3D Printing of Interdigitated Dielectric Elastomer Actuators

Dielectric elastomer actuators (DEAs) are soft electromechanical devices that exhibit large energy densities and fast actuation rates. They are typically produced by planar methods and, thus, expand in‐plane when actuated. Here, reported is a method for fabricating 3D interdigitated DEAs that exhibit in‐plane contractile actuation modes. First, a conductive elastomer ink is created with the desired rheology needed for printing high‐fidelity, interdigitated electrodes. Upon curing, the electrodes are then encapsulated in a self‐healing dielectric matrix composed of a plasticized, chemically crosslinked polyurethane acrylate. 3D DEA devices are fabricated with tunable mechanical properties that exhibit breakdown fields of 25 V µm^?1 and actuation strains of up to 9%. As exemplars, printed are prestrain‐free rotational actuators and multi‐voxel DEAs with orthogonal actuation directions in large‐area, out‐of‐plane motifs.     

Stable and High-Strain Dielectric Elastomer Actuators Based on a Carbon Nanotube-Polymer Bilayer Electrode

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

Enhancement Of Dielectric Permittivity And Electromechanical Response In Silicone Elastomers: Molecular Grafting Of Organic Dipoles To The Macromolecular Network

A novel method is established for permittivity enhancement of a silicone matrix for dielectric elastomer actuators (DEAs) by molecular level modifications of the elastomer matrix. A push‐pull dipole is synthesized to be compatible with the silicone crosslinking chemistry, allowing for direct grafting to the crosslinker molecules in a one‐step film formation process. This method prevents agglomeration and yields elastomer films that are homogeneous down to the molecular level. The dipole‐to‐silicone network grafting reaction is studied by FTIR. The chemical, thermal, mechanical and electrical properties of films with dipole contents ranging from 0 wt% to 13.4 wt% were thoroughly characterized. The grafting of dipoles modifies the relative permittivity and the stiffness, resulting in the actuation strain at a given electrical field being improved by a factor of six.     

New Silicone Composites for Dielectric Elastomer Actuator Applications In Competition with Acrylic Foil

Several polydimethylsiloxane elastomers were developed and investigated regarding their potential use as materials in dielectric elastomer actuators (DEA). A hydroxyl end‐functionalized polydimethylsiloxane was reacted with different crosslinkers and the electromechanical properties of the resulting elastomers were investigated. The silicone showing the best actuation at the lowest electric field was further used as matrix and compounded with encapsulated conductive polyaniline particles. These composites have enhanced properties including increased strain at break, higher dielectric constant as well as, gratifyingly, breakdown fields higher than that of the matrix. One of the newly synthesized composites is compared to the commercially available acrylic foil VHB 4905 (3M) which is currently the most commonly used elastomer for DEA applications. It was found that this material has little hysteresis and can be activated at lower voltages compared to VHB 4905. For example, when the newly synthesized composite was 30% prestrained, a lateral actuation strain of about 12% at 40 V μm^?1 was measured while half of this actuation strain at the same voltage was measured for VHB 4905 film that was 300% prestrained. It also survived more than 100 000 cycles at voltages which are close to the breakdown field. Such materials might find applications wherever small forces but large strains at low voltages are required, in, for example, tactile displays.     

Transparent Soft Robots for Effective Camouflage

Transparency is a surprisingly effective method to achieve camouflage and has been widely adapted by natural animals. However, it is challenging to replicate in synthetic systems. Herein, a transparent soft robot is developed, which can achieve effective camouflage. Specifically, this robot is driven by transparent dielectric elastomer actuators (DEAs). Transparent and stretchable conductive polymers, based on blends of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and water‐borne polyurethane (WPU), are employed as compliant solid‐state electrodes in the DEAs. The electrode exhibits large stretchability, low stiffness, excellent conductivity at large strain, and high transmittance. Consequently, the DEA can achieve a large voltage‐induced area strain of 200% and a high transmittance of 85.5%. Driven by these soft actuators, the robot can realize translations using its asymmetric vibration mode, which can be explained by dynamics analysis and is consistent with finite element modeling. This soft robot can achieve effective camouflage, due to its high transparency as well as thin structure. Furthermore, the robot can become completely flat for even better camouflage by converting its 3D structure to 2D. The transparent soft robot is potentially useful in many applications such as robots for battlefield, reconnaissance, and security surveillance, where effective camouflage is required in dynamic and/or unstructured environments.     

Stimulating Acrylic Elastomers by a Triboelectric Nanogenerator – Toward Self‐Powered Electronic Skin and Artificial Muscle

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

Rapid 3D Printing of Electrohydraulic (HASEL) Tentacle Actuators

A comprehensive material system is introduced for the additive manufacturing of electrohydraulic (HASEL) tentacle actuators. This material system consists of a photo‐curable, elastomeric silicone‐urethane with relatively strong dielectric properties (ε_r ≈ 8.8 at 1 kHz) in combination with ionically‐conductive hydrogel and silver paint electrodes that displace a vegetable‐based liquid dielectric under the application of an electric field. The electronic properties of the silicone material as well as the mechanical properties of the constitutive silicone and hydrogel materials are investigated. The hydraulic pressure exerted on the dielectric working fluid in these capacitive actuators is measured in order to characterize their quasi‐static behavior. Various design features enabled by 3D printing influence this behavior—decreasing the voltage at which actuation begins or increasing the force density in the system. Using a capacitance change of >35% across the actuators while powered, a demonstration of self‐sensing inherent to HASELs is shown. Antagonistic pairs of the 3D printed actuators are shown to exert a blocked force of over 400 mN. An electrohydraulic tentacle actuator is then fabricated to demonstrate the use of this material and actuation system in a synthetic hydrostat. This tentacle actuator is shown to achieve motion in a multi‐dimensional space.     

Reconfigurable and Latchable Shape‐Morphing Dielectric Elastomers Based on Local Stiffness Modulation

Programmable soft materials exhibiting dynamically reconfigurable, reversible, fast, and latchable shape transformation are key for applications ranging from wearable tactile actuators to deployable soft robots. Multimorph soft actuator sheets with high load‐bearing capacity are reported, capable of bending on multiple axis, made by combining a single dielectric elastomer actuator (DEA) with two layers of shape memory polymers (SMPs) fibers and an array of stretchable heaters. The rigidity of the SMP fibers can be reduced by two orders of magnitude by Joule heating, thus allowing the orientation and location of soft and hard regions to be dynamically defined by addressing the heaters. When the DEA is then actuated, it bends preferentially along the soft axis, enabling the device to morph into multiple distinct configurations. Cooling down the SMPs locks these shape changes into place. A tip deflection angle of over 300° at 5 kV is achieved with a blocking force of over 27 mN. Devices using two antagonistic DEAs are also reported that attain more complex shapes. Multimorphing is demonstrated by gripping objects with different shapes. An analytical model is developed to determine the design parameters that offers the best trade‐off between large actuation and high holding forces.     

A Biomimetic Soft Lens Controlled by Electrooculographic Signal

Thanks to many unique features, soft robots or soft machines have been recently explored intensively to work collaboratively with human beings. Most of the previously developed soft robots are either controlled manually or by prewritten programs. In the current work, a novel human–machine interface is developed to use electrooculographic signals generated by eye movements to control the motions and the change of focal length of a biomimetic soft lens. The motion and deformation of the soft lens are achieved by the actuation of different areas of dielectric elastomer films, mimicking the working mechanisms of the eyes of human and most mammals. The system developed in the current study has the potential to be used in visual prostheses, adjustable glasses, and remotely operated robotics in the future.     

Tunable Optical Modulator by Coupling a Triboelectric Nanogenerator and a Dielectric Elastomer

A conjunction system based on triboelectric nanogenerator (TENG) and dielectric elastomer actuator (DEA) is a promising demonstration for the application of TENG in the field of electronic skin and soft robotics. In this paper, a triboelectric tunable smart optical modulator (SOM) has been proposed based on this TENG‐DEA system. The SOM has a very simple structure of an elastomer film and electrodes made of dispersed silver nanowires. Owing to the voltage induced rippling of the elastomer, the output of the TENG for a contact‐separation motion at a velocity ranging from 0.5 to 10 cm s^?1 can decrease the SOM's transmittance from 72% to 40%, which is enough for realizing the function of privacy protection. Meanwhile, an effective operation method is also proposed for this SOM. By serially connecting an accessory DEA to the SOM, an external bias voltage can be applied on the SOM to tune its “threshold” voltage and the output from TENG can smoothly regulate the transmittance on the basis of the bias. The proposed operation method has excellent applicability for all DEA‐based devices, which can promote the practical study of TENG‐DEA system in the field of micro‐electro‐mechanical system and human–robots interaction.     

Bioinspired Tunable Lens with Muscle‐Like Electroactive Elastomers

Optical lenses with tunable focus are needed in several fields of application, such as consumer electronics, medical diagnostics and optical communications. To address this need, lenses made of smart materials able to respond to mechanical, magnetic, optical, thermal, chemical, electrical or electrochemical stimuli are intensively studied. Here, we report on an electrically tunable lens made of dielectric elastomers, an emerging class of “artificial muscle” materials for actuation. The optical device is inspired by the architecture of the crystalline lens and ciliary muscle of the human eye. It consists of a fluid‐filled elastomeric lens integrated with an annular elastomeric actuator working as an artificial muscle. Upon electrical activation, the artificial muscle deforms the lens, so that a relative variation of focal length comparable to that of the human lens is demonstrated. The device combined optical performance with compact size, low weight, fast and silent operation, shock tolerance, no overheating, low power consumption, and possibility of implementation with inexpensive off‐the‐shelf elastomers. Results show that combing bioinspired design with the unique properties of dielectric elastomers as artificial muscle transducers has the potential to open new perspectives on tunable optics.     

Planar Liquid Confinement for Optical Centering of Dielectric Liquid Lenses

In this letter, planar liquid confinement structures along with concentric electrodes are proposed for the optical centering of dielectric liquid lenses at the rest state and during actuation. Both the liquid confinement structures and electrodes that are photolithographically fabricated on glass substrates share the same geometric center, thereby minimizing the deviation of the optical axis at all operation modes. Tilt angles of mesa liquid confinement structure are experimentally found to be 0.11deg in maximum and below 0.03deg during actuation for a liquid lens with a droplet of initially 7 mm in diameter.     

Thermomechanically Driven Polymer Actuator for High-Precision Optical Alignment

Precise thermomechanical positioning has been demonstrated in an actuator device based on a silicone elastomer with a high thermal expansion coefficient. The actuator performance has been characterized using optical microscopy, and the actuator has been deployed in an optical coupling experiment to demonstrate the precise positioning of a ball lens between two single-mode fibers. Tuning of the coupling efficiency has been achieved in excellent agreement with calculated values and precise positioning (better than 200 nm) over a range of 20 mum has been achieved with low power dissipation and temperature control of plusmn0.2 degC. The actuation is linear with temperature over the entire range of motion. This linearity was achieved while amplifying the thermally induced expansion of the elastomer along the alignment axis by a factor of 2.1 over its nominal isotropic expansion value by physically constraining the material in the device. The device performance gives favorable implications for the use of such actuators in optical packaging applications     

基于反射式平行光管法的紫外透镜焦距测试研究

光学透镜是光学仪器中最基本的器件,而焦距又是光学透镜最重要的特性参数,如何精确测量透镜的焦距一直以来都是研究重点,然而目前鲜有针对紫外透镜焦距测试的研究。本文结合紫外透镜的特点,对一种基于反射式平行光管的紫外透镜焦距测试方法进行了研究,并以此设计出了一套紫外镜头焦距测量系统,同时选用了不同焦距的紫外镜头进行了实验,最后对系统进行了误差分析。实验结果表明,该测量系统可以对紫外镜头焦距进行高精度测量,25 mm镜头的测量误差为2.041%,100 mm镜头的测量误差为0.934%,验证了测量系统的准确性。     

Diffraction-limited geodesic lens for integrated optic circuit

Experimental and theoretical results are presented for aberration-free (except field curvatuve) geodesic lenses. A technique of calculating the aspherical lens profile with a rounded edge is summarized. A smooth transition at the lens edge is necessary to prevent undesirable scattering between the planar guide and the guide in the lens depression. Aberration-free lenses with diffraction-limited performance have been fabricated in both glass and LiNbO3substrates. The experimental results indicate lens performance, other than the change of focal length, is not severely affected by the profile deviation resulting from lens fabrication. This is further supported by the profile tolerance analysis described in the paper.     

Rugged Soft Robots using Tough,Stretchable, and Self-Healable Adhesive Elastomers

Soft robots are susceptible to premature failure from physical damages incurred within dynamic environments. To address this, we report an elastomer with high toughness, room temperature self-healing, and strong adhesiveness, allowing both prevention of damages and recovery for soft robotics. By functionalizing polyurethane with hierarchical hydrogen bonds from ureido-4[1H]-pyrimidinone (UPy) and carboxyl groups, high toughness (74.85 MJ m⁻³), tensile strength (9.44 MPa), and strain (2340%) can be achieved. Furthermore, solvent-assisted self-healing at room temperature enables retention of high toughness (41.74 MJ m⁻³), tensile strength (5.57 MPa), and strain (1865%) within only 12 h. The elastomer possesses a high dielectric constant (≈9) that favors its utilization as a self-healing dielectric elastomer actuator (DEA) for soft robotics. Displaying high area strains of ≈31.4% and ≈19.3% after mechanical and electrical self-healing, respectively, the best performing self-healable DEA is achieved. With abundant hydrogen bonds, high adhesive strength without additional curing or heating is also realized. Having both actuation and adhesive properties, a “stick-on” strategy for the assembly of robust soft robots is realized, allowing soft robotic components to be easily reassembled or replaced upon severe damage. This study highlights the potential of soft robots with extreme ruggedness for different operating conditions.     

Towards an ankle-foot orthosis powered by a dielectric elastomer actuator

Foot drop is the inability to dorsiflex the ankle (raise the toes) due to neuromuscular impairment, and this common condition can cause trips and falls. Current treatments for chronic foot drop provide dorsiflexion support, but they either impede ankle push off or are not suitable for all patients. Powered ankle-foot orthosis (AFO) can counteract foot drop without these drawbacks, but they are heavy and bulky and have short battery life. To counteract foot drop without the drawbacks of current treatments or powered AFO, we designed and built an AFO powered by dielectric elastomer actuators (DEAs), a type of artificial muscle technology. This paper presents our design and the results of benchtop testing. We found that the DEA AFO can provide 49 % of the dorsiflexion support necessary to raise the foot. Further, charging the DEAs reduced the effort that would be required for plantarflexion compared to that with passive DEA behavior, and this operation could be powered for 7000 steps or more in actual operation. DEAs are a promising approach for building an AFO that counteracts foot drop without impeding plantarflexion, and they may prove useful for other powered prosthesis and orthosis designs.     

High Breakdown Field Dielectric Elastomer Actuators Using Encapsulated Polyaniline as High Dielectric Constant Filler

A novel method allowing rapid production of reliable composites with increased dielectric constant and high dielectric strength for dielectric elastomer actuators (DEA) is reported. The promising approach using composites of conductive particles and insulating polymers generally suffers from low breakdown fields when applied to DEA devices. The present publication shows how to overcome this deficiency by using conductive polyaniline (PANI) particles encapsulated into an insulating polymer shell prior to dispersion. PANI particles are encapsulated using miniemulsion polymerization (MP) of divinylbenzene (DVB). The encapsulation process is scaled up to approximately 20 g particles per batch. The resulting particles are used as high dielectric constant (?′) fillers. Composites in a polydimethylsiloxane (PDMS) matrix are prepared and the resulting films characterized by dielectric spectroscopy and tensile tests, and evaluated in electromechanical actuators. The composite films show a more than threefold increase in ?′, breakdown field strengths above 50 V μm^?1, and increased strain at break. These novel materials allow tuning the actuation strain or stress output and have potential as materials for energy harvesting.     

Optimized three-dimensional lenses for wide-angle scanning

Three-dimensional bootlace lens antennas with two and four focal points can be optimized to produce high-quality scanned beams over a wide field of view. For two-dimensional scanning, the planar feed locus is replaced by a curved feed locus designed to minimize path length errors. Comparisons with previous bootlace lens designs demonstrate the advantages of this focal distribution. The bifocal lens shows good scanning performance in both principal and orthogonal planes. The quadrufocal lens performs better in its principal plane than in its orthogonal plane. It is also shown that the quadrufocal lens can be realized with a planar outer surface and a circular focal arc, and improved scanning performance is still achievable. Further optimization of the focal arc and/or relaxation of the planar outer surface condition results in quadrufocal lenses with negligible phase errors in the principal plane.     

Pneumatic Networks for Soft Robotics that Actuate Rapidly

Soft robots actuated by inflation of a pneumatic network (a “pneu‐net”) of small channels in elastomeric materials are appealing for producing sophisticated motions with simple controls. Although current designs of pneu‐nets achieve motion with large amplitudes, they do so relatively slowly (over seconds). This paper describes a new design for pneu‐nets that reduces the amount of gas needed for inflation of the pneu‐net, and thus increases its speed of actuation. A simple actuator can bend from a linear to a quasi‐circular shape in 50 ms when pressurized at ΔP = 345 kPa. At high rates of pressurization, the path along which the actuator bends depends on this rate. When inflated fully, the chambers of this new design experience only one‐tenth the change in volume of that required for the previous design. This small change in volume requires comparably low levels of strain in the material at maximum amplitudes of actuation, and commensurately low rates of fatigue and failure. This actuator can operate over a million cycles without significant degradation of performance. This design for soft robotic actuators combines high rates of actuation with high reliability of the actuator, and opens new areas of application for them.