Thermal,Mechanical, and Dielectric Properties of a Dielectric Elastomer for Actuator Applications

Dielectric elastomers (DE) are a new type of electro-active material, which is able to produce a large degree of deformation under electrical stimulation. The thermal, mechanical, and dielectric properties of the most widely used dielectric acrylic elastomer (VHB 4910), commercially available from the company 3M, were studied by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and broadband dielectric spectroscopy (BDS) analyzer, respectively. DSC experiments on the VHB 4910 showed a glass transition at about ?40°C. VHB 4910 started to lose weight at about 250°C from the TGA study. The results of DMA indicated the storage modulus of VHB 4910 increased with frequency and had a strong temperature dependence of elasticity. The dielectric constant of VHB 4910 increased as a function of temperature up to 0°C, followed by a drop till 100°C. The mechanical and electrical efficiency of dielectric elastomer actuators (DEA) of VHB 4910 were analyzed. It was demonstrated that the actuation performance is dominated by the mechanical properties of the elastomer and is less influenced by the frequency and the temperature dependence of the dielectric properties; this may be used to guide the design of actuator configurations, as well as the choice of actuator materials.     

一个新的自由能函数对介电高弹薄膜的多组等双轴预拉伸下力电耦合实验的预测

当介电高弹聚合物薄膜被施以面内等双轴预拉伸后, 受到厚度方向的电压作用时, 薄膜在力场和电场共同作用下产生大变形. 电场采用Maxwell应力分析, 力场采用橡胶弹性模型分析. 拟合这类变形的常用橡胶弹性模型主要有Neo-Hookean, Arruda-Boyce, Gent等模型. 这些模型对实验数据的定量拟合存在不同程度的偏差. 通过对实验数据的分析, 结合数学方法, 提出了一个新的自由能函数模型. 通过该模型对VHB4905介电高弹聚合物薄膜的多组等双轴预拉伸电力耦合实验进行拟合, 并以Neo-Hookean, Gent模型作为对照, 结果与实验数据拟合很好, 比对照模型的偏差明显缩小.     

Dielectric elastomer and ferroelectret films combined in a single device: how do they reinforce each other?

Dielectric elastomers (DE) are soft polymer materials exhibiting large deformations under electrostatic stress. When a prestretched elastomer is stuck to a flat plastic frame, a?complex structure that can be used as an actuator (DEA) is formed due to self-organization and energy minimization. Here, such a DEA was equipped with a ferroelectret film. Ferroelectrets are internally charged polymer foams or void-containing polymer-film systems combining large piezoelectricity with mechanical flexibility and elastic compliance. In their dielectric spectra, ferroelectrets show piezoelectric resonances that can be used to analyze their electromechanical properties. The antiresonance frequencies (f _p ) of ferroelectret films not only are directly related to their geometric parameters, but also are sensitive to the boundary conditions during measurement. In this paper, a?fluoroethylenepropylene (FEP) ferroelectret film with tubular void channels was glued to a plastic frame prior to the formation of self-organized minimum-energy DEA structure. The dielectric resonance spectrum (DRS) of the ferroelectret film was measured in-situ during the actuation of the DEA under applied voltage. It is found that the antiresonance frequency is a monotropic function of the bending angle of the actuator. Therefore, the actuation of DEAs can be used to modulate the f _p of ferroelectrets, while the f _p can also be taken for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets brings a number of possibilities for application.     

Ion implanted dielectric elastomer circuits

Starfish and octopuses control their infinite degree-of-freedom arms with panache—capabilities typical of nature where the distribution of reflex-like intelligence throughout soft muscular networks greatly outperforms anything hard, heavy, and man-made. Dielectric elastomer actuators show great promise for soft artificial muscle networks. One way to make them smart is with piezo-resistive Dielectric Elastomer Switches (DES) that can be combined with artificial muscles to create arbitrary digital logic circuits. Unfortunately there are currently no reliable materials or fabrication process. Thus devices typically fail within a few thousand cycles. As a first step in the search for better materials we present a preliminary exploration of piezo-resistors made with filtered cathodic vacuum arc metal ion implantation. DES were formed on polydimethylsiloxane silicone membranes out of ion implanted gold nano-clusters. We propose that there are four distinct regimes (high dose, above percolation, on percolation, low dose) in which gold ion implanted piezo-resistors can operate and present experimental results on implanted piezo-resistors switching high voltages as well as a simple artificial muscle inverter. While gold ion implanted DES are limited by high hysteresis and low sensitivity, they already show promise for a range of applications including hysteretic oscillators and soft generators. With improvements to implanter process control the promise of artificial muscle circuitry for soft smart actuator networks could become a reality.     

Electroless deposition of platinum on proton-conductive perfluorinated membranes modified with ethylene diamine

Perfluorinated, non-hydrolysed, carbon-chain flat-sheet membranes were treated with ethylene diamine (EDA) to investigate the influence of EDA-treatment on the process of the Pt deposition on these membranes. The electrical resistances of the modified membranes were also measured, to determine the degree of modification of the membranes. Pt-containing membranes were characterised using SEM to compare the profile of the Pt deposition on Pt-containing membranes that were not modified. Dielectric analysis (DEA) was used to investigate the dipole and ion mobility of hydrolysed EDA-modified membranes. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998     

Dynamic performance of dielectric elastomers utilized as acoustic actuators

We report on the frequency dependent behavior of dielectric elastomer actuators (DEA). The introduced smart material actuators consist of 3M^???s elastomer VHB^?4905 (9469) and a compliant, sputtered copper electrode on each side. The presented experiments on these compounds contain the active tuning of their resonance frequency and their application as acoustic actuators. We are able to decrease the membranes?? eigenfrequency by?30% with an electrical offset potential. Alternatively, if an alternating signal is applied, sound pressure levels up to 130?dB in an enclosed volume of 28?ccm are achieved. In order to verify the results, a numerical simulation is introduced incorporating the two physical fields involved: electrical and mechanical.     

Finite element analysis of piezoelectric actuator with PMN–PT single crystals for nanopositioning

A piezoelectric bending actuator has been used widely in areas related to precision position controlling, loudspeakers, and pressure sensing. In this paper, a fine focusing actuator is designed using a computer aided design tools, Solid Works 2004, for an optical disk drive pick-up system. The finite element analyses are performed with the software COSMOS Work 2004 and the ANSYS 5.7. The tip displacement of the piezoelectric bending actuator with PMN-PT single crystals is 46 μm at 10 V. It is 15 times larger than tip displacement of PZT ceramics for the same design. The tip displacement obtained from the finite element analyses agrees with the measured data very well.     

新型低电压大变形微驱动器数值求解及仿真

针对横向加载单向变形MEMS静电微驱动器位移过小或驱动电压过大问题,提出一种基于纵横弯曲变形原理的硅基大位移低驱动电压静电驱动器模型;基于拉格朗日-麦克斯韦机电动分析力学,建立轴向横向同时加载的微驱动器动力方程;分析温度应力、静电调节力和轴向挤压力对轴向载荷的影响;基于龙格-库塔算法和有限差分法分别将横向分布载荷和轴向载荷等效转化为横向集中载荷;仿真得到变形同驱动电压、调节电压、轴向挤压量和温差的关系;结果显示当驱动电压仅为16 V时,位移高达10.861μm,远大于传统横向加载单向变形微驱动器的位移量.实验验证了仿真结果.     

Glassy photomechanical liquid-crystal network actuators for microscale devices

In light-driven liquid-crystal network (LCN) actuators, large performance improvements are obtained by varying the orientation of the molecular director through the thickness of the film actuator. Experiments show that sub-millimeter bending radii are achieved using a splayed molecular orientation. Systems with a splayed or twisted nematic (TN) director profile drive greater amplitude and faster bending than uniaxial planar systems with the same chemical composition. The bending radii of these systems are predicted using a simple model including effects of light intensity, material composition and actuator thickness. Electronic supplementary material Supplementary material in form of video file available from the Journal web page at and are accessible for authorised users.     

Comparison between the Results of Simulating the Synchrotron Radiation from a Bending Magnet and Experimental Data

The results of using two (SPECTRA and SRW) programs for simulating synchrotron radiation (SR) are presented. Calculations are performed for coherent SR from a beam of electrons with moderately relativistic energies in a short bending magnet. Simulation is carried out for real beam parameters. A comparison between simulation and experimental data indicates their good agreement. Both general information for the given codes grouped by a number of criteria and specific data on simulating radiation from bending magnets are presented.     

A piezoelectric bone-conduction bending hearing actuator

A prototype of a novel bone-conduction hearing actuator based on a piezoelectric bending actuator is presented. The device lies flat against the skull which would allow it to form the basis of a subcutaneous bone-anchored hearing aid. The actuator excites bending in bone through a local bending moment rather than the application of a point force as with conventional bone-anchored hearing aids. Through measurements of the cochlear velocity created by the actuator in embalmed human heads, the device is shown to exhibit high efficiency, making it a possible alternative to present-day electromagnetic bone-vibration actuators.     

Dielectric barrier plasma dynamics for active aerodynamic flow control

The paper investigates the dynamics of a new multiple bipolar multiple Dielectric Barrier Discharges(DBD)actuator using in large-scale flow control.Particle image velocimetry experiments are performed to characteristic the effectiveness of the multiple bipolar DBD plasma actuator.The results show that the mutual interaction between the electrodes,one major disadvantage of traditional DBD characterized by reverse discharge can be entirely avoided,and a constantly accelerating electric wind velocity can be obtained by using the new multiple bipolar DBD plasma actuator.     

Structure,electronic and elastic properties of the NbRu shape memory alloys

Under certain conditions the first order geometric auto regressive (AR) process has statistical properties similar to atmospheric boundary layer wind speed. In this contribution, we investigate this similarity and analyse the extent to which this stochastic process is a suitable model for wind speed simulation. In particular, we focus on the fluctuation of the process around its moving average over a given number of time steps. We show that the fluctuation conditioned on the value V of the moving average are of a symmetric normal distribution with a proportionality between its standard deviation and V. This proportionality is empirically observed in wind speed data. Furthermore, we show that the increment distribution of the geometric AR(1) process is in good agreement with the symmetric Castaing distribution which is empirically found in wind speed data.     

Rosensweig instability of ferrogel thin films or membranes

We derive the dispersion relation of surface waves for magnetic gel membranes or thin films at the interface between two fluids in the presence of an external magnetic field normal to the free surface. Above a critical field strength surface waves become linearly unstable with respect to a stationary pattern of surface protuberances. This linear stability criterion generalizes that of the Rosensweig instability for ferrofluid and ferrogel free surfaces to take into account bending elasticity and intrinsic elastic and magnetic surface properties of the film or membrane, additionally. The latter is of interest for uniaxial ferrogel film or membranes, which show a locked-in permanent magnetization.     

Wave membrane filters for estimating the wave spectra of near-wall pressure pulsations of a turbulent boundary layer in the subconvective region

We have obtained results on measuring the levels of the frequency-wave spectrum of the field of near-wall pressure pulsations of a turbulent boundary layer on the smooth wall of a wind tunnel with the use of stretched plastic membranes as wave filters. We compare the experimental data with the classical model.     

Elastic energy of tilt and bending of fluid membranes

Tilt of hydrocarbon chains of lipid molecules with respect to membrane plane is commonly considered to characterize the internal structure of a membrane in the crystalline state. However, membranes in the liquid state can also exhibit tilt resulting from packing constraints imposed on the lipid molecules in diverse biologically relevant structures such as intermediates of membrane fusion, pores in lipid bilayers and others. We analyze the energetics of tilt in liquid membranes and its coupling with membrane bending. We consider three contributions to the elastic energy: constant tilt, variation of tilt along the membrane surface and membrane bending. The major assumption of the model is that the core of a liquid membrane has the common properties of an elastic continuum. We show that the variation of tilt and membrane bending are additive and that their energy contributions are determined by the same elastic coefficient: the Helfrich bending modulus, the modulus of Gaussian curvature and the spontaneous curvature known from previous studies of pure bending. The energy of a combined deformation of bending and varying tilt is determined by an effective tensor accounting for the two factors. In contrast, the deformation of constant tilt does not couple with bending and its contribution to the elastic energy is determined by an independent elastic constant. While accurate determination of this constant requires additional measurements, we estimate its value using a simplified approach. We discuss the relationships between the obtained elastic Hamiltonian of a membrane and the previous models of membrane elasticity. Received 10 February 2000 and Received in final form 19 June 2000     

Elastic rod model of a supercoiled DNA molecule

We study the elastic behaviour of a supercoiled DNA molecule. The simplest model is that of a rod-like chain, involving two elastic constants, the bending and the twist rigidities. Writing this model in terms of Euler angles, we show that the corresponding Hamiltonian is singular and needs a small distance cut-off, which is a natural length scale giving the limit of validity of the model, of the order of the double-helix pitch. The rod-like chain in the presence of the cut-off is able to reproduce quantitatively the experimentally observed effects of supercoiling on the elongation-force characteristics, in the small supercoiling regime. An exact solution of the model, using both transfer matrix techniques and its mapping to a quantum mechanics problem, allows to extract, from the experimental data, the value of the twist rigidity. We also analyse the variation of the torque and the writhe-to-twist ratio versus supercoiling, showing analytically the existence of a rather sharp crossover regime which can be related to the excitation of plectoneme-like structures. Finally we study the extension fluctuations of a stretched and supercoiled DNA molecule, both at fixed torque and at fixed supercoiling angle, and we compare the theoretical predictions to some preliminary experimental data. Received 1 April 1999 and Received in final form 4 January 2000     

A built-in force actuator for active control of lateral rotor vibration in cage induction electrical machines

In this paper means of active control of radial rotor vibrations in electrical machines are considered. We examine a built-in force actuator for active generation of force on the machine rotor. The operation of the actuator is based on electromechanical interaction between the rotor and the stator of the machine. The actuator is given a low-order linear state-space model, which is identified by using simulation data obtained from a detailed time-stepping finite element model of the machine. Simulation results obtained by using real machine data and finite element time-stepping method are presented.     

Unmanned air vehicle flow separation control using dielectric barrier discharge plasma at high wind speed

The present paper described an experimental investigation of separation control of an Unmanned Aerial Vehicle(UAV)at high wind speeds.The plasma actuator was based on Dielectric Barrier Discharge(DBD)and operated in a steady manner.The flow over a wing of UAV was performed with smoke flow visualization in theΦ0.75 m low speed wind tunnel to reveal the flow structure over the wing so that the locations of plasma actuators could be optimized.A full model of the UAV was experimentally investigated in theΦ3.2 m low speed wind tunnel using a six-component internal strain gauge balance.The effects of the key parameters,including the locations of the plasma actuators,the applied voltage amplitude and the operating frequency,were obtained.The whole test model was made of aluminium and acted as a cathode of the actuator.The results showed that the plasma acting on the surface of UAV could obviously suppress the boundary layer separation and reduce the model vibration at the high wind speeds.It was found that the maximum lift coefficient of the UAV was increased by 2.5%and the lift/drag ratio was increased by about 80%at the wind speed of 100 m/s.The control mechanism of the plasma actuator at the test configuration was also analyzed.