Figure 6 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Haptic devices based on DEAs. a) Fingertip tactile display. Reproduced with permission. [157] Copyright 2006, IEEE. b) Bidirectional tactile display. Reproduced with permission. [158] Copyright 2020, IOP Publishing. c) Feel-through haptics. Reproduced with permission. [159] Copyright 2020, John Wiley and Sons. d) Soft tactile interface on the arm. Reproduced with permission. [160] Copyright 2018, IEEE. e) Soft haptic communicator array. Reproduced with permission. [13] Copyright 2019, Mary Ann Liebert, Inc. f ) A wearable textile-embedded haptic display. Reproduced with permission. [161] Copyright 2021, Mary Ann Liebert, Inc.
Source publication
Dielectric elastomer actuators (DEAs) as a typical class of electroactive polymers have been developed rapidly in the last two decades due to their advantages such as large strain, high energy density, and fast response. The high‐frequency characteristics of DEAs enable them to be applied in a wider range of fields. In this review, the high‐frequen...
Contexts in source publication
Context 1
... et al. [157] proposed a tactile stimulating element that contained a 4 Â 5 matrix actuator array, as illustrated in Figure 6a. This haptic feedback device could be worn on a human fingertip. ...
Context 2
... maximum output displacement was 471 μm and the force-toweight ratio reached up to 6.8 N g À1 , which were sufficient for a tactile device. Phung et al. [158] presented a bidirectional haptic device by integrating an antagonistic DEA with a V-shaped electrostatic actuator, as shown in Figure 6b. Due to the introduction of the electrostatic actuator, the output displacement and blocking force of the whole device were significantly improved (680 μm of displacement and 280 mN of blocking force). ...
Context 3
... et al. [159] proposed an untethered "feel-through" haptic device using ultrathin DEAs. Most notably, they designed a wireless driver circuit (mass 1.3 g) for their "feel-through" device, as shown in Figure 6c. This novel haptic device could assist the user to identify randomly oriented black letters on the white background through tactile vibrations. ...
Context 4
... with the haptic device worn on the fingertip, an arm-based wearable device can free the hands. Mun et al. [160] fabricated a wearable interface by embedding DEAs onto curvilinear surfaces such as the forearm band (see Figure 6d). The results of the perception intensity test based on 15 subjects showed that at least five levels of vibrotactile stimuli could be distinguished using the proposed haptic band. ...
Context 5
... results of the perception intensity test based on 15 subjects showed that at least five levels of vibrotactile stimuli could be distinguished using the proposed haptic band. Zhao et al. [13] designed an arm-based haptic device using a 2 Â 2 array of rolled DEAs, as shown in Figure 6e. This device could be used to test human perception of simple elements of touch position and direction with a broad bandwidth (from 10 Hz to 200 Hz). ...
Citations
... Soft electroactive polymer actuators, such as DEAs, offer rapid, efficient, and lightweight alternatives to conventional DC motor actuators in rehabilitation robotics, operating quietly as well. DEAs, which closely mimic the behavior of natural muscles, are highly valued and extensively studied within the field of soft actuators [40][41][42]. These actuators are composed of a flexible dielectric material placed between two compliant electrodes, forming a stretchable capacitor ( Figure 3A). ...
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.
... Rationally designed electrodes that reduce the resistive losses and further increase the actuation frequency could enhance the key advantage of DEAs compared to other soft actuators and enable new application spaces. The fastest DEAs operate in the range of a few kHz 79,80 . Increasing the operation frequency to the range of tens of kHz could enable applications in wearable ultrasound 81 medical devices and high-endurance microrobotics. ...
Dielectric elastomer actuators (DEAs) exhibit fast actuation and high efficiencies, enabling applications in optics, wearable haptics, and insect-scale robotics. However, the non-uniformity and high sheet resistance of traditional soft electrodes based on nanomaterials limit the performance and operating frequency of the devices. In this work, we computationally investigate electrodes composed of arrays of stiff fiber electrodes. Aligning the fibers along one direction creates an electrode layer that exhibits zero stiffness in one direction and is predicted to possess high and uniform sheet resistance. A comprehensive parameter study of the fiber density and dielectric thickness reveals that the fiber density primary determines the electric field localization while the dielectric thickness primarily determines the unit cell stiffness. These trends identify an optimal condition for the actuation performance of the aligned electrode DEAs. This work demonstrates that deterministically designed electrodes composed of stiff materials could provide a new paradigm with the potential to surpass the performance of traditional soft planar electrodes.
... This pioneering exploration has ignited enduring research enthusiasm concerning DE materials, actuator configurations, and their applications. Over the past two decades, researchers have extensively explored diverse material synthesis and processing methods, leading to the development of novel DE formulations and devices with substantially improved actuation performance (Romasanta et al., 2015;Guo YG et al., 2021;Guo YX et al., 2023;Tang et al., 2023). ...
Dielectric elastomers (DEs) have emerged as one of the most promising artificial muscle technologies, due to their exceptional properties such as large actuation strain, fast response, high energy density, and flexible processibility for various configurations. Over the past two decades, researchers have been working on developing DE materials with improved properties and exploring innovative applications of dielectric elastomer actuators (DEAs). This review article focuses on two main topics: recent material innovation of DEs and development of multilayer stacking processes for DEAs, which are important to promoting commercialization of DEs. It begins by explaining the working principle of a DEA. Then, recently developed strategies for preparing new DE materials are introduced, including reducing mechanical stiffness, increasing dielectric permittivity, suppressing viscoelasticity loss, and mitigating electromechanical instability without pre-stretching. In the next section, different multilayer stacking methods for fabricating multilayer DEAs are discussed, including conventional dry stacking, wet stacking, a novel dry stacking method, and micro-fabrication-enabled stacking techniques. This review provides a comprehensive and up-to-date overview of recent developments in high-performance DE materials and multilayer stacking methods. It highlights the progress made in the field and also discusses potential future directions for further advancements.
... Electroactive polymers, also known as electroactive polymers (EAPs), are a type of material that can change shape or size in response to applied electrical or mechanical forces acting as external stimuli [1][2][3][4]. This property makes them useful in various applications, such as actuators, sensors, and energy-harvesting devices [5][6][7][8][9]. In generator mode, EAPs convert external mechanical energy into electrical power by undergoing deformation and redistributing charges within their structure. ...
This paper aims to enhance the capacitance of electroactive polymer (EAP)-based strain sensors. The enhancement in capacitance was achieved by using a free-standing stretchable polymer film while introducing conducting polymer to fabricate a hybrid dielectric film with controlled conductivity. In this work, styrene-ethylene-butylene-styrene (SEBS) rubber was used as the base material, and dodecyl benzene sulfonate anion (DBSA)-doped polyaniline (PANI) was used as filler to fabricate a hybrid composite conducting film. The maleic anhydride group of the SEBS Rubber and DBSA, the anion of the polyaniline dopant, make a very stable dispersion in Toluene and form a freestanding stretchable film by solution casting. DBSA-doped polyaniline increased the conductivity and dielectric constant of the dielectric film, resulting in a significant enhancement in the capacitance of the EAP-based strain sensor. The sensor presented in this article exhibits capacitance values ranging
from 24.7 to 100 μF for strain levels ranging from 0 to 100%, and sensitivity was measured 3 at 100% strain level.
The total internal reflection (TIR) behavior of interface shear waves is crucial for ensuring the reliability of dielectric elastomer (DE) devices. However, due to the complex force-electric coupling and large deformation of DEs, the TIR behavior of shear waves in heterogeneous force-electric interface models is still unclear. This study modeled an elastic/DE bi-material interface to analyze the trajectory of out-of-plane shear waves. Employing Dorfmann and Ogden’s nonlinear electroelastic framework and the related linear small incremental motion theory, a method has been developed to control the TIR behavior of interface shear waves. It has been found that the TIR behavior is significantly influenced by the strain-stiffening effect induced by biasing fields. Consequently, a biasing field principle involving preset electric displacement and pre-stretch has been proposed for TIR occurrence. By controlling the pre-stretch and preset electric displacement, active regulation of TIR behavior can be achieved. These results suggest a potential method for achieving autonomous energy shielding to improve the reliability of DE devices.
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.
High‐dielectric‐constant elastomers always play a critical role in the development of wearable electronics for actuation, energy storage, and sensing; therefore, there is an urgent need for effective strategies to enhance dielectric constants. The present methods mainly involve adding inorganic or conductive fillers to the polymer elastomers, however, the addition of fillers causes a series of problems, such as large dielectric loss, increased modulus, and deteriorating interface conditions. Here, the elastification of relaxor ferroelectric polymers is investigated through slight cross‐linking, aiming to obtain intrinsic elastomers with high‐dielectric constants. By cross‐linking of the relaxor ferroelectric polymer poly(vinylidene fluoride‐ter‐trifluoroethylene‐ter‐chlorofluoroethylene) with a long soft chain cross‐linker, a relaxor ferroelectric elastomer with an enhanced dielectric constant is obtained, twice that of the pristine relaxor ferroelectric polymer and surpassing all reported intrinsic elastomers. This elastomer maintains its high‐dielectric constant over a wide temperature range and exhibits robust mechanical fatigue resistance, chemical stability, and thermal stability. Moreover, the ferroelectricity of the elastomer remains stable under strains up to 80%. This study offers a simple and effective way to enhance the dielectric constant of intrinsic elastomers, thus facilitating advancements in soft robots, biosensors, and wearable electronics.
As is known, the external excitations, material parameters, and ambient environment may affect the electromechanical properties of dielectric elastomers (DEs), which directly induce the occurrence of electrical breakdown. In this paper, we experimentally and theoretically studied the effects of voltage ramp rate, ambient humidity, electrode material, and pre-stretch on electromechanical deformation and electrical breakdown of DEs. By coupling the above four factors, the nonlinear constitutive model and electrical breakdown model of the viscoelastic DE are developed, which are shown to be consistent with the experimental observations. Firstly, when the ramp voltages with different rate are loaded to the same value, a larger voltage ramp rate leads to a smaller stretch and a higher electrical breakdown field strength of the elastomer. Besides, as the humidity increases, the electromechanical deformation increases and the electrical breakdown field decreases. In addition, it is found that different electrode materials show diverse sensitivity to the electromechanical deformation and breakdown field. Finally, with the increase of the pre-stretch from 2 to 4, the deformation and breakdown field both show an upward trend.
