Dielectric Elastomer Membrane Research Articles

Development and experimental characterization of a dielectric elastomer membrane strip actuator

Dielectric elastomer (DE) membrane actuators are of great interest for a number of industrial applications, such as valve control units or pumping systems. Their many features include lightweight, silent motion, and low energy consumption. In particular, the high flexibility permits to shape DE actuators with different geometries, allowing to obtain a wide set of actuation modes. This work aims at investigating and characterizing a novel configuration of DE membrane actuator, namely a strip DE membrane capable of out-of-plane motion. At first, manufacturing of pre-stretched strip membranes without electrodes is performed to study the influence of biaxial and uniaxial pre-stretch on the out-of-plane force-displacement characteristics. Subsequently, electrodes are screen-printed on the membranes, and the impact of their size on the force-displacement characteristics is studied. Evaluation of electro-mechanical transduction performance is performed experimentally. Finally, a performance comparison between novel strip actuators and circular actuators developed in the authors’ previous works is performed, to highlight the advantages of the novel configuration.

Electro-viscoelastic behaviors of circular dielectric elastomer membrane actuator containing concentric rigid inclusion

The time-dependent electro-viscoelastic performance of a circular dielectric elastomer (DE) membrane actuator containing an inclusion is investigated in the context of the nonlinear theory for viscoelastic dielectrics. The membrane, a key part of the actuator, is centrally attached to a rigid inclusion of the radius a, and then connected to a fixed rigid ring of the radius b. When subject to a pressure and a voltage, the membrane inflates into an out-of-plane shape and undergoes an inhomogeneous large deformation. The governing equations for the large deformation are derived by means of non-equilibrium thermodynamics, and viscoelasticity of the membrane is characterized by a rheological spring-dashpot model. In the simulation, effects of the pressure, the voltage, and design parameters on the electromechanical viscoelastic behaviors of the membrane are investigated. Evolutions of the considered variables and profiles of the deformed membrane are obtained numerically and illustrated graphically. The results show that electromechanical loadings and design parameters significantly influence the electro-viscoelastic behaviors of the membrane. The design parameters can be tailored to improve the performance of the membrane. The approach may provide guidelines in designing and optimizing such DE devices.

Voltage-driven torsion of electroactive thick tubes reinforced with helical fibers

This work studies the voltage-driven torsional deformation of a thick-walled circular cylindrical tube composed of a dielectric elastomer (DE) reinforced with a family of helical fibers. The Helmholtz free energy of the DE composite tube involves separate DE matrix and fiber contributions. Upon the application of an electrical voltage difference on its inner and outer surfaces, the DE matrix contracts through the thickness and expands in cylindrical surfaces due to the Maxwell stress. Since the composite is stiffened along the fiber direction, it preferentially expands in the direction orthogonal to the fiber within the cylindrical surfaces. As a result, voltage-driven torsional deformation will occur in the helical fiber-reinforced DE tube. Although membrane theory was usually adopted to model fiber-reinforced thin DE membranes, the finite deformation theory is utilized in the present work to model relatively thick DE composite tubes. It is found that the bending effect plays an important role in the voltage-driven torsional deformation. The reorientation of the fibers and the distribution of the stress carried by the fibers in the tubes are discussed in detail so as to provide an interpretation to some new voltage-driven torsional behaviors. The theoretical model and physical insights provided in this work will aid the design and optimization of soft electroactive actuators and soft robotics.

Scar-Like Self-Reinforced and Failure-Tolerant Dielectric Elastomer Actuator With AgNWs Electrode

Scar structures of natural animals can reinforce the wounds both mechanically and biologically to maintain the functions of the injured muscle and skin. Inspired by the scar structure, we present a dielectric elastomer (DE) with silver nanowire electrodes possessing the scar-like ability. This DE membrane can tolerate the failures by both electric breakdown and mechanical rupture. The DE actuator (DEA) can maintain their performances of force and displacement output after multiple failures. Scanning electronic microscope (SEM) images show that the scar-like structures accumulate around the electromechanical failure locations on the DE membrane as the stiffened and insulated regions, which prevent further short current and membrane rupture. J-integrals and stress distribution around the failure location have been calculated by finite element analysis to verify the mechanical reinforcements of the scar-like structures over crack propagation.

Stretch tuning of the Debye ring for 2D photonic crystals on a dielectric elastomer membrane.

The tunable diffracted pattern (Debye ring) of the well-ordered close-packed 2D photonic crystal (PC) is achieved via large deformation of the dielectric elastomer (DE) membrane for the first time. Two deformation models are proposed, the in-plane deformation driven by voltage and the out-of-plane deformation actuated by pressure. Both experimental and theoretical analyses are conducted to explore the tunability of the DE stretch on the Debye ring of the 2D PC, by voltage and pressure. An excellent agreement is found between the experimental and analytical results. This study shows that tuning the size of the Debye ring by voltage driven in-plane deformation is easy to operate and space-saving. However, it needs a high voltage and the adjustable range is relatively small. On the other hand, the pneumatic tuning by out-of-plane deformation has a widely adjustable range compared with the electric one and the pressure needed is only hundreds to less than two thousand pascal, which is energy-saving. This work may pave the way for the design of various smart sensors and soft displays with the combination of PCs and DEs.

Analytical Modeling of Clamped Dielectric Elastomer Strip Membranes Exhibiting Necking Effect

Dielectric elastomer (DE) strip membranes permit to design mechatronic transducers enabling large-strain, low-energy consumption, and compactness. To optimize the design of strip DE actuators by means of software tools, as well as to synthesize accurate control algorithms, analytical models have to be developed. Modeling of strip DE membranes clamped at both ends, having a nearly unitary aspect ratio (i.e., the ratio between the membrane length and width), turns out to be a particularly challenging task. In fact, such membranes are affected by necking and inhomogeneous deformations. Those phenomena are difficult to be described via analytical models, making it necessary to rely on computationally involved finite element tools. In this paper, we develop a modeling framework which permits to describe behavior of clamped DE strips in an analytical fashion. The model is based on an anisotropic free-energy function, which allows to map the effects of the clamping into the material behavior. A comparison between analytical and finite element models is presented for membranes having different aspect ratios, both in simulation and experimental case of studies, showing a remarkable agreement.

Viscoelastic analysis of a spring-connected dielectric elastomer actuator undergoing large inhomogeneous deformation

A viscoelastic model is developed for a conical dielectric elastomer actuator (CDEA) connected by a spring. The CDEA is composed of a dissipative dielectric elastomer membrane, a rigid disk and a spring. The CDEA undergoes large out-of-plane inhomogeneous deformation by applying the electro-mechanical loadings. The nonlinear spring-dashpot model is employed to model the viscoelastic behavior of the membrane. A differential-algebraic system of equations is derived and the solving technique is developed. Both the creep behaviors under the constant instantaneous electro-mechanical loadings and the cyclic performance under the cyclic mechanical and electrical loadings are presented. The time-dependent behaviors of the CDEA can be tuned by changing the stiffness of the spring, the pre-stretch of the membrane as well as the loading rate and the loading type.

A robust dual-membrane dielectric elastomer actuator for large volume fluid pumping via snap-through

A pressurized dielectric elastomer (DE) diaphragm under electrical actuation can experience snap-through large deformation due to electromechanical instability, which was shown to be a promising mechanism for large volume fluid pumping. However, snap-through actuation in a DE fluid pump will not occur when the inlet pressure to the pump is small and cannot be robustly utilized for different applications. To solve this problem, in this study, we proposed a dual-membrane DE pump design featuring an active DE membrane interacting with a passive elastic membrane. This design enabled snap-through of the DE membrane over a wide range of inlet pressures, making it feasible for large volume fluid pumping even at low pressures. Merits of this dual-membrane DE actuator design were experimentally verified; for example, the pumping volume of the dual-membrane DE pump could be as large as 3944% of the pumping volume of the conventional single-membrane DE pump. We further proposed an analytical framework to describe the mechanism of the dual-membrane DE fluid pump, involving the superimposition of the pressure-volume curves of the active and passive membranes. The theoretically predicted equilibrium states agreed well with experimental observations. Findings in this study will broaden the applications of the DE actuator in scenarios where a large pumping volume is needed over a wide range of pressures.

Inkjet 3D printing of UV and thermal cure silicone elastomers for dielectric elastomer actuators

Dielectric elastomer actuators (DEAs) are an attractive form of electromechanical transducer, possessing high energy densities, an efficient design, mechanical compliance, high speed, and noiseless operation. They have been incorporated into a wide variety of devices, such as microfluidic systems, cell bioreactors, tunable optics, haptic displays, and actuators for soft robotics. Fabrication of DEA devices is complex, and the majority are inefficiently made by hand. 3D printing offers an automated and flexible manufacturing alternative that can fabricate complex, multi-material, integrated devices consistently and in high resolution. We present a novel additive manufacturing approach to DEA devices in which five commercially available, thermal and UV-cure DEA silicone rubber materials have been 3D printed with a drop-on-demand, piezoelectric inkjet system. Using this process, 3D structures and high-quality silicone dielectric elastomer membranes as thin as 2 μm have been printed that exhibit mechanical and actuation performance at least as good as conventionally blade-cast membranes. Printed silicone membranes exhibited maximum tensile strains of up to 727%, and DEAs with printed silicone dielectrics were actuated up to 6.1% area strain at a breakdown strength of 84 V μm−1 and also up to 130 V μm−1 at 2.4% strain. This approach holds great potential to manufacture reliable, high-performance DEA devices with high throughput.

Tunable actuation of dielectric elastomer by electromechanical loading rates

Dielectric elastomer (DE) membranes are able to self-deform with the application of an electric field through the thickness direction. In comparison to conventional rigid counterparts, soft actuators using DE provide a variety of advantages such as high compliance, low noise, and light weight. As one of the challenges in the development of DE actuating devices, tuning the electromechanical actuating behavior is crucial in order to achieve demanded loading paths and to avoid electromechanical failures. In this paper, our experimental results show that the electromechanical loading conditions affect the actuating behaviors of the DE. The electrical actuating force can be tuned by 29.4% with the control of the electrical charging rate. In addition, controllable actuations have been investigated by the mechanical model in manipulating the electromechanical loading rate. The calculated results agree well with the experimental data. Lastly, it is believed that the mechanisms of controlling the electromechanical loading rate may serve as a guide for the design of DE devices and high performance soft robots in the near future.

Parametric study of a novel vibro-impact energy harvesting system with dielectric elastomer

A vibro-impacting mechanical system with two dielectric elastomeric membranes for harvesting energy from ambient vibrations is proposed. The purpose of the paper is to study the system performance under different angles of its inclination with respect to a horizontal position in the effort to determine the best layout of the system. The dimensional, electrical and dynamic parameters of the dielectric elastomeric membrane are analysed and then used to numerically estimate the output voltage of the proposed system. The electrical properties of the dielectric elastomer membrane are validated experimentally, and the dynamic behaviors of the system are fully studied under different initial conditions. The system output performances under harmonic excitation are further discussed. The approach and an application example for the design of the proposed device subjected to a certain vibrational environment is presented.

Energy harvesting from a DE-based dynamic vibro-impact system

Dielectric elastomer (DE) generators may be used in harvesting energy from ambient vibrations. Based on existing research on the mechanical properties of a circular DE membrane, a DE-based dynamic vibro-impact system is proposed in this paper to convert vibrational energy into electrical one. The dimensional, electrical and dynamic parameters of the DE membrane are analysed and then used to numerically estimate the output voltage of the proposed system. The system output performances under harmonic excitation are further discussed. At last, the comparison study has been conducted with an electromagnetic energy harvesting system, served as a ‘shaking’ flashlight.

The mechanism for large-volume fluid pumping via reversible snap-through of dielectric elastomer

Giant deformation of dielectric elastomers (DEs) via electromechanical instability (or the “snap-through” phenomenon) is a promising mechanism for large-volume fluid pumping. Snap-through of a DE membrane coupled with compressible air has been previously investigated. However, the physics behind reversible snap-through of a DE diaphragm coupled with incompressible fluid for the purpose of fluid pumping has not been well investigated, and the conditions required for reversible snap-through in a hydraulic system are unknown. In this study, we have proposed a concept for large-volume fluid pumping by harnessing reversible snap-through of the dielectric elastomer. The occurrence of snap-through was theoretically modeled and experimentally verified. Both the theoretical and experimental pressure-volume curves of the DE membrane under different actuation voltages were used to design the work loop of the pump, and the theoretical work loop agreed with the experimental work loop. Furthermore, the feasibility of reversible snap-through was experimentally verified, and specific conditions were found necessary for this to occur, such as a minimum actuation voltage, an optimal range of hydraulic pressure exerted on the DE membrane and a suitable actuation frequency. Under optimal working conditions, we demonstrated a pumping volume of up to 110 ml per cycle, which was significantly larger than that without snap-through. Furthermore, we have achieved fluid pumping from a region of low pressure to another region of high pressure. Findings of this study would be useful for real world applications such as the blood pump.

Robust Interaction Control of a Dielectric Elastomer Actuator With Variable Stiffness

This paper presents an interaction control algorithm for a dielectric elastomer membrane actuator. The proposed method permits efficient exploitation of the controllable stiffness of the material, allowing to use the membrane as a "programmable spring" in applications such as robotic manipulation or haptic devices. To achieve this goal, we propose a design algorithm based on robust control theory and linear matrix inequalities. The resulting controller permits to arbitrarily shape the stiffness of the elastomer, while providing robust stability and performance with respect to model nonlinearities. A self-sensing displacement estimation algorithm allows implementation of the method without the need of a deformation sensor, thus reducing cost and size of the system. The approach is validated on an experimental prototype consisting of an elastomer membrane preloaded with a bistable biasing spring.

Electromechanical Control and Stability Analysis of a Soft Swim-Bladder Robot Driven by Dielectric Elastomer

Compared to the conventional rigid robots, the soft robots driven by soft active materials possess unique advantages with their high adaptability in field exploration and seamless interaction with human. As one type of soft robot, soft aquatic robots play important roles in the application of ocean exploration and engineering. However, the soft robots still face grand challenges, such as high mobility, environmental tolerance, and accurate control. Here, we design a soft robot with a fully integrated onboard system including power and wireless communication. Without any motor, dielectric elastomer (DE) membrane with a balloonlike shape in the soft robot can deform with large actuation, changing the total volume and buoyant force of the robot. With the help of pressure sensor, the robot can move to and stabilize at a designated depth by a closed-loop control. The performance of the robot has been investigated both experimentally and theoretically. Numerical results from the analysis agree well with the results from the experiments. The mechanisms of actuation and control may guide the further design of soft robot and smart devices.

Development and experimental characterization of a pneumatic valve actuated by a dielectric elastomer membrane

Due to their many features including lightweight and low energy consumption, dielectric elastomer (DE) membrane actuators are of interest for a number of industrial applications, such as pumping systems or valve control units. In particular, the use of DEs in valve control units offers advantages over traditional solenoid valves, including lower power requirements and relative simplicity in achieving proportional control. Additionally, DEs generate low thermal dissipation and are capable of virtually silent operation. The contribution of this work is the development of a new valve system based on a circular DE membrane pre-loaded with a linear spring. The valve is designed for pressurized air and operates by actuating a lever mechanism that opens and closes an outlet port. After presenting the operating principle and system design, several experiments are presented to compare actuator force, stroke, and dissipated energy for several pressure differentials and associated volume flows. It is observed that the DE-driven valve achieves a performance similar to a solenoid-based valve, while requiring a significantly lower amount of input energy. In addition, it is shown that DE-membrane valves can be controlled proportionally by simply adjusting the actuator voltage.

A Thermodynamically Consistent Port-Hamiltonian Model for Dielectric Elastomer Membrane Actuators and Generators

This paper presents a port-Hamiltonian modeling formulation for a Dielectric Elastomer membrane. The model relates electrical and mechanical inputs to corresponding conjugate outputs, allowing to simulate the membrane transducer in actuation and energy harvesting application. Starting from a nonlinear, physics-based model developed in the authors’ previous works, a suitable function is initially proposed to quantify the overall electro-mechanical energy in the system. Subsequently, a complete description in terms of Hamiltonian, dissipation function, and system matrices is provided. The port-Hamiltonian formalism permits to assess the thermodynamic consistency of the model, making it a reliable tool for the prediction of energetic performance in dynamic applications. Furthermore, it opens up the possibility of applying powerful nonlinear analysis and design tools.

Design and Control of a High-Speed Positioning System Based on Dielectric Elastomer Membrane Actuators

Dielectric elastomers (DEs) represent a new family of electromechanical transducers capable of undergoing large actuation stroke (>100%), allowing it to achieve performance that is not attainable with standard transduction technologies (e.g., piezo). Furthermore, DEs’ high flexibility permits us to design actuators with various shapes and sizes, allowing us to meet desired stroke or force specifications in a wide range of applications. This work aims to show the potential of DE technology in micropositioning applications by presenting development, manufacturing, and control of a one-directional flexure system driven by two circular out-of-plane DE actuators (COP-DEAs). The two COP-DEAs are coupled in an antagonistic configuration that, under the application of a voltage, provides push–pull forces on a custom built compliant unidirectional stage. After describing design and fabrication of the actuator, experimental characterization is performed. Finally, a feedforward control strategy is implemented in order to let the displacement follow a desired periodic profile. The unloaded stage is capable of accurately following sinusoidal and triangular trajectories, having a fundamental frequency of 60 Hz and a peak value of 40 μm, with a maximum error of 2 and 5 μm, respectively.

A Self-Sensing Approach for Dielectric Elastomer Actuators Based on Online Estimation Algorithms

This paper develops a position self-sensing approach for a motion actuator based on a dielectric elastomer membrane. The proposed method uses voltage and current measurements to estimate the electrical resistance and capacitance online by means of a high-frequency low-amplitude voltage component injected in the actuation signal. The actual deformation is subsequently reconstructed using a model-based estimate of the electrical parameters implemented on a field programmable gate array platform (FPGA) with a sampling frequency of 20 kHz. The main peculiarity of the approach is the use of recursive identification and filtering algorithms that avoid the need of charge measurements. The self-sensing algorithm is extensively validated on a precision linear-motion actuator, which uses a nonlinear biasing system to obtain large actuation strokes.

Role of nonlinear elasticity in mechanical impedance tuning of annular dielectric elastomer membranes

We use finite elasticity to examine the behavior of a lightweight mechanism for rapid, reversible, and low-power control of mechanical impedance. The device is composed of a central shaft suspended by an annular membrane of prestretched dielectric elastomer (DE), which is coated on both sides with a conductive film. Applying an electrical field across the thickness of the membrane, attractive Coulombic forces (so-called “Maxwell stresses”) are induced that (i) squeeze the annulus, (ii) relieve the membrane stress, and (iii) reduce the mechanical resistance of the elastomer to out-of-plane deflection. This variable stiffness architecture was previously proposed by researchers who performed an experimental implementation and demonstrated a 10× change in stiffness. In this manuscript, we generalize this approach to applications in aerospace and robotics by presenting a complete theoretical analysis that establishes a relationship between mechanical impedance, applied electrical field, device geometry, and the constitutive properties of the dielectric elastomer. In particular, we find that the stiffness reduction under applied voltage is non-linear. Such decay is most significant when the Maxwell stress is comparable to the membrane prestress. For this reason, both the prestretch level and the hyperelastic properties of the DE membrane have a critical influence on the impedance response.