Large strain analysis of a soft polymer electromechanical sensor coupled to an arterial segment

Dielectric elastomers have received a great deal of attention recently as potential materials for many new types of sensors, actuators and future energy generators. When subjected to high electric field, dielectric elastomer membrane sandwiched between compliant electrodes undergoes large deformation with a fast response speed. Moreover, dielectric elastomers have high specific energy density, toughness, flexibility and shape processability. Therefore, dielectric elastomer membranes have gained importance to be applied as micro pumps for microfluidics and biomedical applications. This work intends to extend the electromechanical performance analysis of inflated dielectric elastomer membranes to be applied as micro pumps. Mechanical burst test and cyclic tests were performed to investigate the mechanical breakdown and hysteresis loss of the dielectric membrane, respectively. Varying high electric field was applied on the inflated membrane under different static pressure to determine the electromechanical behavior and nonplanar actuation of the membrane. These tests were repeated for membranes with different pre-stretch values. Results show that pre-stretching improves the electromechanical performance of the inflated membrane. The present work will help to select suitable parameters for designing micro pumps using dielectric elastomer membrane. However this material lacks durability in operation.This issue also needs to be investigated further for realizing practical micro pumps.

Dielectric elastomers (DEs) represent a transduction technology with high potential in many application areas, including industry, due to their low weight, flexibility, and low energy consumption. For industrial applications, it is of fundamental importance to quantify the lifetime of DE technology, in terms of both electrical and mechanical fatigue, when operating in realistic environmental conditions. This work contributes toward this direction, by presenting the development of an experimental setup which allows systematic fatigue testing of DE membranes. The setup permits to apply both mechanical and electrical stimuli to several membranes simultaneously, while measuring at the same time their mechanical (force, displacement) and electrical response (capacitance, resistance). The setup allows to test up to 15 DE membranes at the same time. The setup can be placed in a climate chamber, in order to investigate the fatigue mechanisms at different environmental conditions, i.e. in terms of temperature and humidity. After describing the setup, first fatigue results are shown for several DE membranes loaded at different constant voltage values, and mechanically cycled for several hundred thousands of cycles.

Controlling wrinkles on the surface of a dielectric elastomer balloon

Dielectric elastomers (DEs) are polymeric multi-functional materials that can be used to develop lightweight electrostatic actuators. Among other, DEs allow developing coilfree loudspeakers, in which the acoustic diaphragm and the actuator are embedded into a single DE membrane, whose deformations are driven by electrostatic stresses.In this paper, we present a simulation analysis of a DE loudspeaker with the aim of highlighting the effect of relevant design parameters (namely, the DE membrane thickness, diameter, and geometric aspect ratio) on the acoustic response. For the sake of illustration, we make reference to a simple loudspeaker layout, which does not require any mechanical or pneumatic biasing elements, and only consists in a DE membrane pre-loaded off-plane. Based on a validated finite element multi-physics model of the system, we discuss how the system response (namely, eigenfrequencies and generated sound pressure level) varies with the design parameters. The presented results point out thresholds and trends that are relevant for the choice of DE loudspeakers’ design parameters.

Energy harvesting from a novel contact-type dielectric elastomer generator

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.

Electro-elastomers: Large deformation analysis of silicone membranes

Dielectric elastomers (Des) are a type of EAPs with unique electrical properties and mechanical properties: high actuation strains and stresses, fast response times, high efficiency, stability, reliability and durability. The excellent figures of merit possessed by dielectric elastomers make them the most performing materials which can be applied in many domains: biomimetics, aerospace, mechanics, medicals, etc. In this paper, we present a kind of electroactive polymer composites based on silicone Dielectric elastomers with a high dielectric constant. Novel high DEs could be realized by means of a composite approach. By filling an ordinary elastomer (e.g. silicone) with a component of functional ceramic filler having a greater dielectric permittivity, it is possible to obtain a resulting composite showing the fruitful combination of the matrix's advantageous elasticity and the filler's high permittivity. Here we add the ferroelectric relaxor ceramics (mainly BaTiO3) which has high dielectric constant (>3000) to the conventional silicone Dielectric elastomers, to get the dielectric elastomer which can exhibit high elastic energy densities induced by an electric field of about 15 MV/m. Tests of the physical and chemical properties of the dielectric elastomers are conducted, which verify our supposes and offer the experimental data supporting further researches.

Dielectric Elastomers (DEs) are a very promising technology for the development of energy harvesting devices based on the variable-capacitance electrostatic generator principle. As compared to other technologies, DE Generators (DEGs) are solid-state energy conversion systems which potentially feature: 1) large energy densities, 2) good energy conversion efficiency that is rather independent of cycle frequency, 3) easiness of manufacturing and assembling, 4) high shock resistance, 5) silent operation, 6) low cost. Envisioned applications for DEGs are in devices that convert ocean wave energy into usable electricity. This paper introduces the Lozenge-Shaped DEG (LS-DEG) that is a specific type of planar DE transducer with one degree of freedom. A LS-DEG consists of a planar DE membrane that is connected along its perimeter to the links of a parallelogram four-bar mechanism. As the mechanism is put into reciprocal motion, the DE membrane varies its capacitance that is then employed as a charge pump to convert external mechanical work into usable electricity. Specifically, this paper describes the functioning principle of LS-DEGs, and provides a comparison between different hyper-elastic models that can be used to predict the energy harvesting performances of realistic prototypes. Case studies are presented which address the constrained optimization of LS-DEGs subjected to failure criteria and practical design constraints.

The availability of compliant actuators is essential for the development of soft robotic systems. Dielectric elastomers (DEs) represent a class of smart actuators which has gained a significant popularity in soft robotics, due to their unique mix of large deformation (>100%), lightweight, fast response, and low cost. A DE consists of a thin elastomer membrane coated with flexible electrodes on both sides. When a high voltage is applied to the electrodes, the membrane undergoes a controllable mechanical deformation. In order to produce a significant actuation stroke, a DE membrane must be coupled with a mechanical biasing system. Commonly used spring-like bias elements, however, are generally made of rigid materials such as steel, and thus they do not meet the compliance requirements of soft robotic applications. To overcome this issue, in this paper we propose a novel type of compliant mechanism as biasing elements for DE actuators, namely a three-dimensional polymeric dome. When properly designed, such types of mechanisms exhibit a region of negative stiffness in their force-displacement behavior. This feature, in combination with the intrinsic softness of the polymeric material, ensures large actuation strokes as well as compliance compatibility with soft robots. After presenting the novel biasing concept, the overall soft actuator design, manufacturing, and assembly are discussed. Finally, experimental characterization is conducted, and the suitability for soft robotic applications is assessed.

Dielectric elastomers are soft, lightweight, and highly deformable electroactive polymers that undergo large deformations when subjected to mechanical and electrical loading. This unique property makes them promising candidates for applications in artificial muscles, soft robotics, biomedical actuators, and sensors. In this study, the large deformation behavior of a flat, circular dielectric elastomer membrane, clamped at the boundary, is investigated under the combined influence of lateral pressure and an applied electric potential across its thickness. The resulting model provides a framework for predicting deformation profiles and electromechanical stability limits in dielectric elastomer actuators.

Dielectric elastomer membrane(s) are smart material(s) that produce large actuation strains. They are also a class of electroactive polymers that function as actuators and sensors to convert and sense electrical signals to mechanical deformation and vice versa. Unique properties, such as flexibility, lightweight, and the ability to have an electrical field-induced deformation, make the dielectric elastomer membrane an ideal solution to the challenges faced by many applications, including the wings of unmanned aerial vehicles. This study aims to analyze the modal characteristics and aerodynamics of the dielectric elastomer membrane both computationally and experimentally. An electroactive membrane, VHB 4910, is considered the specimen, and the conductive material of carbon grease is used as an insulator on both surfaces of the membrane. Finite element models are developed to compute the resonance frequencies and mode shapes. The computational results of the modal analysis are validated using a closed-loop vibration testing experimental arrangement and digital image correlation system. Aerodynamic analyses are conducted using a wind-tunnel setup with a data acquisition system. A shape sensitivity study is also performed to see how five different shapes of a constant area affect the aerodynamics and vibrations of the membrane. The modal characteristics are controlled by adjusting the prestretch, true stress, and applied voltages. The natural frequencies decrease as the applied voltage increases. The aerodynamic coefficients increase with the angle of attack up to a particular range.

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.

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

Analytical Modeling of Clamped Dielectric Elastomer Strip Membranes Exhibiting Necking Effect