Dielectric Electroactive Polymer Research Articles

Sensing Capabilities Based on Dielectric Electro Active Polymers—Feasibility and Potential State-of-the-Art Application

This paper presents the work in the area of sensing, using smart materials, more specific dielectric electro active polymers (DEAPs). Sensing is one of the main trio-characteristics of DEAPs; the trio-formations as applicable uses are actuator, transducer, and finally sensor. It is noted that one of the main value propositions whenever DEAP material is used, is the dual characteristics as the sensing/actuating capability. In the following work, the DEAP membrane will be modeled and the relation among the key variables (pressure and capacitance) will be determined. Hence, such a relation depends on the geometrical shape of the used membrane. The development process is carried out to propose alternative solutions for the sensor design using the DEAP and the laminate material. Test methodology, pressure-based test rig, prototypes, and software are developed afterwards to evaluate the prototypes test pieces. In general, the DEAP material has proven to be a very good sensor for pressure taking the advantage of flexibility, wide range of operation, and finally the sensitivity. The theoretical model is benchmarked against the acquired data from the tests, whereby high correlation within an approximate range of 0-23 mmHg (1.7% mean error) has been observed showing a promising application for the DEAP material in pressure sensing in general, and demonstrating the feasibility for the conceptualization of the blood pressure sensing system based on DEAP material.

On the energy conversion and efficiency of a dielectric electroactive polymer generator

Dielectric electroactive polymers are studied for their energy generating ability based on a variable capacitance mechanism. Energy conversion for one cycle is analyzed by considering the energy loss in the charging process, where generated energy is defined as the difference between output and total input electrical energy. Experiments are conducted under two charging modes and different stretch rates to investigate their effect on the energy conversion. Energy conversion efficiency of up to 18.3% is achieved with charging-while-stretching mode and a low stretch rate, with an energy density of 18.9 mJ/g and power of 3.775 mW/g per cycle obtained.

Experimental investigation on energy conversion for dielectric electroactive polymer generator

Dielectric electroactive polymer shows considerable promise for harvesting energy from environmental sources such as wind, water current, and ocean waves. Based on the analysis of an energy conversion cycle, circular energy conversion unit is implemented to conduct experiment. Two main factors, namely, bias voltage and stretch displacement, are subsequently determined to investigate their effect on the generated energy and efficiency. Analytical results indicate that the generated energy and efficiency increase as the bias voltage and displacement increase in a certain range of bias voltage, while over high electrical field reduces electrical energy and efficiency due to charge leakage. Furthermore, the effect of stretch speed on transformed voltage is analyzed. Antagonistic connection of two same energy conversion units is investigated, which can boost the total efficiency to 20% because the retracting force of one energy conversion unit is used to stretch the other. To make full use of the input mechanical energy, a generator with multiple energy conversion units, which are deformed by slider–crank mechanisms, is analyzed. The torque needed to actuate generator with more than two energy conversion units is positive in the whole cycle, which means all the mechanical energy is converted to electrical energy. Moreover, fluctuation of torque becomes smaller as the number of energy conversion units increases.

Elastic Behaviour of DEAP Film in the Development of Actuators

Smart materials are used in many critical actuation systems for different applications and among them Dielectric Electroactive polymer (DEAP) material produce flexible actuators. These materials are anisotropic and hence knowledge on their mechanical properties becomes a critical factor when such materials are used to develop various smart actuators. Young's modulus is an important design parameter and DEAP has three different modulus values for the three directions. The change in the Young's modulus values is studied and presented in this work. The influence of geometrical parameter on the actuation behaviour of an actuator made of DEAP is also investigated. A few results obtained from scanning electron microscope, optical microscope and nano-indentation test are also presented. The analytical results are compared with experimental results and presented here and they agree with each other if the operating voltage is less than 1500V.

Energy conversion analysis and performance research on a cone-type dielectric electroactivepolymer generator

As a type of intelligent material, dielectric electroactive polymer (DEAP) has shownconsiderable promise for energy harvesting purposes as well as in actuator mode.Theoretical analysis on DEAP generators is important to guide the optimization anddesign of a DEAP generator. In this paper, firstly, four working phases of a DEAPgenerator and energy conversion between mechanical energy input and electrical energygenerated have been studied. Then, the model of a cone-type DEAP generator isestablished. On the basis of that, some key issues of a DEAP generator, such ascapacitance, force–displacement relationship, distribution of stress and stretch ratio in themembrane, have been achieved by solving the differential and algebraic equations. It isdemonstrated that the stretch displacement of a DEAP generator and bias voltage are themain factors influencing the amount of electrical energy generated and the efficiency ofenergy conversion. In addition, the failure rule of a DEAP generator has alsobeen discussed. Finally, the proposed model is proved by experimental results,which shows the model is reliable for analyzing the cone-type DEAP generator.

Wind Power Micro-Generator Using Dielectric Electric Active Polymer

Wind power is emerging as a particularly attractive form of renewable energy. Dielectric Electric Active Polymers (DEAP) has shown great potential as actuator materials. Their predomination has been shown to operate in transforming mechani­cal to electrical energy in a generator mode. This work investigates the principle of wind power dielectric electro active polymer generator, simulation and experimental verification of the phenomenon. Dielectric Electro Active Polymer have proved to provide electrical energy with density as high as 1.5J.g-1.This value is very important compared to the density available with piezoelectric polymer (0.3J.g-1). The prototype has been set up on the DEAP wind power generator in the article. It is a membrane with an area of 1.5 m2 and 30μm in thickness, which is fabricated by Danfoss PolyPower A/S using smart compliant electrode technology in conjunction with a silicone elastomer. In the last part of this article, experimental results are detailed with our prototype for wind application.

Modeling and experimental validation of a bi-stable out-of-plane DEAP actuatorsystem

This paper presents modeling and experimental validation of a small profile, scalableDEAP actuator system. The actuator system consists of a bi-stable mechanism (anegative-rate bias spring, or NBS) coupled with an out-of-plane dielectric electro-activepolymer (DEAP). The NBS biases the DEAP allowing actuation when the voltage is cycledand is shown to have a major impact on the overall system performance. Particularly incomparison with conventional linear springs, the NBS-biased actuator exhibits aconsiderably larger displacement stroke. A first order model of the NBS–DEAPcoupled system is developed based on minimization of the system’s potential energy.This approach allows for the determination of quasi-static force equilibria in thepresence of multiple stable positions. The model is validated with experimentaldata and provides insight into system trends and related parameter optimization.

Experiment and Analysis of Dielectric EAP Electrical Model

Energy harvesting using Dielectric Electroactive Polymer (DEAP) is an interesting possibility to convert mechnical energy to electrical energy. The fundamental of generator mode of DEAP is first described, and then an equivalent RC electrical model for the DEAP generator is given. Based on the RC model, we analyze the relationship between the electrical model parameters and the influencing factors, and then get their theoretical formulas. In the experiment, the annular type DEAP generator unit is used. Using the discharging method, the experimental data about the electrical parameters influenced by the applied voltage and the axial displacement are obtained respectively. We modify the theoretical formulas based on the experimental data. The modified formuals can serve as a significant guide for energy conversion and generator design using dielectric elastomer.

Development of Dielectric Electroactive Polymer Actuator for Robotic Applications

This paper presents a compliant actuator based on Dielectric Electroactive Polymer (DEAP) technology. The presented advanced robotics concept requires smart materials, mostly in the form of actuators, for the development of biomimetic and flexible robotic systems. Smart materials such as Shape Memory Alloys (SMAs) and Electroactive Polymers (EAPs) are promising candidates for developing Bio-inspired smart robots without using conventional rigid links and joints. However, a major issue with SMAs is their slow response and limited bandwidth. The actuator made of DEAP is composed of a pre-stretched silicon film sputtered with very thin silver electrodes on both sides so as to form a smart capacitor as explained in patent [1, 20]. When an electric field is applied across the capacitor, the silicon film, which is of highly deformable dielectric medium, strains in the direction of application of voltage due to electrostatic pressure. Hence, thickness of the capacitor reduces that leads to corresponding enlargement of area in the other two directions. Different varieties of DEAP actuator models have been studied by various researchers for large displacement, precision motion and for associated control difficulties. Some of the applications are given in patent [23-28]. The experimental results obtained show that a suitable nonlinear control algorithm is required for obtaining accurate results. The suitability of DEAP actuator towards development of a spatial compliant mechanism is discussed and presented here. Keywords: DEAP actuator, electrostatic pressure, shape memory alloy, smart materials, spatial compliant mechanism, EAP material, Actuation Process, electrode, voltage

Spray deposited multilayered dielectric elastomer actuators

Dielectric elastomer electroactive polymers are an emerging class of actuation technology which is inherently compliant and capable of large actuation stresses and strains. Despite promising performance characteristics, their fabrication has been inhibited by two significant factors: (i) the requirement for consistently thin dielectric layers, to minimise activation voltages; (ii) automated production of multilayered configurations, to increase the actuation power. This paper presents a robust, low-cost fabrication technique that overcomes these issues by utilising optimised spray deposition. Spray deposition of silicone dielectric elastomer actuators (DEAs) offers numerous benefits including scalability, flexibility for different DEA configurations and multilayered assembly with a high degree of automation. A predictive model based on the Gaussian distribution is used to characterise the profile of deposited elastomer layers for principal fabrication parameters. This model enables individual dielectric layers to be composed from multiple parallel depositions, which greatly increases scalability as demonstrated by fabricated DEA films with planar dimensions from 25 mm 2 to over 10,000 mm 2. Using the predictive model, a new figure of merit is introduced for analyzing DEA film profiles by considering the estimated mean Maxwell stress that is feasible for a specific dielectric breakdown strength. The analysis suggests that compared to a single deposition, a film composed of four parallel depositions will increase the maximum characteristic DEA dimension by an order of magnitude, while producing a comparable mean Maxwell stress. A significant advantage of the presented spray deposition technique is the semi-automated layering process, creating stratified solid-state actuators. By eliminating the stacking of layers from the fabrication process, inherent electrical isolation, good layer-to-layer bonding and capacity for more complex 3D geometries is achieved. A proof-of-concept multilayer unimorph and stack DEA is presented to validate the fabrication technique through static and dynamic displacement tests.

Active Vibration Isolation Using a Dielectric Electro-Active Polymer Actuator

Dielectric Electro-Active Polymer (DEAP) devices consist of a dielectric polymer sandwiched between two electrodes. This paper describes the use of a tubular DEAP actuator for active vibration isolation. First, the quasi-static and dynamic characteristics of the actuator are discussed. These involve the voltage-strain-force behaviour of the actuator. It is seen that the actuator is inherently non-linear, involving an approximately quadratic relationship between excitation and extension under given loading conditions. In a control context, this can be compensated for either by driving the actuator about some d.c. off-set excitation in a quasi-linear manner, or by including a linearization component within the control. Next, issues concerning the frequency response over a wide range of frequency are considered. Internal resonances exist in the actuator, which limit the bandwidth over which it can be used for active control. The actuator has significant internal damping. The potential for active vibration isolation is then explored. The dynamic performance is limited by the potential bandwidth, the maximum force that can be generated and the maximum range of movement, together with the inherent nonlinearity. Performance for harmonic disturbances is investigated within an adaptive feedforward control scheme. Experimental results are presented. Good attenuation of the excitation frequency is achieved but compensation is required to get good attenuation of higher harmonics introduced by the actuator nonlinearity. Isolation in response to a band-limited random input is then demonstrated, with attenuation of 19dB being achieved over a frequency range from 2-8 Hz.

Experimental characterization of the hysteretic and rate-dependent electromechanicalbehavior of dielectric electro-active polymer actuators

Dielectric electro-active polymers (DEAPs) can achieve substantial deformation (>300% strain) while sustaining, compared to their ionic counterparts, large forces. This makesthem attractive for various actuation and sensing applications such as in lightweight and energy efficient valve and pumping systems. Many applications operateDEAP actuators at higher frequencies where rate-dependent effects influencetheir performance. This motivates the seeking of dynamic characterization ofthese actuators beyond the quasi-static regime. This paper provides a systematicexperimental investigation of the quasi-static and dynamic electromechanicalproperties of a DEAP actuator. In order to completely characterize the fully coupledbehavior, force versus displacement measurements at various constant voltages andforce versus voltage measurements at various fixed displacements are conducted.The experiments are conducted with a particular focus on the hysteretic andrate-dependent material behavior. These experiments provide insight into theelectrical dynamics and viscoelastic relaxation inherent in DEAP actuators. Thisstudy is intended to provide information, including high frequency performanceanalysis, useful to anyone designing dynamic actuator systems using DEAPs.

Dielectric electroactive polymer applications in buildings

The use of smart materials in buildings is investigated. In particular, a new category of smart materials, called dielectric electroactive polymers (DEAPs), is discussed. DEAPs are materials whose shape and stiffness can be changed by electric stimulus. These properties led the author to investigate the potential application of DEAPs in buildings. DEAPs are produced by covering a soft polymer with dielectrics on both sides. The properties of DEAPs are described to illustrate the differences between these and other smart materials. A description of the electric behaviour of the material is also presented. Applications of DEAPs in heating, ventilation and air-conditioning systems, to control air or water motion, are additionally considered. Applications in large flexible structures such as building envelopes are described. As DEAPs can be laminated easily and they have great power density, they can be used in the management systems of facades, to control transparency or ventilation of the building envelopes. Finally, vibration isolation possibilities and building monitoring purposes are discussed. The state-of-the-art of DEAP science is reviewed and possible applications in buildings are described.

Preliminary investigation of a balloon-shape actuator based on electroactive elastomers

This paper presents a novel actuator which has spherical shape and is potentiallysuitable to display large deformations under high compression loads. Dielectricelectroactive polymers are used as the actuation elements of the proposed system.The materials used and the simplified manual manufacturing procedure thatwas implemented are presented and analysed in this note. Tests performed tocharacterize the force–displacement relationship are described and results arediscussed.

Stacked dielectric elastomer actuator for tensile force transmission

This paper presents a novel approach for active structures driven by soft dielectric electro-active polymers (EAPs), which can perform contractive displacements at external tensile load. The active structure is composed of an array of equal segments, where the dielectric films are arranged in a pile-up configuration. The proposed active structure has the capability of exhibiting uniaxial contractive deformations, while being exposed to external tensile forces. The serial arrangement of active segments has one contracting degree of freedom in the thickness direction of the dielectric EAP film layers. Due to the envisaged tension force transmission capability, special attention is paid to the electrode design which is of paramount importance with regard to functionality of the actuator. A compliant electrode system with anisotropic deformation properties is presented based on nano scale carbon powder. In experiments, the free deformation as well as the contractive motion under external tensile loading of several actuator configurations with different setups is characterized. These involve the study of various sizes and numbers of stacked film layers as well as different electrode designs.

Ion-implanted compliant electrodes used in dielectric electroactive polymer actuators with large displacement

Metal ion implantation is shown here as an effective technique to fabricate highly compliant electrodes at room temperature on polymer substrates. By implanting 5 keV gold ions in polydimethylsiloxane we have fabricated micron-scale electrodes that conduct at 175% strain, have low surface resistance (< 1 kΩ/square) and negligible thickness (50 nm). These electrodes have been cycled over 105 times to 30% strain with minimal change in electrical characteristics, and find applications in flexible electronics, polymer sensors and actuators. Using these ion-implanted electrodes, we have fabricated arrays of mm-size dielectric electroactive polymer actuators capable of out-of-plane deflection up to 25% with excellent stability.

Concept design of novel bio-inspired distributed actuators for space applications

Space technology is often considered very conservative, since reliability and robustness are necessarily its main drivers. However, novel concepts coming from research activities are the lymph for the development of successful and competitive new space system solutions. The aim of this paper is to present new concepts and ideas inspired by natural systems with distributed actuators embedded in their structure for possible uses in space operations. Preliminary technical solutions for long-term future implementations are proposed and analyzed in order to assess both feasibility and performance of such novel concepts. Peristaltic movement obtained by using dielectric electroactive polymer actuators is proposed as one of the most promising solutions that is worth of future investigations. Preliminary experimental tests and numerical simulations on single actuation units are also presented and discussed.

Mechanical and actuation behavior of electroactive nanostructured polymers

Electroactive polymers (EAPs) can exhibit relatively large actuation strain responses upon electrical stimulation. For this reason, in conjunction with their light weight, robust properties, low cost and facile processability, EAPs are of considerable interest in the development of next-generation organic actuators. Within this class of materials, dielectric electroactive polymers (D-EAPs) have repeatedly exhibited the most promising and versatile properties. A new family of D-EAPs derived from swollen poly[styrene- b-(ethylene- co-butylene)- b-styrene] triblock copolymers has been recently found to undergo ultrahigh displacement at relatively low electric fields compared to previously reported D-EAPs. The present work examines the mechanical and actuation response of these electroactive nanostructured polymer (ENP) systems under quasi-static, and electromechanical loading conditions. Careful measurement of the quasi-static properties under tensile and compressive loading yield similar results that are significantly influenced by the introduction of in-plane strain, as well as by copolymer concentration or molecular weight. Blocking stress measurements reveal that the actuation effectiveness achieved by some of the ENPs is comparable to that of the VHB 4910 acrylic D-EAP, thus providing a novel and efficient avenue to designer D-EAPs for advanced engineering, biomimetic and biomedical applications.

Voltage Control of the Resonance Frequency of Dielectric Electroactive Polymer (DEAP) Membranes

We report on the characterization, active tuning, and modeling of the first mode resonance frequency of dielectric electroactive polymer (DEAP) membranes. Unlike other resonance frequency tuning techniques, the tuning procedure presented here requires no external actuators or variable elements. Compliant electrodes were sputtered or implanted on both sides of 20-35-mum-thick and 2-4-mm-diameter polydimethylsiloxane membranes. The electrostatic force from an applied voltage adds compressive stress to the membrane, effectively softening the device and reducing its resonance frequency, in principle to zero at the buckling threshold. A reduction in resonance frequency up to 77% (limited by dielectric breakdown) from the initial value of 1620 Hz was observed at 1800 V for ion-implanted membranes. Excellent agreement was found between our measurements and an analytical model we developed based on the Rayleigh-Ritz theory. This model is more accurate in the tensile domain than the existing model for thick plates applied to DEAPs. By varying the resonance frequency of the membranes (and, hence, their compliance), they can be used as frequency-tunable attenuators. The same technology could also allow the fine-tuning of the resonance frequencies in the megahertz range of devices made from much stiffer polymers.

Design and characterization of an actively deformable shell structure composed of interlinked active hinge segments driven by soft dielectric EAPs

Active shell structures with large out-of-plane displacement potential may be used to generate an interaction between the structural shape and the environment. Among the electroactive polymers (EAPs), in particular, the soft dielectric EAPs represent a promising technology to drive shell actuators due to their huge active strain potential and intrinsic compliance. This paper presents a shell actuator based on soft dielectric EAPs, which can actively take complex, single-curved shapes. The actuator is composed of seven interlinked active hinge segments, where the pre-strained dielectric films are arranged in an agonist–antagonist configuration. The soft dielectric EAP films, which act as an active skin, are thereby mounted to a hinged mechanical backbone structure. A computer-controlled system for the individual supply of the agonist–antagonist segments is proposed, where the DC high voltages provided by only one single HV amplifier is consecutively switched in a repeated loop to the active hinge segments. The experimental characterization included, on the one hand, the quasi-static full angular displacement potential of the shell actuator. Angles of displacement exceeding 90° back and forth at the free end of the actuator were observed. On the other hand, we examined the dynamic behaviour of the shell actuator under phase-shifted sinusoidal activation of the hinge segments. As expected, the actuator displayed an “organic” propagation of transversal displacement waves along its principal axis (similar to the swimming motion of fish).