Dielectric Elastomer Generators Research Articles

Exploring the performance of a dielectric elastomer generator through numerical simulations

An explicit finite element (FE) scheme for thin hyperelastic-viscoelastic membranes with a high electric field applied across its thickness is used to study an energy harvesting device, namely a conical dielectric elastomer generator (DEG). While large scale implementations of such devices have been reported in the literature, we show that systematic design of conical DEGs can be aided significantly by the numerical tools developed. In particular, meeting operational goals, honouring design constraints and guarding against failure require study of the complex interplay between several factors. The amount of charge transported, potential across which the operation occurs, amount of energy harvested, frequency of actuation, extent of actuation, mechanical and electrical properties of the material, its modes of failure and geometry of the configuration are some of the factors that affect efficiency. We demonstrate that the numerical solution of the involved finite deformation based multiphysics problem can lead to a practicable design that can operate in a desired and fail-safe way over a long period of time.

Dielectric elastomer generator with piezoelectric offset

In the past studies, dielectric elastomer generators (DEGs) need a high voltage DC power supply to provide an offset voltage, which restricts the application of DEG technology in practical projects. To solve this problem, this study adopts piezoelectric materials to provide an offset voltage for DEGs and a self-priming circuit to recycle the energy generated by DEGs. A new DEG with piezoelectric offset is designed to solve the problem of self-supply in the DEG power generation process. Before the experiment, the mathematical model is established by analyzing the dielectric elastomer generator and piezoelectric offset circuit and self-priming circuit, and the above models are simulated through the MATLAB/Simulink software. The simulation results demonstrate that the elastic restoring force of dielectric elastomers overcomes the electric field force and converts mechanical energy into electrical energy, and piezoelectric materials can provide an offset voltage for DEGs. The experimental results are in good agreement with the simulation analysis, and the calculated power of DEG-SPC is 673 mW, which lay a foundation for further research on dielectric elastomer power generation technology.

Energy harvesting from a dynamic vibro-impact dielectric elastomer generator subjected to rotational excitations

A vibro-impact (VI) dielectric elastomer generator (DEG) subjected to rotational excitations is studied in this paper for energy harvesting (EH). The VI DEG that has been demonstrated as an advanced vibrational energy harvester is first introduced, and an impact model is proposed to experimentally validate the energy harvesting mechanism of the impact-based DEGs. The VI DEG is then considered to harvest energy from a rotational excitation by being installed onto rotational machinery. The dynamical and electrical responses of the proposed system are fully studied through both theoretical analysis and numerical simulations. It is found that the system presents rich dynamical behaviors under the rotational excitation, and the rotational speed and the distance between two membranes are two key parameters to affect the system’s response and EH performance. Research results show the superiority of the proposed system which can produce a maximal output power as high as 0.88 mW from rotational excitations, and also provide guidelines to study the rotational speed-related system EH performance with given dimensional parameters or optimize the dimensional parameters under a given rotational speed.

A hybrid piezo-dielectric wind energy harvester for high-performance vortex-induced vibration energy harvesting

This paper proposes a novel hybrid piezo-dielectric (PD) wind energy harvester, to efficiently harvest the vortex-induced vibration (VIV) energy from low-speed wind. The hybrid PD harvester brings together the following two electromechanical transduction mechanisms: piezoelectric ceramic (PZT) sheets and a vibro-impact (VI) dielectric elastomer generator (DEG). The PZT sheets directly transduce the beam’s vibration into electricity, whereas the VI DEG transduces the impacts between the inner ball and the dielectric elastomer membranes resulting from the bluff body’s vibration into electricity. The theoretical model of the hybrid PD harvester subjected to VIV is formulated. Wind tunnel experiments are performed to validate the aerodynamic part of the theoretical model and identify the aerodynamic coefficients. Afterward, based on the theoretical model, the numerical investigation of the hybrid PD harvester is conducted, which uncovers the insights of the conjunction of the PZT and VI DEG for VIV energy harvesting enhancement. It is seen that in the lock-in region of the VIV, where both the PZT and VI DEG can effectively harvest the VIV energy, the VI DEG can generate much higher power. This demonstrates the superiority of the hybrid PD harvester. Parametrical studies show that the smaller mass, higher stiffness and larger diameter of the bluff body are beneficial designs, which broadens the working wind range and enhances the generate power.

A Review of Dielectric Elastomer Generator Systems

Dielectric elastomer generator systems (DEGSs) are a class of electrostatic soft‐transducers capable of converting oscillating mechanical power from different sources into usable electricity. Over the past years, a diversity of DEGSs has been conceived, integrated, and tested featuring diverse topologies and implementation characteristics tailored on different applications. Herein, the recent advances on DEGSs are reviewed and illustrated in terms of design of hardware architectures, power electronics, and control, with reference to the different application targets, including large‐scale systems such as ocean wave energy converters, and small‐scale systems such as human motion or ambient vibration energy harvesters. Finally, challenges and perspectives for the advancement of DEGSs are identified and discussed.

Wind energy harvesting from a conventional turbine structure with an embedded vibro-impact dielectric elastomer generator

In this paper, a novel wind energy harvester is proposed and studied. The wind energy harvester consists of a conventional two-blade horizontal wind turbine and a vibro-impact (VI) dielectric elastomer generator (DEG) embedded symmetrically at the end of a rotating shaft. The wind energy is harvested by the VI DEG due to the rotational motion of the turbine's blades and the shaft. The dynamic model of the proposed system under wind-induced rotations is established theoretically, and the energy harvesting (EH) process of the VI DEG is introduced with the system output voltage and power being derived. The impact-based rotational energy harvesting process of the system is validated experimentally by measuring the output voltages of a single-sided impact (SSI) DEG under different impact velocities, and by measuring the ball's impact moments under rotational excitations, thus demonstrating the feasibility of the impact-based EH of DE material. Furthermore, the dynamical and electrical behaviors of the system under different wind speeds are fully studied through numerical simulations. The influences of the wind speed, tip speed ratio and the distance between dielectric elastomer membranes (DEMs) on the system EH performance are further discussed. It is found that the proposed wind energy harvester can work effectively in a range of small wind speed and produce a relatively high output power as large as 0.7125 mW under a wind speed of 3.99 ms−1. The tip speed ratio, distance between two DEMs can be selected as the adjusting parameter to produce optimal EH performance under different wind speeds, thus providing an effective solution for the design and improvement of the proposed system under different wind environments.

Energy dissipation in natural rubber latex films: The effect of stabilizers, leaching and acetone‐treatment

AbstractNatural rubber (NR) is a versatile material possessing outstanding mechanical properties, which can be used in multiple applications including the rapidly developing dielectric elastomer generators (DEGs). One of the drawbacks of the existing DEGs is their low efficiency, which can be improved by lowering the dielectric and mechanical losses originating from the material. Therefore, the present research was focusing on assessing the ways to minimize the dielectric and mechanical losses of NR films rather than developing a DEG. In this article, the effect of natural proteins and the rubber stabilizers on energy dissipation of NR films was evaluated. Moreover, the effect of sample posttreatment (with water and acetone), curing and time after cure was discussed. As a result, deproteinized NR stabilized by ammonium caseinate outperformed unmodified NR due to reduced dielectric losses, mechanical hysteresis and stress relaxation. Moreover, the posttreatment methods were found to moderately reduce the material‐relates losses.

Programing polyurethane with rational surface-modified graphene platelets for shape memory actuators and dielectric elastomer generators

The filler network in smart nanocomposites is capable of dictating the strain actuation and electric generation behaviour in shape-memory and dielectric-elastomer systems, respectively. Noteworthy, the dissipation parameters, such as loss modulus and dielectric loss, are the critical criteria for designing an ideal smart polymeric composite. For manipulating dissipation parameters, we developed three types of nanofiller, including (I) simple graphene-oxide (GO), (II) reduced graphene-oxide (rGO), and (III) noncovalent-factionalized graphene with (polyamine-anchored)-perylene-bisimide (XGO). After fabrication of poly-urethane (PU) nanocomposites at various filler loading, the robust correlation between microstructure, electrical and mechanical, including static and dynamic (linear and nonlinear viscoelasticity), properties of nanocomposites has been deduced. These smart polymeric nanocomposites demonstrate the capability of shape-memory actuating as well as harvesting the electric energy from mechanical work. First and foremost, the harvested-energy-density of PU was meaningfully improved when blended with XGO. A composite-film containing 5 wt% XGO with the harvested energy density of 2.97 mJ/cm3 was achieved, which is about 6.7 times superior to that of pristine PU. Furthermore, the shape-memory recovery ratio of functionalized 2 wt%-nanocomposite significantly improved from 86.2% for pure PU to 93.4% for the XGO sample. The observations in this work strongly suggest compositing is an auspicious-way to provide proper shape-memory actuator and better dielectric-elastomer candidates for forthcoming practical generators.

Mechanics of dielectric elastomer structures: A review

In the past decade, the development of theory has deeply revealed the electromechanical coupling deformation mechanism of dielectric elastomer (DE). Many theoretical predictions on highly nonlinear deformation of dielectric elastomer have been verified by experiments. With the guidance of theory, the voltage-induced areal strain of dielectric elastomer has been increased from 100% in the pioneering work to the current record of 2200% and the energy density of a dielectric elastomer generator has reached 780 mJ/g. Much more developments have been realized on the applications of DE transducers in the fields of bioinspired artificial muscles, soft robotics, tunable lenses, and haptic interfaces. However, there is a gap between theory and application. Great potentials of developing DE transducers with the aid of a systematic theory have yet to be explored. This paper reviews the recent advances in the theory of dielectric elastomer and demonstrates some examples of using theory to design DE transducers. 9 boundary value problems of DE structures are analyzed from the simplest homogeneous deformation of a flat membrane to the highly complex bifurcations of a tube. Comparisons between theory and experiment are discussed. The viscous effect and the vibration of dielectric elastomer are reviewed. The developments of DE transducers and new dielectric materials are also reviewed. We summarize the performance of existing DE transducers with different configurations and make some discussions. It is hoped that the mechanics of DE structures can help to develop high-performance DE transducers in the future.

Harvest rotational energy from a novel dielectric elastomer generator with crank-connecting rod mechanisms

Rotational energy, which is abundant in our living and working environments, provides available sources for energy harvesting (EH) to support wireless sensors and wearable devices. In order to convert rotational energy into electrical one, a novel dielectric elastomer generator (DEG) with crank-connecting rod mechanisms is proposed and studied in this paper. The system structure is first introduced, and the system operation mechanism under rotations is elaborated with the system motion and energy harvesting processes being analyzed theoretically. Next, the theoretical analysis is verified experimentally by measuring the output voltages of a prototype of the proposed DEG system, thus making further numerical simulation results credible. Moreover, the system electrical responses under rotational excitation are presented through numerical simulations, and the influences of some key parameters, including the rotational velocity, the gear ratio, the system dimensional parameters and the initial angles, on the system EH performances are discussed. The simulated results show that the system EH performance can be enhanced by increasing the rotational velocity and gear ratio, and appropriately setting the system dimensional parameters and initial angles. This work also presents how to optimize the system parameters, thus providing some effective guidelines for the design and improvement of the proposed system in rotational EH. A further comparative study demonstrates the superiority of the proposed device in rotational EH.

The effect of nonlinear material viscosity on the energy harvesting performance of dielectric elastomer generators

Dielectric elastomer generators are capable of converting mechanical energy from a variety of sources into electrical energy. The energy harvesting performance depends on the interplay between electromechanical coupling, material viscosity, and multiple failure modes. Experiments also suggest that the material viscosity of dielectric elastomers is deformation-dependent, which makes the prediction of the performance of dielectric elastomer generators more challenging. By adopting the coupled field theory, finite-deformation viscoelasticity theory, and the theory for polymer dynamics, this work investigates the harvested energy and conversion efficiency of dielectric elastomer generators from theoretical perspective. By comparing the simulation results from the nonlinear viscosity model to the experimental data and the simulation results from the linear viscosity model, we further examine the possible factors that may strongly influence the performance of dielectric elastomer generators. It is found that dielectric elastomer generators exhibit higher harvested energy when nonlinear material viscosity is considered. Moreover, by selecting a higher voltage of the power supply for the generator, the conversion efficiency of dielectric elastomer generators can be greatly improved. The theoretical framework in this study is expected to offer some new insights into optimizing the design of dielectric elastomer generators and thus improving their performance.

Optimizing energy harvesting performance of cone dielectric elastomer generator based on VHB elastomer

Dielectric Elastomer Generator (DEG) has been used to harvest energy from reciprocating mechanical motion due to its variable capacitance under tension, and thus it has attracted widespread attention in the last decade. In this study, a cone DEG based on VHB elastomer was developed and its energy harvesting performance was optimized by combining equibiaxial prestretching to cone stretching mode and then tailoring the variables such as the equibiaxial prestretch ratio, input bias voltage and cone displacement. The coupling relationship among these variables and their combined influences on generated energy, energy density and conversion efficiency were systematically studied for the first time. The results indicate that prestretching plays an important role in achieving the target energy harvesting performance at shorter displacement and lower bias voltage, which means lighter weight and portability of the device. More importantly, an up-to-date highest energy density of 130 mJ/g or a maximum electromechanical conversion efficiency of 40% could be obtained by optimizing the variables. In addition, the concept of “displacement threshold” in DEG was firstly proposed and discussed based on leakage and viscoelastic. This work provides ideas for future applications of DEG on portable power and array power generators with high energy harvesting performance.

A Controlled Conditioning Interface Unit for Dielectric Elastomer Generator

Dielectric elastomer (DE) generator (DEG) employs a soft capacitive transducer. This transducer is mainly used to convert ambient mechanical motion into electricity. The amplitude of the converted electrical signal is analogous to the magnitude of the mechanical motion. However, the inherently unpredictable nature of ambient mechanical motion causes instability in the energy conversion process. This article aims to develop a controlled conditioning unit, which is to be interfaced with DEG to eliminate this instability. This article generalizes a previously reported conditioning circuit with the help of a proportional and integral (PI) controller under the DEG domain to make the energy conversion process stable. Indeed, the overall analysis is carried out in two different stages. At first, an electromechanical prototype for DEG is designed, which is responsible for converting mechanical motion into a corresponding electrical signal. Second, the generated electrical signal is processed through a conditioning circuit, which constitutes a regulator followed by a switching mode converter. Intuitive analysis of stability is presented for different magnitudes of mechanical motion and for different dynamic resistive loads. As the output voltage is found to vary with the DEG dynamics and resistive load, the inclusion of a controller to the conditioning interface unit is essential for constant voltage application. The experimental investigation shows that the DEG, along with the controlled conditioning unit, could maintain different desired quasi-constant output voltages in spite of variation at mechanical source and electrical load.

Investigation on the Impact-Based Energy Conversion of a Dielectric Elastomer Membrane

Dielectric elastomer generators (DEGs) provide a new solution for vibrational energy harvesting. Currently, a type of impact-based DEGs, which can harvest energy from ambient vibrations, has been proposed and studied through simulations. However, the energy conversion mechanism and the performance evaluation approach of such impact-based DEGs have not been fully studied yet, thus limiting the reliability of the research on the system design/optimization and performance evaluation. In this paper, a single-sided impact (SSI) model is proposed to reveal the impact-based energy conversion mechanism. Based on this model, a complete four-stage impact process is analyzed to reveal the energy conversion mechanism, and the electrical outputs and energy conversion efficiency are derived as the energy harvesting performance evaluation indexes. To use the developed analytical model to predict the system electrical response accurately, some important parameters including the coefficient of restitution (COR) and largest deflection of the membrane at impacts were obtained experimentally, and the system output voltages at impacts were measured to verify the theoretical approaches in calculating the system electrical outputs and studying the parameters’ influences. Furthermore, the influences of the pre-stretched ratio, impact velocity, and input voltage on the system energy harvesting performance are studied through simulations. The research results can provide guidelines to improve the energy harvesting performance of the impact-based DEGs in real applications.

Power generation of dielectric elastomer generator with diaphragm configuration under triangular harvesting cycle

Power generation of dielectric elastomer generator with diaphragm configuration under triangular harvesting cycle

The effect of dissipative factors on energy conversion efficiency of dielectric elastomer generator

The effect of dissipative factors on energy conversion efficiency of dielectric elastomer generator

Energy harvesting from a novel contact-type dielectric elastomer generator

A novel contact-type (CT) dielectric elastomer generator (DEG), which can harvest energy from two dielectric elastomer membranes (DEMs) under a regular contact-type displacement excitation, is proposed and studied in this paper. The operating principle of the proposed CT DEG is introduced with its electrical outputs under a contact being derived. This is further verified by capacitance and output voltage measurement experiments, thus making the theoretical analysis credible. Furthermore, the energy harvesting (EH) performance of the CT DEG in simulated contact environments is fully investigated through the conducted numerical simulations, and the influences of the excitation parameters, the system structure parameters, the pre-stretched ratio of DEM and input voltage are studied. It was found that the system demonstrates a better EH performance under a larger amplitude and a smaller period of the excitation, and the system EH performance can be enhanced by increasing the plate’s radius, the pre-stretched ratio, the input voltage or decreasing the DEM’s radius. By adjusting these parameters appropriately, the system output voltage can be 10 times higher than the input voltage, and the system output power can be achieved as high as 22.94 mW under a given displacement excitation. The research results can provide some effective solutions for the design and improvement of the proposed CT DEG in contact-type energy harvesting.

Power generation performance of dielectric elastomer generator with laterally-constrained configuration

A new loading method with laterally-constrained configuration was proposed to study the energy conversion behavior of dielectric elastomer generator (DEG) based on experimental tests and theoretical calculation. The influence of lateral pre-stretch ratio and the loading rate on the energy transformation of DEG (VHB 4905) was investigated under both the quadrangular and triangular harvesting schemes, and the latter shows higher energy density and conversion efficiency than the former. The energy density increases with the lateral pre-stretch ratio at the range of 2 to 4, with the maximum value of 76 mJ g−1 for the quadrangular cycle and 186 mJ g−1 for the triangular cycle at the loading rate of 90 mm s−1 (strain rate of 2 s−1), respectively. The advantage of larger lateral pre-stretch ratio is mainly attributed to the increased capacitance density of the elastomer membrane at the maximum stretch, which enlarges the operational area confined by multiple failure limits on the voltage-charge work-conjugate plane. As the loading rate decreases, the energy density within each cycle decreases monotonically due to the increased charges leakage. Since the mechanical energy loss within a single cycle decreases at the lower loading rate, the conversion efficiency for the triangular cycle shows slight increase at the lower loading rate, with the maximum value of 15.4% for stretching rate of 50 mm s−1 (strain rate of 1.11 s−1).

A self-amplifying dielectric-elastomer-amplified piezoelectric for motion-based energy harvesting

The dielectric elastomer generator is a stretchable generator that converts low-frequency motions into electrical output, with excellent impedance matching capabilities. However, the dielectric elastomer requires an external high-voltage priming source to initialize its operation. We previously proposed a piezoelectric generator as the priming source, and demonstrated a net amplification of specific output energy of 1.8 times by the dielectric elastomer generator, as compared with that of the piezoelectric working in isolation. We termed our prototype the dielectric-elastomer-amplified piezoelectric (DEAmP). In this version, we introduce a self-priming circuit that will progressively charge up the dielectric elastomer generator to a much higher potential, thereby allowing the system to approach its optimized operating voltage. We term this the DEAmPx generator, with the letter “x” denoting progressive voltage/charge amplification by the self-priming circuit. The DEAmPx attained an output voltage of about 2000 V in 18 cycles and generates a dielectric elastomer generator–specific energy output of 3.1 mJ/g per cycle—19 times higher than that of the piezoelectric generator working in isolation. The system-specific energy output of DEAmPx is 0.49 mJ/g, with just a single layer of elastomer film. With this significantly larger output, we demonstrate the capability of a single-layer DEAmPx to power dielectric elastomer actuators.

Novel self-biasing circuit for dielectric elastomer generator and its parameter optimization

In order to solve the problem that a dielectric elastomer generator (DEG) requires an external high voltage bias supply to improve the autonomy and security of the power generation system so that it could adapt to a changeable environment, and to improve the efficiency of power generation, based on the simulation research and analysis of three traditional self-biasing circuits, a new self-biasing circuit integrated with a self-supplementary circuit has been proposed in this paper. Under the same input conditions, the maximum output potential of the new self-biasing circuit is 2.23 times that of the traditional circuit. The pumping capability of the self-biasing circuit is greatly improved. At the same time, based on this circuit, in order to explore the factors affecting the energy conversion of the DEG, the overall electromechanical parameters of the circuit are compared and optimized by simulation experiments in this paper. The simulation and experimental results show that the capacitance-to-strain ratio of DEG and the mechanical frequency should be as large as possible within the safe range to obtain larger output potential, and the capacitance of charge pump should be 0.75 times of the capacitance of DEG in the initial state to improve efficiency.