Performance Of Dielectric Elastomer Actuators Research Articles

Nano-Sized rGO-Encapsulated TiO2 Nanowire-Filled PDMS cone type dielectric elastomer actuator operating at low applied electric field

Dielectric elastomer actuators (DEAs) have versatile applications in soft robotics, medical devices, and environmental monitoring, making them a highly anticipated area for future applications. On the other hand, developing DEAs exhibiting high strain at low voltages remains challenging. This paper reports a strategy for enhancing the actuating performance of polydimethylsiloxane (PDMS) at low voltages by preparing a hybrid filler comprised of TiO2 nanowires (TiO2 NWs), polydopamine (PDA), and nano-sized reduced graphene oxide (nrGO). This hybrid filler, merging the virtues of these three materials, was added at 15 parts per hundred of rubber (phr), resulting in a 2.3-fold increase in the dielectric permittivity of PDMS while mitigating the increase in loss tangent and enhancing efficiency. Actuators fabricated using this composite exhibited the highest deformation at 10 phr, reaching approximately 27.31 % (at 28 V/µm), representing a remarkable 15.2-fold improvement compared to pure PDMS. Moreover, even at a low voltage of 1.6 V/µm, they displayed a substantial actuated strain of 2 %. This novel strategy for manufacturing hybrid fillers is a promising example of enhancing the performance of DEAs, offering innovative solutions for future technological advancements.

The role of chemical microstructures and compositions on the actuation performance of dielectric elastomers: A materials research perspective

AbstractDielectric elastomer actuators (DEAs) are one of the emerging areas of investigation in smart elastomer research and have attracted considerable interests due to their wide‐ranging applications, for instance in automation and soft robotic components. Commonly utilized dielectric elastomers (DEs) such as nitrile butadiene rubber (NBR) and its hydrogenated and carboxylated derivatives along with the dielectric fillers (titanium oxide, barium titanate, etc.) were considered to be one of the most established composite systems demonstrating high actuation performance. When subjected to external electrical field, the DEAs derived from the composites were, therefore, capable of reproducing high energy density and large deformation with fast response time. The recent research emphasizes that tunable material properties eventually triggered the improved actuation performance. The exploration of compliant electrodes fabricated by the conventional and state‐of‐the‐art lithographic methods was also crucial to improve actuation performance for the soft robotic applications. This review summarizes the commonly used DEs and dielectric fillers, their performances and challenges, and outlines the research progress (experimental and theoretical) in the field of actuators. Finally, a brief introduction to DEA‐based soft robotics application is also presented.

Proxy-based sliding-mode tracking control of dielectric elastomer actuators through eliminating rate-dependent viscoelasticity

Dielectric elastomer actuators (DEAs) usually suffer from rate-dependent viscoelastic nonlinearity, which manifests as hysteresis in their deformation cycles, leading to huge challenges in their modeling and control. In this work, we propose a model-free, proxy-based, sliding-mode tracking control approach to mitigate viscoelastic nonlinearity, achieving high-precision tracking control of DEAs. To this end, we first investigate the viscoelastic nonlinearity of DEAs, revealing its asymmetric and rate-dependent characteristics. Then, by combining the benefits of the PID control for small positioning errors and sliding-mode control for large errors, a proxy-based, sliding-mode tracking controller (PBSMC) is established. Finally, the stability of the controller is analyzed. To verify the effectiveness of the controller, several experiments are conducted to demonstrate the performance of DEAs in tracking sinusoidal trajectories under different frequencies. The experimental results demonstrate that with the PBSMC, the DEA can precisely track sinusoidal trajectories within a frequency range of 0.1 Hz–4.0 Hz by effectively minimizing the effect of inherent viscoelastic nonlinearity. Compared with open-loop tracking performance, the proxy-based, sliding-mode controlled DEA shows a significant reduction in maximum tracking errors from 45.87% to 8.72% and in root-mean-square errors from 24.46% to 3.88%. The main advantages of the proxy-based, sliding-mode control are: (a) it adopts a model-free approach, avoiding the need for complex dynamic modeling; (b) it can achieve high-precision tracking control of DEAs, thereby paving the way for the adoption of DEAs in several emerging applications.

(Digital Presentation) 3D Printing and Laser for Fabrication and Interface Modification of Origami-Inspired Dielectric Elastomer Actuators

The soft and flexible materials with shape and size adaption characteristics are gaining much attention for many applications, including wearable electronics, biomedical devices, microfluidic systems, tunable optics, soft robotics, and adaptive systems. Despite the several advancements in this area, the automated manufacturing and interface modification of these devices is still a major challenge. Here, we report 3D printing and laser for the rapid and scalable fabrication of dielectric elastomer actuators. The elastomer-based inks of dielectric matrix and electrodes were prepared with desirable rheology to obtain excellent print quality and required mechanical and electrical properties. This process can produce thin and ultrathin layers, porous structures, and interface modification of the device components. The device with printed elastomer patterns exhibited a breakdown strength of 40 V µm-1 at 8 % strain. The finite elemental simulation was also performed to determine the device performance under different strain conditions. The proposed technique is highly beneficial for improving the manufacturing and performance of dielectric elastomer actuators.

The dissipative dynamic performances of dielectric elastomer actuator with viscoelastic effects

With large deformability and high energy density, Dielectric elastomers (DEs) deserve interest in soft robotics. Many challenges remain in the real-world applications, for the dynamic performance of dielectric elastomer actuator and their energy efficiency are affected by the dissipation mechanisms in the actuators. Concerning the viscoelasticity of DEs, we present a modeling approach to describe the dissipation mechanism to predict how the dissipative process affects the dynamic behavior. The validity and generalization of the model have been extensively verified under various excitation voltages (different peak voltages, frequencies, pre-stretching, and signal waveforms). For harmonic voltages at different frequencies (0.05, 0.1, 0.2, 0.5, 1 Hz), the root mean square error is less than 5.99%. The phase difference was adopted to quantify the viscoelastic hysteresis dissipative behavior of DEs. The results show that the viscoelastic hysteresis is sensitive to frequency and waveform. In addition, we found that the viscoelastic hysteresis of the DEs under harmonic excitation can be improved by inserting a small amount of saw-tooth excitation loads. This finding is particularly useful for the actuation of soft actuators and soft robots, which use alternating loads as the dominant excitation signal. For future applications, this model presents a method to describe the dissipative behaviors in dynamic actuation quantitatively and paves the way to high-performance actuation control and manipulations for soft robots.

Effects of Ferroelectric Fillers on Composite Dielectric Elastomer Actuator

Integrating nano- to micro-sized dielectric fillers to elastomer matrices to form dielectric composites is one of the commonly utilized methods to improve the performance of dielectric elastomer actuators (DEAs). Barium titanate (BaTiO3) is among the widely used ferroelectric fillers for this purpose; however, calcium copper titanate CaCu3Ti4O12 (CCTO) has the potential to outperform such conventional fillers. Despite their promising performance, CCTO-based dielectric composites for DEA application are studied to a relatively lower degree. Particularly, the composites are characterized for a comparably small particle loading range, while critical DEA properties such as breakdown strength and nonlinear elasticity are barely addressed in the literature. Thus, in this study, CCTO was paired with polydimethylsiloxane (CH3)3SiO[Si(CH3)2O]nSi(CH3)3 (PDMS), Sylgard 184, to gain a comprehensive understanding of the effects of particle loading and size on the dielectric composite properties important for DEA applications. The dielectric composites’ performance was described through the figures of merit (FOMs) that consider materials’ Young’s modulus, dielectric permittivity, and breakdown strength. The optimum amounts of the ferroelectric filler were determined through the FOMs to maximize composite DEA performance. Lastly, electromechanical testing of the pre-stretched CCTO-composite DEA validated the improved performance over the plain elastomer DEA, with deviations from prediction attributed to the studied composites’ nonlinearity.

Enhancing the performance of dielectric elastomer actuators through the approach of distributed electrode array with fractal interconnects architecture

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.

Effect of polymer chains entanglements, crosslinks and finite extensibility on the nonlinear dynamic oscillations of dielectric viscoelastomer actuators

Soft materials exhibiting large deformation under external stimuli have gained an increasing attention in the recent past because of their potential applications in soft transducers aimed at achieving biomimetic actuation. This paper theoretically analyzes the effect of internal properties, including entanglements, crosslinks and finite extensibility of polymer chains along with inherent viscoelastic properties of polymers on the performance of Dielectric Elastomer actuator (DEA) in dynamic modes of actuation. A physics based nonaffine material model proposed by Davidson and Goulbourne is used to model the polymer chains entanglements, crosslinks and finite extensibility. To incorprate the viscoelastic properties, a rheological material model based on the additive decomposition of the isotropic strain energy density into equilibrium and viscous parts is implemented. A computationally efficient method, which relies on the principle of least action is used for extracting the governing equation representing the dynamic motion of the DE actuator. The results demonstrate that DEAs with strong entanglements and crosslinks along with small finite extensibility of polymer chains exhibits lower deformation level in DC dynamic modes of actuation. It is inferred that the strong entanglements and crosslinks in polymer chains enhances the resonant frequency, but debilitate the intensity of vibration of viscoelastic DEAs. Further, the periodicity and stability of the nonlinear oscillations exhibited by the viscoelastic DEAs are assessed by employing the Poincare maps and phase portraits. The results of the present investigation can be applied effectively in bridging the mechanism between the microcosmic polymer chains and macroscopic dynamic behavior of viscoelastic DE actuators.

Design of dielectric elastomer actuators using topology optimization on electrodes

Dielectric elastomer actuators (DEAs) are a recent type of electroactive actuators, which have drawn much attention because of their properties of large deformation, fast response and high efficiency. As electrodes on dielectric elastomer (DE) films will affect the performance of DEAs, different electrode patterns have been studied in previous studies. However, the electrode patterns are mostly designed by the trial and error, limited by the designer’s experience and inspirations. This paper introduces a computational method termed topology optimization for the design of electrode patterns to maximize the output displacement of DEAs. With the theoretical model of DEAs, the optimization model of electrode patterns on DE films is built and solved by the solid isotropic material with penalization (SIMP) gradient method. Two actuators are designed as examples and tested for verification. The designed motions are obtained in experiments and the results agree well with the simulations, which shows the proposed method is effective.

Plasticizer-induced enhanced electromechanical performance of natural rubber dielectric elastomer composites

Herein, high-dielectric-constant titanium dioxide (TiO2) nanoparticles, modified by γ-methacryloxypropyl trimethoxy silane (referred as mTiO2) and polar dioctyl phthalate (DOP), were introduced into natural rubber (NR) to obtain high-performance dielectric elastomer composites. The incorporation of DOP sharply decreased the elastic modulus of mTiO2/NR composites by decreasing the entanglement between NR chains and weakening the enforcement effect of mTiO2 nanoparticles. At the same time, highly polar DOP improved the dielectric constant of mTiO2/NR composites and resulted in high electromechanical sensitivity (β). Finally, a large actuated strain of 25.3% has been rendered by 50 phr DOP/mTiO2/NR composite at 40 kV/mm, which is ~10 times higher than pure NR (2.6%) under the same electric field. The present study reveals that the plasticizer-enhanced flexibility of inorganic dielectric filler/polymer composites is an effective method to enhance the electromechanical performance of dielectric elastomer actuators.

Towards the material limit and field concentration smoothing in multilayer dielectric elastomer actuators

Performance of dielectric elastomer actuators is closely related to its breakdown field. On the other hand, to enhance the available energy, multilayer configuration is needed to increase the amount of active material. However, multilayer configuration suffers from a drastic reduction of the affordable electric field related to field concentration at edges. After showing how the conductivity of the air helps to smooth the field in a single layer configuration, this effect has been mimicked in the multilayer by adding carbon particles in a thin silicone layer around the electrode. A change in the electric properties around the edges reduces the local concentration of the electric field and allows a significant improvement of the voltage breakdown in the multilayer structure. Therefore, the performance of multilayer has been considerably enhanced.

Ambient humidity altering electromechanical actuation of dielectric elastomers

The electromechanical actuation performance of dielectric elastomers is strongly affected by the environmental conditions, such as ambient humidity. The dielectric constant of the Very-High-Bond (VHB) 4910 elastomer is first experimentally investigated under different ambient humidities. Subsequently, at a constant DC voltage, the induced deformation of the VHB 4910 elastomer is found to be augmented when the ambient humidity increases. Theoretical simulation is simultaneously performed for the electromechanical actuation of VHB 4910 under several humidities. Finally, by applying a ramp voltage, the experimental results demonstrate that the electromechanical breakdown field of the VHB elastomer decreases with humidity.

Enhancing dynamic actuation performance of dielectric elastomer actuators by tuning viscoelastic effects with polar crosslinking

Dielectric elastomer actuators (DEAs) have shown great potential in the field of robotics, energy harvesting, or haptics for wearables. However, existing DEA materials typically require prestretching and exhibit time-dependent deformations due to their inherent viscoelastic properties. In this work, we address these issues by designing and synthesizing a polyurethane acrylate (PUA) DEA copolymerized with a polar crosslinker, polyethylene glycol diacrylate (PEGDA), to reduce viscoelastic effects through chemical crosslinking. We realized a buckling-mode actuator that displays out-of-plane deformations triggered by an electric field without the need for prestretching. Copolymerization with PEGDA showed improved dynamic response actuation performances compared to pristine PUA, wherein the former reached 90% of its maximum actuation in <1 s. In addition, precise and stable actuation was achieved, reducing viscoelastic drifts to a negligible amount. Despite the higher elastic modulus of the DEA incurred by the chemical crosslinks, the polar groups present in the PEGDA comonomer effectively increased the dielectric constant. As such, a higher area strain was achieved in comparison to that exhibited by low viscoelastic elastomers such as silicone. By eliminating the need for prestretching, rigid components can be avoided, thereby enabling greater prospects for the integration of fast response and stable DEAs into soft bodies.

Influence of pre-stretch ratio on the electrical actuation performance of VHB elastomer

In this work, the influences of pre-stretch ratio on the electrical actuation performance of dielectric elastomer actuator (VHB 4905) are systematically investigated based on theoretical calculation and experimental tests. As the pre-stretch ratio increases, the maximum actuation strain increases at the initial phase, while decreases as pre-stretch ratio further increases. The peak value of actuation strain is attained when the electromechanical instability is just refrained by the pre-stretch, which is experimentally measured to be 3.25, with the maximum actuation strain of 90%.

Design of dielectric elastomer actuators for vibration control at high frequencies

This study evaluates the basic characteristics of smart structures composed of dielectric elastomer actuators (DEAs) to suppress vibrations. A DEA, which is a lightweight, flexible polymer that can induce high deformations, should realize next-generation actuators. Additionally, DEA can achieve vibration control of structures with complex shapes or curved surfaces. Herein the performance and efficacy of DEAs are evaluated as an actuator for vibration control at high frequencies. First, the appropriate DEA structure is considered. Second, the control system for the smart structure using the DEA is modeled and designed as an actuator. Third, a method to determine DEA's optimum arrangement and shape is discussed by focusing on the structure's strain energy. Finally, a control simulation and a control experiment validate the vibration suppression effects and the efficacy of the DEA.

Effect of crosslinks, entanglements, and chain extensibilities on dynamic electromechanical instability of dielectric elastomers

Dynamic electromechanical instability (EMI) can affect the actuation performance of dielectric elastomers (DEs). This letter develops a theoretical framework to investigate the dynamic EMI of DEs with diverse crosslinks, entanglements, and chain extensibilities under a step voltage and equal biaxial pre-stresses. Based on the work-energy principle combining the EMI condition, the dynamic instability parameters at transition state between the stable and instable states are determined. At the small pre-stress, weak crosslinks or strong entanglements contribute to achieving a high actuation stretch ratio. When the pre-stress further increases, the DE with strong entanglements is prone to the dynamic EMI, and the variation in the dynamic instability actuation stretch ratio with the level of crosslinks is non-monotonic, which forms a peak. Moreover, as the level of chain extensibilities reduces, the dynamic instability actuation stretch ratio increases, and the enhancement effect can be significant at the large pre-stress. These results can help optimize the dynamic DE to obtain a stable oscillation without the dynamic EMI or utilize dynamic EMI to achieve a dramatic deformation.

Viscoelastic effects on the actuation performance of a dielectric elastomer actuator under different equal, un-equal biaxial pre-stretches

Dielectric elastomers (DEs) are belonged to a group of polymers which cause a time-dependence deformation due to the effect of viscoelastic. In recent years, viscoelasticity has been accounted in the modeling in order to understand the complete electromechanical behavior of dielectric elastomer actuators (DEAs). In this paper, we investigate the actuation performance of a circular DEA under different equal, un-equal biaxial pre-stretches, based on a nonlinear rheological model. The theoretical results are validated by experiments, which verify the electromechanical constitutive equation of the DEs. The viscoelastic mechanical characteristic is analyzed by modeling simulation analysis and experimental to describe the influence of frequency, voltage, pre-stretch, and waveform on the actuation response of the actuator. Our study indicates that: The DEA with different equal or un-equal biaxial pre-stretches undergoes different actuation performance when subject to high voltage. Under an un-equal biaxial pre-stretch, the DEA deforms unequally and shows different deformation abilities in two directions. The relative creep strain behavior of the DEA due to the effect of viscoelasticity can be reduced by increasing pre-stretch ratio. Higher equal biaxial pre-stretch obtains larger deformation strain, improves actuation response time, and reduces the drifting of the equilibrium position in the dynamic response of the DEA when activated by step and period voltage, while increasing the frequency will inhibit the output stretch amplitude. The results in this paper can provide theoretical guidance and application reference for design and control of the viscoelastic DEAs.

Performance improvement of planar dielectric elastomer actuators by magnetic modulating mechanism

In this paper, a novel planar dielectric elastomer actuator (DEA) with magnetic modulating mechanism is proposed. This design can provide the availability of wider actuation range and larger output force, which are significant indicators to evaluate the performance of DEAs. The DEA tends to be a compact and simple design, and an analytical model is developed to characterize the mechanical behavior. The result shows that the output force induced by the DEA can be improved by 76.90% under a certain applied voltage and initial magnet distance. Moreover, experiments are carried out to reveal the performance of the proposed DEA and validate the theoretical model. It demonstrates that the DEA using magnetic modulating mechanism can enlarge the actuation range and has more remarkable effect with decreasing initial magnet distance within the stable range. It can be useful to promote the applications of DEAs to soft robots and haptic feedback.

On the improvement of the dynamic performance of dielectric elastomer actuators for active compression

Dielectric elastomer actuators have been considered for an increasing number of applications due to their desirable characteristics of low weight, high strain outputs and favourable material costs. The present work describes the use of a dielectric elastomer actuator in conjunction with a belt mechanism to apply cyclic active compression. The belt mechanism helps convert the stress relaxation upon the voltage application to the dielectric elastomer actuator to a compressive force. Testing is conducted using multi-layered silicone–based dielectric elastomer actuators. A novel method of dynamically charging dielectric elastomer actuators through manipulating the input signal shape, termed the hold method, is introduced. Using this method, cyclic actuation strain output can be increased by 24% with insignificant change in actuation output curve shape. Furthermore, the effect of pre-stretch ratios on the output force amplitudes is characterized. The optimized hold time parameters obtained through cyclic dielectric elastomer force and strain are utilized for active compression physiological testing and a pressure gradient of 10 mmHg is achieved.

Improved electromechanical response in acrylic rubber by different carbon‐based fillers

Dielectric elastomers are materials often utilized for the fabrication of electroactive actuators. Acrylic rubber (ACM) is very widely used in dielectric elastomer actuators (DEAs). However, its overall good performance is limited by the high operating electric field required. In the present work, we compare the effect of different types of conventionally used carbon black (CB) as well as other carbon‐based fillers on the dielectric and actuation properties of ACM in order to show that performance of DEAs can be improved by the development of ACM composites. Indeed, addition of CB, carbon nanotubes (CNTs), and synthetic graphite leads to an increase in the relative dielectric permittivity of elastomeric material. Moreover, incorporation of nanodiamonds results in reduction of dielectric losses. Finally, actuation stress is remarkably improved by CNTs and different grades of CB. POLYM. ENG. SCI., 58:395–404, 2018. © 2017 Society of Plastics Engineers