Dielectric Actuators Research Articles

Performance of PMMA-P nBA-PMMA dielectric film actuator with controllable phase morphology

Electromechanical responses were investigated for poly(methyl methacrylate)(PMMA) -b-poly( n-butyl acrylate)(P nBA)- b-poly(methyl methacrylate)(PMMA) films with cylindrical and lamellar morphologies, prepared with two casting solvents. Toluene and acetone were used as casting solvents because their solubility parameters are very similar to the solubility parameters of P nBA and PMMA, respectively. The mechanical responses of films revealed that when acetone was used as a casting solvent the film formed with PMMA as a continuous phase, and when toluene was used as a casting solvent, the film formed with P nBA continuous phase. Films were pre-strained right before actuation to increase actuation performance. The film with a P nBA continuous phase with cylindrical structure showed almost 12% strain, whereas the film forms with PMMA continuous phase showed almost 4% strain in an electric field with same magnitude. These results were consistent with the results of dielectric constant data. Moreover the film that formed a P nBA continuous phase started to actuate at a lower electric field strength, and showed rapid deformation with and without electric field, compared to film with PMMA continuous phase.

Lifetime investigation of dielectric elastomer stack actuators

The term electroactive polymers (EAP) represents a large class of materials which exhibit an electro-mechanical transduction. We shortly classify dielectric elastomer stack actuators (DESA) in the broad field of electroactive polymers. The scope of this paper relates to our first results on lifetime investigation on DESA. We describe the developed measurement setup, the data which is acquired and the way we finally identify lifetime out of the measurements. In a very rough number, regardless of electrical and mechanical driving conditions, dielectric elastomer stack actuators made of Elastosil P7670 (Wacker) can be driven for more than 320 million cycles. The subsequently arising degradation can be lead back to the interconnection. As this connection can be easily re-established even longer lifetimes are supposable with better interconnections.

Fabrication and Application of Miniaturized Dielectric Elastomer Stack Actuators

In dielectric elastomer stack actuators (DEAs), the driving voltage is reduced using thin dielectric layers. They are efficiently fabricated in an automated process. To produce thin dielectric films, uncured polydimethylsiloxane (PDMS) is spun to a thickness below 100 μm. After curing graphite, electrodes are sprayed on the PDMS surface and the next dielectric film can be applied on top. The main process steps are explained in detail. We show that the thickness variation within one layer is smaller than 4%. The electrodes are sprayed to have a sheet resistance of 10 kΩ/sq. The technology presented here is able to produce DEAs with layer thicknesses down to 5 μm. Hence, it is possible to design and fabricate actuators, which are driven only at 150 V. Arrays of small actuators with a resolution of 1 mm can be produced as well as single actuator elements with a diameter up to 40 mm. Finally, the potential of this technology is demonstrated by two examples varying highly in their application. The first application is a vibrotactile display. It generates a perceptive vibration of 125 Hz at a driving voltage of 600 V. The second application is a peristaltic pump with a maximum flow rate of 12 μL/min.

S055032 DBDプラズマアクチュエータにおいてバースト周波数がもたらす剥離制御の実験的解析([S05503]流れの抵抗低減(3))

The dielectric barrier electric discharge plasma actuator is expected as a new technology which can make the design of an aerofoil etc. unnecessary. The boundary layer control might be able to be performed by induced velocity in the boundary layer as an effect of the dielectric substance barrier electrical discharge plasma actuator. Moreover, it also turns out that the control effectiveness increases by repeating ON and OFF of the applied voltage, which is called burst. In this study, separation control on an airfoil by a plasma actuator was performed, and its control effectiveness was evaluated. This paper showed the effective mechanism of burst control by PIV.

Elastic block copolymer nanocomposites with controlled interfacial interactions for artificial muscles with direct voltage control

Soft, physically crosslinking, block copolymer elastomers were filled with surface-treated nanoparticles, in order to evaluate the possibility for improvement of their properties when used as soft dielectric actuators. The nanoparticles led to improvements in dielectric properties, however they also reinforced the elastomer matrix. Comparing dielectric spectra of composites with untreated and surface-treated particles showed a measurable influence of the surface on the dielectric loss behaviour for high filler amounts, strongly indicating an improved host–guest interaction for the surface-treated particles. Breakdown strength was measured using a test bench and was found to be in good agreement with the results from the actuation measurements. Actuation responses predicted by a model for prestrained actuators agreed well with measurements up to a filler amount of 20%vol. Strong improvements in actuation behaviour were observed, with an optimum near 15%volnanoparticles, corresponding to a reduction in electrical field of 27% for identical actuation strains. The use of physically crosslinking elastomer ensured the mechanical properties of the matrix elastomer were unchanged by nanoparticles effecting the crosslinking reaction, contrary to similar experiments performed with chemically crosslinking elastomers. This allows for a firm conclusion about the positive effects of surface-treated nanoparticles on actuation behavior.

Influence of Prestrain on Output Characteristic of Dielectric Elastomer Film Actuators

Prestrain affects the performance of dielectric elastomer actuators so much that rare actuators is used before pre-stretching. In this article, the author made a series of circular actuators with acrylic VHB4910 and graphite mixture electrodes, and performed contrast experiments, under non-prestrain, uniaxial prestrain and equibiaxial prestrain, respectively, to figure out the changing of area strain against prestrain. Result of experiment indicates that the film actuator obtains the highest output strain while applying equibiaxial prestrain. An optimum prestrain ratio of actuators, in this research, occurs between 150%~200% under equibiaxial prestrain condition. This result has practical value in the future design and use of dielectric elastomer actuators.

The mechanism of plasma shock flow control for enhancing flow sepa-ration control capability

Since the induced flow velocity and flow separation control capability by dielectric barrier discharge plasma aerodynamic actuation are difficult to be raised remarkably, some new way must be adopted to improve the plasma aerodynamic actuation’s capability for flow separation control. This paper put forwards a new concept of “plasma-shock-based flow control”, including shock actuation, vortex control and frequency coupling. Through theoretical, experimental and simulational researches, the mechanism of plasma shock aerodynamic actuation and using such actuation to improve flow separation control capability are investigated. The effectiveness of “plasma-shock-based flow control” was validated at the freestream velocity of 100 m/s.

Large deformation and electromechanical instability of a dielectric elastomer tube actuator

This paper theoretically analyzes a dielectric elastomer tube actuator (DETA). Subject to a voltage difference between the inner and outer surfaces, the actuator reduces in thickness and expands in length, so that the same voltage will induce an even higher electric field. This positive feedback may cause the actuator to thin down drastically, resulting in electrical breakdown. We obtain an analytical solution of the actuator undergoing finite deformation when the elastomer obeys the neo-Hookean model. The critical strain of actuation is calculated in terms of various parameters of design. We also discuss the effect of the strain-stiffening on electromechanical behavior of DETAs by using the model of freely joined links.

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.

Cathode-sheath driven low-speed aerodynamic flow actuation using direct-current surface glow discharges

Flow actuation by a continuous/pulsed, direct-current (DC) surface glow discharge is explored. The discharge comprises an array of pin electrode pairs flush mounted on a dielectric actuator surface that lies adjacent to stagnant air. Strong electrostatic fields produced in the cathode sheath region of the discharge provides a motive force on the ions which in turn drag the background gas resulting in directed air flow from the anode to the cathode. The induced flow velocity is estimated by particle image velocimetry (PIV) at 10 Hz with TiO 2 seeding. For a pulsed DC discharge with peak power of 5 W per electrode pair, the induced flow velocity reaches peak values of about 1.7 m/s which is comparable to dielectric-barrier discharge (DBD) or corona discharge actuators. The actuation effect quantified by the magnitude of induced velocity increases as the pulse frequency increases from 0 to 1 kHz. The actuation effect decreases for further increase in frequency above 1 kHz. Decreased actuation effect at high frequency is accompanied by structural change in the discharge. At fixed frequency of 1 kHz, flow actuation effect is highest for a square wave pulse with a duty cycle of 50% indicating that pulsed DC discharges produces better actuation than continuous DC with a corresponding reduction in energy consumption.

Tunable two-dimensional photonic crystal couplers made of dielectric elastomer inclusions

We propose a tunable directional coupler based on a two-dimensional photonic crystal made of dielectric elastomer rods embedded in air background. In the interaction region, the inclusions are a dielectric elastomer cylindrical actuator made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between the compliant electrodes, the radial strain of the silicon-made actuator and the coupling characteristics of the photonic crystal coupler are investigated. The coupling length of the photonic crystal coupler depends on the voltage applied between the electrodes, which is analyzed by the plane wave expansion method. Due to the radial strain of the dielectric elastomer under external voltage, the tunable photonic crystal coupler is realized. Numerical simulations obtained by the finite-difference time-domain method confirmed the feasibility of the tunable photonic crystal coupler.

Modeling the Kelvin polarization force actuation of micro- and nanomechanical systems

Polarization forces have become of high interest in micro- and nanomechanical systems. In this paper, an analytical model for a transduction scheme based on the Kelvin polarization force is presented. A dielectric beam is actuated by placing it over the gap of two coplanar electrodes. Finite element method simulations are used to characterize the scheme and to evaluate a field correction factor, which results from simplifying the form of the electric field. The model has been shown to be valid for dielectrics with different permittivities. The presented model facilitates the design of microresonators and nanoresonators with dielectric actuation, which offers a great freedom in the choice of structural material.

Dielectric electro‐active polymer push actuators: performance and challenges

AbstractProgress in research and development in the field of electro‐active polymers has enabled prototype fabrication, which demonstrates the future potential and versatility offered by this technology. These prototypes can be qualified as laboratory demonstrators. A new design of dielectric elastomer linear actuators is presented here. These actuators have the unique properties of being self‐supporting and core‐free. They are capable of large push forces and are fabricated based on large‐scale industrial manufacturing processes. Actuators can be easily scaled to fit specific application needs. Actuator design and construction principles, as well as modelling are presented and discussed for push InLastor® actuators. The actuators exhibit modest strokes and high actuation forces. Current design considerations indicate that the achievable force output is reduced by about 40% due to the passive ends of the actuator. Dielectric electro‐active polymer DEAP film manufacturing challenges contribute to reducing the achievable breakdown strength to 35 V µm−1 and limit the strain to modest figures. It is shown that push InLastor actuators can be operated at field strength levels above 45 V µm−1, and exhibit larger strokes and forces in good agreement with the model. At these elevated electric field levels, risks of catastrophic breakdown increase, resulting in reduced actuator lifetime. A major milestone in the manufacturing of actuators based on the DEAP technology has been achieved by Danfoss PolyPower. Large‐scale manufacturing of robust and reliable push tubular actuators is possible. Roll‐to‐roll manufacturing processes make it possible to manufacture these powerful actuators, based on PolyPower compliant electrode design. Copyright © 2010 Society of Chemical Industry

Experimental Investigation into Characteristics of Plasma Aerodynamic Actuation Generated by Dielectric Barrier Discharge

This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation. The rotational and vibrational temperatures of an N2(C3IIu) molecule are measured in terms of the optical emission spectra from the N2 second positive system. A simplified collision-radiation model for N2(C) and N2+ (B) is established on the basis of the ratio of emission intensity at 391.4 nm to that at 380.5 nm and the ratio of emission intensity at 371.1 nm to that at 380.5 nm for calculating temporal and spatial averaged electron temperatures and densities. Under one atmosphere pressure, the electron temperature and density are on the order of 1. 6 eV and 1011 cm−3 respectively. The body force induced by the plasma aerodynamic actuation is on the order of tens of mN while the induced flow velocity is around 1. 3 m/s. Starting vortex is firstly induced by the actuation; then it develops into a near-wall jet, about 70 mm downstream of the actuator. Unsteady plasma aerodynamic actuation might stimulate more vortexes in the flow field. The induced flow direction by nanosecond discharge plasma aerodynamic actuation is not parallel, but vertical to the dielectric layer surface.

S0502-3-6 DBDプラズマアクチュエータにおける駆動周波数が翼剥離制御に与える影響([S0502-3]噴流,後流および剥離流れ現象の解明と制御(3))

The dielectric barrier electric discharge plasma actuator is expected as a new technology which can make the design of an aerofoil etc. unnecessary. The boundary layer control might be able to be performed by induced velocity in the boundary layer as an effect of the dielectric substance barrier electrical discharge plasma actuator. Moreover, it also turns out that the control effectiveness increases by repeating ON and OFF of the applied voltage, which is called burst. But, the control mechanism is unknown. In this study, separation control on an airfoil by a plasma actuator was performed, and its control effectiveness was evaluated. The result showed a possibility to change the control effectiveness with the burst frequency mainly.

Optimal Design of Lozenge-shaped Dielectric Elastomer Linear Actuators: Mathematical Procedure and Experimental Validation

A novel mathematical procedure is presented, which makes it possible to optimize lozenge-shaped dielectric-elastomer-based linear actuators for known materials and desired force/stroke requirements. Simulation and experimental results are provided which both demonstrate the efficacy of the proposed optimization procedure with respect to traditional design approaches and show that simpler, cheaper, lighter, and better-behaved lozenge-shaped actuators can be conceived, which do not require any integration of compliant frame elements.

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.

Dielectric elastomer film actuators: characterization, experiment and analysis**This article was originally submitted for the special section ‘Smart Composite Materials:Selected Papers from the International Conference on Multifunctional Materials andStructures (MFMS 08) (Hong Kong, 28–31 July 2008)’, Smart Materials and Structures,volume 18, issue 7.

Silicone is a common dielectric elastomer material. Actuators made from it show excellentactivation properties including large strains (up to 380%), high energy densities (up to3.4 J g−1), high efficiency, high responsive speed, good reliability and durability, etc. When a voltageis applied on the compliant electrodes of the dielectric elastomers, the polymer shrinksalong the electric field and expands in the transverse plane. In this paper, a siliconedielectric elastomer is synthesized and the area strains are tested under different electricfields. Pre-strain and a certain driving electric field are applied to the film andthe induced large strain by the Maxwell stress is measured. Barium titanate (BaTiO3) was incorporated into the silicone to fabricate a new dielectric elastomer: theexperimental results show that the elastic modulus and dielectric constant weresignificantly improved. The experimental results coincide well with those of finite elementanalysis at a large deformation. Also, a theoretical analysis is performed on the couplingeffects of the mechanical and electric fields. A nonlinear field theory of deformabledielectrics and hyperelastic theory are adopted to analyze the electromechanical fieldbehavior of these actuators. Also the mechanical behavior of the dielectric elastomerundergoing large free deformation is studied. Finally, the constitutive model of a dielectricelastomer composite under free deformation and restrained deformation is derived.

Anisotropic electrostatic actuation

We examine the theoretical basis for the enhancement of classical, dielectric actuation by first imposing an elongation (‘pre-strain’) in one of the two directions in the plane of the working elastomeric filling between flexible electrodes. Such anisotropic actuation has been shown experimentally to be effective in delivering more mechanical work from a given applied voltage. A wrinkling instability in the in-plane direction perpendicular to the load limits the applicability of this strategy. It is shown to intervene before pull-in.

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.