Characteristics of electroactive polymer actuators using graphene electrodes

As alternatives to precious gold/platinum electrodes, graphene-based ionic polymer-metal composite actuators were successfully demonstrated by reduced graphene oxide and direct grown graphene on both sides of the perfluorinated sulfonic acid polymer layer using electronic spray coating and wet transfer methods. In addition, a platinum electrode was prepared as a reference. We characterized the electrical and structural properties of the graphene electrodes using a four-point probe system and atomic force microscopy. The static actuation ranges were analyzed, and a modeling procedure was carried out to obtain the linear curvature–voltage relations. Furthermore, the periodic actuation range was dynamically tested to evaluate the changes in the actuation performance over time. The experimental results showed that the reduced graphene oxide electrodes are a good alternative to platinum electrode that provide better flexibility and restoration of the original shape. And also direct grown graphene electrode is also valuable to access the stacked actuator owing to the hydrophobic sub-nanometer electrode.     

Materials development for thin film actuators

In the development of microsystems, actuators are required which can be triggered in various different ways. The actuating principles to be used are magnetostriction, the inverse piezoelectric effect, the shape memory effect, and the bimetallic effect. The variables triggered in these cases are magnetic fields, electric fields, or temperature changes. Thin film actuators are of special interest for the development of microsystems, as they can be easily scaled down to the m-range and as their manufacturing is compatible to microsystem fabrication processes. The common property of these materials is their ability to transform electrical into mechanical energy by the effects mentioned above. Of special interest are magnetostrictive or piezoelectric materials as they allow energy transformation in both directions. These inverse effects can therefore be employed as sensoric mechanism for mechanical sensors (e.g. for stress, pressure, torque) as well. The report contains a discussion of various PVD techniques sucessfully used for producing magnetostrictive films (TbFe, TbDyFe, SmFe), piezoelectric films (PbtiO₃, ZnO, AlN), shape memory films (TiNi, TiNiPd, TiPd) and bimetallic film composites (e.g. FeNi₂₀Mn₆-FeNi₄₂). The properties of these layers are presented and compared. Possible applications and future development are outlined.     

Design, modeling, fabrication, and performances of bridge-type high-performance electroactive polymer micromachined actuators

Bridge-type high- performance polymer micromachined actuators (PMATs) based on an electroactive polymer, modified poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer had been designed, modeled, fabricated, and characterized. The results show that the material enables the PMAT to exhibit a high stroke level (60 /spl mu/m displacement with 1 mm lateral dimension microactuator) with high-load capability and high-displacement voltage ratio (DVR) over a broad frequency range (>100 kHz). The stroke reduction in fluid (Silicone oil) is less than 5% comparing with the displacement in air. Impedance analysis and displacement measurement indicate that the PMAT has strong resonance behavior and the resonance frequency can be tuned by varying the dc bias field. Furthermore, the resonance peak, as expected by theoretical study, shifted to 6.5 times lower in fluid than in air with the mechanical Q value reduction less than 40%. In addition, the performance of the PMAT was modeled based on the elastic and electromechanical properties of the materials utilized in the PMAT and the configuration of the device. The comparison between the model and the experimental result shows a good agreement and validates the model as an effective method for the future development of PMAT for various applications. The high frequency response and respected performance in fluid medium demonstrate that the PMAT has potential for high performance MEMS components in the applications of microfluid systems, air dynamic control, under water transducers, and mass sensors, etc.     

Fabrication of piezoelectric multilayer thin-film actuators

In this study, we fabricated multilayer ceramics (MLCs) composed of multilayered Pb(Zr,Ti)O₃ (PZT) piezoelectric thin films with internal electrodes and evaluated their dielectric and piezoelectric properties. The stack of PZT ferroelectric layers (550 nm) and SrRuO₃ (SRO, 80 nm) electrodes were alternatively deposited on Pt/Ti-coated silicon-on-insulator substrates by radio-frequency magnetron sputtering. The MLCs composed of one, three, and five PZT layers were fabricated by the alternate sputtering deposition of PZT ferroelectric layers and SRO electrodes through the movable shadow mask. The capacitances of MLCs were proportionally increased with the number of PZT layers, while their relative dielectric constants were almost same among the each MLC. The MLCs exhibited symmetric and saturated P–E hysteresis loops similar to the conventional PZT thin films. We estimated that the piezoelectric properties of MLCs by FEM simulation, and confirmed that the effective transverse piezoelectric coefficients (d _31,eff ) increased with the number of PZT layers. The piezoelectric coefficients calculated to be d _31,eff  = ?2964 pC/N at 25 PZT layers, which is much higher than those of conventional single-layer piezoelectric thin films.     

MEMS器件中多层金属薄膜溅射工艺研究

溅射工艺是制作微机电系统(MEMS)器件金属薄膜的主要方式,金属薄膜作为MEMS器件中的掩模层和功能层,要求薄膜应力小,粘附性、均匀性和可焊性好.通过对常用金属薄膜材料特性、多层金属薄膜溅射工艺和质量评价方法的研究得出了优化工艺的的方法,提高了多层金属薄膜的质量.     

高温薄膜传感器制备与性能研究

利用微机电系统（MEMS）工艺在 Al2 O3基片上制备了 Pt—PtRh 薄膜热电偶,其工作温度最高可达到1300℃,最大输出电势达14.8 mV。薄膜热电偶的电势—温度曲线与标准热电偶的曲线基本重合,同时研究了不同粘结层对薄膜微结构、器件寿命的影响。实验结果表明：以 Ta 为粘结层时薄膜传感器的寿命最长,在1300℃下可达到14 h。     

导电聚合物薄膜声表面波传感器敏感特性研究

利用旋涂方法在声表面波(SAW)器件的延迟通道上制备了酞菁铜(CuPC)掺杂的聚乙烯吡咯烷酮(PVP)敏感薄膜,并对制备的薄膜用四探针法和扫描电子显微镜(SEM)进行了测试和表征。结果表明:薄膜中的CuPC颗粒均匀分散在聚合物薄膜中,其粒径尺寸约为20 nm,薄膜的电导率在10-6Ω-1.cm-1量级。根据提出的理论模型,计算出由于敏感膜的质量变化与电导率的变化导致了中心频率的漂移,该漂移值的理论计算结果与实验验证结果相符。     

Effect of temperature on humido-sensitive conducting polymer actuators

Temperature dependence of water vapor sorption and electro-active polymer actuating behavior of free-standing films made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) was investigated by means of sorption isotherm and electromechanical analyses. The non-porous PEDOT/PSS film, having a specific surface area of 0.13 m² g^?1, sorbed water vapor of 1080 cm³(STP) g^?1, corresponding to 87 wt%, at relative water vapor pressure of 0.95. A temperature rise from 25 °C to 40 °C lowered sorption degree, indicative of an exothermic process, where isosteric heat of sorption decreased with increasing water vapor sorption and the value reached 43.9 kJ mol^?1, being consistent with the heat of water condensation (44 kJ mol^?1). Upon application of 10 V, the film underwent contraction of 2.46% at 5 °C caused by desorption of water vapor due to Joule heating, which slightly decreased to 2.10% at 45 °C. The speed of contraction was one order of magnitude faster than that of expansion and less dependent on the temperature since water vapor sorbed in the film were forced to desorb by Joule heating. In contrast, the higher the temperature the faster the film expansion because diffusion coefficient increased as the temperature became higher.     

Micro actuators on the basis of thin SMA foils

Three innovative micro actuator concepts on the basis of the differential SMA principle are presented in this paper: a high adaptive multi-actuator system, which is driven by numerous identical single actuators connected in parallel and in series, a micro gripper for handling and assembling of complex hybrid micro systems and a micro actuator system in medical tools for the percutaneous resection of aortic valves. The SMA material is used in the form of 50 μm thin NiTi foils because of their well-defined properties and high strength. In order to integrate them into micro systems, different manufacturing methods have been applied and improved at the Institute for Microtechnology. Laser cutting and wet chemical etching are used for example to microstructure the actuator elements. Different methods for electrical and mechanical connections of the actuators are employed like soldering by the use of an additional gold layer. A batch fabrication process of SMA actuators is realized by embedding NiTi foil elements into SU-8 structures. To optimize the design of SMA actuator elements according to its application different simulation procedures are used.     

Non-linear vibration behavior of thin multilayer diaphragms

The vibration spectrum of piezoelectrically driven (ZnO) thin silicon diaphragms in the driving frequency range up to 200 kHz has been studied. The response of the structure on the driving conditions (a.c. voltage amplitude and frequency) is presented. The limits of the linear plate theory and specific non-linear effects are discussed. Non-linear effects in the vibration behavior occur for vibration amplitudes even smaller than 4% of the diaphragm thickness. Superharmonic, harmonic and subharmonic vibration modes are observed. The vibration amplitudes of the subharmonic modes are of the same order as the diaphragm thickness. The characteristic non-symmetric resonance peaks of the subharmonic vibration modes indicate the existence of a hard-spring effect in the system. In the case of a system with a hard-spring effect, the concept of vibration modes with fixed resonance frequencies fails.     

Bending control of Nafion-based electroactive polymer actuator coated with multi-walled carbon nanotubes

Electrical bending control of Nafion-based ionic polymer-metal composite (IPMC) is quite difficult. Unlike a conventional fully hydrated noble metal-coated Nafion type IPMC, however, highly dehydrated silver-coated Nafion type IPMC exhibited better electrical bending controllability. Embedding of the multi-walled carbon nanotube (MWCNT) into Nafion surface promoted adsorption of a larger quantity of silver on the Nafion surface, since the MWCNT surface served as adsorption sites for silver. A MWCNT-embedded Nafion coated with such a large quantity of silver (SCNT-Naf) exhibited large bending curvature under an applied voltage when in a highly dehydrated state, because of large scale induction of silver redox reaction. We could even achieve autonomous bending curvature control of the highly dehydrated SCNT-Naf quantitatively by automatically monitoring total charge imposed on it.     

Neural-network-based identification and control of a thin plate using piezoelectric actuators and sensors

This paper proposes a novel neural network approach for the identification and control of a thin simply supported plate. For the control purpose, the piezoelectric sensors and actuators are attached on a flexible structure. The motion behaviour of a two-dimensional model of piezoelectric materials bounded to the surface of the plate is analytically investigated. A novel linear differential inclusion is developed for a class of multilayer feedforward networks. With this technique, it is shown that the plant identified by the neural network can be represented as a linear time-invariant system. On the basis of the identified model, advanced linear control theory can be directly applied to design the stabilizing flexible structure controller. Extensive simulations are conducted to show the effectiveness of the proposed method.     

Electro-adaptive microfluidics for active tuning of channel geometry using polymer actuators

With the expanding role of microfluidics in biology and medicine, methodologies for on-chip fluid sample manipulation become increasingly important. While conventional methods of microfluidic actuation, such as pneumatic and piezoelectric valves, are well characterized and commonly used, they require bulky external setups and complex fabrication. To address the need for a simple microfluidic actuator, we introduce a hybrid device consisting of an electroactive polymer that controls the shape of a microfluidic channel with an applied bias voltage. The electro-adaptive microfluidic (EAM) device allowed tuning of fluidic resistances by up to 18.1 %. In addition, we have shown that the EAM device is able to clear microchannel blockages by actively expanding the channel cross section. Biocompatibility tests show the EAM device has little effect on cell viability within a voltage range and thus has the potential to be utilized in bio-microfluidic systems. All of these results indicate that this EAM device design may find use in applications from cell sorting and trapping and self-clearing channels, to the reduction of lab-on-a-chip complexity via tunable channel geometries.     

Influence of residual stress on performance of AlN thin film based piezoelectric MEMS accelerometer structure

Microsystem Technologies - The presence of residual stress is inevitable and major constraint for MEMS devices as they induce deformation, fracture, fatigue and micro structural changes in the...     

导电聚合物驱动器悬臂梁模型建立及柔性抓取装置设计

基于导电聚合物具有柔韧性好、驱动电压低、能耗小等特性,采用自制的多层弯曲型导电聚合物驱动器搭建实验系统,依据等效悬臂梁理论建立驱动器力学模型。通过测量驱动器的弯曲变形量建立偏转位移与电压、长度的函数关系式,并且计算出等效均布载荷值。实验结果表明,驱动器偏转位移与电压、长度成线性关系;当驱动电压达到1.0 V时,驱动器偏转速度趋于稳定,且偏转效果最佳。为改善普通微操作装置结构复杂、能耗大的缺点,采用导电聚合物智能材料设计并制作出微型手爪制动器,最后验证了手爪可稳定抓起0.0111 g左右的重物。     

Hybrid-stress isoparametric elements for moderately thick and thin multilayer plates

A hybrid-stress formulation of isoparametric elements for the analysis of moderately thick and thin multilayer laminated composite plates is presented. The element displacement behavior is characterized by laminate reference-surface inplane and transverse displacements and laminate nonnormal crosssection rotations; as a result, the number of degrees of freedom is independent of the number of layers. All components of stress are included and are related to a set of laminate stress parameters, the number of which is independent of the number of layers. By isolating and analytically integrating all through-thickness contributions to the element matrices, the computation time for the element stiffness generation becomes nearly independent of the number of layers, and thus a computationally efficient element is produced. The formulation is used to develop an 8-node isoparametric multilayer plate element which is naturally invariant, of correct rank, and nonlocking in the thin-plate limit. Results for selected example problems show the range of applicability and convergence behavior of the element.     

Preparation and performance of IPMC actuators with electrospun Nafion-MWNT composite electrodes

A new ionic polymer actuator was prepared with Nafion^®-117 membrane and electrodes made of an electrospun Nafion^®/multiwalled carbon nanotube (MWNT) web. The surfaces of composite electrodes were ion-beam coated with gold layers of 2-3 μm thickness to reduce the surface resistance. The composite electrodes offer several advantages over conventional platinum electrodes prepared via electroless plating process, i.e. flexibility, simple processability in large scales, and batch-to-batch reproducibility. The new ionic polymer-metal composite (IPMC) actuators showed a rapid and large bending motion. Under an applied potential of 3 V dc, the maximum horizontal displacement (δ_max) measured at the tip of IPMC strip (cantilever length: 20 mm) was 16.7 mm, the tip velocity in the initial linear region was 10.5 mm/s, 88% of the δ_max was reached within initial 5 s, and the generated strain% was 0.79 (13.6 mm, 7.2 mm/s, 85%, and 0.88, respectively for a conventional Nafion^®-IPMC made via the electroless plating of platinum). It was noted that the energy efficiency of strain was over 10 times higher than that of the conventional Nafion^®-IPMC. And the crack formation of metal electrode after repeated bending deformation significantly reduced with the introduction of relatively flexible electrode assembly into the IPMC architecture. The remarkable improvements in its performance were considered to be due to the efficient quantum chemical and double-layer electrostatic effects in a charge injection model, induced by the good dispersion of MWNTs through a typical electrospinning technique.     

利用层次网格索引提高WebGIS性能

层次网格索引是在传统网格索引的基础上,进一步改进,减少了传统网格索引的冗余和索引的大小。在层次网格索引的基础上,利用客户端和服务器端的双缓冲机制,可以减轻网络传输和服务器的负担,提高WebGIS应用的整体性能。     

Modeling of single and multilayer polyvinylidene fluoride film for micro pump actuation

Micro pumps are essential components of micro devices such as drug delivery systems. Large numbers of pumps have been proposed based on different actuating principles. Piezoelectric actuation offers advantages such as reliability and energy efficiency. Lead zirconate titanate (PZT) based piezoelectric actuation for micro pumps is predominantly explored despite its disadvantages such as brittle nature, low straining and difficulties in processing. Polymer piezoelectric materials like polyvinylidene fluoride (PVDF) could be promising replacements for PZT owing to their availability in form of films and good strain coefficients. Very limited literature on micro pump with PVDF as an actuator is available. In this paper, finite element analysis (FEA) model of a micro pump actuator using single and multilayer PVDF for actuation is developed in ANSYS^?. The model takes into account the influence of driving voltage and actuator geometry. The central deflection of the pump diaphragm which is instrumental in defining the pump performance is studied for driving voltages of 100?C200?V. The deflection of the pump diaphragm for single layer and multilayer actuation are determined from the model. It could be inferred from the initial part of the study that pump performance depends on driving voltage and actuator film thickness. In order to reduce driving voltage requirement multilayer stacked actuator is tried with four different configurations of the layers. It is concluded that stacking configuration of parallel energized straight polarity PVDF layers yielded best central deflection. An attempt is made to compare the performance of multilayer actuator with an equivalent single thick layer actuator. It is noticed that the multilayer actuator performance was better by about 101% when number of layers is doubled.