Pumping of electrolytes using travelling-wave electro-osmosis: a weakly nonlinear analysis

The interaction between ac electric fields and the induced charge in the double layer formed on top of electrodes generates steady motion of aqueous solutions. This phenomenon is termed ac electro-osmosis. Unidirectional fluid motion is obtained when the electrolyte is placed on top of an array of microelectrodes subjected to a travelling-wave potential. In this work, we analyse the generated fluid motion assuming that the electrodes are perfectly polarisable and making use of the nonlinear Gouy–Chapman model for the diffuse double layer. We approximate the applied potential at the level of the electrodes by a single-mode travelling wave. We present numerical and analytical solutions obtained in the weakly nonlinear regime and the results are discussed and related with previous experimental observations.

基于介电泳的电极阵列电场仿真研究

介电泳方法被广泛地应用于微纳颗粒的分离和操纵中,实现介电泳操作的关键是设计满足所需电场分布的电极阵列.针对目前在微电极阵列设计中尚缺乏简单有效的电场解析方法的现状,提出一种基于格林公式的电极阵列电场的解析方法.首先介绍了传统介电泳和行波介电泳的概念和计算模型,分析了介电泳过程与电极上所施加的交变电压的频率和幅度的关系,然后在确立电极电势的边界条件的基础上,采用基于格林公式的电场解析方法,建立了非均匀电场的解析模型,得出不同条件下的电极阵列电场分布的仿真结果,最后利用FEMLAB有限元仿真软件对解析模型进行了对比仿真, 验证了该解析模型的可行性.基于格林公式的电场解析求解方法能够有效地提高电极阵列设计中的针对性以及缩短电极设计的时间.     

Fabrication of High-Aspect-Ratio Electrode Arrays for Three-Dimensional Microbatteries

Silicon-micromachining techniques have been combined with conventional material-synthesis methods to develop microelectrodes for 3-D microbatteries. The resulting electrodes feature an organized array of high-aspect-ratio microscale posts fabricated on the current collector to increase their surface area and volume for a given footprint area of the device. The diameter of the posts ranges from a few micrometers to a few hundred micrometers, with aspect ratios as high as 50. The fabrication approach is based on micromolding of the electrode materials and subsequent etching of the mold to release the electrode structures. Deep reactive-ion-etching or photo-assisted anodic etching has been used to form an array of deep holes in the silicon mold. Electroplating or colloidal-processing method has been used to fill the mold with battery-electrode materials. Measurements on electrochemical half-cells indicated that the 3-D electrode arrays, which are composed of vanadium oxide nanorolls or carbon, exhibited much greater energy densities (per-footprint area) than that of the traditional 2-D electrode geometries. The use of electroplating enabled us to fabricate 3-D interdigitated arrays of nickel and zinc; and battery operation was demonstrated. [2006-0293].     

Mercury-electroplated-iridium microelectrode array based sensors for the detection of heavy metal ultratraces: optimization of the mercury charge

Mercury-electroplated-Ir microelectrode array based sensors have been developed; their electroanalytical performance is investigated for the simultaneous detection of ultratraces of Pb, Cd and Zn. Two Ir microelectrode array geometries were used, namely: (i) an array of 1089 microelectrodes of 3-μm diameter and (ii) an array of 1764 microelectrodes of 6-μm diameter. Prior to the Hg electroplating, the arrays were systematically characterized by means of cyclic voltammetry at various scan rates ranging from 5 to 500 mV s⁻¹ and found to exhibit a steady-state voltammetric behavior. The effect of the Hg charge (over a range as wide as 0.05–40 mC) on the electroanalytical performance (net peak current, peak potential and peak width) of the metal trace sensors has been systematically studied by using square wave anodic stripping voltammetry (SWASV). It is clearly shown that the net peak current not only depends on the magnitude of Hg charge, but also presents a maximum value for an optimum Hg charge. Optimum Hg charges of 4 and 15 mC were identified for the 3- and 6-μm diameter Ir microelectrodes, respectively. At the optimum Hg charges, calibration plots demonstrated good linearity for the three metal traces over a concentration range as wide as (100 ppt–1 ppm). By increasing the preconcentration time from 5 to 20 min, it is shown that the detection limit of metal ultratraces can be decreased from 100 to 20 ppt.     

AC electrokinetic pumping on symmetric electrode arrays

AC electro-osmotic (ACEO) pumping is experimentally demonstrated on a symmetric gold electrode array. Using asymmetric connection of electrodes to the applied AC voltage, spatial asymmetry along the array is created, which produces unidirectional flow of electrolyte. An aqueous solution of 100 μM KCl is selected as the pumping fluid. The liquid velocity obtained as a function of voltage and frequency is compared to that generated using travelling-wave electroosmosis (TWEO) with the same electrode array. The expected velocities from the linear electrokinetic models of ACEO and TWEO are computed numerically. The comparison shows that TWEO generates greater velocity amplitudes and the streamlines are smoother than those generated by ACEO.     

基于Parylene的柔性神经微电极的研制和表征

衬底集成的微电极是植入式微系统中的重要部件,起着对神经进行电刺激并记录神经信号的关键作用。采用微细加工技术在新型柔性基底——聚对二甲苯(Parylene)上制作微电极阵列。阐述了Parylene基微电极阵列的加工工艺,并利用光学显微镜和电化学表征技术对微电极的表面形貌和电学性能进行了研究。结果表明:在工作频率范围内(104~105Hz),柔性神经微电极的阻抗值低(400~1000Ω),相位延迟小(-20°),适于用作视网膜修复。     

Two-phase AC electrothermal fluidic pumping in a coplanar asymmetric electrode array

The ability to achieve fast fluid flow yet maintain a relatively low temperature rise is important for AC electrothermal (ACET) micropumping, especially in applications such as bioMEMS and lab-on-a-chip systems. In this paper, we propose a two-phase ACET fluidic micropump using a coplanar asymmetric electrode array. The proposed structure applies a two-phase AC voltage, i.e., voltage of phase 0°/180°, to the narrow electrodes while the wide electrodes are at ground potential. Numerical simulation demonstrates that this simple coplanar electrode configuration can achieve at least 25% faster fluid flow rates than using a single AC signal. By selecting certain design parameters, a two-phase ACET structure can achieve up to 50% faster fluid flow rates than a corresponding single-phase structure. The simple two-phase AC signal sources are easily produced by using inverter buffers, which is a considerable improvement compared to the multi-phase AC signals required by other electrokinetic micropumping methods, such as traveling wave structures.     

Design of a relaying electroosmosis pump driven by low-voltage DC

Electroosmosis pumps (EOPs) have been widely used for manipulating small amounts of reagents for chemical and biological analysis. Traditionally, a high-voltage DC has to be applied in order to achieve the required flow rate. One alternative is to use low AC voltage. Here we propose another solution, which, instead of using a high-voltage DC or low AC voltage, adds a low-voltage DC to an array of electrodes. This design of EOP is called a relaying EOP or cascade EOP. In this study, we intend to push the limit of the low-voltage further down to 2 V by patterning a dense electrode array in a straight microchannel. Two patterns of interdigitated electrodes, symmetric with equal size electrodes and asymmetric with unequal size electrodes, are proposed. Simulations are performed to optimize the distribution and geometrical parameters of the electrode array in order to achieve the maximum flow rate. The proposed low-voltage DC electroosmosis pump shows an advantage in integrating EOP into portable Lab-on-a-chip devices. In addition, the low-voltage DC EOP shows a good promise for in vivo biomedical applications such as drug delivery.     

Novel systems for configurable AC electroosmotic pumping

In this paper we present a novel method of creating and using geometric asymmetries for AC electroosmotic pumping. The method relies on grouping similar electrodes together in terms of applied voltage, in order to create configurable asymmetries in periodic electrode arrays, which induce a net pumping AC electroosmotic velocity. Using a numerical model for a system designed by applying the described method, it is demonstrated that by varying the degree of asymmetry it is possible to control the direction of the pumping velocity at a given voltage by simple switching of the voltages on the electrodes.     

Measuring the size distribution of microelectrodes in an array

Microdisc arrays are considered for which the constituent disc electrodes are nonuniform in size. A method is described for using linear sweep voltammetry to calibrate the array to find the mean and standard deviation of the microdisc radii. Numerical simulation is used to model linear sweep voltammetry at arrays of single-sized microdiscs and of nonuniformly sized microdiscs.     

基于ITD的高压直流输电线路行波故障测距法

针对行波测距时波头到达母线时间精度提取困难的问题,提出了应用固有时间尺度分解(ITD)原理提取行波时频信息,通过ITD自适应地将故障行波信号分解得到原始信号完整的时频分布,可以准确得到行波波头到达母线的时刻.针对行波速度难以准确确定的问题,利用A型测距法与D型测距法相结合,提出了一种不受行波波速影响的测距法,以克服预设波速与实际波速存在的误差,提高测量精度.仿真实验表明:方法有效,误差精度较D型测距法好,在一定程度上提高了故障测距精度.     

细长圆柱体涡激振动行波动力学特征的实验研究

通过实验研究给出了细长圆柱体涡激振动行波的动力学特征.实验是在拖曳水池中进行.为了能在拖曳水池宽度有限的情况下出现行波,采用实验模型为0.006m直径、3.31m长度的铝管,模型长径比超过了500.拖车拖动模型以最高1.5m/s的速度在水槽中行进.模型一端采用2.5kg的砝码来提供端部张力.给出了评估行波在整个振动波中所占比例的方法.该方法采用行波圆来拟合模型空间振幅的分布.实验结果显示,在给定的拖车速度范围内,出现了行波振动,并且当拖曳速度达到0.9m/s时,行波现象非常显著.实验结果给出了振动波随拖曳速度变化的规律,得到了行波比随流速的变化规律.实验中观察到了低阶模态下的行波传播,这超出了已有行波判据限定的范围.通过实验数据的观察和理论分析,给出一种新的行波产生方式.     

面向电阻抗成像检测的多电极阵列微流控芯片设计

设计了一种用于微尺度流动状态下电阻抗成像检测的多电极阵列微流控芯片,包括微流控芯片的结构设计、材料选择和加工工艺。设计的微流控芯片包含3个圆形电极横截面,每个横截面包含一组电极阵列。该阵列有3种数目的电极,分别为8电极,12电极和16电极。之后通过数值仿真方法实现了三种电极数目（8,12和16）微流控芯片的电阻抗成像,并与之前研究出来的菱形横截面8电极微流控芯片进行了对比,发现设计出来的16电极圆形微流控芯片具有较高的成像质量,验证了微流控芯片用于细胞电阻抗成像检测的可行性。     

Integration of Au Nanorods With Flexible Thin-Film Microelectrode Arrays for Improved Neural Interfaces

In neural prosthetic systems, a low-impedance electrode–tissue interface is important for maintaining signal quality for recording, as well as effective charge transfer for stimulation. However, neural microelectrodes often have high impedance due to their small surface areas. In this paper, we present a simple method of increasing their effective surface areas by introducing nanostructures on the electrode sites. The method combines photolithography and electron-beam evaporation with a locally patterned anodized porous alumina template to integrate Au-nanorod arrays on the flexible thin-film microelectrode, which can significantly increase the effective surface area and decrease impedance due to its 3-D and compact nanostructures. Moreover, the geometrical and electrical properties of Au-nanorod electrodes were demonstrated and compared with conventional planar microelectrodes by using a scanning electron microscope and an impedance spectroscopy system. Experimental results showed that approximately 25 times lower interface impedance was achieved for this nanostructured microelectrode. Such Au-nanorod integrated microelectrode arrays will be a promising tool for neural engineering. $hfill$[2008-0136]      

浮标阵形对搜潜效能影响的研究

搜潜效能是评估浮标阵形性能的重要依据.为了研究不同浮标阵形对搜潜效能的影响,以航空应招反潜作战为背景,建立了航空搜潜过程中的潜艇运动模型和浮标布阵数学模型,并结合浮标阵阵无数量、反潜基地距潜艇初始发现点的距离、反潜机巡航速度以及潜艇规避速度的变化,运用Monte-Carlo方法对不同浮标阵形的搜潜效能进行了仿真和比较分析.仿真结果表明,在相同条件下,不同浮标阵形的搜潜效能存在较大差异,单层圆形浮标阵的搜潜效能相对较高.为声纳员优化浮标布阵提供有效的辅助决策依据.     

Batch mode micro-electro-discharge machining

This paper describes a micro-electro-discharge machining (micro-EDM) technique that uses electrode arrays to achieve high parallelism and throughput in the machining. It explores constraints in the fabrication and usage of high aspect ratio LIGA-fabricated electrode arrays, as well as the limits imposed by the pulse discharge circuits on machining rates. An array of 400 Cu electrodes with 20 μm diameter was used to machine perforations in 50-μm-thick stainless steel. To increase the spatial and temporal multiplicity of discharge pulses, arrays of electrodes with lithographically fabricated interconnect and block-wise independent pulse control resistance-capacitance (RC) circuits are used, resulting in >100× improvement in throughput compared to single electrodes. However, it was found to compromise surface smoothness. A modified pulse generation scheme that exploits the parasitic capacitance of the interconnect offers similarly high machining rates and is more amenable to integration. Stainless steel workpieces of 100 μm thickness were machined by 100 μm×100 μm square cross-section electrodes using in 85 s using an 80-V power supply. Surface smoothness was unaffected by electrode multiplicity. Using electrode arrays with four circuits, batch production of 36 WC-Co gears with 300 μm outside diameter and 70 μm thickness in 15 min is demonstrated     

Fabrication of a stainless steel shadow mask using batch mode micro-EDM

A metal shadow mask for organic thin-film transistors (OTFTs) has been fabricated by batch mode electro-discharge machining (EDM). Batch mode micro-electro-discharge machining method was applied for productivity improvement. Negative electrode with multiple holes (3 × 3 or 4 × 4) was fabricated using a single tool electrode. With the negative electrode, 3 × 3 and 4 × 4 tool electrode arrays are EDMed; 6 × 6 and 16 × 16 square hole array masks were batch mode EDMed with the fabricated multi-electrodes arrays. With 4 × 4 electrode array, the productivity is improved to five times of that in the case using a single electrode. Source and drain electrodes of OTFTs were successfully patterned on a pentacene active layer through the mask, and the fabricated pentacene TFTs had good output characteristics.     

高通量细胞电融合芯片研究进展

高通量细胞电融合芯片设计中采用微阵列结构的电极设计方案可提高芯片上微电极的数量,使细胞电融合芯片向高通量、高效率、高集成度的芯片实验室方向发展。通过设计微小尺度的电极间距,降低了对细胞电融合信号高压的要求和融合信号源的制造难度,提高了融合过程的安全性。对微电极形状、融合信号进行优化设计,提高细胞电融合的效率。同时,对芯片制造技术和芯片材料加以优化选择,提高了芯片制造的可靠性和电气与生化等性能。     

A Thin-Film Cochlear Electrode Array With Integrated Position Sensing

A thin-film electrode array with integrated position sensors has been developed for a cochlear prosthesis. The array is designed to minimize tissue damage during array insertion and achieve deep implants that hug the modiolus inside the cochlea. The array is fabricated using bulk micromachining technology and contains embedded polysilicon piezoresistive sensors for wall-contact detection and array-shape recognition. Nine strain gauges are distributed at the tip and along the array, covering the 8-mm-long shank. Each sensor is arranged in a half Wheatstone bridge whose output signal is time multiplexed, amplified (10 or 30 times), and band limited. The equivalent gauge factors are typically about 15, permitting array-tip position to be determined within a 50-mum resolution while providing wall-contact output signals of more than 50 mV at the tip. The arrays use a parylene-silicon-dielectric-electrode structure, improving flexibility while maintaining enough robustness to facilitate a modiolus-hugging shape defined by a polymeric backing device. Integrated with an articulated position-control device, such arrays are the first step toward providing closed-loop control of array insertion and improved perception of speech and music.     

基于Fluent的超声波换能器测风阵列模型改进研究

针对垂直相交型阵列易受阴影效应影响的问题,根据时差法原理,采用三组超声波换能器互成120°放置,设计了一种具有三条独立测风路径的改进型测风阵列,并建立了风速计算模型。该阵列保证至少有两组换能器正常工作的前提下,对某一条受到绕流干扰严重的测风路径进行校正。利用SpaceClaim软件建立测风阵列及风洞模型,通过Meshing软件进行网格划分,使用FLUENT软件改变模拟风洞内的风速及雷诺数等指标,仿真两种阵列在不同流态下的性能表现,得到速度分布云图以及测风路径速度曲线图,说明了改进型测风阵列能明显提升测风精度。