Search

In order to obtain high dielectric properties nitrile rubber (NBR) dielectric elastomer composites, in this work, polypyrrole (PPy) was encapsulated on the surface of SrTiO3 (STO) ceramic particles, and an insulating layer of poly (catechol/polyamine) (PCPA) was also covered on the outer surface of the STO‐PPy core‐shell particles (denoted as STO‐PPy‐PCPA particles), then the dielectric elastomer composites were prepared by adding STO and STO‐PPy‐PCPA to NBR, respectively. Due to the electrical conductivity of PPy, the dielectric constant of the STO‐PPy‐PCPA particles increases substantially. At the same time, the insulating layer of PCPA further prevents current leakage from the composite, which not only avoids premature electrical breakdown but also effectively reduces the dielectric loss. Compared with pure NBR, the dielectric constant of the prepared dielectric elastomer composites increased from 13 to 17.19 (20 phr STO‐PPy‐PCPA/NBR), and the actuated strain increased from 3.28 % to 13.86 % (5 phr STO‐PPy‐PCPA/NBR), which is 4.2 times that of pure NBR. This work successfully solves the current problems of requiring a large amount of ceramics to improve the dielectric constant and the tendency of conductive particles to agglomerate and premature breakdown. [ABSTRACT FROM AUTHOR]

This paper investigates the stochastic nonlinear dynamic response of a single-degree-of-freedom dielectric elastomer generator under the combined action of harmonic excitation and stochastic disturbance. First, the nonlinear vibration model of a single-degree-of-freedom dielectric elastomer generator is established. The average method and fourth-order Runge–Kutta method are used to analyze the influence of pre-stretching, the initial membrane length, the charge amount, and the external excitation amplitude on the system response. Considering stochastic disturbance, the stochastic average method is applied to determine the probability density function (PDF) of the system’s steady-state response, and Monte Carlo numerical simulations are compared with the theoretical calculations for verification. The oscillation amplitude of the steady-state response can be increased by increasing the pre-stretching, harmonic excitation amplitude, and stochastic disturbance intensity. In the case of stochastic disturbance, as the intensity of the disturbance increases, the system becomes more likely to exhibit large amplitude responses for longer durations. [ABSTRACT FROM AUTHOR]

Flexible grippers are a promising and pivotal technology for robotic grasping and manipulation tasks. Remarkably, magnetorheological (MR) materials, recognized as intelligent materials with exceptional performance, are extensively employed in flexible grippers. This review aims to provide an overview of flexible robotic grippers and highlight the application of MR materials within them, thereby fostering research and development in this field. This work begins by introducing various common types of flexible grippers, including shape memory alloys (SMAs), pneumatic flexible grippers, and dielectric elastomers, illustrating their distinctive characteristics and application domains. Additionally, it explores the development and prospects of magnetorheological materials, recognizing their significant contributions to the field. Subsequently, MR flexible grippers are categorized into three types: those with viscosity/stiffness variation capabilities, magnetic actuation systems, and adhesion mechanisms. Each category is comprehensively analyzed, specifying its unique features, advantages, and current cutting-edge applications. By undertaking an in-depth examination of diverse flexible robotic gripper types and the characteristics and application scenarios of MR materials, this paper offers a valuable reference for fellow researchers. As a result, it facilitates further advancements in this field and contributes to the provision of efficient gripping solutions for industrial automation. [ABSTRACT FROM AUTHOR]

Since dielectric elastomers (DEs) exhibit obvious nonlinear visco-hyperelasticity, and remarkable temperature dependence, it is difficult to accurately predict the cyclic deformation of DEs at various temperatures. To address this issue, an improved visco-hyperelastic constitutive model is proposed here to reproduce the complex temperature-dependent cyclic deformation of DEs. In the improved model, the Ogden model is chosen to provide the strain energy density representing the hyper-elastic response, a nonlinear viscosity evolution equation is used to depict the strong viscosity of DEs, and specific temperature-dependent parameters are incorporated to describe the cyclic deformation of DEs at various temperatures. Finally, the prediction capability of the proposed visco-hyperelastic model is validated by reproducing the cyclic deformation of VHB 4910 DE observed in experiments at different temperatures. This study provides a theoretical basis for the rational design of DE devices. [ABSTRACT FROM AUTHOR]

The molecular structure of dielectric elastomers dictates their mechanical, electrical, and properties to react under external stimuli, influencing their suitability for applications such as actuators, sensors, and energy harvesting devices. The molecular structure of polymers can be tailored by incorporating plasticizers and particulate fillers to achieve multifunctional properties. However, achieving a balance between flexibility and maintaining mechanical strength due to incorporation of fillers induced phase separation and compromised intermolecular interactions remains challenging. In the present work, polydimethylsiloxane (PDMS) composites are synthesized using plasticizer and particulate fillers, polyethylene glycol (H‐(OCH2CH2)nOH) and titanium diboride (TiB2) respectively in various concentrations using shear mixing and doctor blade casting technique. Molecular structure of synthesized PDMS composite is confirmed by observing peaks of Raman spectra sift, which exhibits robust CO bonds dominating for both fillers. Chain entanglement due to filler incorporation significantly affects the crosslink density of PDMS composite, it increases with the concentration of plasticizer and possesses inverse relation for particulate. Furthermore, interdependence of the filler types and concentration are found on the mechanical as well as electrical properties. The specific deformation energy exhibits a significant increase of 118.9% when comparing particulate to the plasticizer at concentration of 8 wt.%. Although plasticizer increases the actuation strain and energy conversion efficiency but decreases the electrical breakdown voltage in comparison to particulate. By systematically varying fillers concentration, subtle changes in multifunctional properties are achieved. Overall, this investigation provides a framework for tailoring dielectric elastomer composites with desired electromechanical characteristics through the amalgamation of filler types and crosslinking densities, all intricately tied to the molecular architecture for electromechanical sensors. Highlights: Filler incorporation changes DE molecular structure and materials properties.Formation of additional bonds and micro‐capacitors in DE enhances capacitance.Actuation strain in DE depends on filler type and concentration.Energy conversion efficiency varies with the concentration of filler. [ABSTRACT FROM AUTHOR]

Precision research and technological equipment, as a rule, is not able to provide its specification characteristics without a high-quality vibration protection system. Active vibration control of an object is provided with the help of an additional source of movement, an actuator. The most promising high accuracy actuators are based on smart materials, such as materials with shape memory, piezoelectric and magnetostrictive materials, electro- and magnetic active fluids and elastomers. Dielectric elastomer is one of the types of electroactive polymers. Actuators based on a dielectric elastomer show high performance in terms of accuracy and speed and operate due to the controllable deformation of the elastomer under the action of a high voltage electric field. The paper provides a comparison of actuators based on sheet and thin film control electrodes. The influence of the quality of the polymer surface and the type of electrodes on the travel range of the actuator and maximum amplitude of vibrations the system can suppress on the basis of a dielectric elastomer is estimated. The formation of the electrode by magnetron sputtering in vacuum makes it possible to create a thin-film layer of copper that covers the elastomer, despite the developed surface. The effect of ion treatment of an elastomer before coating on the quality of the formed electrode is considered. After the ion treatment, the surface of the elastomer acquires a more uniform regular structure. A thin-film electrode layer is formed according to the topology of the elastomer to an accomplished standard.

Dielectric elastomers (DEs) have attracted significant attention in many engineering fields due to their excellent deformation capabilities and mechanical properties. In this work, the nonlinear vibrations of the DE spherical shell characterized by the third-order Ogden model are investigated. The governing equation describing the radially symmetric motions of the shell is derived by the incompressibility constraint and the variational method. Through the qualitative and quantitative analyses, the nonlinear dynamical behaviors are discussed, along with the parameter analyses of the structural damping, pressure, direct current (DC) voltage and alternating current (AC) voltage. It is shown that with the increasing pressure and voltage, the vibrations transition from periodic vibrations to chaotic vibrations via the period-doubling bifurcation. Particularly, the self-similar structure of the system is found. [ABSTRACT FROM AUTHOR]

Theoretically, separating the positive and negative charge centers of the chain segments of dielectric elastomers (DEs) is a viable alternative to the conventional decoration of chain backbone with polar handles, since it can dramatically increase the dipole vector and hence the dielectric constant (ε′) of the DEs while circumvent the undesired impact of the decorated polar handles on the dielectric loss (tan δ). Herein, a novel and universal method is demonstrated to achieve effective separation of the charge centers of chain segments in homogeneous DEs by steric hindrance engineering, i.e., by incorporating a series of different included angle‐containing building blocks into the networks. Both experimental and simulation results have shown that the introduction of these building blocks can create a spatially fixed included angle between two adjacent chain segments, thus separating the charge center of the associated region. Accordingly, incorporating a minimal amount of these building blocks (≈5 mol%) can lead to a considerably sharp increase (≈50%) in the ε′ of the DEs while maintaining an extremely low tan δ (≈0.006@1 kHz), indicating that this methodology can substantially optimize the dielectric performance of DEs based on a completely different mechanism from the established methods. [ABSTRACT FROM AUTHOR]

The demand for high‐performance flexible electronic devices has propelled research toward dielectric elastomer composites that exhibit excellent stretchability, high dielectric constant, exceptional transparency, and enduring stability. Compositing with soft fillers is an emerging method that can increase the dielectric constant of the materials while retaining good flexibility. However, liquid metals inclusion results in opaque composites while liquid electrolytes inclusion brings issues with long‐term stability. In this study, compositing polymeric ionic liquids with elastomeric matrix is proposed to address these requisites. Benefiting from adjustable refractive index, high ionic conductivity, softness, and excellent stability, the prepared dielectric elastomer composites exhibit remarkable transparency, excellent elasticity, and increased dielectric constants. Notably, the composites demonstrate resilience to high temperatures up to 250 °C without compromising dielectric or mechanical properties. Furthermore, the composites retain all properties after prolonged exposure at 80 °C for 6 months, highlighting the potential for sustained performance in real‐world applications. Utilizing the exceptional characteristics of polymeric ionic liquid including dielectric elastomers, strain sensors, and alternating current electroluminescence devices are demonstrated, which also presents excellent stability over prolonged use, emphasizing the reliability and long‐term stability of the composites, and showcasing potentials for multifaceted applications in flexible electronics. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuator (DEA) is one of the most promising types of soft actuation technology, which has great potential in the fields of wearable devices and soft robotics. It consists of a dielectric elastomer layer, which is an electroactive polymer that can produce large deformation, and compliant electrodes to bring charges to certain locations. In this article, direct ink writing (DIW) technology, an emerging 3D printing method, was used to realize the preparation of the electrode‐elastomer‐electrode stack of the DEA. The dielectric and electrode materials were designed with suitable rheological properties to fulfill the need for the extrusion process. The formulated silicone material not only presented excellent dielectric and mechanical properties, but also good printability. Extrudable electrodes were prepared based on silicone composites with the characteristics of mechanical compliance and high conductivity. The fully printed DEA achieved a maximum actuation strain of 11.11%, a fast response time of 0.76 s and excellent electromechanical repeatability. DEA arrays were also achieved, possessing the ability to carry out on‐demand actuation, allowing each actuator to be activated singly or work in groups. Thanks to the design freedom of the DIW technology, this strategy is able to manufacture fine and complex structures with precise active zones, paving a way for the fabrication of next‐generation smart devices. Highlights: Printable silicone ink was formulated with good dielectric property and softness.Carbon black/silicone composites were obtained with high conductivity and compliant nature.The silicone composites were printed into thin films to act as electrodes.Fully 3D printed dielectric elastomer actuators (DEA) were achieved by direct ink writing.DEA arrays with on‐demand actuation were realized by well‐defined printing. [ABSTRACT FROM AUTHOR]

Dielectric elastomers in the shape of thin films are heavily investigated, but they do not produce beneficial strains and forces comparable to that of skeletal muscles without entailing extremely complicated fabrication processes, rendering their practical use limited. Here, a silicone elastomer fiber is reported that can be produced by the meter and turned into an actuator by a simple process entailing the injection of an ionic liquid as the inner electrode and dipping in an ionogel to form the outer electrode. The fibers range from 174 to 439 µm in outer diameter with wall thicknesses from 62 to 108 µm and can be produced by the meter with regular diameter and thickness. The mechanical properties of the fibers are unaffected by the electrodes and actuation strains of 10% can be achieved, in both dry and wet environments. The fiber actuator can be bundled to mimic human skeletal muscle bundles or used in folded configurations, rendering it ideal as a building block for macroscopic actuators that can be used for many products such as body‐compliant actuators and wearables. [ABSTRACT FROM AUTHOR]

Conventional passive ankle foot orthoses (AFOs) have not seen substantial advances or functional improvements for decades, failing to meet the demands of many stakeholders, especially the pediatric population with neurological disorders. Our objective is to develop the first comfortable and unobtrusive powered AFO for children with cerebral palsy (CP), the DE-AFO. CP is the most diagnosed neuromotor disorder in the pediatric population. The standard of care for ankle control dysfunction associated with CP, however, is an unmechanized, bulky, and uncomfortable L-shaped conventional AFO. These passive orthoses constrain the ankle's motion and often cause muscle disuse atrophy, skin damage, and adverse neural adaptations. While powered orthoses could enhance natural ankle motion, their reliance on bulky, noisy, and rigid actuators like DC motors limits their acceptability. Our innovation, the DE-AFO, emerged from insights gathered during customer discovery interviews with 185 stakeholders within the AFO ecosystem as part of the NSF I-Corps program. The DE-AFO is a biomimetic robot that employs artificial muscles made from an electro-active polymer called dielectric elastomers (DEs) to assist ankle movements in the sagittal planes. It incorporates a gait phase detection controller to synchronize the artificial muscles with natural gait cycles, mimicking the function of natural ankle muscles. This device is the first of its kind to utilize lightweight, compact, soft, and silent artificial muscles that contract longitudinally, addressing traditional actuated AFOs' limitations by enhancing the orthosis's natural feel, comfort, and acceptability. In this paper, we outline our design approach and describe the three main components of the DE-AFO: the artificial muscle technology, the finite state machine (the gait phase detection system), and its mechanical structure. To verify the feasibility of our design, we theoretically calculated if DE-AFO can provide the necessary ankle moment assistance for children with CP—aligning with moments observed in typically developing children. To this end, we calculated the ankle moment deficit in a child with CP when compared with the normative moment of seven typically developing children. Our results demonstrated that the DE-AFO can provide meaningful ankle moment assistance, providing up to 69% and 100% of the required assistive force during the pre-swing phase and swing period of gait, respectively. [ABSTRACT FROM AUTHOR]

The compound eye is a natural multi-aperture optical imaging system. In this paper, a continuous optical zoom compound eye imaging system based on Alvarez lenses is proposed. The main optical imaging part of the proposed system consists of a curved Alvarez lens array (CALA) and two Alvarez lenses. The movement of the CALA and two Alvarez lenses perpendicular to the optical axis is realized by the actuation of the dielectric elastomers (DEs). By adjusting the focal length of the CALA and the two Alvarez lenses, the proposed system can realize continuous zoom imaging without any mechanical movement vertically to the optical axis. The experimental results show that the paraxial magnification of the target can range from ∼0.30× to ∼0.9×. The overall dimensions of the optical imaging part are 54 mm × 36 mm ×60 mm (L × W × H). The response time is 180 ms. The imaging resolution can reach up to 50 lp/mm during the optical zoom process. The proposed continuous optical zoom compound eye imaging system has potential applications in various fields, including large field of view imaging, medical diagnostics, machine vision, and distance detection. [ABSTRACT FROM AUTHOR]

Dielectric elastomers, such as thermoplastic polyurethanes (TPUs), are widely used as the dielectric layer, encapsulation layer, and substrate of flexible and stretchable devices. To construct capacitors and actuators that work stably upon deformation, it has become urgent to investigate the evolution of dielectricity under stress and strain. However, the lack of effective methods for estimating the dielectric constant of elastomers under strain poses a big challenge. This study reports a device for the in situ measurement of the dielectric constant of TPU under strain. It is found that upon stretching TPU to a strain of 400%, its dielectric constant decreases from 8.02 ± 0.01 to 2.88 ± 0.25 (at 1 MHz). In addition, combined Fourier-transform infrared spectroscopy, the X-ray scattering technique, and atomic force microscopy were utilized to characterize the evolution of the microstructure under strain. The investigation under tensile strain reveals a decreased density and average size of polarized hard domains, along with a tendency of the molecular chains to align in parallel with the tensile stress. The evolution of the microstructures results in a reduction in the measured dielectric constant in TPU. [ABSTRACT FROM AUTHOR]

Cables are critical in engineering structures for load‐bearing, electronic connection, and mechanical transmission. Various cable‐crawling robots (CCRs) have been developed to perform scheduled inspection or convey supplies. Most existing CCRs are often actuated by motors and used in large‐scaled engineering structures. The heavy bodies of these CCRs can cause damage or even casualties once slippage or drop occurs. A small and lightweight CCR that can crawl on thin cables is highly demanded for safety inspection in narrow and confined inner spaces of engineering structures. Herein, a soft CCR (weight, 2.1 g; length, 43 mm) is developed by utilizing multilayered dielectric elastomer actuators. Compared with existing solutions, this CCR achieves crawling on thin cables (diameter: <1 mm) while crawling fastest (horizontal: 0.72 body length per second). The CCR is also capable of transporting objects (horizontal: 3.69 times its own weight; vertical: 0.76 times its own weight), climbing upward on a vertical cable, and locomoting across the water–air interface. The CCR is also demonstrated to crawl on a slack cable and circular/spiral cables. Finally, the soft robot, equipped with an endoscope, demonstrates inspections on a tensegrity structure as well as in an airplane wing model with a preplaced cable. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuator (DEA) is considered as an ideal artificial muscle with soft and light in nature, widespread application in soft robotics and sensors. Dielectric elastomer (DE), the core component of DEA, with high output force and large actuation strain under relatively low driving electric field is critical for high‐performance DEA. However, the widely used VHB series (3M) DE suffered from very large pre‐strain and high driving voltage to get their high actuation performance, limiting their scope of application. In this work, the DEs with good mechanical and dielectric properties were prepared via UV curing method consisting of acrylic acid (AA) with strong polar groups as functional monomer, n‐butyl acrylate (BA) as soft monomer and urethane acrylate as cross‐linker (c‐p(BA‐AA)). The c‐p(BA‐AA) DE films obtained the simultaneous increasing of dielectric constant and breakdown strength with the increasing content of AA, which guaranteed the good actuation performance. The c‐p(BA‐AA) film exhibited excellent actuating performance (44.11% actuation strain at 45 kV/mm) without pre‐strain. Besides, a simple linear actuator based on the c‐p(BA‐AA) film could easily output weight that is tens of times of its own active weight (654.1 mN/g at 30 kV/mm). [ABSTRACT FROM AUTHOR]

A Dielectric Elastomer Actuator (DEA) consists of electrodes with a dielectric layer between them. By controlling the design of the electrodes, voltage, and frequency, the operating range and speed of the DEA can be adjusted. These DEAs find applications in biomimetic robots, artificial muscles, and similar fields. When voltage is applied to the DEA, the dielectric layer undergoes compression and expansion due to electrostatic forces, which can lead to electrical breakdown. This phenomenon is closely related to the performance and lifespan of the DEA. To enhance stability and improve dielectric properties, a DEA Reservoir layer is introduced. Here, stability refers to the ability of the DEA to perform its functions even as the applied voltage increases. The Reservoir layer delays electrical breakdown and enhances stability due to its enhanced thickness. The proposed DEA in this paper is composed of a Reservoir layer and electrode layer. The Reservoir layer is placed between the electrode layers and is independently configured, not subjected to applied voltage like the electrode layers. The performance of the DEA was evaluated by varying the number of polymer layers in the Reservoir and electrode designs. Introducing the Reservoir layer improved the dielectric properties of the DEA and delayed electrical breakdown. Increasing the dielectric constant through the DEA Reservoir can enhance output characteristics in response to electrical signals. This approach can be utilized in various applications in wearable devices, artificial muscles, and other fields. [ABSTRACT FROM AUTHOR]

Three‐dimensional (3D) printed bionic products play an important role in intelligent robotics, microelectronics, and polymers. The printing and manufacturing process of 3D printers is conducive to obtaining soft structures that meet specific requirements, and saves time and cost. Soft intelligent robotics, an emerging research field, has always been developed based on soft materials and actuators with their biological properties. This article reviews the current understanding of 3D bioprinting technologies for dielectric elastomers (DEs), DE actuators (DEAs) and soft robots, such as inkjet, extrusion, laser‐induced and stereolithography bioprinting. 3D printers for fabricating soft materials are presented and classified. The approaches to exploit 3D bioprinters for DEs/DEAs are as follows: (1) 3D printing DEAs utilize ionic hydrogel–elastomer hybrids that are analogous to human muscles, and the DEAs usually have flexible structures and large deformations with multiple functionalities. (2) An electrohydrodynamic (EHD) 3D printer confers high printing resolution and high production efficiency, which offers advantages such as full automation and flexible design. The optimal printing conditions are mainly determined by the effects of printing voltages and ink properties, which are related to the formation of the liquid cone and the printed line width. Furthermore, the advantages of 3D bioprinting technologies have accelerated their development and applications. [ABSTRACT FROM AUTHOR]

Inorganic nanoparticles have been widely used as fillers to modify dielectric elastomers to simultaneously improve mechanical and dielectric performances. Elegant interface design is crucial for achieving synergy between fillers and elastomers. Herein, we show that diborate ester polymers can both improve the interfacial compatibility between inorganic nanoparticles and elastomers and enhance the dielectric performances. The diborate ester polymers are derived from the condensation reaction between tetrakis(dimethylamino)diborane (or tetrahydroxydiborane) and a three‐armed catechol monomer. Choosing TiO2 nanoparticles as the inner core, a series of TiO2@diborate ester polymer core‐shell nanoparticles are synthesized. Density functional theory (DFT) calculations indicate that the diborate ester polymer shell tightly bonds to the surface of TiO2 through two dissociative bidentate bridging modes of the catechol monomer (absorption energy: −11.049 eV). These core‐shell nanoparticles can soften and tough polydimethylsiloxane (PDMS) and show enhanced interfacial binding affinity to PDMS than naked TiO2 nanoparticles. The fabricated composites have high dielectric constants (up to 6.8) and low dielectric losses (<0.03). The actuated strain and puncture voltage of the composites reach 25.9% and 80 V μm−1, respectively, which are much higher than those of PDMS and TiO2/PDMS. This work provides a promising route to fabricate core‐shell nanoparticles for high‐performance dielectric elastomers. [ABSTRACT FROM AUTHOR]

Modern transducers and actuators may have functional layers with multi-field coupling and some elastic layers. This paper considers a tubular bilayer system consisting of a thin dielectric tube coated with a thick elastic layer. We study the nonlinear electromechanical response and the linear axisymmetric vibration of the system subject to different applied voltages and inner/outer pressures within the framework of the general nonlinear theory of electro-elasticity, the related linear incremental theory, and by considering the continuity conditions at the interface. We investigate instability behaviour using the same basic formulae. The state-space method provides efficient and accurate free vibration analysis, considering the dynamic response at the lowest frequencies, so we can neglect the viscous and damping effects, which is well suited to this problem. New results indicate that the bilayer system improves its frequency capability and stability compared to the monolayer dielectric tube. The thick outer elastic layer stiffens the bilayer system against axisymmetric bifurcation, bulging and necking instabilities. It also performs better in front of axisymmetric instability, increasing the system's capability to receive or produce higher voltages, especially for long waves.This work thoroughly explains bilayer functional systems' behaviour when exposed to extreme environments such as high voltage or pressure. [ABSTRACT FROM AUTHOR]

Loss of an upper limb exerts a negative influence on an individual's ability to perform their activities of daily living (ADLs), reducing quality of life and self-esteem. A prosthesis capable of performing basic ADLs functions has the capability of restoring independence and autonomy to amputees. However, current technologies present in robotic prostheses are based on rigid actuators with several drawbacks, such as high weight and low compliance. Recent advances in robotics have allowed for the development of flexible actuators and artificial muscles to overcome the limitations of rigid actuators. Dielectric elastomer actuators (DEAs) consist of a thin elastomer membrane arranged between two compliant electrodes capable of changing dimensions when stimulated with an electrical potential difference. In this work, we present the design and testing of a finger prosthesis driven by two DEAs arranged as agonist–antagonist pairs as artificial muscles. The soft actuators are designed as fiber-constrained dielectric elastomers (FCDE), enabling displacement in just one direction as natural muscles. The finger prosthesis was designed and modeled to show bend movement using just one pair of DEAs and was made of PLA in an FDM 3D printer to be lightweight. The experimental results show great agreement with the proposed model and indicate that the proposed finger prosthesis is promising in overcoming the limitations of the current rigid based actuators. [ABSTRACT FROM AUTHOR]

This paper proposes a flexible vibrotactile actuator based on a dielectric elastomer which is fabricated by mixing a PDMS-Ecoflex elastomer and PC (propylene carbonate) solution. The proposed flexible vibrotactile actuator is composed of a top electrode, an adhesive tape, the PDMS-Ecoflex-PC-based elastomer, and a bottom electrode. The applied electric field between two parallel electrodes (top and bottom electrodes) creates an electrostatic force in the actuator, resulting in the actuator being compressed. The performance of the vibrotactile actuator based on dielectric elastomers is affected by the mechanical and dielectric properties of the dielectric elastomer. So, in this paper, we experimentally optimize the design of the haptic actuator and then quantitatively evaluate the actuator. For evaluation, the six samples of PDMS-Ecoflex-PC elastomers having different mixing ratios are prepared and their material properties are investigated by experiments. We fabricate the haptic actuators based on PDMS-Ecoflex-PC elastomers and then measure the haptic behaviors of the proposed actuator as a function of the applied voltage amplitude and frequency. Furthermore, we inquire the response time of the proposed actuator. Maximum vibrational force of the optimized sample is about 0.556 N at 140 Hz which is strong enough to stimulate human finger, and the response time is 21 ms which is fast enough to obtain the touch feedback in real time. From the results, we show that the proposed vibrotactile actuator creates a variety of haptic sensations in real time. [ABSTRACT FROM AUTHOR]

Cables are critical in engineering structures for load‐bearing, electronic connection, and mechanical transmission. Various cable‐crawling robots (CCRs) have been developed to perform scheduled inspection or convey supplies. Most existing CCRs are often actuated by motors and used in large‐scaled engineering structures. The heavy bodies of these CCRs can cause damage or even casualties once slippage or drop occurs. A small and lightweight CCR that can crawl on thin cables is highly demanded for safety inspection in narrow and confined inner spaces of engineering structures. Herein, a soft CCR (weight, 2.1 g; length, 43 mm) is developed by utilizing multilayered dielectric elastomer actuators. Compared with existing solutions, this CCR achieves crawling on thin cables (diameter:

Inorganic nanoparticles have been widely used as fillers to modify dielectric elastomers to simultaneously improve mechanical and dielectric performances. Elegant interface design is crucial for achieving synergy between fillers and elastomers. Herein, we show that diborate ester polymers can both improve the interfacial compatibility between inorganic nanoparticles and elastomers and enhance the dielectric performances. The diborate ester polymers are derived from the condensation reaction between tetrakis(dimethylamino)diborane (or tetrahydroxydiborane) and a three‐armed catechol monomer. Choosing TiO2 nanoparticles as the inner core, a series of TiO2@diborate ester polymer core‐shell nanoparticles are synthesized. Density functional theory (DFT) calculations indicate that the diborate ester polymer shell tightly bonds to the surface of TiO2 through two dissociative bidentate bridging modes of the catechol monomer (absorption energy: −11.049 eV). These core‐shell nanoparticles can soften and tough polydimethylsiloxane (PDMS) and show enhanced interfacial binding affinity to PDMS than naked TiO2 nanoparticles. The fabricated composites have high dielectric constants (up to 6.8) and low dielectric losses (

The widespread use of battery-powered electronic devices creates the need to develop methods to extend their maximum operating time. This can be achieved by using ambient energy, which would otherwise be dissipated. The conversion of energy, usually mechanical energy, into electric energy takes place in energy harvesters. Energy harvester systems based on a dielectric elastomer (DE) are a relatively new field that is being constantly developed. Due to their features, dielectric elastomer generators (DEGs) may complement the currently dominant piezoelectric harvesters. The major feature of employing a hyperelastic material is that it allows relatively large displacements to be utilised for generating energy, which is impossible in the case of piezoceramics. This article presents a DEG designed to operate under uniaxial tensile loads and which has a multilayer structure, describes the general operating principles of a DEG, explains the construction and assembly process of the investigated design and shows the electric circuit necessary to properly direct current flow during the DEG operation. The experimental part consists of two series of tests based on a central composite design (CCD). The objective of the first part was to map a capacitance response surface of the DEG in the selected range of the cyclic mechanical load. The second part concerned the amount of generated energy for the specific load case as a function of operating voltages. The result of the work is the formulation of regression models that allow the characteristics of the presented DEG design to be identified. [ABSTRACT FROM AUTHOR]

Dielectric elastomers are widely used as electroactive polymer materials due to their high energy density, high strain, and low loss. However, the practical applications are limited sometimes by their low electromechanical strain ability due to relatively low dielectric permittivity for polymers. Herein, multiwalled carbon nanotube (MWCNT) filled silicone rubber (SR) composites with a five‐layered structure are prepared with the outer two layers of neat SR while the middle three layers are MWCNT filled SR, in which the former functions as insulating layers while the latter acts as the dielectric permittivity enhancement layers. Further, by differing the MWCNT content within the middle three layers, we find that as the concentration distribution increases from 1:1:1 to 1:2:1 and 1:3:1, both Young's modulus and dielectric permittivity gradually improve while dielectric loss remains extremely low even though the total MWCNT content reaches 1.6 wt%. With the combined effects of dielectric permittivity and modulus, the composite with evenly distributed MWCNT content (1:1:1) shows the highest actuation strain under a given electric field strength. Meanwhile, the electric breakdown strength of the composite 1:1:1 is also the highest, leading ultimately to a maximum actuation strain of 10.87% at the breakdown strength of 14.6 kV/mm. [ABSTRACT FROM AUTHOR]

PDMS-based composites such as silicone elastomers are commonly found in high-voltage engineering, especially in outdoor insulation as coatings or structural elements or at interfaces between network elements, such as cable sealing ends (CSE). They are also promising prospects for dielectric elastomer generators (DEG), which are retrieving electrostatic energy from large strain amplitudes. The upper limit of energy conversion from these transducers is determined by the dielectric breakdown strength (DBS). Therefore, developing reliable systems that operate under high electric fields and variable repeated strains requires a thorough understanding of the mechanisms behind electrical breakdown and its coupling to mechanical cycling. In this study, the effect of Mullins damage and mechanical fatigue on silicone elastomers has been investigated. An electro-mechanical instability model that considers cyclic softening allows for predicting the evolution of the breakdown strength depending on the loading history. The results highlight the importance of the "first cycle," where up to a 30% reduction in the mean DBS was measured. However, subsequent mechanical fatigue only marginally contributes to the degradation, which is a promising perspective for the long-term performance of any silicone elastomer as long as the precise impact of the first cycle is known. [ABSTRACT FROM AUTHOR]

Dielectric Elastomer (DE) has been recognized for its remarkable potential in actuation and sensing applications. However, the functionality of most DE materials is restricted by their high viscoelastic effects. Currently, there is a lack of dynamic models that consider both viscoelasticity and stiffening effects. To address this research gap, we propose a fractional-order model in this study. Specifically, the model comprehensively integrates both viscoelastic and stiffening effects under electromechanical coupling, utilizing the principle of virtual work. Further, the effects of the system parameters are analyzed. The results indicate that the fractional-order derivative influences the hysteresis behaviors during the transient state and affects the duration of the transient process. Furthermore, when the system's energy surpasses a certain threshold, the steady-state response can transition between two distinct potential wells. Through the manipulation of electromechanical coupling parameters, bifurcation can be induced, and the occurrence of snap-through and snap-back behaviors can be controlled. These findings have significant implications for the design and optimization of DE materials in various applications. [ABSTRACT FROM AUTHOR]

A dielectric elastomer actuator (DEA) is regarded as an intelligent actuator that can reproduce the performance of human muscle. A core–shell structured dielectric filler is synthesized by modifying carbon nanotube (CNT) with polydopamine (PDA) noncovalently and 3‐mercaptopropyl ethyoxyldi (tridecyl‐pentaethoxy) silane (Si747) covalently, designated as PDA‐Si747@CNT. Then, the filler is incorporated into an epoxy natural rubber (ENR) matrix to yield dielectric elastomer composites, denoted as PDA‐Si747@CNT/ENR. The PDA and Si747 modifications improve not only the filler dispersion but also the dielectric strength of the ENR composites. More importantly, Si747 is involved in vulcanization and provides chemical bonds between CNT and ENR chains. The maximum actuated strain of the PDA‐Si747@CNT/ENR composites increases to 17.9% at 55.5 kV mm−1, which is 152% higher than that of CNT/ENR composites (7.1% at 30 kV mm−1). Furthermore, the ENR composite‐based DEA demonstrates excellent stability and reliability, which is advantageous for practical applications. © 2023 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

Windows are one of the least energy-efficient components of a building. It allows energy to escape, leading to high cooling demand in summer and energy loss in winter. Sunlight and temperature in the building also affect people's health, comfort, and even productivity. As a result, controlling the heat and light entering the building dynamically is critical for improving the comfort of building occupants and reducing energy consumption. In this work, we develop a tunable smart window based on transparent dielectric elastomer actuators (DEAs) as an alternative solution to sunlight and temperature control. The transparency-tuning is achieved by creating wrinkles in a soft elastomer film made of waterborne polyurethane (WPU). The actuation mechanism is based on highly transparent dielectric elastomer actuators that use all solid-state stretchable transparent conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/(PEDOT:PSS/WPU) as compliant electrodes. The modulation range of the smart tunable window with direct viewing is achieved to be 35% to 90%, which is one of the largest among existing tunable windows. At the low-transparency state, the window can also effectively block the heat and decrease the temperature rise to 2°C over 200 s, while the ambient temperature rises by 6°C with direct sunlight. We anticipate that this transparency-tuning mechanism is potentially useful for privacy protection, smart glass, projector screens, displays, and camouflage. The heat isolation feature also has the potential to reduce carbon emissions and improve the sustainability of buildings and greenhouses. [ABSTRACT FROM AUTHOR]

Copyright of China Plastics / Zhongguo Suliao is the property of Journal Office of CHINA PLASTICS and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Prestretch plays an indispensable role in programming the voltage-induced deformation of dielectric elastomer actuators (DEAs). However, lacking rational design methods, the level of prestretch is usually determined through time-consuming experiments and trial-and-error tests. In this paper, we aim to quantitatively determine the optimal biaxial prestretch ratios for maximizing the voltage-induced displacement of interest. Based on the Lagrange method and adjoint sensitivity analysis, we obtain the derivative of the displacement field with respect to the principal prestretch ratios, in which the nonlinearities and complex electromechanical coupling of DEAs are rigorously taken into consideration. The derivative information allows for performing gradient-based optimization at a high convergence rate. We propose a comprehensive optimization framework connecting the nonlinear finite element analysis and sensitivity analysis to iteratively identify the optimal prestretch ratios. We validate our method on two classical types of DEAs, i.e., planar DEAs with fixed boundaries and free-standing three-dimensional dielectric elastomer minimum energy structures (DEMES). The simulation and experiment results both show that remarkable improvements in concerned displacements are obtained compared with the non-optimized designs. [ABSTRACT FROM AUTHOR]

The compound eye is a natural multi-aperture optical imaging system. In this paper, a continuous optical zoom compound eye imaging system based on Alvarez lenses is proposed. The main optical imaging part of the proposed system consists of a curved Alvarez lens array (CALA) and two Alvarez lenses. The movement of the CALA and two Alvarez lenses perpendicular to the optical axis is realized by the actuation of the dielectric elastomers (DEs). By adjusting the focal length of the CALA and the two Alvarez lenses, the proposed system can realize continuous zoom imaging without any mechanical movement vertically to the optical axis. The experimental results show that the paraxial magnification of the target can range from ∼0.30× to ∼0.9×. The overall dimensions of the optical imaging part are 54 mm × 36 mm ×60 mm (L × W × H). The response time is 180 ms. The imaging resolution can reach up to 50 lp/mm during the optical zoom process. The proposed continuous optical zoom compound eye imaging system has potential applications in various fields, including large field of view imaging, medical diagnostics, machine vision, and distance detection.

Conventional passive ankle foot orthoses (AFOs) have not seen substantial advances or functional improvements for decades, failing to meet the demands of many stakeholders, especially the pediatric population with neurological disorders. Our objective is to develop the first comfortable and unobtrusive powered AFO for children with cerebral palsy (CP), the DE-AFO. CP is the most diagnosed neuromotor disorder in the pediatric population. The standard of care for ankle control dysfunction associated with CP, however, is an unmechanized, bulky, and uncomfortable L-shaped conventional AFO. These passive orthoses constrain the ankle’s motion and often cause muscle disuse atrophy, skin damage, and adverse neural adaptations. While powered orthoses could enhance natural ankle motion, their reliance on bulky, noisy, and rigid actuators like DC motors limits their acceptability. Our innovation, the DE-AFO, emerged from insights gathered during customer discovery interviews with 185 stakeholders within the AFO ecosystem as part of the NSF I-Corps program. The DE-AFO is a biomimetic robot that employs artificial muscles made from an electro-active polymer called dielectric elastomers (DEs) to assist ankle movements in the sagittal planes. It incorporates a gait phase detection controller to synchronize the artificial muscles with natural gait cycles, mimicking the function of natural ankle muscles. This device is the first of its kind to utilize lightweight, compact, soft, and silent artificial muscles that contract longitudinally, addressing traditional actuated AFOs’ limitations by enhancing the orthosis’s natural feel, comfort, and acceptability. In this paper, we outline our design approach and describe the three main components of the DE-AFO: the artificial muscle technology, the finite state machine (the gait phase detection system), and its mechanical structure. To verify the feasibility of our design, we theoretically calculated if DE-AFO can provide the necessary ankle moment assistance for children with CP—aligning with moments observed in typically developing children. To this end, we calculated the ankle moment deficit in a child with CP when compared with the normative moment of seven typically developing children. Our results demonstrated that the DE-AFO can provide meaningful ankle moment assistance, providing up to 69% and 100% of the required assistive force during the pre-swing phase and swing period of gait, respectively.

A series of pure-shear cyclic tests were performed on VHB™4910 dielectric elastomer at various temperatures, and the investigations were focused on the influence of temperature variations on the cyclic deformation of the elastomer and the influences of loading level and loading rate on the temperature-dependent cyclic deformation. The results demonstrate that the temperature-dependent deformation of VHB™4910 dielectric elastomer primarily manifests its viscoelasticity, while the hyper-elastic part shows comparatively weaker temperature-dependence. At different temperatures, the elastomer exhibits a cyclic softening during the strain-controlled cyclic loading. Both the peak stress and residual strain reduce with increasing the temperature and reach a stable state more rapidly at higher temperatures. A more pronounced temperature-dependence is exhibited in the stress response of the elastomer at a high loading rate; while a lower rate-dependence is observed at a high temperature. The ratchetting of the elastomer presented in the stress-controlled tests becomes more prominent as the temperature increases, but the rate-dependence of ratchetting is weaker at higher temperatures. Moreover, the temperature-dependence of ratchetting is more significant at a high-stress level as compared to that at a low-stress level.

The modeling, design, and optimization of an embedded dielectric elastomer (DE) membrane acoustic liner is considered. The acoustic impedance of the liner is modified when the DE is subjected to voltage, resulting in a reduction of the in-plane stress. A lumped element model of an embedded dielectric elastomer acoustic liner is derived and validated in a normal incidence impedance tube and is subsequently used to optimize its performance. The optimization cost functions include (1) maximization of the average absorption coefficient over a targeted frequency range, 400 – 1600 Hz and (2) maximization of the change in the liner fundamental resonance frequency when the membrane is activated. Good agreement between measured and predicted absorption is observed. Tuning of the resonant frequency requires a numerical solution for resonance using the imaginary part of the impedance, since a simple analytical expression for resonance cannot be derived due to the complex coupling between the acoustics of the liner and the electro-mechanics of the DE membrane. Nonetheless, resonant frequency shifts predicted with the lumped element model compare favorably to those measured with the activated liner sample, with a shift of 213 Hz. [ABSTRACT FROM AUTHOR]

Designing smart devices with tunable shapes has important applications in industrial manufacture. In this paper, we investigate the nonlinear deformation and the morphological transitions between buckling, necking and snap-through instabilities of layered dielectric elastomer (DE) balloons in response to an applied radial voltage and an inner pressure. We propose a general mathematical theory of nonlinear electro-elasticity able to account for finite inhomogeneous strains provoked by the electro-mechanical coupling. We investigate the onsets of morphological transitions of the spherically symmetric balloons using the surface impedance matrix method. Moreover, we study the nonlinear evolution of the bifurcated branches through finite-element numerical simulations. Our analysis demonstrates the possibility to design tunable DE spheres, where the onset of buckling and necking can be controlled by geometrical and mechanical properties of the passive elastic layers. Relevant applications include soft robotics and mechanical actuators. [ABSTRACT FROM AUTHOR]

Conventional robotic systems are built with rigid materials to deal with large forces and predetermined processes. Soft robotics, however, is an emerging field seeking to develop adaptable robots that can perform tasks in unpredictable environments and biocompatible devices that close the gap between humans and machines. Dielectric elastomers (DEs) have emerged as a soft actuation technology that imitates the properties and performance of natural muscles, making them an attractive material choice for soft robotics. However, conventional DE materials suffer from electromechanical instability (EMI), which reduces their performance and limits their applications in soft robotics. This review discusses key innovations in DE artificial muscles from a material standpoint, followed by a survey on their representative demonstrations of soft robotics. Specifically, we introduce modifications of DE materials that enable large strains, fast responses, and high energy densities by suppressing EMI. Additionally, we examine materials that allow variable stiffness and self‐healing abilities in DE actuators. Finally, we review dielectric elastomer actuator (DEA) applications in soft robotics in four categories, including automation, manipulation, locomotion, and human interaction. [ABSTRACT FROM AUTHOR]

ABSTRACTDielectric elastomer actuators have attracted growing interest for soft robot due to their large deformation and fast response. However, continuous high-voltage loading tends to cause the electric breakdown of the actuator due to heat accumulation, and viscoelasticity complicates precise control. The snap-through bistability of the Venus flytrap is one of the essential inspirations for bionic structure, which can be adopted to improve the shortcoming of dielectric elastomer actuators and develop a new actuation structure with low energy consumption, variable configuration, and multi-mode actuation. Hence, in this paper, the structural design principles of electroactive bistable actuators are first presented based on the total potential energy of the structure. Following that, a feasible design parameter region is provided, the influence of crucial parameters on the actuation stroke, trigger voltage, and actuation charge are discussed. Finally, according to the coupling relationship between the bending stiffness and the bistable property of the actuator, the adjusting methods of bistable actuation are explored. A qualitative experiment was performed to verify the feasibility and correctness of the bistable design methodology and the actuation regulation strategy. This study provides significant theoretical guidance and technical support for developing and applying dielectric elastomer actuators with multi-mode, high-performance, and long-life characteristics.

• Computational framework for the design of Dielectric Elastomer prototypes attaining predefined target configurations. • Two-field Finite Element implementation, with displacements and the scalar electric potential as unknown fields. • Phase-field driven multi-material topology optimisation. • Consideration of arbitrary number of different Dielectric Elastomer materials. • Numerical experiments support the applicability of the proposed approach. This paper presents a novel engineering strategy for the design of Dielectric Elastomer (DE) based actuators, capable of attaining complex electrically induced shape morphing configurations. In this approach, a multilayered DE prototype, interleaved with compliant electrodes spreading across the entire faces of the DE, is considered. Careful combination of several DE materials, characterised by different material properties within each of the multiple layers of the device, is pursued. The resulting layout permits the generation of a heterogenous electric field within the device due to the spatial variation of the material properties within the layers and across them. An in-silico or computational approach has been developed in order to facilitate the design of new prototypes capable of displaying predefined electrically induced target configurations. Key features of this framework are: (i) use of a standard two-field Finite Element implementation of the underlying partial differential equations in reversible nonlinear electromechanics, where the unknown fields ot the resulting discrete problem are displacements and the scalar electric potential; (ii) introduction of a novel phase-field driven multi-material topology optimisation framework allowing for the consideration of several DE materials with different material properties, favouring the development of heterogeneous electric fields within the prototype. This novel multi-material framework permits, for the first time, the consideration of an arbitrary number of different N DE materials, by means of the introduction of N − 1 phase-field functions, evolving independently over the different layers across the thickness of the device through N − 1 Allen-Cahn type evolution equations per layer. A comprehensive series of numerical examples is analysed, with the aim of exploring the capability of the proposed methodology to propose efficient optimal designs. Specifically, the topology optimisation algorithm determines the topology of regions where different DE materials must be conveniently placed in order to attain complex electrically induced configurations. [ABSTRACT FROM AUTHOR]

This article aims to establish a theoretical model of a vibration-driven robot driven by a conical dielectric elastomer actuator and analyze its characteristics, in order to make up for the lack of theoretical model construction and parameter evolution analysis for this type of robot. This article introduces a vibration-driven robot driven by a conical dielectric elastomer actuator, and then establishes its dynamic model based on its electromechanical coupling and viscoelastic characteristics. Subsequently, simulation research is conducted using this model. Overall, this article derived a dynamic equation that can be applied to this type of robot, analyzed its motion characteristics, studied the effects of different parameters on it, and discussed the influence of viscoelasticity on vibration-driven robots. The proposed dynamic model and evolution law of vibration robots can provide theoretical guidance for subsequent control and optimization. [ABSTRACT FROM AUTHOR]

Intelligent electroactive polymer-based dielectric elastomer actuators (DEAs) are capable of geometrical disorientation. These actuators are susceptible to electro-thermo-mechanical instability due to their ability to be electrically powered at various stresses and temperatures. This proposed work provides mathematical derivations for the study of instability in coupled electro-thermo-mechanical anisotropic bimorph convex DEAs. The equilibrium equations are formulated assuming the taper ratio because of the convex structure and the ply angles due to anisotropy. MATLAB is employed to numerically solve the complicated equations for critical stretch, nominal electric field, and entropy under a variety of mechanical, electrical, and thermal loads. The observations indicate that under conditions of C b = C h = 0.1 , θ 1 = θ 2 = 45 ∘ and T = 300 K , an increase in nominal stress from σ ˜ = 0.05 M P a to σ ˜ = 5 M P a leads to a corresponding increase in the peak point of the nominal electric field, specifically from E ˜ = 0.4 × 10 4 V / m to E ˜ = 4 × 10 4 V / m for axial stretch values of 2.107 and 2.159, respectively. When the nominal electric field is reported against nominal electric displacement, it enhances with the rise in temperature and reduces with the hike in nominal stress and taper ratio. When the fibers are arranged parallel to the axial stretch direction then the failure point of stretch is least, compared to that oriented in a perpendicular direction. The present study demonstrates that elevated temperature and nominal stress result in an increase in entropy, leading to a corresponding increase in system disorder. Furthermore, the perpendicular alignment of fibers with respect to axial stretch is found to decrease the degree of system randomness. [ABSTRACT FROM AUTHOR]

A large part of research on membrane mufflers focuses on the sound insulation performance of the membrane, and there is less research on the sound absorption performance of the membrane. In most cases, membrane mufflers only have some narrow absorption peaks in the low frequency band. In this paper, a micro-perforated dielectric elastomer membrane sound absorber is introduced to broaden the sound absorption frequency band of the membrane in the low frequency band. Different initial thickness, perforation aperture, and perforation spacing of the dielectric elastomer membranes were designed and fabricated, and the effect of the variation of the parameters was investigated by testing the sound absorption performance of the structural specimens. It was found that increasing the initial thickness of the membrane, appropriately decreasing the perforation aperture, and appropriately controlling the perforation spacing could improve the sound absorption performance of the structure. And based on the perforated membrane, a ring electrode structure was further designed to realize the electrically adjustable sound absorption frequency of the membrane. After the membrane with the ring electrode structure was perforated in the central region, the sound absorption band of the membrane was broadened significantly, and the applied voltage could realize the electrically adjustable sound absorption performance of the structure in the low frequency band. [ABSTRACT FROM AUTHOR]