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Dielectric elastomer actuators (DEAs) are emerging as promising candidates for various applications in robotics and optical devices due to their lightweight, miniaturization potential, high energy density, simple structure, and low power consumption. However, their effective actuation always demands sophisticated high-voltage driving circuits that are compact and responsive. DEAs need to be capable of generating intricate high-voltage waveforms or simultaneously controlling multiple quadrants with distinct high-voltage levels. This paper proposes a high-voltage power supply for DEAs, featuring a four-quadrant high-voltage driving circuit. The circuit is capable of independently generating high-voltage signals ranging from 100 V to 6000 V and producing arbitrary waveforms with adjustable frequencies. The independent operation of the quadrants without crosstalk showcases the system's integration and potential for cross-disciplinary applications. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators (DEAs) are soft, electrically powered actuators that have no discrete moving parts, yet can exhibit large strains (10%–50%) and moderate stress (∼100 kPa). This Tutorial describes the physical basis underlying the operation of DEA's, starting with a simple linear analysis, followed by nonlinear Newtonian and energy approaches necessary to describe large strain characteristics of actuators. These lead to theoretical limits on actuation strains and useful non-dimensional parameters, such as the normalized electric breakdown field. The analyses guide the selection of elastomer materials and compliant electrodes for DEAs. As DEAs operate at high electric fields, this Tutorial describes some of the factors affecting the Weibull distribution of dielectric breakdown, geometrical effects, distinguishing between permanent and "soft" breakdown, as well as "self-clearing" and its relation to proof testing to increase device reliability. New evidence for molecular alignment under an electric field is also presented. In the discussion of compliant electrodes, the rationale for carbon nanotube (CNT) electrodes is presented based on their compliance and ability to maintain their percolative conductivity even when stretched. A procedure for making complaint CNT electrodes is included for those who wish to fabricate their own. Percolative electrodes inevitably give rise to only partial surface coverage and the consequences on actuator performance are introduced. Developments in actuator geometry, including recent 3D printing, are described. The physical basis of versatile and reconfigurable shape-changing actuators, together with their analysis, is presented and illustrated with examples. Finally, prospects for achieving even higher performance DEAs will be discussed. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the preparation and several electrical properties of two ionic Liquid Crystal Elastomers. We show that iLCEs can be used as electric actuators, bending sensors and as solid electrolytes of organic electrochemical transistors. We summarise the results using one type of LCE and two types of ionic liquids. It is found that the ionic liquid that phase separates from the reactive mesogenic monomers and forms micron size ionic channels performs better than the less phase separating ionic liquid. The switching time of the order of a second was found to be possible using the ionic liquid with smaller ions and larger channels. These results provide many exciting opportunities in various areas and impact future applications, although they are far from optimised. Fine tuning of the high-performance iLCEs require an intricate compatibility between the LCE and the electrodes and appears to be laborious. On the other hand, the first promising results justify the efforts to study more type of liquid crystal elastomers, ionic liquids and compliant electrodes. [ABSTRACT FROM AUTHOR]

Dielectric Elastomer Actuator (DEA) shows the complex characteristics such as the inherent nonlinearity, intricate electromechanical coupling, time-dependent viscoelastic behavior, etc., which make it difficult to establish a dynamic model. This paper proposes a dynamic model based on the physical properties of DE materials to describe the above characteristics. The Gent model and the generalized Kelvin model are used to describe the free energy and the viscoelastic characteristics of DEA, respectively. Based on the experimental results, the differential evolution algorithm is used to identify the model parameters. Comparing the experimental data with the model prediction, the validity and generalization of the model are demonstrated. [ABSTRACT FROM AUTHOR]

A dynamic model for the soft dielectric elastomer actuator (SDEA) is developed in this paper to describe its intricately nonlinear behaviors considering different input frequencies and external loads. Firstly, the characteristics of the SDEA are observed by several groups of experiments. A phenomenological model is proposed to describe the asymmetric hysteresis behavior of the SDEA, which consists of a Prandtl-Ishlinskii model with one-side play operator and a dead-zone model with one-side dead-zone operator. Meanwhile, a mathematical model is built to depict the creep behavior of the SDEA. The dynamic model including a module and a linear system is proposed to further handle the rate-dependent and the stress-dependent hysteresis behaviors of the SDEA, in which the module is the superposition of the asymmetric hysteresis model and the creep model. To ensure that the inverse solution of the module is existing, as well as the linear system is controllable and observable, the constraint conditions of parameter values of the dynamic model are constructed. Next, the parameter identification is divided into two steps, and the differential evolution algorithm is employed in each step. Finally, the generalization of the proposed dynamics model is demonstrated by comparing the model output with the experimental data. [ABSTRACT FROM AUTHOR]

A new electrode architecture for dielectric elastomer actuators (DEAs) is introduced in which a soft polyacrylate film is coated with a biphasic mixture of silver, indium, and gallium. This Ag–In–Ga coating functions as a soft electrode that is ultrathin, highly compliant, highly conductive, stretchable, and non‐smearing. Compared to carbon grease, sputter‐deposited metal coating, and particle‐filled conductive elastomers, this biphasic coating exhibits a unique combination of solid‐state integrity, extreme mechanical compliance, and low electrical resistivity. Herein, how DEAs with an Ag–In–Ga coating exhibit a 5× larger actuation speed compared to carbon‐coated dielectric films is shown. The influence of coating thickness on the mechanical stiffness and blocking force is also examined. [ABSTRACT FROM AUTHOR]

Cylindrical dielectric elastomer actuator (CDEA) is known as an effective type of dielectric elastomer actuators. Owing to the advantageous properties of compact structure, CDEA has shown promising potential application in the development of the soft robotics. However, the inherent nonlinear viscoelasticity of dielectric elastomers causes the strain of actuators to change with time. This feature of CDEA is challenging to modeling and control of DE actuator and may limit their motion accuracy in practical applications. In this paper, to accurately describe the time-dependent nonlinear viscoelasticity properties of the actuator, by combining the advantages of the Kelvin–Voigt model and the Generalized Maxwell, a generalized combination model is proposed. The comparisons between the model prediction and experimental results demonstrate that the proposed model can accurately predict the response of the actuator under step voltage excitation, and the minimum prediction error can be achieved by 1.97%. This research results can provide theoretical guidance for the design of CDEA and is helpful to reduce the creep effect and improve the control efficiency of the CDEA. [ABSTRACT FROM AUTHOR]

In this work, the Cosserat formulation of geometrically exact beam dynamics is extended by adding the electric potential as an additional degree of freedom to account for the electromechanical coupling in the dielectric elastomer actuators. To be able to generate complex beam deformations via dielectric actuator, a linear distribution of electric potential on the beam cross section is proposed. Based on this electric potential, the electric field and the strain-like electrical variable are defined for the beam, where the strain-like electrical variable is work-conjugated to the electric displacement. The electromechanically coupled strain energy for the beam is derived consistently from continuum electromechanics, which leads to the direct application of the material models in the continuum to the beam model. The electromechanically coupled problem in beam dynamics is first spatially semidiscretized by 1D finite elements and then solved via variational time integration. By applying different electrical boundary conditions, different deformations of the beam are obtained in the numerical examples, including contraction, shear, bending and torsion. The damping effect induced by the viscosity as well as the total energy of the beam are evaluated. The deformations of the electromechanically coupled beam model are compared with the results of the 3D finite element model, where a good agreement of the deformations in the beam model and that in the 3D finite element model is observed. However, less degrees of freedom are required to resolve the complex deformations in the beam model. [ABSTRACT FROM AUTHOR]

This article proposes a dynamic model and a tracking control strategy for a dielectric elastomer (DE) actuator based on the model predictive controller (MPC). First, the dynamic model of the DE actuator is established, which can describe its asymmetric hysteresis, creep, and even rate-dependent hysteresis behaviors simultaneously. Then, on the basis of the established dynamic model, an inverse compensation controller (ICC) is designed to compensate the hysteresis and creep nonlinearities of the DE actuator on its tracking control. Moreover, the MPC is designed to cooperate with the ICC, which can overcome the influences of the modeling error and uncertainties on the control precision. Finally, several experiments demonstrate the effectiveness of the proposed dynamic model and control strategy. [ABSTRACT FROM AUTHOR]

A long strip of a pre-stretched dielectric elastomer actuator (DEA) is necessary for strain accumulation, but it relaxes laterally and thickens non-uniformly. As compared to a short strip under the same voltage activation, the long relaxed strip is subjected to a less electric field and, thus, undergoes less active strain. Here, we developed a flexible ladder frame to reinforce and divide the long DEA in a bowtie series. When being pulled, the ladder frame unbuckled; it, in turn, helped to pre-stretch tautly the DEA membrane. Interestingly, its flanges enhance force transmissions, acting like tensioning cables for a suspension bridge. Hence, the maximum isometric stress of this bowtie series was 24% higher than the short pure-shear one and 6.5 times the long uniaxial one. With 2.2 times enhanced dielectric strength across a taut DEA membrane, the bowtie series generated an isotonic strain 3.2 times that a long non-reinforced and relaxed DEA did. Hence, the reinforced DEAs can provide a more forceful drive for bio-inspired robots. [ABSTRACT FROM AUTHOR]

This paper presents an electroactive and soft vibrotactile actuator based on a dielectric elastomer. The vibrotactile actuator is composed of an upper layer, an adhesive tape layer, a dielectric layer with bumps, and a lower layer. When a voltage is applied to the actuator, an electrostatic force created between the upper and lower layers pulls the upper layer down, compressing the dielectric layer. As soon as the applied voltage is released, the upper layer is quickly restored to its initial state by the elastic force of the compressed dielectric elastomer. Because two forces contribute to the actuation at the same time, the created vibration is sufficiently strong to stimulate human mechanoreceptors. When the applied voltage is removed, the upper layer and dielectric elastomer return to their initial shapes. We conducted experiments to determine the best weight ratio of polydimethylsiloxane (PDMS) and Ecoflex, and to quantitatively investigate the haptic performance of the proposed vibrotactile actuator. The experiments clearly show that the plasticized vibrotactile actuator can create a variety of haptic sensations over a wide frequency range. [ABSTRACT FROM AUTHOR]

Dielectric elastomer (DE) possesses attributes such as large deformation and fast response. As a typical DE actuating structure, the multilayered DE bending actuator (MDEBA) is lightweight and can actuate in relatively low voltage without a rigid frame and pre-stretch. These attributes arouse wide research interest in the MDEBA on the application of soft robots. However, due to its large deformation and nonlinear electromechanical dynamics, the control of MDEBA remains highly challenged. Considering the large bending deformation and gravity effect, we develop an electromechanical dynamic model-based control strategy, which can adaptively compensate for the parameter uncertainties during the actuation of MDEBA. Experimental results validate that this control strategy provides highly enhanced control performance compared to the proportional integral derivative (PID) controller. The electromechanical modeling method and dynamic control strategy may guide the further study of MDEBA, soft robots, and flexible devices. [ABSTRACT FROM AUTHOR]

Unlike the conventional tunable lens which contains cumbersome elements to fulfill the focus adjustment, soft liquid lens shows distinct advantages in compactness and flexibility. This paper presents a computational model of a dielectric elastomer (DE)-based, liquid-coupled soft tunable lens. The vital component of the lens system is a DE film which is divided into lens part and actuation part. The actuation part is annular which is coated with compliant electrodes while the lens part is circular and uncoated. A fixed volume of glycerol is injected into the lens to act as a transparent medium. An applied voltage will trigger the transmission of liquid between the two parts and eventually change the focal length. Governing equations for the two parts are established and the shooting method with two initial guesses is developed to solve the boundary value problems. The simulation results agree well with the experimental data. Several parametric analyses are carried out based on the developed model. It is found that the film thickness, initial volume of the liquid, the prestretch, and areas of the two parts all have significant effects on the focusing ability of the tunable lens. Both the homogeneous and inhomogeneous prestretched schemes are considered. An inhomogeneous prestretch on the annular actuation part is beneficial for improving the focusing ability of the tunable lens. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators fabricated from thin and miniaturized metal electrodes integrated with highly soft and stretchable elastomers offer the promise of opening new possibilities in the field of microrobotics. To achieve large displacements O(10−4) m at actuation voltages O(103) V in actuators with thin metal electrodes, the approach of distributed electrode array with fractal interconnects is proposed, where a single large electrode is replaced with an array of N small individual electrodes physically linked together with fractal interconnects. To investigate the effect of distributed electrode array with fractal interconnects on the static and dynamic response of the actuators, elastomer actuators with different electrode arrays—comprised of N ∈ {1,5,13,25} individual electrodes in the shape of circles—are fabricated and characterized. This study shows that the approach of distributed electrode array with fractal interconnects results in achieving large actuator displacements O(10−4) m at high speeds O(100) mm s−1, making these actuators suitable for driving microrobots. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators (DEAs) are energy efficient, compact, and operate silently. DEAs consist of an elastomer membrane sandwiched between two stretchable electrodes. Optimizing the quality of both the elastomer and the stretchable electrodes is essential to improve the DEAs performance. Herein, novel strategies are reported to achieve fast, reliable, and low‐cost fabrication of DEAs. The strategies utilize a soft brush to directly pattern carbon nanotube (CNT) powder on the elastomer membrane and tune the mechanical and surface‐adhesiveness characteristics of a polydimethylsiloxane (PDMS) membrane by altering the mixing ratio of the curing agent and base polymer. A uniaxial engineering tensile test on PDMS indicates that a softer material is formed when less curing agent is used. The softer PDMS has a sticky surface, which allows the CNT powder to be physically bound to the surface. Field‐emission scanning electron microscopy (FE‐SEM) images prove that the strong CNT network is formed on the surface of the elastomer. The electromechanical investigation also indicates that the electrical conductivity is improved for a stickier PDMS surface. The optimal performance of PDMS 30‐1 in static and cyclic DEA tests shows that the brushing of CNT combined with soft and sticky elastomer membranes can increase the DEA performance. [ABSTRACT FROM AUTHOR]

The first dielectric elastomer actuators based on electroactive nanocomposites with octakis(phenyl)‐T8‐silsesquioxane (phenyl‐T8), obtained ex‐situ, used as voltage stabilizer filler for silicone elastomers are reported. The incorporation and homogeneous dispersion of crystalline phenyl‐T8 in percentages of 2.5, 3.5, 5, and 10 into the amorphous matrix consisting in a polydimethylsiloxane‐α,ω‐diol with Mn = 240,000 g/mol was successfully achieved by solution mixing and crosslinking. For the sample with the best actuation performance (that containing 3.5 wt.% filler), an optimized filled elastomer was obtained by dispersing 3.6 wt. % phenyl‐T8 in the matrix using a suitable surfactant (Pluronic L81), thus gaining an increased electrical breakdown of 30% compared with the pristine sample. Beside dielectric strength, the matured films were characterized in terms of morphology, mechanical, dielectric and actuation tests. In spite of structural incompatibility between the filler and the matrix, the obtained materials are soft elastomers showing high strain (~800%) and low Young's modulus of 50–100 kPa. The use of phenyl‐T8 in a silicone matrix lead to electroactive films with slightly increased lateral actuation strain and electric breakdown strength. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators (DEAs) have shown promises in numerous applications such as bio‐inspired robotics, tactile displays, tunable optics, and microfluidics, owing to their unique combination of large actuation strain, high energy density, and light weight. However, the practical applications of the DEAs have been hindered partly due to their poor reliability and durability under high‐strain actuation. A major failure mechanism is from the localized electrical breakdown. Compliant electrodes with self‐clearing capability have been studied to prevent premature failures. Here, an interpenetrating bilayer compliant electrode comprising a thin layer of a water‐based polyurethane (WPU) overcoated on an ultrathin single‐walled carbon nanotube (SWNT) layer is reported. The thin polyurethane layer serves as the dielectric barrier to suppress corona discharges of the nanotubes in air. The SWNT+WPU bilayer electrode has the capability to self‐clear at the breakdown sites, enhancing the fault tolerance and mendability of the DEA at a large‐strain actuation. Stable actuation at 150% area strain for 1000 cycles under square‐wave voltage and 5.5‐h continuous actuation at a constant voltage have been achieved for acrylic elastomer‐based DEAs. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the deformation shape of a balloon-type dielectric elastomer actuator (DEA) that has been prestretched with water pressure. We fabricated the DEA with poly(dimethylsiloxane) (PDMS) as the elastomeric material and carbon grease as the electrode. We derived analytical solutions for the deformation of the DEA based on structural mechanical models. Additionally, we compared the deformation shapes obtained by theoretical analysis and experimental results. Our model can partially predict the deformation shape of the DEA with good accuracy. In addition, we discuss the applicable range of the theoretical model and error relative to the experimental results. [ABSTRACT FROM AUTHOR]

This article analytically investigates the temperature influence on the performance of laterally constrained dielectric elastomer actuators. The effects of both temperature and stretches on the permittivity are taken into consideration. The governing equations of state are established by modeling the actuator as a thermodynamic system of three degrees of freedom. Various failure modes, including electromechanical instability, electric breakdown, loss of tension, and tensile rupture are considered to restrict the operation state and to determine the region of allowable state. Numerical calculations are performed to depict the variations of some important physical quantities with generalized coordinates and to gain insight on the influence of temperature on the critical curves of failures. It is shown that the temperature has obvious effects on the operation state and the allowable region. The present results can be used for designing and optimizing an actuator, and the present approach can be extended to other kinds of dielectric elastomer actuators with complex geometries. [ABSTRACT FROM AUTHOR]

Dielectric elastomers (DEs) are a class of highly deformable electroactive polymers (EAPs) employed for electromechanical transduction technology. When electrostatically actuated dielectric elastomer actuators (DEAs) are subjected to an input signal comprising multiple Heaviside voltage steps, the emerging inherent residual vibrations may limit their motion accuracy in practical applications. In this paper, the systematic development of a command-shaping scheme is proposed for controlling residual vibrations in an electrically driven planar DEA. The proposed scheme relies on invoking the force balance at the point of maximum lateral stretch in an oscillation cycle to bring the actuator to a stagnation state followed by the application of an additional electric input signal of predetermined magnitude at a specific time. The underlying concept of the proposed control scheme is articulated for a single Heaviside step input-driven actuator and further extended to the actuator subjected to the multistep input signal. The equation governing the dynamic motion of the actuator is derived using the principle of virtual work. The devised dynamic model of the actuator incorporates the effects of strain stiffening of elastomer and viscous energy dissipation. The nonlinear dynamic governing equation is solved using matlab ode solver for extracting the dynamic response of the actuator. The applicability of the devised command-shaping control scheme is illustrated by taking a wide range of parameters including variations in the extent of equilibrium state sequences, damping, and polymer chain extensibility. The proposed scheme is found to be adaptable in controlling the vibrations of the actuator for any desired equilibrium state. The results presented in this paper can find its potential application in the design of an open-loop control system for DEAs. [ABSTRACT FROM AUTHOR]

Electrically driven dielectric elastomers (DEs) suffer from an electromechanical instability (EMI) when the applied potential difference reaches a critical value. A majority of the past investigations address the mechanics of this operational instability by restricting the kinematics to homogeneous deformations. However, a DE membrane comprising both active and inactive electric regions undergoes inhomogeneous deformation, thus necessitating the solution of a complex boundary value problem. This paper reports the numerical and experimental investigation of such DE actuators with a particular emphasis on the EMI in quasistatic mode of actuation. The numerical simulations are performed using an in-house finite element framework developed based on the field theory of deformable dielectrics. Experiments are performed on the commercially available acrylic elastomer (VHB 4910) at varying levels of prestretch and proportions of the active to inactive areas. In particular, two salient features associated with the electromechanical response are addressed: the effect of the flexible boundary constraint and the locus of the dielectric breakdown point. To highlight the influence of the flexible boundary constraint, the estimates of the threshold value of potential difference on the onset of electromechanical instability are compared with the experimental observations and with those obtained using the lumped parameter models reported previously. Additionally, a locus of localized thinning, near the boundary of the active electric region, is identified using the numerical simulations and ascertained through the experimental observations. Finally, an approach based on the Airy stress function is suggested to justify the phenomenon of localized thinning leading to the dielectric breakdown. [ABSTRACT FROM AUTHOR]

This study presents modelling and control of a high-voltage ratio flyback converter for driving capacitive loads including smart material dielectric elastomer actuators (DEAs). These actuators find various applications including artificial muscles, optical devices, smart skin, and acoustics but require high actuation voltages. To this end, a high-voltage bidirectional flyback converter for driving a capacitive load is studied in terms of modelling and control and applied to a DEA. The state-space model of the converter is obtained for the capacitor charge and discharge modes when the converter operates in the continuous conduction mode and used to obtain a load voltage controller using the feedback linearisation method. The converter can be used to regenerate the capacitor charge into the dc source. The proposed hardware and control strategy was built and validated by driving DEA capacitive loads operating at high voltages around 4 kV. The experimental results are presented which validate the performance of the proposed converter and its control strategy. [ABSTRACT FROM AUTHOR]

Electro-active elastomer actuators have been widely studied, and many applications have been proposed for them. However, nearly all studies are focused on driving principle, structures, and control, and investigations on the mechanical properties and efficiency are insufficient. Using a strip-like actuator as a model case, this study revealed the maximum deformation, the relationship between driving force and deformation, and the maximum efficiency to provide a basic guide for the design of such actuators. First, the strains without mechanical constraints were studied, and the maximum strain was discussed under a linear assumption. Second, the displacement and driving force were analyzed considering the effects of electrodes and the margins of dielectric elastomer, and the results were compared. Finally, the electromechanical efficiency was investigated, and the approaches for improving efficiency were discussed. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators (DEAs) are a promising enabling technology for a wide range of emerging applications, including robotics, artificial muscles, and microfluidics. This is due to their large actuation strains, rapid response rate, low cost and low noise, high energy density, and high efficiency when compared with alternative actuators. These properties make DEAs ideal for the actuation of soft submersible devices, although their use has been limited because of three main challenges: (i) developing suitable, compliant electrode materials; (ii) the need to effectively insulate the actuator electrodes from the surrounding fluid; and (iii) the rigid frames typically required to prestrain the dielectric layers. We explored the use of a frameless, submersible DEA design that uses an internal chamber filled with liquid as one of the electrodes and the surrounding environmental liquid as the second electrode, thus simplifying the implementation of soft, actuated submersible devices. We demonstrated the feasibility of this approach with a prototype swimming robot composed of transparent bimorph actuator segments and inspired by transparent eel larvae, leptocephali. This design achieved undulatory swimming with a maximum forward swimming speed of 1.9 millimeters per second and a Froude efficiency of 52%. We also demonstrated the capability for camouflage and display through the body of the robot, which has an average transmittance of 94% across the visible spectrum, similar to a leptocephalus. These results suggest a potential for DEAs with fluid electrodes to serve as artificial muscles for quiet, translucent, swimming soft robots for applications including surveillance and the unobtrusive study of marine life. [ABSTRACT FROM AUTHOR]

Soft dielectric elastomer actuators (DEAs) exhibit interesting muscle-like behavior for the development of soft robots. However, it is challenging to model these soft actuators due to their material nonlinearity, nonlinear electromechanical coupling, and time-dependent viscoelastic behavior. Most recent studies on DEAs focus on issues of mechanics, physics, and material science, while much less importance is given to quantitative characterization of DEAs. In this paper, we present a detailed experimental investigation probing the voltage-induced electromechanical response of a soft DEA that is subjected to cyclic loading and propose a general constitutive modeling approach to characterize the time-dependent response, based on the principles of nonequilibrium thermodynamics. In this paper, some of the key observations are found as follows: 1) Creep exhibits the drift phenomenon, and is dominant during the first three cycles. The creep decreases over time and becomes less dominant after the first few cycles; 2) a significant amount of hysteresis is observed during all cycles and it becomes repeatable after the first few cycles; 3) the peak of the displacement is shifted from the peak of the voltage signal and occurs after it. To account for these viscoelastic phenomena, a constitutive model is developed by employing several dissipative nonequilibrium mechanisms. The quantitative comparisons of the experimental and simulation results demonstrate the effectiveness of the developed model. This modeling approach can be useful for control of a viscoelastic DEA and paves the way to emerging applications of soft robots. [ABSTRACT FROM AUTHOR]

Tunable optical elements are mostly realized by microelectromechanical systems, which require expensive and complex lithography during processing. We demonstrate an alternative device based on an electrically tunable microcavity employing a dielectric soft elastomer actuator. The cavity resonance is varied by changing the physical cavity thickness due to electrostriction of the soft elastomer. We realize a tunable metal-elastomer-distributed Bragg reflector multi-half wavelength microcavity with a cavity layer thickness around 12 μm and quality factors up to 700. Applying a voltage up to 60 V between bottom ITO and top metal electrode tunes the wavelength of the cavity modes up to Δλ = 14 nm, which relates to a cavity thickness change of about 200 nm. This concept allows the implementation of tunable optical elements like tunable filters or resonators with low cost and simple processing. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators (DEAs) have been increasingly investigated as alternative actuators to conventional ones. However, DEAs suffer from high rates of premature failure. Therefore, this study proposes a dielectric oil-based polymer actuator, also called a Dielectric liquid actuator (DLA), to compensate for the drawbacks of DEAs. DLA was experimentally compared with conventional DEAs. Results showed that DLA successfully prevented thermal runaway at defects in the electrode and excessive thinning of the film, resulting in increased breakdown voltage. Consequently, premature failure was inhibited, and the performance was improved. The breakdown voltages of DLA and DEA were 6000 and 2000 V, respectively, and their maximum thickness strains were 49.5% and 37.5%, respectively. [ABSTRACT FROM AUTHOR]

Dielectric elastomers are a type of actuator materials that exhibit excellent performance as artificial muscles, but a high driving voltage is required for their operation. By using the amazingly high output voltage generated from a triboelectric nanogenerator (TENG), a thin film dielectric elastomer actuator (DEA) can be directly driven by the contact-separation motion of TENG, demonstrating a self-powered actuation system. A TENG with a tribo surface area of 100 cm2 can induce an expansion strain of 14.5% for the DEA samples (electrode diameter of 0.6 cm) when the system works stably within the contact-separation velocity ranging from 0.1 to 10 cm s−1. Finally, two simple prototypes of an intelligent switch and a self-powered clamper based on the TENG and DEA are demonstrated. These results prove that the dielectric elastomer is an ideal material to work together with TENG and thereby the fabricated actuation system can potentially be applied to the field of electronic skin and soft robotics. [ABSTRACT FROM AUTHOR]

We present an electrically actuated tunable optical grating based on dielectric elastomer actuators. A simple fabrication protocol is presented, which integrates the grating with the actuating mechanism both made of soft elastomers, improving the tunability of the grating. The device is designed to be operated in the transmission mode. It exhibits a continuous period tunability of 34.4% at an actuation voltage of 5.5 kV, which is an improvement over reported tunable optical gratings. [ABSTRACT FROM AUTHOR]

It is previously known that under inflation alone a spherical rubber membrane balloon may bifurcate into a pear shape when the tension in the membrane reaches a maximum, but the existence of such a maximum depends on the material model used: the maximum exists for the Ogden model, but does not exist for the neo-Hookean, Mooney–Rivlin or Gent model. This paper discusses how such a situation is changed when a pressurized dielectric elastomer balloon is subjected to additional electric actuation. A similar bifurcation condition is first deduced and then verified numerically by computing the bifurcated solutions explicitly. It is shown that when the material is an ideal dielectric elastomer, bifurcation into a pear shape is possible for all material models, and similar results are obtained when a typical non-ideal dielectric elastomer is considered. It is further shown that whenever a pear-shaped configuration is possible it has lower total energy than the co-existing spherical configuration. [ABSTRACT FROM AUTHOR]

Indium-tin-oxide (ITO) thin films are perceived to be stiff and brittle. This letter reports that crumpled ITO thin films on adhesive poly-acrylate dielectric elastomer can make compliant electrodes, sustaining compression of up to 25%25% equi-biaxial strain and unfolding. Its optical transmittance reduces with crumpling, but restored with unfolding. A dielectric elastomer actuator (DEA) using the 14.2%14.2% initially crumpled ITO thin-film electrodes is electrically activated to produce a 37% areal strain. Such electric unfolding turns the translucent DEA to be transparent, with transmittance increased from 39.14% to 52.08%. This transmittance tunability promises to make a low-cost smart privacy window. [ABSTRACT FROM AUTHOR]

Dielectric elastomers represent a class of electroactive polymers that are capable of undergoing large reversible deformations when driven electrically. Pneumatically connected DE (PCDE) actuator is one of the prevalently used configurations, wherein an electrically driven DE membrane is connected to another passive DE membrane via an intervening air column. This paper outlines the development of a theoretical model, well-supported by experimental observations, for analyzing the dynamic electromechanical response of PCDE actuators. The underlying energetics of the model is developed in the setting of the Hamilton's principle taking into account the effects of membrane pre-stretch, initial inflation pressure, membrane viscoelasticity, and time-dependent electric loading. An idea of pseudo air-spring, responsible for the transfer of deformation from the active to passive sides of the actuator, is introduced and the analytical expressions are developed for the coupling function. Both pressurized and depressurized states are considered in the analysis. The developed nonlinear dynamic model is then used for building insights into several influential parameters, such as initial inflation pressure, time-dependent (DC and AC) electric actuation, height of the confined air column, volume of the intervening chamber, etc. The proposed model predicts the transfer efficiency of about 80% between the active and the passive membranes. The predictive capability of the theoretical model is established through comparisons with the experimental observations. The proposed investigation can find its potential use in the design and analysis of interconnected DE actuators subjected to a dynamic electromechanical actuation. • A theoretical model for analyzing the dynamic electromechanical response of PCDE actuator is developed. • The hypothesis of pseudo air-spring to couple the motion of two DE membranes is considered. • Euler–Lagrange's (E–L) equation of motion is utilized to deduce the equation of motion of the PCDE actuator. • The predictive capability of the theoretical model is verified with the experimental observations. • A detailed parametric study highlighting the effect of various parameters on the dynamic response of PCDE actuator is presented. [ABSTRACT FROM AUTHOR]

Dielectric elastomers (DEs) are gaining acceptance as potential actuator materials because of their exhibition of a large amount of deformation when stimulated by electrostatic forces. However, time-dependent behaviour such as creep and stress relaxation still pose a great challenge for the design, modelling and control of the DE-based actuators. In this work, attempts are made for experimental estimation and modelling of creep and relaxation properties of one of the most widely used dielectric acrylic elastomers, VHB 4910. Experimental investigation shows that the material possesses strong time-dependent creep and stress relaxation. It has been shown that creep and stress relaxation characteristics vary with the holding stress and holding strain respectively. Creep and stress relaxation properties are also shown to depend on the number of cycles in the case of cyclic loading. Results also show that Findley's power law can successfully model the creep and stress relaxation behaviour of the VHB 4910 elastomer. [ABSTRACT FROM AUTHOR]

This paper presents a model for the electromechanically coupled dynamic behavior of dielectric elastomer actuators (DEA). The main goal is to develop a lumped, dynamic model which can be used for the optimization of actuator design in specific applications as well as for the synthesis of high precision, model-based feedback control algorithms. A mass-biased membrane actuator with an annular geometry is chosen as a reference case to introduce the modeling concept. The mechanical model extends standard linear visco-elasticity through the introduction of a nonlinear hyperelastic Ogden element. Electromechanical coupling is implemented through the Maxwell stress concept. The DEA model is then experimentally calibrated and validated for both quasi static and dynamic loading conditions. It can be shown that both mechanical preloading and electric actuation can be reproduced over a relevant range of masses and frequencies. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators coupled with liquid have recently been developed as soft pumps, soft lenses, Braille displays, etc. In this paper, we investigate the performance of a dielectric elastomer actuator, which is coupled with water. The experiments demonstrate that the membrane of a dielectric elastomer can achieve a giant voltage-induced area strain of 1165%, when subject to a constant pressure. Both theory and experiment show that the pressure plays an important role in determining the electromechanical behaviour. The experiments also suggest that the dielectric elastomer actuators, when coupled with liquid, may suffer mechanical instability and collapse after a large amount of liquid is enclosed by the membrane. This failure mode needs to be taken into account in designing soft actuators. [ABSTRACT FROM AUTHOR]

Highlights: [•] Influence of temperature and deformation on permittivity is considered. [•] Relations between different work conjugated parameters are theoretically described. [•] Allowable energy range of dielectric elastomer is calculated. [•] Electric induced variation of elastomer’s temperature and entropy is studied. [•] Results should offer assistances in guiding the design of excellent actuators. [Copyright &y& Elsevier]

Dielectric elastomers are widely used for actuation applications in emerging domains such as tunable optics, tactile displays and soft robotics. However, dielectric elastomer actuators (DEAs) are prone to suffering from electrical or mechanical damage under the conditions of high operating voltage and mechanical stress, leading to a short service time and a low reliability. To address these issues, we in this work made an attempt to facilely develop a self-healable dielectric elastomer that combines high stretchability, dielectric properties, large actuation and effective repairing of mechanical and electrical failure by constructing multitype noncovalent interactions under surfactant assistance. It is demonstrated that the as-prepared elastomer possesses good healability at room temperature. After mechanical injury, a gentle pressure can initiate the recovery of damaged region, and the elastomer film could be subjected to a huge strain of 750% after healing for 24 h. In particular, this as-fabricated DEA that suffered from accidental or repetitive breakdown could still be re-actuated stably without significantly decreasing its actuated strain after quick healing (∼5 min). It is also found that embedding a fluoroelastomer with a fluorosurfactant can achieve larger deformation (tan α = 0.57 at 30 MV/m) due to the improved electromechanical properties. Our strategy for achieving self-healing feature and high actuation performance is favorable for extending lifetime, strengthening damage tolerance and lowering excitation voltages required for the DEAs. [Display omitted] • A self-healable dielectric elastomer with multitype dynamic interactions is prepared. • Mechanically cut damage can be quickly and effectively healed at room temperature. • Dielectric elastomer actuator can be re-actuated after accidental breakdown. • The improved electromechanical performance leads to desirable deformation. [ABSTRACT FROM AUTHOR]

Wound roll electroactive polymer actuators fabricated with dielectric elastomer (DE) materials provide high bandwidth actuation for robots, minipumps, loudspeakers, valves, and prosthetic devices. In this paper, we develop a DE wound roll actuator fabrication process that produces high strain (12%), reliable (3480 cycles at maximum strain), and stiff (144 N/m) actuators. An axisymmetric Unite element model with electrostatic and radial bulk modulus nonlinearity predicts actuator displacement and stress. The maximum compressive radial stress occurs at the center of the innermost active layer. This layer also has the thinnest material, indicating the most likely failure point. The nonlinear model predicts actuator displacement in response to applied voltage and load, matching experiments to within 1 mm. [ABSTRACT FROM PUBLISHER]

Dielectric elastomers (DE) belong to a very performant and efficient class of functional materials for actuators, while being compliant, low-weight and silent, they offer high energy efficiencies and large deformations under an applied electric field. In this work, a comparison of different approaches to derive expressions for the electrically induced stress states in dielectric materials is given. In particular, the focus is on three different ways to analytically describe stress states in planar actuator setups and to show how they are connected to each other regarding their resulting deformations. This is the basis to evaluate the suitability of these approaches for cylindrical actuator geometries together with exemplary calculations for concrete use cases. As an outcome, conclusions on the suitability of the different approaches for certain actuator setups are drawn. In particular cylindrical actuator geometries are taken into account and a recommendation on which approach is useful to describe a certain actuator effect is given. [ABSTRACT FROM AUTHOR]

• The multi-balloon actuator is designed on the basis of a pneumatic rubber actuator and a DEA. • The fully soft actuator was successfully fabricated by screen printing, rubber casting, and plasma treatment processes. • The multi-balloon actuator's components assembled and interacted with each other and could transport an object linearly. • This design can be applied to portable small-scale robots and annelid robots with high reliability and body compliance. [Display omitted] Recently, various soft actuators with biologically inspired motions have emerged in the field of robotics. The present study focuses on the development of a multi-balloon dielectric elastomer actuator (DEA) to provide a traveling wave motion for the linear transportation of an object. The multi-balloon actuator is designed on the basis of a pneumatic rubber actuator and a DEA, which itself consists of a dielectric membrane mounted on a silicone air chamber. An actuator that is inflated by pre-charged air pressure induces a rapid response speed and large deformations using only electric power; thus, it does not require the bulky external system which is essential for conventional pneumatic actuators. A multi-balloon actuator made of only soft materials was successfully fabricated by screen printing, rubber casting, and plasma treatment processes. Throughout the experiment, the maximum displacements of the balloon actuator with respect to height and width were obtained at an air pressure of 12.2 kPa. Importantly, the multi-balloon actuator's components assembled and interacted with each other and could successfully transport an object linearly via a traveling wave. In the object transfer experiment of this study, the linear velocity reached 0.97 mm/s with an initial air pressure and the applied voltage maintained at 13.3 kPa and 7.5 kV, respectively. The potential applicability of this system as a portable robot is demonstrated by replaying the traveling wave motions using a multi-balloon actuator. In the future, this design can be applied to portable small-scale robots and annelid robots with high reliability and body compliance. [ABSTRACT FROM AUTHOR]

The present contribution aims towards a thermo-electro-mechanical characterization of dielectric elastomer actuators (DEA) based on polydimethylsiloxane (PDMS). To this end, an experimental setup is proposed in order to evaluate the PDMS-based DEA behavior under the influence of various rates of mechanical loading, different ambient temperatures, and varying values of an applied electric voltage. To obtain mechanical, electro-mechanical and thermo-mechanical experimental data, the passive behavior of the material, as well as the material's response when electrically activated, was tested. The influence of the solid electrode on the dielectric layer's surface was also examined. Moreover, this work focuses on the production of such DEA, the experimental setup and the interpretation and evaluation of the obtained mechanical hysteresis loops. Finite element modeling approaches were used in order to model the passive and the electro-mechanically active response of the material. A comparison between experimental and simulation results was performed. [ABSTRACT FROM AUTHOR]

• The dielectric properties of dynamic ion crosslink (DIC) elastomers are evaluated. • The performance when DIC elastomers are used in a dielectric elastomer actuator (DEA) are also evaluated. • The relative permittivity of the DIC elastomers was approx. 3.0 and was constant below 2.70 V/μm at 20 Hz. • The expected large-scale ionic polarization was not observed. • The Young's modulus of DIC elastomer under an electric field was 1.4 times higher than in the absence of an electric field. • The max. blocking stress of the DEA using the DIC elastomer (DIC-DEA) was 22.6 times larger than DEA using VHB 4910. • DIC-DEA self-healed even after the mechanical damage. • DIC-DEA is a sustainable DEA that exhibits no deterioration of the performance. [Display omitted] The dielectric properties of self-healing dynamic ion crosslink (DIC) elastomer and its performance as a dielectric elastomer actuator (DEA) were evaluated. The relative permittivity of the DIC elastomer was approximately 3.0 and it was almost constant in the frequency range of 20–200,000 Hz and in the field strength below 2.70 V/μm at 20 Hz. The expected large-scale ionic polarization of the ionic aggregates was not observed under the electric field examined. The maximum blocking stress of the DEA using the DIC elastomer (DIC-DEA) was much larger (approximately 22.6 times) than that of the DEA using a commercial tape (VHB4910) (VHB-DEA). This is brought by the advantage that the breakdown strength of DIC-DEA is much higher than that of VHB-DEA. The Young's modulus of DIC showed a peculiar behavior; it was higher (1.4 times) under an electric field (3.00 V/μm) than in the absence of an electric field (0.39 ± 0.07 MPa). The maximum blocking stress at 1.0 kV/s was the same as that at 0.2 kV/s. This would reflect the fact that the blocking stress is independent of the Young's modulus as a function of the deformation rate. In addition, cut DIC elastomer reconnected at room temperature, and the blocking stresses at 5.80 V/μm of the self-healed DIC-DEA was the same as that of the prior-to-cut DIC-DEA, regardless of the rate of change of voltage. These results suggest that DIC-DEA is a sustainable DEA that exhibits no deterioration of the performance because of its self-healing behavior even after the mechanical damage. [ABSTRACT FROM AUTHOR]

[Display omitted] • BSEP is UV-curing synthesized with electroactive and thermal shape-memory property. • Ag NWs are embedded in active layer for stable joule-heating. • 3 Paralleled stiff strips are used to direct the actuation. • The soft actuators maintain actuating motion without external stimuli. Soft actuators based on electroactive polymer (EAP) and shape memory polymer (SMP) have drawn increasing attention, whereas EAP and SMP usually are used as independent functional components. In this work, bistable electroactive polymer (BSEP) with tunable modulus that can be actuated by Maxwell pressure was synthesized. The phase-transition points around ambient temperature were tuned by adjusting the ratio of octadecyl acrylate and soft segment. Bilayer structure was adopted by combining BSEP and passive layer to realize out-of-plane actuation. This actuator can maintain actuating shape without continuously applied stimuli when it is at stable states. Ag nanowires network embedded in BSEP was used as heating electrode, along with carbon nanotube network as high-voltage electrode. Finite element analysis and experiment results show that stiff strips parallelly attached to the actuator can effectively control the actuating direction. [ABSTRACT FROM AUTHOR]

Suction cups of cephalopods show a preeminent performance when absorbing irregular or flat objects. In this paper, an octopi-inspired suction cup, driven by hydraulically coupled dielectric elastomer actuators (HCDEAs), is proposed, which is considered to be controlled easily and have compact structure. To investigate the performance of suction cups, experiments have been conducted to clarify the effect of the pre-stretch ratio and chamber angle on suction forces. It could be seen that both factors have a complicated influence on suction forces, and the best performance obtained was a reasonable combination of the pre-stretch ratio and chamber angle. Here, we achieved a maximum suction force of 175 mN with λp = 1.2, α = 23° under a DC voltage of 3500 V. To enhance the capacity and adaptation of the suction cup, flat objects of various types of materials were introduced as targets. Experimental results displayed that for tested materials, including a dry/wet acrylic plate, CD, ceramic wafer, and aluminum plate, the suction cup showed outstanding performance of absorbing and lifting the target without any damage or scratch to them. Our research may serve as a guide to the optimal design and provide insights into the performance of the HCDEAs-actuated suction cup. [ABSTRACT FROM AUTHOR]

In this work, we develop a coreless rolled dielectric elastomer actuator (CORDEA) to be used as artificial muscles in soft robotic structures. The new CORDEA concept is based on a 50 µm silicone film with screen-printed electrodes made of carbon black suspended in polydimethylsiloxane. Two printed silicone films are stacked together and then tightly rolled in a spiral-like structure. Readily available off-the-shelf components are used to implement both electrical and mechanical contacts. A novel manufacturing process is developed to enable the production of rolled actuators without a hollow core, with a focus on simplicity and reliability. In this way, actuator systems with high energy density can be effectively achieved. After presenting the design, an experimental evaluation of the CORDEA electromechanical behavior is performed. Finally, actuator experiments in which the CORDEA is pre-loaded with a mass load and subsequently subject to cycling voltage are illustrated, and the resulting performance is discussed. [ABSTRACT FROM AUTHOR]

This paper proposes a simple but effective method for characterizing dielectric elastomer actuators (DEAs), especially for thin stacked DEAs, which are promising for haptic devices but which measure the dynamic elastic modulus with great difficulty. The difficulty of the measurement of such a thin stacked DEA arises from the friction and local deformation of the surface between the DEA and a contact, as shown in this paper. In the proposed method, a DEA is vertically suspended and a weight is attached to it. The proposed method requires no contact with the surface of a DEA and uses only a weighting mass. Experimental results demonstrated the proposed method can estimate almost essential constants, such as the dynamic elastic modulus (Young's modulus and damping time constant), the electrical constants (permittivity and resistivity), and the coefficient of electromechanical coupling, through the forced vibration induced by voltage actuation. [ABSTRACT FROM AUTHOR]

• DEA is applied to reduce multiple modes vibration of a membrane structure. • Frequency responses are measured with laser excitation/measurement system. • Controller for vibration control is designed based on H ∞ control method. • Vibration control experiment is conducted in a vacuum environment. • Effectiveness of the proposed method is validated by experiments. A vibration suppression technique for lightweight and flexible membrane structures is proposed using smart structure technology with a dielectric elastomer actuator (DEA). DEA, which is a lightweight flexible polynomial material with a large deformation and high response time, can easily be applied to membrane structures for vibration suppression over a wide frequency range. Herein, active vibration control for membrane structures with DEA is examined. A non-contact excitation system with a high-power Nd:YAG pulsed laser precisely measures the vibration responses of membrane structures. A laminated DEA is fabricated and attached to the membrane surface, generating a highly reproducible ideal impulse excitation. Then a digital control system is constructed with the laser excitation system. To demonstrate the effectiveness of the proposed method, vibration control experiments are conducted using a controller designed by H ∞ control theory with the identified membrane model in both atmospheric and vacuum environments. Image, graphical abstract [ABSTRACT FROM AUTHOR]