Dielectric Elastomer Generators Research Articles

Modeling and control of planar dielectric elastomer energy harvester

Dielectric Elastomer Generators (DEGs) have been used as mechanical-electrical transducers in energy harvesting systems. However, material safety assurance control, which prevents dielectric elastomer (DE) failures, is not fully investigated. Since various DEG configurations share common failure modes, incorporating these modes into the system is crucial for extending DEG lifetime and improving output power capacity of DE energy harvesters. This paper develops a physics-based model for a planar DE energy harvester and material failure modes identified through analytical analysis of the model. A real-time algorithm for internal safety control is developed to allow operation within a broader feasible region while preventing electrical breakdown (EB), electromechanical instability (EMI), loss of tension (LT), or rupture by stretch (RS). The algorithm prioritizes safety control when the feasible space is violated and allows primary control when operating within the safe space. As a step towards prototyping of an energy harvester using a DE, a prototype concept model is outlined. By using the safety control algorithm, energy harvesting output power is maximized without violating material safety rules, making it applicable to various energy source conversions like human motion, tidal wave, and wind energy.

Largely Enhanced Energy Harvesting Performance of Silicone-Based Dielectric Elastomer Generators through Controlling the Uniaxial Device Structure

Largely Enhanced Energy Harvesting Performance of Silicone-Based Dielectric Elastomer Generators through Controlling the Uniaxial Device Structure

A 3D coordination polymer of Cd(II) with conformationally flexible mixed ligands as an active filler for silicone elastomers

The electronic configuration of d10 metals enables for a wide range of coordination numbers and geometries which, together with the use of mixtures of ligands for their coordination, allows fine-tuning of the properties of the complexes formed. By treating Cd(ClO4)2 with 1,3-bis(carboxypropyl)tetramethyldisiloxane (H2Cx) and 4,4′-azopyridyne (AzPy) in solution, a 3D coordination polymer, [Cd(Cx)(AzPy)·1.85H2O]n (1), was mostly formed. The compound was investigated by elemental and spectral analysis, as well as by powder and single crystal X-ray diffraction. Thermal behavior of compound 1 was evaluated by TGA and DSC, while the moisture behavior was studied by dynamic vapor sorption (DVS) analysis. Compound 1 contains a five-dentate Cx2− ligand with Cd atoms in a pentagonal-bipyramidal geometry, as determined by X-ray analysis. The conformational flexibility of the ligands allows the establishment of all possible intermolecular interactions in a very dense packing, the resulting structure having an extremely low free volume (14.8%). The compound is hydrophobic, adsorbing up to 2.4 wt% water vapor, thermally stable up to 160 °C, and has a phase transition around 6 °C, which, based on analysis by polarized optical microscopy (POM), is considered as a second-order crystal-to-crystal transition, facilitated by the mobility of the siloxane fragment. Due to the constraints imposed by the covalent 3D architecture, the conformational photoisomerization of 1 is extremely limited, as indicated by UV–Vis spectroscopy studies on solutions with solvents of different polarities as well as dielectric spectroscopy studies on silicone composites in which it is in solid state with 5 and 20 wt% loading. Instead, it was found that compound 1 significantly increases the dielectric strength of the resulting materials (up to 46 V/μm compared to 18 V/μm in the empty matrix) by incorporating it as a filler, making them suitable for dielectric elastomer generators, as the results of theoretical calculations indicate. In the purification process, a 2D coordination polymer, [Cd(Cx)(AzPy)·H2Cx]n (2), was also identified in traces.

Largely Enhanced Service Life and Energy Harvesting Stability of Dielectric Elastomer Generator by Designing and Optimizing Compliance of Electrodes.

Dielectric elastomer generator (DEG), which consists of a dielectric elastomer (DE) film sandwiched between two flexible electrodes (FEs), has the advantages of lightweight, high energy density, and high energy conversion efficiency, providing a simple and feasible solution for harvesting energy from human motion or nature. As crucial constituents of DEG, FEs are expected to possess excellent conductivity and compliance. Nevertheless, there is currently no quantitative characterization method for FE compliance. In addition, the impact mechanism of FE compliance on the energy harvesting performance and fatigue life of the DEG remains unclear. In this study, the dynamic mechanical property (DMP) was used to assess the compliance of FEs, and the quantitative characterization method of FE compliance was proposed. A series of silicone rubber electrodes (SREs) with different DMPs and compliance were designed and prepared, and the impact mechanism of FE compliance on the energy harvesting stability and fatigue life of the DEG was investigated. The results indicate that the key to achieving excellent FE compliance lies in reducing the difference in the magnitude of the complex modulus and phase angle between the FEs and DE, which can significantly reduce interfacial friction and extend the fatigue life of DEG. Benefiting from the enhanced FE compliance, the fatigue life and full-life energy density of the DEG device increase by 20.3 times and 26.4 times, respectively, compared with those of the commonly used carbon-based electrodes.

Highly stretchable and self-healing SEBS-PVDF composite films for enhanced dielectric elastomer generators

Highly stretchable and self-healing SEBS-PVDF composite films for enhanced dielectric elastomer generators

An Integrated Charge Excitation Alternative Current Dielectric Elastomer Generator for Joint Motion Energy Harvesting

AbstractJoint movement is a plentiful source of energy in living organisms; however, it is challenging to harvest due to its multidirectional nature, and effective technologies for harnessing this energy are lacking. In this study, a novel approach is presented to harvest joint motion energy by combining an alternating current dielectric elastomer generator (AC‐DEG) with an electret nanogenerator (ENG). The ACENG‐DEG, utilizing ion hydrogel electrodes and ENG, exhibits remarkable stretchability (860%) and efficiently converts mechanical energy into electrical energy through a stretch‐based mechanism. With only 37 cycles, the device reaches a saturation voltage of 1.18 kV and generates an output charge of 1.96 µC per cycle. Notably, the charge output response speed is approximately four times faster than that of traditional AC‐DEGs. The proposed strategy for harvesting human mechanical energy in this study represents a promising pathway for developing high‐performance energy harvesting devices and self‐powered systems.

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.

Dielectric Breakdown Strength of PDMS Elastomers after Mechanical Cycling

PDMS-based composites such as silicone elastomers are commonly found in high-voltage engineering, especially in outdoor insulation as coatings or structural elements or at interfaces between network elements, such as cable sealing ends (CSE). They are also promising prospects for dielectric elastomer generators (DEG), which are retrieving electrostatic energy from large strain amplitudes. The upper limit of energy conversion from these transducers is determined by the dielectric breakdown strength (DBS). Therefore, developing reliable systems that operate under high electric fields and variable repeated strains requires a thorough understanding of the mechanisms behind electrical breakdown and its coupling to mechanical cycling. In this study, the effect of Mullins damage and mechanical fatigue on silicone elastomers has been investigated. An electro-mechanical instability model that considers cyclic softening allows for predicting the evolution of the breakdown strength depending on the loading history. The results highlight the importance of the “first cycle,” where up to a 30% reduction in the mean DBS was measured. However, subsequent mechanical fatigue only marginally contributes to the degradation, which is a promising perspective for the long-term performance of any silicone elastomer as long as the precise impact of the first cycle is known.

Nonlinear dynamics and chaos control of circular dielectric energy generator

The current study focuses on the nonlinear dynamics of the dielectric elastomer generator (DEG). To begin with, we will go through DEG’s operating principles, parameters, materials, and deformation modes. On this basis, the dynamical modeling for the nonlinear behavior of the DEG system is described, and the second-order nonlinear ordinary differential equation representing radially symmetric motion is derived using Hamilton’s variational principle. A static applied electric field allows the DEG system to attain two equilibrium states: thick and thin. The effects of the stiffening phenomenon on the dynamics of the DEG system are investigated. The system converges to a stable equilibrium point under constant loads, and the convergence position and velocity are closely related to both the initial states. Subjected to periodic loads, certain phenomena such as quasiperiodicity and chaos are detected, and the chaotic phenomena are explored using the bifurcation diagram and 0-1 chaos test. Furthermore, parametric studies are carried out using numerical analyses to demonstrate the influence of load amplitude and external frequency on the dynamics of the DEG system. Once the DEG enters the chaotic regime, the chaotic zone is transformed into a stable manifold using established chaos control techniques such as system parameter change and parametric perturbation. However, because these techniques require changes in system design, we proposed a chaos control by using a non-linear controller, specifically, adaptive integral backstepping sliding mode control (AIBSMC) as one demonstrative candidate. The controller also enables the DEG system to follow motion along a predefined trajectory. The current work may be expected to substantially impact the future design and performance of energy harvesters.

Size effect and electrical ageing of PDMS dielectric elastomer with competing failure modes

Large-scale dielectric elastomer generators dielectric elastomer generators (DEGs) such as those employed in wave energy converter projects require a significant volume of electrically stressed materials. Meanwhile, predictions of energy output from such systems are generally extrapolated from electrical and mechanical breakdown measurements performed on small scale samples, where the presence of small defects can be extremely small. This can lead to overly optimistic upscaled predictions for the performance and reliability of full-scale devices. In this study, multilayer DEGs were prepared to evaluate the dielectric breakdown strength of thin polydimethylsiloxane PDMS elastomer at different values of active areas. The results indicated the presence of two separate breakdown mechanisms resulting in an enhanced size effect and a reduced reliability for the larger samples. Electrical ageing tests were performed on three different sample geometries and the dielectric breakdown strength was found to be marginally affected by the time under stress. A Weibull competing failure model was applied to the distribution of experimental breakdowns and electrical reliability was accurately modeled over more than four decades of variation in the electrode area.

Improving rotational energy harvesting performance of DEGs with cam follower mechanism by optimizing cam profile

This letter explores feasible methods for improving the rotational energy harvesting (EH) performance of a dielectric elastomer (DE) generator with a cam follower mechanism by adjusting the time ratio of the rise segment in a cam cycle period. The theoretical analysis model of the DE-based EH device under the rectangle EH scheme is developed by considering material viscosity and leakage current and verified by the existing experimental data. On this basis, the effect of the time ratio of the rise segment in a cam cycle period on the EH performance of the DE-based EH device under the rectangle scheme is also studied for different system parameters, such as the rotational frequency of the cam, and the pre-stretch ratio and the viscoelastic parameter of the DE generator. Results show that at small viscoelastic parameter, reducing the time ratio of the rise segment in a cam cycle period can improve the harvested electrical energy, while at large viscoelastic parameter, the harvested electrical energy can increase with the increase of the time ratio of the rise segment. Conclusions can help provide guidance for the cam design in the DEG with the cam follower mechanism so as to improve the EH performance in harvesting the rotational energy.

Experimental Investigation of a Uniaxial Dielectric Elastomer Generator

Abstract The widespread use of battery-powered electronic devices creates the need to develop methods to extend their maximum operating time. This can be achieved by using ambient energy, which would otherwise be dissipated. The conversion of energy, usually mechanical energy, into electric energy takes place in energy harvesters. Energy harvester systems based on a dielectric elastomer (DE) are a relatively new field that is being constantly developed. Due to their features, dielectric elastomer generators (DEGs) may complement the currently dominant piezoelectric harvesters. The major feature of employing a hyperelastic material is that it allows relatively large displacements to be utilised for generating energy, which is impossible in the case of piezoceramics. This article presents a DEG designed to operate under uniaxial tensile loads and which has a multilayer structure, describes the general operating principles of a DEG, explains the construction and assembly process of the investigated design and shows the electric circuit necessary to properly direct current flow during the DEG operation. The experimental part consists of two series of tests based on a central composite design (CCD). The objective of the first part was to map a capacitance response surface of the DEG in the selected range of the cyclic mechanical load. The second part concerned the amount of generated energy for the specific load case as a function of operating voltages. The result of the work is the formulation of regression models that allow the characteristics of the presented DEG design to be identified.

An asymmetric bistable vibro-impact DEG for enhanced ultra-low-frequency vibration energy harvesting

In order to enhance the performance of bistable energy harvesters with dielectric elastomers (DEs) under ultra-low frequency vibrations, this paper proposes an asymmetric bistable vibro-impact dielectric elastomer generator (ABVI DEG), which mainly consists of a vibro-impact (VI) DEG, two identical pre-compressed springs, two pairs of undeformed springs, and a base. Two kinds of dynamics models of the proposed energy harvester under ultra-low frequency harmonic excitations are developed, and the instantaneous impact model is selected due to its computational efficiency and accuracy. The instantaneous impact model is extended by a series of impact experiments and validated by comparing the dynamical responses of the proposed energy harvester obtained from the two kinds of dynamics models. On this basis, the dynamical behavior and the energy harvesting (EH) performance of the proposed energy harvester under ultra-low frequency harmonic excitations are studied for the initial conditions of the system, different bistable potential wells, and various parameters, which include the pre-stretched ratio of the membranes and the distance between the two membranes. A further comparative study demonstrates the superiority of the proposed energy harvester under the ultra-low frequency harmonic excitation. This work not only provides an insight into dynamical behavior of the proposed ABVI DEG, but helps guide the design and optimization of the proposed EH system in the ultra-low frequency vibration environment.

On high-performance rotational energy harvesting with a novel cam-like dielectric elastomer generator

On high-performance rotational energy harvesting with a novel cam-like dielectric elastomer generator

A dielectric elastomer and electret hybrid ocean wave power generator with oscillating water column

Dielectric elastomer generator (DEG) is promising ocean wave energy harvesting technology with high reliability and low cost. This paper proposes an innovative oscillating water column wave energy harvester based on dielectric elastomer(DE), equipped with a bipolar free-standing electret rotary generator(B-FEG) which concurrently provides the bias voltage for the DEG. The novel idea is to exploit the pressure and airflow generated by the motion of the oscillating water column to inflate the DE-film in each wave period and synchronously rotate the ingenious B-FEG continuously. This hybridized energy harvesting technology is conceived to allow the DEGs to generate electricity from ocean waves without conventional bias-voltage supply. A theoretical model is derived to characterize the output performance of the proposed wave energy harvester and further verified by the finite element simulation. The output energy of the DEGs and B-FEG is then estimated theoretically and verified experimentally. The experimental results show that the B-FEG is capable of producing a bias voltage for DEGs. The proposed hybrid electric power of wave energy harvesters popularizes the DEG more conveniently by utilizing the bias voltage of B-FEG.

High Energy Harvesting Performances Silicone Elastomer via Filling Soft Dielectric with Stretching Deformability.

Dielectric elastomer generators (DEGs) with high generated energy density and high conversion efficiency are of great interest. Among several dielectric elastomers (DEs), silicone elastomer filled with ceramic fillers have been extensively studied for their high elasticity, insulation and permittivity. However, the stretched breakdown strength (Ebs ) of such composites decreases significantly under large strain, thus sharply reduces its energy harvesting performances. In this study, a polar rubber-based dielectric (GNBR) is synthetized and creatively used as "soft filler" for silicone elastomer. Benefiting from the deformability under stretching and its inherent strong interface bonding with silicone elastomer, this soft filler effectively avoids the formation of weak interface under large strain and reduces the local field strength of interface area. As expected, the composite filled with soft filler (GNBR/PMVS) shows enhanced Ebs of 2.8 times that of composite with traditional hard filler (TiO2 /PMVS) under equibiaxial strain of 200%. As a result, GNBR/PMVS composite exhibits maximum energy density of 130.5 mJ/g with up-to-date highest power conversion efficiency of reported DEG (44.5%). The findings will provide new insights in the rational design of DE composites characterized by high stretched breakdown strength for advanced energy harvesting system. This article is protected by copyright. All rights reserved.

Fatigue-resistant high-performance dielectric elastomer generator in alternating current method

Dielectric elastomer generator (DEG) is a solid-state electrostatic device with variable capacitance. As an energy harvester, it should be passive, high performance, and fatigue-resistant. However, no such DEGs can satisfy these requirements simultaneously as the high performance strongly depends on a high external voltage and large capacitance change, which are prone to dielectric elastomer film fatigue and failure. In this study, we developed a passive alternating current dielectric elastomer generator (AC-DEG) to reconcile the contradiction and satisfy these requirements. Based on the AC method, a high performance by structural parameters could be obtained with a small capacitance change, which avoids the large capacitance change, and consequently, fatigue and failure. The AC-DEG exhibits energy density of 111 mJ/g with an energy conversion efficiency of 51.8% and charge density of 5.6 mC/m2 per cycle at 1.5 Hz with only a two-fold capacitance change. Furthermore, the AC-DEG can maintain over 100 mJ/g and 4.6 mC/m2 per cycle in a continuous operation for over 7 days (> 1 million cycles) at 1.5 Hz. We developed an integrated device with two AC-DEGs to charge commercial Li-polymer batteries with different capacities. This study provides an effective route for development of DEGs toward practical applications and industrialization.

Numerical investigation on a bistable vibro-impact dielectric elastomer generator mounted on a vibrating structure with ultra-low natural frequency

Numerical investigation on a bistable vibro-impact dielectric elastomer generator mounted on a vibrating structure with ultra-low natural frequency

Multi-Objective Model-Predictive Control for Dielectric Elastomer Wave Harvesters

This contribution deals with multi-objective model-predictive control (MPC) of a wave energy converter (WEC) device concept, which can harvest energy from sea waves using a dielectric elastomer generator (DEG) power take-off system. We aim to maximise the extracted energy through control while minimising the accumulated damage to the DEG. With reference to system operation in stochastic waves, we first generate ground truth solutions by solving an optimal control problem, comparing it to the performance of MPC to determine a prediction horizon that trades off accuracy and efficiency for computation. Fixed weights in the MPC scheme can produce unpredictable costs for variable sea conditions, meaning the average rate of cost accumulation can vary vastly. To steer this cost growth, we propose a heuristic to adapt the algorithm by changing the weighting of the cost functions for fulfilling the long-time goal of accumulating a small enough damage in a fixed time. A simulated case-study is presented in order to evaluate the performance of the proposed MPC framework and the weight-adaptation algorithm. The proposed heuristic proves to be able to limit the amount of accumulated damage while improving the energy yield obtained with a comparable fixed-weight MPC.

Influence of charge leakage on energy density of dielectric elastomer generator with transversely restrained configuration

Influence of charge leakage on energy density of dielectric elastomer generator with transversely restrained configuration