath (Dow Corning Fluid 200 50cSt), can survive the pull-instability and operates beyond the pull-in voltage. Membrane DEAs (VHB 4905), which were pre-stretched bi-axially at 200% strain and immersed in the oil bath, survived a very high eld strength (>800 MV/m) and demonstrated areal strains up to 140%. The dielectric strength, achieved in the immersion, is approximately two times larger than that in the air (450 MV/m). This is achieved because the dielectric liquid bath helps to quench the localized electrical breakdown, which would have discharged sparks and burnt the dielectric lm in the air.

Dielectric elastomer generators are a promising solution to scavenge energy from human motion, due to their lightweight, high efficiency low cost and high energy density. Performances of a dielectric elastomer used in a generator application are generally evaluated by the maximum energy which can be converted. This energy is defined by an area of allowable states and delimited by different failure modes such as: electrical breakdown, loss of tension, mechanical rupture and electromechanical instability, which depend deeply on dielectric behaviors of the material. However, there is controversy on the dielectric constant (permittivity) of usual elastomers used for these applications. This paper aims to investigate the dielectric behaviors of two popular dielectric elastomers: VHB 4910 (3M) and Polypower (Danfoss). This study is undertaken on a broad range of temperature. We focus on the influence of pre-stretch in the change of the dielectric constant. An originality of this study is related to the significant influence of the nature of compliant electrodes deposited on these elastomers. Additionally, the electrical breakdown field of these two elastomers has been studied as a function of pre-stretch and temperature. Lastly, thanks to these experiments, analytic equations have been proposed to take into account the influence of the temperature, the pre-stretch and the nature of the compliant electrodes on the permittivity. These analytic equations and the electrical breakdown field were embedded in a thermodynamic model making it possible to define new limits of operation closer to the real use of these elastomers for energy harvesting applications.

In this paper, we have developed electrochemical and electromechanical kinetic model of a bucky-gel actuator which is composed of an ionic liquid (IL) gel electrolyte layer sandwiched by electrode layers based on single-walled carbon nanotubes (SWNTs) and ILs. The electrochemical model can be applied to the electromechanical effect only due to the electric double-layer (DL) charging, or due to both the DL charging and redox reaction of SWNTs. The model was compared with the experimental results of the bucky-gel actuators.

The emergence of novel electronic systems and their requirements have necessitated the evolution of new material classes. The traditional electronic semiconductors and components are shifting from silicon based substrates to polymers and other organic compounds. Sensor components are no exceptions, where compliant polymeric materials offer the possibility of flexible electronics. This paper examines the fabrication and characterization of piezoresistive nanocomposites for pressure sensing applications. The matrix material employed was Polyvinylidene Fluoride (PVDF). The PVDF phase was reinforced with conductive particles, in order to form a conductive filler network throughout the nanocomposite. Multiwall carbon nanotubes (MWNT) were selected as conductive particles to form the networks. The composites were prepared by melt mixing the PVDF and conductive particles in compositions ranging from 0.25 to 10 wt% conductive particle in PVDF. The dielectric permittivity and electrical conductivity of the composites was characterized and the electrical percolation behavior of PVDF nanocomposites fitted to the statistical percolation model. Scanning electron was employed to understand the morphology of the filler networks in the PVDF nanocomposites. Quasi-static piezoresistance of the nanocomposites was characterized using a custom-built force-resistance measurement setup under compressive loading conditions.

Low voltage, dry electrochemical actuators can be prepared by using a gel made of carbon nanotubes and ionic liquid.¹ Their performance can be significantly improved by combining physical and chemical modifications with a proper engineering. We demonstrated that multi walled carbon nanotubes can be effectively used for actuators preparation;² we achieved interesting performance improvements by chemically cross linking carbon nanotubes using both aromatic and aliphatic diamines;³ we introduced a novel hybrid material, made by in-situ chemical polymerization of pyrrole on carbon nanotubes, that further boosts actuation by taking advantage of the peculiar properties of both materials in terms of maximum strain and conductivity;⁴ we investigated the influence of actuator thickness showing that the generated strain at high frequency is strongly enhanced when thickness is reduced. To overcome limitations set by bimorphs, we designed a novel actuator in which a metal spring, embedded in the solid electrolyte of a bimorph device, is used as a non-actuating counter plate resulting in a three electrode device capable of both linear and bending motion. Finally, we propose a way to model actuators performance in terms of purely material-dependent parameters instead of geometry-dependent ones.⁵

The geometric characterization of low-voltage dielectric electro-active polymer (EAP) structures, comprised of nanometer thickness but areas of square centimeters, for applications such as artificial sphincters requires methods with nanometer precision. Direct optical detection is usually restricted to sub-micrometer resolution because of the wavelength of the light applied. Therefore, we propose to take advantage of the cantilever bending system with optical readout revealing a sub-micrometer resolution at the deflection of the free end. It is demonstrated that this approach allows us to detect bending of rather conventional planar asymmetric, dielectric EAP-structures applying voltages well below 10 V. For this purpose, we built 100 μm-thin silicone films between 50 nm-thin silver layers on a 25 μm-thin polyetheretherketone (PEEK) substrate. The increase of the applied voltage in steps of 50 V until 1 kV resulted in a cantilever bending that exhibits only in restricted ranges the expected square dependence. The mean laser beam displacement on the detector corresponded to 6 nm per volt. The apparatus will therefore become a powerful mean to analyze and thereby improve low-voltage dielectric EAP-structures to realize nanometer-thin layers for stack actuators to be incorporated into artificial sphincter systems for treating severe urinary and fecal incontinence.

Shape memory nanofibers are capable of fixing a temporary shape and recovering a permanent shape in response to stimulus. Nafion nanofibers with shape memory effect are achieved via electrospinning technology. The resulting nanofibres exhibit the smooth, continuous, uniform fibrous structure. The diameter of nanofibers increases after annealing progress at different temperatures. The shape memory effect is evaluated in a fixed force controlled tensile test. Electrospun Nafion nanofibers show excellent shape memory properties upon heat. The shape fixity rates and shape recovery rates are about 95-96% and 87-89% after consecutive three shape memory cycles, respectively. The structure of electrospun nanofibers is stable and reversible for at least three cycles of shape memory tests. These results indicate that shape memory Nafion nanofibers can be used in a wide potential application fields such as smart materials and structures in the future.

Elastomers currently used as transducers have not been designed with this specific application in mind and there is therefore a need for new target engineered materials to bring down driving voltages and increase actuator performance. A proposed method of optimization involves the development of new types of interpenetrating polymer networks (IPNs) to be used as dielectric elastomer (DE) transducers. This work demonstrates the use of polypropylene glycol (PPG) as a novel DE material. The IPNs formed were shown to exhibit excellent thermal stability and mechanical properties including lower tendency for viscous dissipation with higher dielectric permittivity compared to state of the art polydimethylsiloxane (PDMS) materials.

Ionic polymer-metal composites (IPMCs) have intrinsic actuation and sensing capabilities, and they need hydration to operate. For an IPMC sensor operating in air, the water content in the polymer varies with the humidity level of the ambient environment, which leads to its strong humidity-dependent sensing behavior. However, the study of this behavior has been very limited. In this paper, the influence of environmental humidity on IPMC sensors is characterized and modeled from a physical perspective. Specifically, a cantilevered IPMC beam is excited mechanically at its base inside a custom-built humidity chamber, where the humidity is feedback-controlled by activating/deactivating a humidifier or a dehumidifier properly. We first obtain the empirical frequency responses of the sensor under different humidity levels, with the IPMC base displacement as input and the tip displacement and short-circuit current as outputs. Based on physics-based model for a given humidity level, we then curve-fit the measured frequency responses to identify the humidity-dependent physical parameters, including Young’s modulus and strain-rate damping coefficient for the mechanical properties, and ionic diffusivity for the mechanoelectrical dynamics. These parameters show a clear trend of change with the humidity. By fitting the identified parameters at a set of test humidity levels, the humidity-dependence of the physical parameters is captured with polynomial functions, which are then plugged into the physics-based model for IPMC sensors to predict the sensing output under other humidity conditions. The latter humidity-dependent model is further validated with experiments.

In this paper, we analyze the charge dynamics of ionic polymer metal composites (IPMCs) in response to voltage inputs composed of a DC bias and a small AC voltage. IPMC chemoelectrical behavior is described through the Poisson-Nernst-Planck framework. The physics of charge build up and mass transfer at the electrodes are modeled through metal particle layers. Perturbation methods are used to establish an equivalent circuit model for the IPMC electrical response. The proposed approach is validated through comparison with finite element results.

Ionic polymer-metal composites (IPMCs) are some of the most well-known electro-active polymers. This is due to their large deformation provided a relatively low voltage source. IPMCs have been acknowledged as a potential candidate for biomedical applications such as cardiac catheters and surgical probes; however, there is still no existing mass manufacturing of IPMCs. This study intends to provide a theoretical framework which could be used to design practical purpose IPMCs depending on the end users interest. By explicitly coupling electrostatics, transport phenomenon, and solid mechanics, design optimization is conducted on a simulation in order to provide conceptual motivation for future designs. Utilizing a multi-physics analysis approach on a three dimensional cylinder and tube type IPMC provides physically accurate results for time dependent end effector displacement given a voltage source. Simulations are conducted with the finite element method and are also validated with empirical evidences. Having an in-depth understanding of the physical coupling provides optimal design parameters that cannot be altered from a standard electro-mechanical coupling. These parameters are altered in order to determine optimal designs for end-effector displacement, maximum force, and improved mobility with limited voltage magnitude. Design alterations are conducted on the electrode patterns in order to provide greater mobility, electrode size for efficient bending, and Nafion diameter for improved force. The results of this study will provide optimal design parameters of the IPMC for different applications.

One of the constraining properties of the IPMC actuators is their back-relaxation. An excited IPMC actuator, instead of holding its bent state, relaxes back towards its initial shape even when the exciting signal is a DC voltage. This behavior is reported by many authors and is usually explained with diffusion of water back, or out of the electrodes. However, a non-traditional approach to the well-known elements of the traditional viscoelastic schemes – spring and damper – results with a qualitatively new model of viscoelasticity. This mechanical analogy of viscoelastic behavior elucidates the naturalness of the back-relaxation behavior of the actuators. The model is described by a system of PDEs and gives an intuitive and accurate charge-deflection correlation with back-relaxation included. The experiments carried out with actuators of different shapes show excellent accordance with the model.

In this paper, the pH value of working solution of Ionic Polymer Metal Composite (IPMC) actuators was systematically changed and the effect of pH on the deformation behavior was experimentally investigated. IPMC actuators, which consist of a thin perfuorinated ionomer membrane and electrodes plated on both surfaces, can undergo a large bending motion when a small electric field is applied across its thickness direction. Because of its lightness, softness and usableness in wet conditions, IPMC actuators are promised to be used for artificial muscles, biomimetic actuators and medical applications. The deformation properties of IPMC actuators are influenced by working solutions. However, the basic understandings about the effect of pH value of working solution on the deformation properties have not been clarified yet. Therefore, the pH characteristics of IPMC actuator were evaluated in this paper. IPMC actuators with the palladium electrodes were used and the responses for step voltage in several pH solutions were investigated. The results showed that the deformation behavior is drastically changed between acid and alkali solutions. In acid solutions, IPMC actuator showed a relaxation motion, though IPMC actuator in alkali solutions kept its deformed shape during applying a voltage.

This contribution describes the development, the potential and the limitations of planar actuators for controlling bending devices with variable stiffness. Such structures are supposed to be components of new smart, self-sensing and -controlling composite materials for lightweight constructions. To realize a proper stiffness control, it is necessary to develop reliable actuators with high actuation capabilities based on smart materials. Several actuator designs driven by electroactive polymers (EAPs) are presented and discussed regarding to their applicability in such structures. To investigate the actuators, variable-flexural stiffness devices based on the control of its area moment of inertia were developed. The devices consist of a multi-layer stack of thin, individual plates. Stiffness variation is caused by planar actuators which control the sliding behavior between the layers by form closure structures. Previous investigations have shown that actuators with high actuation potential are needed to ensure reliable connections between the layers. For that reason, two kinds of EAPs Danfoss PolyPower and VHB 4905 by 3M, have been studied as driving unit. These EAP-driven actuators will be compared based on experimental measurements and finite element analyses.

A soft dielectric polymer, plasticized poly(vinyl chloride) (PVC gel), has been known as a characteristic actuator with electrotactic creep deformation. The deformation can be applied for bending and contraction. The mechanism of the deformation has been attributed to the colossal dielectric constant of the gel induced by dc field. The dielectric constant at 1 Hz, jumps from less than10 to thousand times larger value. The huge dielectric constant suggests the gel can have electro-optic function. In this paper, we introduce the gel can bend light direction by applying a dc electric field. The PVC gel can bend light direction depending on the electric field. Detailed feature of the light bending will be introduced and discussed. Bending angle can be controlled by dielectric plasticizer and electric field. The components of the gel, PVC and plasticizer themselves, did not show any effect of electro-optical function like the PVC gel. The same feature can be observed in other polymer, like poly(vinyl alcohol)-dimethyl sulphoxide gel, too.

The development of elastomer materials with a high dielectric permittivity has attracted increased interest over the last years due to their use in for example dielectric electroactive polymers. For this particular use, both the electrically insulating properties - as well as the mechanical properties of the elastomer - have to be tightly controlled in order not to destroy favorable elastic properties by the addition of particles. In the following, expanded graphite in low concentrations (up to 5 wt%) are investigated as a possible candidate as filler materials in very soft elastomers, which by the addition of traditional fillers in the necessary amounts would either lose their stability or their softness. Furthermore the influence of several mixing procedures on the electrical and mechanical properties is investigated.

The polyelectrolyte of high-strength gels was made to improve the mechanical properties in our previous study. In the field of electronic devices, the demand of polymer electrodes, which have high conductivity, high flexibility and transparence, is increasing. In this study, we attempt to make a transparent polymer electrode by laminating polymer thin film and silver nanowire (AgNW). High transparenct poly(methyl methacrylate) (PMMA) film, which is produced by using solvent cast method is used. AgNW is prepared by reacting Silver chloride (AgCl) with Silver nitrate (AgNO₃) based on previous study. The AgNWs taking on different shapes were obtained. Fibrous AgNWs are formed by using high molecular weight polyvinylpyrrolidone (PVP). These results showed a possibility of developing the polymer electrode with high conductivity, high flexibility and transparence.

We have previously presented “nastic” actuators based on electroosmotic (EO) pumping of fluid in microchannels using high electric fields for potential application in soft robotics. In this work we address two challenges facing this technology: applying EO to meso-scale devices and the stability of the pumping fluid. The hydraulic pressure achieved by EO increases with as 1/d², where d is the depth of the microchannel, but the flow rate (which determines the stroke and the speed) is proportional to nd, where n is the number of channels. Therefore to get high force and high stroke the device requires a large number of narrow channels, which is not readily achievable using standard microfabrication techniques. Furthermore, for soft robotics the structure must be soft. In this work we present a method of fabricating a three-dimensional porous elastomer to serve as the array of channels based on a sacrificial sugar scaffold. We demonstrate the concept by fabricating small pumps. The flexible devices were made from polydimethylsiloxane (PDMS) and comprise the 3D porous elastomer flanked on either side by reservoirs containing electrodes. The second issue addressed here involves the pumping fluid. Typically, water is used for EO, but water undergoes electrolysis even at low voltages. Since EO takes place at kV, these systems must be open to release the gases. We have recently reported that propylene carbonate (PC) is pumped at a comparable rate as water and is also stable for over 30 min at 8 kV. Here we show that PC is, however, degraded by moisture, so future EO systems must prevent water from reaching the PC.

Electrically tunable adaptive lenses provide several advantages over traditional lens assemblies in terms of compactness, speed, efficiency, and flexibility. We present an elastomer-liquid lens system which makes use of an in-line, transparent electroactive polymer actuator. The lens has two liquid-filled cavities enclosed within two frames, with two passive outer elastomer membranes and an internal transparent electroactive membrane. Advantages of the lens design over existing systems include large apertures, flexibility in choosing the starting lens curvature, and electrode encapsulation with a dielectric liquid. A lens power change up to 40 diopters, corresponding to focal length variation up to 300%, was recorded during actuation, with a response time on the order of tens of milliseconds.

The mechanical contacting of a dielectric elastomer actuator is investigated. The actuator is constructed by coiling the dielectric elastomer around two parallel metal rods, similar to a rubber band stretched by two index fingers. The goal of this paper is to design the geometry and the mechanical properties of a polymeric interlayer between the elastomer and the rods, gluing all materials together, so as to optimize the mechanical durability of the system. Finite element analysis is employed for the theoretical study which is linked up to experimental results performed by Danfoss PolyPower A/S.

We report on the use of capacitive self-sensing to operate a DEA-based tunable grating in closed-loop mode. Due to their large strain capabilities, DEAs are key candidates for tunable optics applications. However, the viscoelasticity of elastomers is detrimental for applications that require long-term stability, such as tunable gratings and lenses. We show that capacitive sensing of the electrode strain can be used to suppress the strain drift and increase the response speed of silicone-based actuators. On the other hand, VHB actuators exhibit a time-dependent permittivity, which causes a drift between the device capacitance and its strain.

Dielectric elastomers with low modulus and large actuation strain have been investigated for applications in which they serve as “active” microfluidic channel walls. Anisotropically prestrained acrylic elastomer membranes are bonded to cover open trenches formed on a silicone elastomer substrate. Actuation of the elastomer membranes increases the cross-sectional area of the resulting channels, in turn controlling hydraulic flow rate and pressure. Bias voltage increases the active area of the membranes, allowing intrachannel pressure to alter channel geometry. The channels have also demonstrated the ability to actively clear a blockage. Applications may include adaptive microfilters, micro-peristaltic pumps, and reduced-complexity lab-on-a-chip devices.

Piezoelectric electroactive polymers (EAP) are promising materials for applications in microfluidic lab-on-chip systems. In such systems, fluids can be analyzed by different chemical or physical methods. During the analysis the fluids need to be distributed through the channels of the chip, which requires a pumping function. We present here all inkjet-printed EAP actuators that can be configured as a membrane-based micropump suitable for direct integration into lab-on-chip systems. Drop-on-demand inkjet printing is a versatile digital deposition technique that is capable of depositing various functional materials onto a wide variety of substrates in an additive way. Compared to conventional lithography-based processing it is cost-efficient and flexible, as no masking is required. The actuators consist of a polymer foil substrate with an inkjet-printed EAP layer sandwiched between a set of two electrodes. The actuators are printed using a commercially available EAP solution and silver nanoparticle inks. When a voltage is applied across the polymer layer, piezoelectric strain leads to a bending deflection of the beam or membrane. Circular membrane actuators with 20 mm diameter and EAP thicknesses of 10 to 15 μm exhibit deflections of several μm when driven at their resonance frequency with voltages of 110 V. From the behavior of membrane actuators a pumping rate of several 100 μL/min can be estimated, which is promising for applications in lab-on-chip devices.

New polyaniline (PANi) synthesis was performed starting from non-toxic N-phenil-p-phenylenediamine (aniline dimer) using reverse addition of monomer to oxidizing agent, the synthesis allows to produce highly soluble PANi. Several types of doped PANi were prepared to be used on electromechanical active actuators. Different techniques were used to include carbon nanoparticles such as carbon nanotubes and graphene. Bimorph solid state ionic actuators were prepared with these novel nanocomposites using a variety of supporting polymers.

The six axis F/T sensor is a primary component for the robotic technologies, but its high unit cost hampers the popularization to the robotic applications. In this paper, we present a six-axis force-torque capacitive sensor based on dielectric elastomer. Dielectric elastomer is compressed and deformed with external forces acting on it. Its deformation results in the variation of capacitance, which can be used as a kind of capacitive sensing scheme. The proposed sensor consists of plastic structure and dielectric elastomer capacitors. Since it takes a simple structure, it is possible to fabricate by using a plastic molding process, which results in extremely lower cost than existing off-the-shelf products. We present the basic structure and design of the sensor with the explanation of its working principle. A fabrication method dedicated to the sensor is developed and finally, a prototype will be demonstrated with calibration procedures.

Being able to accurately record body motion allows complex movements to be characterised and studied. This is especially important in the film or sport coaching industry. Unfortunately, the human body has over 600 skeletal muscles, giving rise to multiple degrees of freedom. In order to accurately capture motion such as hand gestures, elbow or knee flexion and extension, vast numbers of sensors are required. Dielectric elastomer (DE) sensors are an emerging class of electroactive polymer (EAP) that is soft, lightweight and compliant. These characteristics are ideal for a motion capture suit. One challenge is to design sensing electronics that can simultaneously measure multiple sensors. This paper describes a scalable capacitive sensing device that can measure up to 8 different sensors with an update rate of 20Hz.

We report on a new structure of Dielectric Elastomer Actuators (DEAs) called zipping DEAs, which have a set of unique characteristics that are a good match for the requirements of electrically-powered integrated microfluidic pumping and/or valving units as well as Braille displays. The zipping DEAs operate by pulling electrostatically an elastomer membrane in contact with the rigid sidewalls of a sloped chamber. In this work, we report on fully functional mm-size zipping DEAs that demonstrate a complete sealing of the chamber sidewalls and a tunable bistable behavior, and compare the measurements with an analytical model. Compared to our first generation of devices, we are able vary the sidewall angle and benefit therefore from more flexibility to study the requirements to make fully functional actuators. In particular, we show that with Nusil CF19 as membrane material (1.2 MPa Young’s modulus), it is possible to zip completely 2.3 mm diameter chambers with 15° and 21° sidewalls angle equibiaxially prestretched to λ₀=1.12 and 15° chambers with λ₀=1.27.

In previous work, a dual-axis hybrid-type tactile sensor using PDMS (Polydimethylsiloxane) with a pair of metal electrodes, (which were deposited directly on the PDMS surface), was proposed. The hybrid sensor can measure the normal force and the shear force from the measurement of the change of capacitance and resistance values from the one pair of electrodes. However, the metal is hard to be deposited on the surface of the PDMS because the PDMS is hydrophobic. The hydrophobic surface can be changed to hydrophilic using O2 Plasma treatment or UV treatment. When O2 plasma treatment or UV treatment is used, there is the problem that the processing of the metal deposition and the wiring completed in a very short period of limited time. Also, the deposited metal on the surface of the PDMS is easy to break because the deposited metal is exposed in the air. In this paper, we propose a dual-axis hybrid-type tactile sensor where the PET (polyethylene terephthalate) film is inserted between the PDMS films. The deposited metal is not removed easily from the PET film because the adhesion is strong. Also, the PDMS surrounding the PET film plays the roles of dielectric elastomer and shielding the deposited metal from the external environment at same time. Experimental results verify the effectiveness of the fabricated dual-axis hybrid-type force sensor.

Beside the characteristics of the elastomer material itself, the performance of dielectric elastomers in actuator, sensor as well as generator applications depends also on the properties of the electrode material. Various electrode materials based on metallic particles dispersed in a silicone matrix were manufactured and investigated. Anisotropic particles such as silver-coated copper flakes and silver-coated glass flakes were used for the preparation of the electrodes. The concentration of the metallic particles and the thickness of the electrode layers were varied. Specific conductivities derived from resistance measurements reached about 100 S/cm and surmount those of the reference materials based on graphite and carbon black by up to three orders of magnitude. The high conductivities of the new electrode materials can be maintained even at very large stretch deformations up to 200 %.

Due to high electrical conductivity, metals have been the traditional material for electrodes. However, as metal films have low fracture strains, they are not commonly used as compliant electrodes in the field of dielectric elastomer actuators and generators. We have recently demonstrated that the use of metal films as electrodes can in fact allow dielectric elastomer actuators to have large actuated area strains of more than 100%. The metal film electrodes used have a network of crumples that unfolds as it is subjected to in-plane strains. This mechanism enables the metal electrodes to have a relatively low stiffening effect on the soft dielectric elastomer and to be able to retain its low resistance despite being highly strained; the latter characteristic would facilitate in the reduction of parasitic losses in dielectric elastomer generator applications. By metalizing a highly bi-axially pre-stretched dielectric elastomer that was subsequently partially relaxed, a bi-axial compressive force was introduced into the metal films, thereby causing a network of folds to form. In this paper, we study the change in the topography of the crumpled metal electrodes as the metal films are subjected to varying extents of bi-axial compression. It was also found that the way in which the metal films fold does in fact alter the electrodes’ stretchability, as manifested in the performance of the dielectric elastomer actuators using these crumpled metal films as electrodes.

Ionic polymer metal composites (IPMCs) are one of the most widely used types of electro-active polymer actuator, due to their low electric driving potential and large deformation range. In this research a tube type IPMC was investigated. This IPMC has a circular cross section with four separate electrodes on its surface and a hole through the middle. The four separate electrodes allows for biaxial bending and accurate control of the tip location. One of the main advantages of using this type of IPMC is the ability to embed a specific tool and accurately control the tool tip location using the large deflection range of the IPMC. This ability has widespread applications including in the biomedical field for use in catheter procedures. In this paper the results of the bending and force experiments were examined to validate the performance of this actuator obtained from the theoretical three dimensional COMSOL Multipysics model. An electromechanical model of the IPMC was developed and integrated into a closed loop control system. To improve functionality and the user interface the control system was designed to work on a laptop touchpad. This will provide a more familiar and intuitive interaction and cut down on operator training time.

Dielectric elastomer actuators (DEAs) can be optimized by modifying the dielectric or mechanical properties of the electroactive polymer. In this work both properties were improved simultaneously by a simple process, the one-step film formation for polyurethane and silicone films. The silicone network contains polydimethylsiloxane (PDMS) chains, as well as cross-linker and grafted molecular dipoles in varying amounts. The process leads to films, which are homogenous down to the molecular level and show higher permittivities as well as reduced stiffnesses. The dipole modification of a new silicone leads to 40 times higher sensitivities, compared to the unmodified films. This new material reaches the sensitivity of the widely used acrylate elatomer VHB4905. A similar silicone modification was obtained by using smart fillers consisting of organic dipoles and additional groups realizing a high compatibility to the silicon network. Polyurethanes are alternative elastomers for DEAs which are compared with the silicones in important properties. Polyurethanes have an intrinsically high dielectric constant (above 7), which is based on the polar nature of the polyurethane fragments. Polyurethanes can be made in roll-to-roll process giving constant mechanical and electrical properties on a high level.

Dielectric elastomer is able to produce a large electromechanical deformation which is time-dependent and unstable due to the visco-hyper-elasticity. In the current study, we use a thermodynamic model to characterize the viscoelastic relaxation in the electromechanical deformation and instability of a viscoelastic dielectric. The parameters in the model were verified experimentally. We investigate the time-dependent mechanical deformation, electrical breakdown strength, polarization, and the electromechanical stability which are coupled by viscoelastic relaxation. The results show the electromechanical stability has strong time-dependence, due to the stress relaxation when the pre-stretch is applied.

Dielectric Elastomers (DEs) can be actuated under high electric field to produce large strains. Most high-performing DE materials such as the 3M^™ VHB^™ membranes are commercial products designed for industrial pressure-sensitive adhesives. The limited knowledge of the exact chemical structures of these commercial materials has made it difficult to understand the relationship between molecular structures and electromechanical properties. In this work, new acrylic elastomers based on n-butyl acrylate and acrylic acid were synthesized from monomer solutions by UV-initiated bulk polymerization. The new acrylic copolymers have a potential to obtain high dielectric constant, actuation strain, dielectric strength, and a high energy density. Silicone and ester oligomer diacrylates were also added onto the copolymer structures to suppress crystallization and to crosslink the polymer chains. Four acrylic formulations were developed with different amounts of acrylic acid. This gives a tunable stiffness, while the dielectric constant is varied from 4.3 to 7.1. The figure-of-merit performance of the best formulation is 186 % area strain, 222 MV/m of dielectric strength, and 2.7 MJ/m³ of energy density. To overcome electromechanical instability, different prestrain ratios were investigated, and under the optimized prestrain, the material has a lifetime of thousands of cycles at 120 % area strain.

Soft robotics may provide many advantages compared to traditional robotics approaches based on rigid materials, such as intrinsically safe physical human-robot interaction, efficient/stable locomotion, adaptive morphology, etc. The objective of this study is to develop a compliant structural actuator for soft a soft robot using dielectric elastomer minimum energy structures (DEMES). DEMES consist of a pre-stretched dielectric elastomer actuator (DEA) bonded to an initially planar flexible frame, which deforms into an out-of-plane shape which allows for large actuation stroke. Our initial goal is a one-dimensional bending actuator with 90 degree stroke. Along with frame shape, the actuation performance of DEMES depends on mechanical parameters such as thickness of the materials and pre-stretch of the elastomer membrane. We report here the characterization results on the effect of mechanical parameters on the actuator performance. The tested devices use a cm-size flexible-PCB (polyimide, 50 μm thickness) as the frame-material. For the DEA, PDMS (approximately 50 μm thickness) and carbon black mixed with silicone were used as membrane and electrode, respectively. The actuators were characterized by measuring the tip angle and the blocking force as functions of applied voltage. Different pre-stretch methods (uniaxial, biaxial and their ratio), and frame geometries (rectangular with different width, triangular and circular) were used. In order to compare actuators with different geometries, the same electrode area was used in all the devices. The results showed that the initial tip angle scales inversely with the frame width, the actuation stroke and the blocking force are inversely related (leading to an interesting design trade-off), using anisotropic pre-stretch increased the actuation stroke and the initial bending angle, and the circular frame shape exhibited the highest actuation performance.

In the past decade, several high-strength gels have been developed. These gels are expected to use as a kind of new engineering materials in the fields of industry and medical as substitutes to polyester fibers, which are materials of artificial blood vessels. The gels have both low surface friction and well permeability due to a large amount of water absorbed in the gels, which are superiority of the gels compering to the polyester fibers. It is, however, difficult for gels to be forked structure or cavity structure by using cutting or mold. Consequently, it is necessary to develop the additive manufacturing device to synthesize and mode freely gels at the same time. Here we try to develop an optical 3D gel printer that enables gels to be shaped precisely and freely. For the free forming of high-strength gels, the 1st gels are ground to particles and mixed with 2nd pregel solution, and the mixed solution is gelled by the irradiation of UV laser beam through an optical fiber. The use of the optical fiber makes one-point UV irradiation possible. Since the optical fiber is controlled by 3D-CAD, the precise and free molding in XYZ directions is easily realized. We successfully synthesized tough gels using the gel printer.

Polyelectrolyte gels are ionic electroactivematerials. They have the ability to react as both, sensors and actuators. As actuators they can be used e.g. as artificial muscles or drug delivery control; as sensors they may be used for measuring e.g. pressure, pH or other ion concentrations in the solution. In this research both, anionic and cationic polyelectrolyte gels placed in aqueous solution with mobile anions and cations are investigated. Due to external stimuli the polyelectrolyte gels can swell or shrink enormously by the uptake or delivery of solvent. In the present research a coupled multi-field problem within a continuum mechanics framework is proposed. The modeling approach introduces a set of equations governing multiple fields of the problem, including the chemical field of the ionic species, the electrical field and the mechanical field. The numerical simulation is performed by using the Finite Element Method. Within the study some test cases will be carried out to validate our model. In the works by Gülch et al., the application of combined anionic-cationic gels as grippers was shown. In the present research for an applied electric field, the change of the concentrations and the electric potential in the complete polymer is simulated by the given formulation. These changes lead to variations in the osmotic pressure resulting in a bending of different polyelectrolyte gels. In the present research it is shown that our model is capable of describing the bending behavior of anionic or cationic gels towards the different electrodes (cathode or anode).

Novel bending actuators were made solely from electrochemically polymerized conducting polymer materials. The working principle for these free-standing conducting polymer (CP) films is based on different anion- and cation-dominated actuation for the two layers. Synthesis conditions for the two layers of the same polymer film have been chosen such that the mobility of cations and anions in the considered potential window is different. Polymerization of CP layers of this nature on top of each other results in a sandwich structure with bilayer functionality in a properly chosen electrolyte. The results of a comparative study of various combinations of sandwiched PEDOT films in terms of actuation properties are presented in this study. Free-standing films of PEDOT linear actuators electrodeposited in the same electrolyte at different polymerization potentials were investigated by means of electro-chemo-mechanical deformation measurements. PEDOT-PEDOT bilayer functionality is studied in this work with a view to their bending actuation properties.