Optimized deformation behavior of a dielectric elastomer generator

Dielectric elastomer generators (DEG) produce electrical energy by converting mechanical into electrical energy. Efficient operation requires homogeneous deformation of each single layer. However, by different internal and external influences like supports or the shape of a DEG the deformation will be inhomogeneous and hence negatively affect the amount of the generated electrical energy. Optimization of the deformation behavior leads to improved efficiency of the DEG and consequently to higher energy gain. In this work a numerical simulation model of a multilayer dielectric elastomer generator is developed using the FEM software ANSYS. The analyzed multilayer DEG consists of 49 active dielectric layers with layer thicknesses of 50 μm. The elastomer is silicone (PDMS) while the compliant electrodes are made of graphite powder. In the simulation the real material parameters of the PDMS and the graphite electrodes need to be included. Therefore, the mechanical and electrical material parameters of the PDMS are determined by experimental investigations of test samples while the electrode parameters are determined by numerical simulations of test samples. The numerical simulation of the DEG is carried out as coupled electro-mechanical simulation for the constant voltage energy harvesting cycle. Finally, the derived numerical simulation model is validated by comparison with analytical calculations and further simulated DEG configurations. The comparison of the determined results show good accordance with regard to the deformation of the DEG. Based on the validated model it is now possible to optimize the DEG layout for improved deformation behavior with further simulations.

As a new transduction technology, dielectric elastomer generators (DEGs) are capable of converting mechanical energy from diverse sources into electrical energy. However, their energy harvesting performance is strongly affected by the material viscoelasticity. Based on the finite-deformation viscoelasticity theory and the nonlinear coupled field theory for dielectric elastomers, this work presents a theoretical framework to model the performance of DEGs. Motivated by the recent experiments of DEGs with a triangular harvesting scheme, we propose a method to optimize the harvesting cycle, which could significantly improve the conversion efficiency of viscoelastic DEGs. From our simulation results, choosing a higher voltage power source appears to be an effective way to improve the performance of DEGs. In addition, optimizing the period of the discharging process of DEG can markedly increase its efficiency. Also, we have uncovered that the triangular harvesting scheme for DEGs, which is expected to harvest energy close to the maximum achievable energy, could be actually realized by choosing dielectric elastomers with a higher fraction of time-independent polymer networks. The theoretical framework and simulation results presented in this work are expected to benefit the optimal design of DEGs for different applications.

In this letter, a theoretical framework describing an energy harvesting cycle including the loss of tension (LT) process is proposed to investigate the energy harvesting performance of a dielectric elastomer generator (DEG) with a triangular energy harvesting scheme by considering material viscosity and leakage current. As the external force that is applied to the membrane decreases, the membrane is relaxed. When the external force decreases to zero, the condition is known as LT. Then the membrane undergoing LT can further relax, which is referred to as the LT process. The LT process is usually ignored in theoretical analysis but observed from energy harvesting experiments of DEGs. It is also studied how shrinking time and transfer capacitor affect the energy conversion of a DEG. The results indicate that energy density and conversion efficiency can be simultaneously improved by choosing appropriate shrinking time and transfer capacitor to optimize the energy harvesting cycle. The results and methods are expected to provide guidelines for the optimal design and assessment of DEGs.

Modelling and field testing of a breakwater-integrated U-OWC wave energy converter with dielectric elastomer generator

Dielectric Elastomer Generator(s) (DEG) have many unique properties that give them advantages over conventional electromagnetic generators. These include the ability to effectively generate power from slow and irregular motions, low cost, relatively large energy density, and a soft and flexible nature. For DEG to generate usable electrical energy circuits for charging (or priming) the stretched DEG and regulating the generated energy when relaxed are required. Most prior art has focused on the priming challenge, and there is currently very little work into developing circuits that address design issues for extracting the electrical energy and converting it into a usable form such as low DC voltages (~10 V) for small batteries or AC mains voltage (~100 V). This paper provides a brief introduction to the problems of regulating the energy generated by DEG. A buck converter and a charge pump are common DC-DC step-down circuits and are used as case studies to explore the design issues inherent in converting the high voltage energy into a form suitable for charging a battery. Buck converters are efficient and reliable but also heavy and bulky, making them suitable for large scale power generation. The smaller and simpler charge pump, though a less effective energy harvester, is better for small and discrete power generation. Future development in miniature DE fabrication is expected to reduce the high operational voltages, simplifying the design of these circuits.

A dielectric elastomer generator (DEG) can be used for converting mechanical energy from natural motion sources, such as walking, waves, trees, etc., into electrical energy. A DEG is comprised of a soft and flexible dielectric elastomer (DE) capacitor, a priming circuit (PC), which transfers high potential charge onto/off the DE electrodes, and a power extraction circuit that harvests the generated power. To generate power, the PC must charge and discharge the DE in synchronization with the DE's capacitance change. A simple circuit to do this exists: the self-priming circuit (SPC). The SPC consists of diodes and capacitors that passively switch between charge delivery and charge receiving states in synchronization with the DE's capacitance change. Until now, there has been no understanding of how to design an SPC in order to maximize harvested energy from the DE. A new mathematical model for an SPC is presented, leading to design and optimization. An accuracy of 0.1% between model, simulation, and experiment over five cycles is obtained, once losses are taken into consideration. The behavior of the SPC is shown to be related to the maximum and minimum capacitances of the DE, but is unaffected by the exact shape of the capacitance waveform.

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.

Dielectric elastomer(DE) could be used in generator design and fabrication, which has been verified by experiments. The function principle of DE generator is contrary to that of DE actuator. By imposing a low voltage to the dielectric elastomer membrane, electric charges are accumulated on the two surfaces. Then we apply mechanical force to the sides of the membrane to produce pre-stretch, and the thickness of the membrane becomes thinner and the capacitance increases, where mechanical energy is converted to elastic energy. After the mechanical force being withdrawn, because of elasticity, the thickness of membrane increases while the capacitance decreases, and elastic energy is converted to electrical energy. This is a work cycle of conversion from elastic to electric energy. Researchers have always been expecting to find a model that can well predict and evaluate the performance of dielectric elastomer generator. Suo et al. proposed the typical failure model of neo-Hooken type dielectric elastomer generator and calculates the maximal energy converted in a mechanical and electrical cycle. In this paper, we demonstrate the area of allowable states of various Mooney-Rivlin type dielectric elastomer generators, which can be employed to direct the design and fabrication of Mooney-Rivlin silicone generator, and the results coincide with Suo's theory.

Energy harvesting from a novel contact-type dielectric elastomer generator

Among the main issues with the implementation of Dielectric Elastomer Generators (DEGs) is the need for pre-charging to perform mechanical-to-electrical energy conversion. In cases when energy harvesting has to be performed in an environment with unpredictable characteristics (e.g., wind, waves, human walking), defining the best times for charge injection and energy extraction in a cycle is a non-trivial problem. In this paper, we present a novel Self-Sensing with Peak Detection (SSPD) method to control the charges on the material using capacitive self-sensing techniques, which defines an optimal cycle and requires no knowledge of the mechanical excitation amplitude or frequency. The effectiveness of the approach is proved by means of numerical simulations based on an highly accurate model of the DEG device.

Dielectric elastomers offer several advantages such as low cost, high efficiency, high output, large deformations, light weight, and ease of stacking. Recently, it has become possible to lift a weight of 8 kg by more than 1 mm at a speed of 88 ms using 0.15 g of a dielectric elastomer. Additionally, transparent or nearly transparent electrodes can be fabricated using carbon nanotubes or carbon black, respectively. Through leveraging these properties, researchers are exploring applications such as transparent lenses and high-performance transparent speakers, with the ultimate aim of integrating this technology into portable devices like digital cameras, video cameras, and mobile phones. New potential applications being considered include transparent power-assist devices, wearable generators, wind power generators, and wave power generators. Transparency allows these devices to blend into their surroundings, whilst not being obtrusive to observers and the environment. In this study, we review elastomer and electrode materials aimed at improving the performance of dielectric elastomer actuators, sensors, and generators. We also discuss challenges related to transparent electrodes and propose potential solutions. Based on these results, potential applications are also discussed.

Paper 764211

This paper developed a theoretical model substantially based on the principle that only the normal component of solar radiation is actually converted into electrical energy. This theoretical model helped to predict minimum and maximum daily energy gain (compared to static PV system tilted with certain angle) when using dual axis PV solar tracking systems, at any given location on earth without prior experimental data. Based on equations derived from model, minimum and maximum energy gain is computed and summarized in tables of minimum and maximum. Furthermore, the model equations could be used to set up future experimental studies related to the matter.

Herein, we report hybrid fibrous artificial muscles with reversible actuation, i.e., expansion upon cooling and contraction upon heating, under external compression. Although many fibrous polymeric artificial muscles by twist insertion in precursor fibers have been developed, most of them cannot reversibly actuate without an external tensile load. While heterochiral Nylon muscles can reversibly actuate under external compressive load, the compressive stress applied is low (0.078 MPa). In this study, we inserted pre-tensioned polymeric fibers with reversible actuation into pre-compressed helical metallic spring and obtained hybrid fibrous artificial muscles. We employed two types of two-way shape memory polymers, one type of fishing line artificial muscle, and seven types of helical springs in preparing seven types of hybrid muscles. A structural mechanics model was developed, and numerical simulation was conducted to evaluate the effect of the design parameters on the actuation strain. It is found that all the hybrid muscles were free-standing (reversibly actuate without external load) and beyond free-standing (reversibly actuate under external compression load). As an example, one hybrid muscle actuated reversibly under 24 MPa compressive stress without buckling. We expect that this study will open new opportunities for the use of fibrous artificial muscles as linear actuators in soft robotics or other applications that need reversible actuation under external compression.

Summary form only given. Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery. This is a new initiative in today's energy research for mico/nano-systems in searching for sustainable self-sufficient power sources. It is essential to explore innovative nanotechnologies for converting mechanical energy, vibration energy, and hydraulic energy into electric energy that will be used to power nanodevices. We have invented an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire arrays. The operation mechanism of the nanogenerator relies on the piezoelectric potential created by an external strain; a dynamic straining of the nanowire results in a transient flow of the electrons in the external load due to the driving force of the piezopotential. We have developed the nanogenerator from fundamental science, to engineering integration and to technological scale-up. As today, a gentle straining can output 1.2 V from an integrated nanogenerator, using which a self-powered nanosensor has been demonstrated. A commercial LED has been lid up. This is a key step for developing a totally nanowire-based nanosystem. Alternatively, by substituting the gate voltage in a field effect transistor (FET) with the piezopotential creating by an external strain, we have fabricated a series of devices that rely on a coupling between semiconductor and piezoelectric properties and are controlled/tuned by externally applied force/pressure, such as diode, strain sensor and strain-gated logic unites, which are a new field called piezotronics. A three way coupling among piezoelectricity, semiconductor and photonic excitation has demonstrated the piezo-phototronic effect.