Dielectric Elastomer Transducers Research Articles

Examination of factors to improve the performance of dielectric elastomer transducers and their applications

Abstract Actuators, sensors, and generators using dielectric elastomers are inexpensive and light, and can be easily to structured, multilayer-able, and very efficient. They are　ideal for an eco-energy society. In the latest technology, an only 0.15 g dielectric elastomer can lift an 8 kg weight by 1 mm or more in just 88 ms. the near future, it can be applied to efficient drive systems of humanoid robots, systems that assist in driving the motors of electric vehicles, and various industrial machinery. It is highly likely that very thin and miniaturized dielectric elastomer sensors would also support the driving of motors. In addition, dielectric elastomer generators, which can be applied to various external forces, have attracted significant attention as a renewable energy source. In this paper, we discuss the R&D status of dielectric elastomers using mainly commercially available elastomer materials, give examples of issues, and discuss and their potential applications, and usefulness.
The excellent performance of the dielectric elastomers mentioned above is largely due to their carbon-based electrodes. In this study, various carbon materials (including carbon grease, carbon black, MWCNT, and SWCNT) and their dielectric elastomer performances were compared.

Energy-based modeling of rate-independent hysteresis and viscoelastic effects in dielectric elastomer actuators

Dielectric elastomer (DE) transducers are known to exhibit a rate-dependent hysteresis in their force-displacement response, which is commonly attributed to the viscoelastic behavior of elastomer materials and compliant electrodes. In the case of DE materials characterized by low mechanical losses, such as silicone, the mechanical hysteresis often turns out to be practically rate-independent in the low frequency range (sub-Hz), whereas rate-dependent hysteretic effects only become relevant at higher deformation rates. Most of the existing literature focuses on describing DE hysteretic losses using viscoelasticity theory. This approach results in relatively simple dynamic models, which are not capable of describing rate-independent hysteretic behaviors. In this work, we propose a control-oriented modeling framework for both rate-dependent and rate-dependent hysteresis occurring in uniaxially loaded DE actuators. To this end, classic thermodinamically-consistent modeling approaches for DEs are combined with a new energy-based Maxwell-Lion formalization of the hysteretic losses. The resulting dynamic model comprises a set of nonlinear ordinary differential equations, and is capable of simultaneously describe geometric dependencies, large deformation nonlinearities, electro-mechanical coupling, and rate-independent and rate-dependent hysteretic effects. To deal with the large number of involved parameters, a novel systematic identification algorithm based on quadratic programming is also proposed. After presenting the theory, the model is validated based on experiments conducted on a silicone-based rolled DE actuator. Its superiority compared to classic DE viscoelastic models is quantitatively assessed.

Effects of Solvents on the Material Properties of Screen‐printed Electrodes and a PDMS Dielectric for Dielectric Elastomer Transducers

Dielectric elastomer transducers (DETs), namely highly stretchable dielectric membranes sandwiched between two compliant electrodes, allow to develop sensors, actuators, and generator systems. DET performance is strongly influenced by the material properties of dielectric and electrodes, as well as the type of manufacturing process. For instance, when manufacturing the electrodes via screen‐printing, significant amounts of solvents are needed to adjust the printing materials viscosity, but they potentially alter DET properties. The investigation of this effect, however, is largely unexplored. Addressing this issue, this paper investigates the influence of various solvents on a DET consisting of a polydimethylsiloxane (PDMS) membrane with PDMS/carbon black electrodes. Physical and chemical interactions between dielectric and solvents are characterized by infrared‐spectroscopy (IR), optical investigations, and light microscopy. Different solvents used for screen‐printing are analyzed in terms of their effects on the electrode electrical resistance, screen‐print image, and breakdown strength. Even though the solvent strongly affects the electrodes electrical resistance (ranging from ∽22 kΩ to >MΩ), it does not modify the breakdown strength of the pure dielectric (113 V/µm). In the IR, no chemical ageing was found. The obtained results provide systematic guidelines for the choice of solvents in DET electrode manufacturing.This article is protected by copyright. All rights reserved.

Feedforward-Cascaded Adaptive Generalized Predictive Control of Dielectric Elastomer Transducer

Feedforward-Cascaded Adaptive Generalized Predictive Control of Dielectric Elastomer Transducer

Superstretchable Liquid-Metal Electrodes for Dielectric Elastomer Transducers and Flexible Circuits.

Dielectric elastomer transducers (DETs), with a dielectric elastomer (DE) film sandwiched between two compliant electrodes, are highly sought after in the fields of soft robotics, energy harvesting, and human-machine interaction. To achieve a high-performance DET, it is essential to develop electrodes with high conductivity, strain-insensitive resistance, and adaptability. Herein, we design an electrode (Supra-LMNs) based on multiple dynamic bond cross-linked supramolecular networks (Ns) and liquid metal (LM), which realizes high conductivity (up to 16,000 S cm-1), negligible resistance changes at high strain (1.3-fold increase at 1000% strain), instantaneous self-healability at ambient temperature, and rapid recycling. The conductive pathway can be activated through simple friction by transmitting stress through the silver nanowires (AgNWs) and cross-linking sites of LM particles. This method is especially attractive for printing circuits on flexible substrates, especially DE films. Utilized as dielectric elastomer generator (DEG) electrodes, it reduces the charge loss by 3 orders of magnitude and achieves high generating energy density and energy conversion efficiency on a low-resistance load. Additionally, serving as sensor (DES) and actuator (DEA) electrodes, it enables a highly sensitive sensing capability and complex interaction.

Wave field synthesis using buckling dielectric elastomer transducers

This work presents a wave field synthesis (WFS) system using a novel loudspeaker concept based on dielectric elastomers. In WFS, large numbers of densely packed, individual audio channels are controlled to recreate arbitrary acoustic scenarios in the listener space, (i.e. listener zones in a room where different audio content can be radiated in different directions from the array, as seen in the supplemental material). Spatial resolution of the system increases with the increasing number of audio channels and with decreasing loudspeaker spacing. This motivates the use of buckling dielectric elastomer transducers (BDETs) as loudspeakers, which feature a simple setup, rendering them extremely thin and lightweight, and which promises ease of manufacture through the low demand on resources. In this work, a WFS system featuring 480 BDET has been developed. The prototype includes software, electronics, and the loudspeaker array. The electronical and mechanical design of the system is presented in detail. A nonlinear model based on the third-order shear deformation theory is applied to the BDET; the BDET is then experimentally assessed and compared to the model. Further, the final loudspeaker array is characterized by directivity measurements in an anechoic room to validate the reproducibility and quality of the setup. The presented technology highlights the structural advantages of smart materials over conventional transducers, which often are too large, heavy, and expensive for such array applications.

Piezoelectric-Based Energy Conversion and Storage Materials

The world’s energy crisis and environmental pollution are mainly caused by the increase in the use of fossil fuels for energy, which has led scientists to investigate specific cutting-edge devices that can capture the energy present in the immediate environment for subsequent conversion. The predominant form of energy is mechanical energy; it is the most prevalent energy in the environment and can be harvested for conversion into useful, electrical energy. Compared with electromagnetic, electrostatic, magneto strictive, dielectric elastomer and frictional electric transducers, piezoelectric transducers have higher high electrical and mechanical constants, large electromechanical coupling coefficients, high dielectric numbers and low losses and are currently the most dominant method of mechanical energy acquisition. Therefore, the research of piezoelectric transducers has received great attention from the scientific community. This paper reviews the research progress of piezoelectric energy acquisition technology. The main objective of this paper is to compile, discuss and summarize the recent literature on piezoelectric energy harvesting materials and applications. Piezoelectric catalytic materials, piezoelectric supercapacitors (SCs), piezoelectric self-charging devices and piezoelectric electrochemical energy storage are mainly introduced. This review briefly introduces the recent advances in piezoelectric-based catalysts and electrochemical energy storage, concentrating on the attributes of various piezoelectric materials and their uses.

Manufacturing Process for Multilayer Dielectric Elastomer Transducers Based on Sheet-to-Sheet Lamination and Contactless Electrode Application

Dielectric elastomer transducers (DETs) consist of thin elastomer films and compliant conductive electrodes on each side. Several DE-based systems, e.g., DE actuators, loudspeakers or sensors, have great potential in industrial applications. Different manufacturing processes for DE-based transducers have been realized so far. An alternative manufacturing process, based on sheet-to-sheet lamination of pre-fabricated elastomer films, appears promising for the manufacturing of large numbers of DETs, as, on the one hand, the commercially available elastomer films produced are characterized by homogeneous and reproducible properties and, on the other hand, the curing time during processing can be avoided. However, the handling of thin elastomer films and a controlled film transfer onto a surface is a challenge, as pre-stretch and wrinkles can easily occur. The presented sheet-to-sheet lamination mechanism facilitates controllable film handling well, whereby a high number of DE layers can be achieved. This paper focuses on the developed, automated film lamination of pre-cut film sheets and the electrode application via a jetting system, representing core components of the corresponding overall manufacturing process of DE laminates. The process realization on a laboratory scale is presented and manufactured DET specimens investigated for validation purposes.

A Review of Cooperative Actuator and Sensor Systems Based on Dielectric Elastomer Transducers

This paper presents an overview of cooperative actuator and sensor systems based on dielectric elastomer (DE) transducers. A DE consists of a flexible capacitor made of a thin layer of soft dielectric material (e.g., acrylic, silicone) surrounded with a compliant electrode, which is able to work as an actuator or as a sensor. Features such as large deformation, high compliance, flexibility, energy efficiency, lightweight, self-sensing, and low cost make DE technology particularly attractive for the realization of mechatronic systems that are capable of performance not achievable with alternative technologies. If several DEs are arranged in an array-like configuration, new concepts of cooperative actuator/sensor systems can be enabled, in which novel applications and features are made possible by the synergistic operations among nearby elements. The goal of this paper is to review recent advances in the area of cooperative DE systems technology. After summarizing the basic operating principle of DE transducers, several applications of cooperative DE actuators and sensors from the recent literature are discussed, ranging from haptic interfaces and bio-inspired robots to micro-scale devices and tactile sensors. Finally, challenges and perspectives for the future development of cooperative DE systems are discussed.

Effects of Electrode Materials and Compositions on the Resistance Behavior of Dielectric Elastomer Transducers

Dielectric elastomer (DE) transducers possess various advantages in comparison to alternative actuator technologies, such as, e.g., electromagnetic drive systems. DE can achieve large deformations, high driving frequencies, and are energy efficient. DEs consist of a dielectric membrane sandwiched between conductive electrodes. Electrodes are especially important for performance, as they must maintain high electrical conductivity while being subjected to large stretches. Low electrical resistances allow faster actuation frequencies. Additionally, a rate-independent, monotonic, and hysteresis-free resistance behavior over large elongations enables DEs to be used as resistive deformation sensors, in contrast to the conventional capacitive ones. This paper presents a systematic study on various electrode compositions consisting of different polydimethylsiloxane (PDMS) and nano-scaled carbon blacks (CB). The experiments show that the electrode resistance depends on the weight ratio of CB to PDMS, and the type of CB used. At low ratios, a high electrical resistance accompanied by a bimodal behavior in the resistance time evolution was observed, when stretching the electrodes cyclic in a triangular manner. This phenomenon decreases with increasing CB ratio. The type of PDMS also influences the resistance characteristics during elongation. Finally, a physical model of the observed phenomenon is presented.

Study of a Mixed Conductive Layer Fabricated by Ion Implantation and Distribution Theory.

Electrodes are essential parts of capacitors that can consist of a variety of materials depending on the application. In dielectric elastomer transducers (DETs)-a type of special variable capacitor-the electrode needs to deform with a soft base. However, the current carbon-based electrodes are not stable, and the metal-based ones are not flexible for use in DETs. Thus, the need to fabricate an electrode which can meet both the stability and flexibility requirements is extremely important. In this work, silver ions with energy levels of 40 keV were implanted into the surface of polydimethylsiloxane (PDMS) to explore the effect of ion implantation on surface conductivity. The experimental results showed that the surface resistivity of PDMS reached 251.85 kΩ per square and dropped by 10 orders of magnitude after ion implantation. This indicates that the surface conductivity was significantly improved. EDS characterization results showed that the maximum penetration depth that ions could reach was about 2.5 μm. The surface resistivity of the sample coated with carbon black was further reduced by an order of magnitude after ion implantation and changed more stably with time. A quasi-melting-collision model was established to investigate the distribution of carbon black particles. The concentration of carbon black particles at a distance from the PDMS surface followed a Gaussian-like distribution.

Recent Development of Dielectric Elastomer Transducers and Potential Applications

Power generation using dielectric elastomer transducers is cheap, light, stackable, easy to install, and highly efficient. Also, since the dielectric elastomer transducer is an actuator developed into an artificial muscle, if the DE motor is further developed, it might be possibly be able to drive a vehicle. Efficient robot driving, various industrial machines and the use of dielectric elastomer sensors to optimize the driving may also help solve the above problems from the perspective of eco-driving. This paper describes the latest level of development of dielectric elastomers, their main problems and solutions to these problems, and their potential applications. The possibilities and concrete plans for building local global smart cities (including local generation power for local consumption), efficient transportation, and environmental monitoring systems utilizing dielectric elastomers are also discussed.

Synthesis of polysiloxane elastomers modified with sulfonyl side groups and their electromechanical response.

Dielectric elastomer transducers are elastic capacitors that respond to mechanical or electrical stress. They can be used in applications such as millimeter-sized soft robots and harvesters of the energy contained in ocean waves. The dielectric component of these capacitors is a thin elastic film, preferably made of a material having a high dielectric permittivity. When properly designed, these materials convert electrical energy into mechanical energy and vice versa, as well as thermal energy into electrical energy and vice versa. Whether a polymer can be used for one or the other application is determined by its glass transition temperature (Tg), which should be significantly below room temperature for the former and around room temperature for the latter function. Herein, we report a polysiloxane elastomer modified with polar sulfonyl side groups to contribute to this field with a powerful new material. This material has a dielectric permittivity as high as 18.4 at 10 kHz and 20 °C, a relatively low conductivity of 5 × 10-10 S cm-1, and a large actuation strain of 12% at an electric field of 11.4 V μm-1 (0.25 Hz and 400 V). At 0.5 Hz and 400 V, the actuator showed a stable actuation of 9% over 1000 cycles. The material exhibited a Tg of -13.6 °C, which although is well below room temperature affected the material's response in actuators, which shows significant differences in the response at different frequencies and temperatures and in films with different thicknesses.

Dielectric elastomer actuators as artificial muscles for wearable robots

Current powered prosthetic and orthotic devices are mostly based on rigid actuators, which exhibit some intrinsic limitations, such as the reduced number of degrees of freedom, high weight, and limited flexibility. As progress is made in the soft robotics field, artificial muscles arise as potential candidates to replace current rigid actuator technologies. Dielectric elastomer actuators (DEAs) are a very promising class of soft actuator and are attracting attention due to their high energy density, fast response, and high actuation strains, similar or even superior to natural muscles. Such remarkable properties can lead the DEAs to be the next generation of actuators for wearable robots, and overcome the limitations imposed by the rigid actuators currently used. This paper reviews the state of art of the applications of DEAs to prostheses, orthoses, and rehabilitation devices. We analyzed the main configurations that are suitable as artificial muscles for the above-mentioned applications and presented the basic model of a dielectric elastomer transducer. When compared to the properties of natural skeletal muscle, some of these configurations stand out. However, there are still some drawbacks that prevent the large-scale application of DEAs, for instance the high operating voltages, durability issues, and nonlinearities that make them difficult to control. We investigated recent advances in materials, control strategies and fabrication methods that tackle these drawbacks, and they indicate that dielectric elastomers are great candidates to be the next generation of actuators for bionic devices.

Buckling Dielectric Elastomer Transducers as Loudspeakers

Buckling Dielectric Elastomer Transducers as Loudspeakers

Finite element modeling and validation of a soft array of spatially coupled dielectric elastomer transducers

Dielectric elastomer (DE) transducers are suitable candidates for the development of compliant mechatronic devices, such as wearable smart skins and soft robots. If many independently-controllable DEs are closely arranged in an array-like configuration, sharing a common elastomer membrane, novel types of cooperative and soft actuator/sensor systems can be obtained. The common elastic substrate, however, introduces strong electro-mechanical coupling effects among neighboring DEs, which highly influence the overall membrane system actuation and sensing characteristics. To effectively design soft cooperative systems based on DEs, these effects need to be systematically understood and modeled first. As a first step towards the development of soft cooperative DE systems, in this paper we present a finite element simulation approach for a 1-by-3 silicone array of DE units. After defining the system constitutive equations and the numerical assumptions, an extensive experimental campaign is conducted to calibrate and validate the model. The simulation results accurately predict the changes in force (actuation behavior) and capacitance (sensing behavior) of the different elements of the array, when their neighbors are subjected to different electro-mechanical loads. Quantitatively, the model reproduces the force and capacitance responses with an average fit higher than 93% and 92%, respectively. Finally, the validated model is used to perform parameter studies, aimed at highlighting how the array performance depends on a relevant set of design parameters, i.e. DE-DE spacing, DE-outer structure spacing, membrane pre-stretch, array scale, and electrode shape. The obtained results will provide important guidelines for the future design of cooperative actuator/sensor systems based on DE transducers.

Energy-based nonlinear dynamical modeling of dielectric elastomer transducer systems suspended by elastic structures

This paper presents the Hamilton principle approach to model, design and control mechatronic systems using dielectric elastomer transducers (DET) suspended with elastic structures. An overall dynamical modeling approach for dielectric elastomer-based actuators is presented, taking into account the dynamical effects, e.g., electrical input quantities, inertia, viscous effects, and the nonlinear behavior of DETs and elastic structures. Energy-based techniques are used to obtain a coherent modeling of the electrical and mechanical domains. Based on the variational principle and using the Rayleigh–Ritz method to approximate the field variable, a nonlinear state space model is derived considering various geometric deformations and boundary conditions. The presented approach leads to a set of ordinary differential equations that can be used for control and engineering applications. The proposed method is finally applied to a multilayer DET coupled with a nonlinear buckled beam structure and analyzed based on analytical considerations and numerical simulations.

Solvent-Free Synthesis and Processing of Conductive Elastomer Composites for Green Dielectric Elastomer Transducers.

Stretchable electrodes are more suitable for dielectric elastomer transducers (DET) the closer the mechanical characteristics of the electrodes and elastomer are. Here, a solvent-free synthesis and processing of conductive composites with excellent electrical and mechanical properties for transducers are presented. The composites are prepared by in situ polymerization of cyclosiloxane monomers in the presence of graphene nanoplatelets. The low viscosity of the monomer allows for easy dispersion of the filler, eliminating the need for a solvent. After the polymerization, a cross-linking agent is added at room temperature, the composite is solvent-free screen-printed, and the cross-linking reaction is initiated by heating. The best material shows conductivity σ=8.2Scm-1 , Young's modulus Y10% =167kPa, and strain at break s=305%. The electrode withstands large strains without delamination, shows no conductivity losses during repeated operation for 500000 cycles, and has an excellent recovery of electrical properties upon being stretched at strains of up to 180%. Reliable prototype capacitive sensors and stack actuators are manufactured by screen-printing the conductive composite on the dielectric film. Stack actuators manufactured from dielectric and conductive materials that are synthesized solvent-free are demonstrated. The stack actuators even self-repair after a breakdown event.

Dataset for "Solvent-free synthesis and processing of conductive elastomer composites for "green" dielectric elastomer transducers"

Dataset for "Solvent-free synthesis and processing of conductive elastomer composites for "green" dielectric elastomer transducers"

One Soft Step: Bio-Inspired Artificial Muscle Mechanisms for Space Applications.

Soft robots, devices with deformable bodies and powered by soft actuators, may fill a hitherto unexplored niche in outer space. All space-bound payloads are heavily limited in terms of mass and volume, due to the cost of launch and the size of spacecraft. Being constructed from stretchable materials allows many possibilities for compacting soft robots for launch and later deploying into a much larger volume, through folding, rolling, and inflation. This morphability can also be beneficial for adapting to operation in different environments, providing versatility, and robustness. To be truly soft, a robot must be powered by soft actuators. Dielectric elastomer transducers (DETs) offer many advantages as artificial muscles. They are lightweight, have a high work density, and are capable of artificial proprioception. Taking inspiration from nature, in particular the starfish podia, we present here bio-inspired inflatable DET actuators powering low-mass robots capable of performing complex motion that can be compacted to a fraction of their operating size.