Micro-PIV measurements of induced-charge electro-osmosis around a metal rod

A cylindrical gold-coated stainless steel rod was positioned at the center of a straight microchannel connecting two fluid reservoirs on either end. The microchannel was filled with 1 mM KCl containing 0.5 μm diameter carboxylate-modified spherical particles. Induced-charge electro-osmotic (ICEO) flow occurred around the metallic rod under a sinusoidal AC electric field applied using two platinum electrodes. The ICEO flows around the metallic rod were measured using micro particle image velocimetry (micro-PIV) technique as functions of the AC electric field strength and frequency. The present study provides experimental data about ICEO flow in the weakly nonlinear limit of thin double layers, in which, the charging dynamics of the double layer cannot be presented analytically. The measured ICEO flow pattern qualitatively agrees with the theoretical results obtained by Squires and Bazant (J Fluid Mech 509:217–252, 2004). Flow around the rod is quadrupolar, driving liquid towards the rod along the electric field and forcing it away from the rod in the direction perpendicular to the imposed electric field. The measured ICEO flow velocity is proportional to the square of the electric field strength, and depends on the applied AC frequency.     

Design and simulation of a thermo transfer type MEMS based micro flow sensor for arterial blood flow measurement

Thermo transfer type MEMS (Micro Electro Mechanical System) based micro flow sensing device have promising potential to solve the limitation of implantable arterial blood flow rate monitoring. The present paper emphasizes on modeling and simulation of MEMS based micro flow sensing device, which will be capable of implantable arterial blood flow rate measurement. It describes the basic design and model architecture of thermal type micro flow sensor. A pair of thin film micro heaters is designed through MEMS micro machining process and simulated using CoventorWare; a finite element based numerical code. A rectangular cross section micro channel has been modeled where in micro heater and thermal sensors are embedded using the same CoventorWare tools. Some promising and interesting results of thermal dissipation depending upon very small amount of flow rate through the micro channel are investigated. It is observed that measuring the variation of temperature difference between downstream and upstream, the variation of fluid flow rate in the micro channel can be measured. The numerical simulation results also shows that the temperature distribution profile of the heated surface depends upon microfluidic flow rate i.e. convective heat transfer is directly proportional to the microfluidic flow rate on the surface of the insulating membrane. The simplified analytical model of the thermo transfer type flow sensor is presented and verified by simulation results, which are very promising for application in arterial blood flow rate measuring in implantable micro devices for continuous monitoring of cardiac output.     

Autonomous planar conductivity array sensor for fast liquid distribution imaging in a fluid coupling

In this article, we introduce a new autonomous planar array sensor based on the measurements of electrical conductivity which has been applied to the visualization of fluid distributions inside a fluid coupling during normal operation. The sensor is composed of approximately 1000 interdigital sensing structures which are used to measure the two-dimensional electrical conductivity distribution at the sensor's surface with a fast multiplexed probing–sensing scheme at up to 10 kHz frame rate. Two such sensors were used to measure dynamic two-phase flow patterns in a fluid coupling at full operation at 790 rpm speed. Therefore, the sensors were mounted on the pressure-side and the suction-side walls of a blade channel inside a test coupling. The whole measurement system is run on a battery and controlled via wireless link, thus being fully autonomous, which enables sensor and electronics to rotate together with the coupling.     

Contactless sensing of the conductivity of aqueous droplets in segmented flow

We present an electrode arrangement for the inline measurement of the conductivity of droplets in segmented flow by impedance spectroscopy. We use a thin-walled glass capillary with electrodes contacting the outer surface, so that the contactless measurement of conductivity of the liquid within the capillary is possible. The surface of the glass capillary is silanized resulting in a single hydrophobic surface across which droplets can freely move. We model the impedance of such insulated electrodes and use the model to optimize the electrode system. Measurement of solutions with various salt concentrations allows the performance of the electrode structure to be characterized. Subsequently, the measurement of the impedance response of the aqueous segments in two-phase flow was demonstrated. Measurements were firstly performed with an impedance analyzer and subsequently with a multi-sine measurement setup that is better suited to high-speed measurement of droplets. Previous electrical measurements of segmented flow sensed the difference in dielectric constant between the aqueous phase and the carrier fluid through measurement of capacitance. This work describes an electrical measurement of the conductivity of droplets in segmented flow, that is, the sensor senses a variable property of the droplet itself.     

Performance of Low Output Impedance Composite pH Glass Electrodes

Low output impedance composite pH sensors were constructed by direct attachment of an impedance converter to laboratory purpose combined pH glass electrodes. The signal was transmitted in analog form by unshielded electric cable. The performance of new and aged composite pH sensors was determined by the multiple-point calibration method. In case of new electrodes, the slope and the response time, as well as the reproducibility, were insignificantly influenced by the converter attached (the mean slope values calculated for the six electrode group studied were 57.80 mV/pH for unmodified electrodes and 57.97 mV/pH for modified electrodes). The electrode response was not affected by the presence of various electromagnetic noise sources or by the input impedance value of the measuring instrument. The slope and the response time of aged sensors were considerably improved using the impedance converter. The response time decreased from about 150–180 sec to about 30 sec and the average slope value increased from 54.94 mV/pH, calculated for unmodified electrodes, to 56.96 mV/pH, for modified electrodes.     

High-Speed Flow Sensing as A Diagnostic Tool in the Development of Microfluidic Systems

Seyonic is developing a family of high-speed micro flow sensors with full-scale sensitivities between 0.25 and 10 microliter per second. The flow rate is determined by the measurement of a pressure difference across a fluidic restriction, using two integrated piezo-resistive pressure sensors. Main applications are in sub-microliter dispensing systems, where both sensor accuracy and speed provide real-time validation of the requested liquid volumes. The very fast response of the sensor, less than 2 ms, allows for measurement of liquid volumes down to the nL range. The sensor is able to measure not only the flow, but also the instantaneous pressure in the systems under evaluation. It is therefore possible to obtain valuable information on the system's operation for the characterization of fluidic components such as micromachined pumps, solenoid valves and jet dispensers     

Electrical measurement of cross-sectional position of particles flowing through a microchannel

The first high-throughput system for the electrical detection of cross-sectional position and velocity of individual particles flowing through a rectangular microchannel is presented. Lateral position (along channel width) and vertical position (along channel height) are measured using two different sets of coplanar electrodes. In particular, the ratio of travel times measured with electrodes generating a current flow transverse or oblique with respect to particle trajectory yields lateral position. The relative prominence and transit time of a bipolar double-Gaussian signal obtained with a suited electrode configuration, respectively, supply vertical position and velocity. The operating principle is presented by means of finite element numerical simulations. The method is experimentally validated by comparing the electrical estimates of position and velocity of polystyrene beads with optical estimates obtained by processing high-speed images. The system is used to observe bead focusing at different particle Reynolds numbers. This system, providing a fully electrical characterization of single-particle motion, represents a powerful tool, e.g. to understand fluid motion at the microscale, in particle separation studies, or to assess the performance of particle focusing devices. Moreover, it can be simultaneously used to perform single-cell impedance spectroscopy, thus achieving an unprecedented multiparamteric characterization.     

Liquid film thickness measurement underneath a gas slug with miniaturized sensor matrix in a microchannel

Measurement of liquid film thickness is essential for understanding the dynamics of two-phase flow in microchannels. In this work, a miniaturized sensor matrix with impedance measurement and MEMS technology to measure the thin liquid film underneath a bubble in the air–water flow in a horizontal microchannel has been developed. This miniaturized sensor matrix consists of 5 × 5 sensors where each sensor is comprised of a transmitter and a receiver electrode concentrically. The dimension and performance of the sensor electrodes were optimized with simulation results. The maximum diameter of the sensor ring is 310 µm, allowing a measurable range of liquid film thickness up to 83 µm. These sensors were distributed on the surface of a wafer with photolithography technology, covering a total length of 8 mm and a width of 2 mm. A spatial resolution of 0.5 × 2.0 mm² and a temporal resolution of 5 kHz were achieved for this sensor matrix with a measurement accuracy of 0.5 µm. A series of microchannels with different heights were used in the calibration in order to achieve the signal-to-thickness characteristics of each sensor. This delicate sensor matrix can provide detailed information on the variation of film thickness underneath gas–water slug directly, accurately and dynamically.     

A micro PDMS flow sensor based on time-of-flight measurement for conductive liquid

Transdermal extraction of interstitial fluid (ISF) offers an attractive method for non-invasive blood glucose monitoring. In order to calculate blood glucose concentration accurately, precise volume measurement of transdermally extracted ISF is required due to human skin’s varying permeability. In this paper, we presented a novel flow sensor fabricated from polydimethylsiloxane (PDMS), designed to measure the volume of conductive liquid. The flow sensor consists of two pairs of metal electrodes, which are fabricated in the PDMS channel. The volume of liquid is measured utilizing the time-of-flight of the two electrode pairs’ resistance while the liquid is flowing through the flow sensor. 1–14 μL normal saline solution was measured, the flow sensor measured volumes correlate very well (R ² = 0.9996 and R ² = 0.9975 for vacuum pump and syringe pump situations respectively) with the actual volumes. And the coefficient of variation for 10 times 10 μL normal saline solution measurement is 0.0077 (vacuum pump) and 0.0381 (syringe pump), respectively. The demonstrated flow sensor provides excellent functionality for conductive liquid.     

A dielectrophoretic chip packaged at wafer level

The paper presents a dielectrophoretic chip, fully enclosed, with bulk silicon electrodes fabricated using wafer-to-wafer bonding techniques and packaged at the wafer level. The silicon electrodes, which are bonded to two glass dies, define in the same time the walls of the microfluidic channel. The device is fabricated from a silicon wafer that is bonded (at wafer level) anodically and using SU8 photoresist between two glass wafers. The first glass die includes drilled holes for inlet/outlet connections while the second glass die assure the electrical connections, through via holes and a metallization layer, between the silicon electrodes and a printing circuit board.     

基于电镀技术的微间隔制作及在气体检测中应用的研究

本文开发了一种基于电离现象的气体传感器。文章首先研究了采用低成本的电镀方法来制作具有微米间隔的镍电极对,然后通过测试在不同条件下电极对的击穿电压和电流来实现气体检测。实验结果表明该器件对乙醇气体,其击穿电压在300 V左右;而对水蒸气,其击穿电压在320 V左右。同时,对乙醇而言,随着乙醇浓度的增加,在同一击穿电压下击穿电流也不断增大。对不同浓度的水蒸气的实验中也得到相类似的结果。     

多孔硅基微型直接甲醇燃料电池用催化电极的制备

针对硅基微型直接甲醇燃料电池小型化的需要,提供一种新型多孔硅基催化电极的制备方法,即采用硅片阳极氧化的方法首先得到多孔硅作为催化电极的基底材料,然后采用化学镀铂及铂钌的方法分别在多孔硅上沉积出催化剂镀层,制备出阴极和阳极催化电极.多孔硅具有巨大的比表面积,使化学镀的催化剂层拥有不连续的三维结构,能显著的增加催化剂的活性面积,同时化学镀液中贵金属的利用率高达95%,可以有效地节约贵金属用量.研究中采用扫描电镜(SEM),X射线衍射(XRD),能量色散X射线分析(EDX)对多孔硅的形貌及催化剂层的物理性能进行了分析.     

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。     

新型双并联电渗微泵的制备与测试

设计了一个双并联电渗驱动泵,它由三条并联的主通道和叉指型电极两部分组成,其中每条主通道由若干个与电渗流形成方向成45°角的沟槽并联构成。通过选用ITO载玻片作为芯片基底并获得其最佳工艺参数,制作了带电极的PDMS-玻璃微流控芯片。最后对制作的电渗微泵进行测试,通过记录一段时间内单个主通道泵输送液体的体积,得出单个主通道的流速与微泵总流速。实验发现在5V内,微泵泵送液体的能力随着电压的增加而增大,微泵流速可以达到正常人体眼球房水生成速度,该结构在未来房水引流器件制作方面具有潜在的应用价值。     

A dielectrophoretic chip packaged at wafer level

The paper presents a dielectrophoretic chip, fully enclosed, with bulk silicon electrodes fabricated using wafer-to-wafer bonding techniques and packaged at the wafer level. The silicon electrodes, which are bonded to two glass dies, define in the same time the walls of the microfluidic channel. The device is fabricated from a silicon wafer that is bonded (at wafer level) anodically and using SU8 photoresist between two glass wafers. The first glass die includes drilled holes for inlet/outlet connections while the second glass die assure the electrical connections, through via holes and a metallization layer, between the silicon electrodes and a printing circuit board.

     

基于电镀技术的微间隔制作及其在气体检测中应用的研究

开发了一种基于电离现象的气体传感器。首先研究了采用低成本的电镀方法来制作具有微米间隔的镍电极对,然后通过测试在不同条件下电极对的击穿电压和电流来实现气体检测。实验结果表明该器件对乙醇气体,其击穿电压在300 V左右;而对水蒸气,其击穿电压在320 V左右。同时,对乙醇而言,随着乙醇浓度的增加,在同一击穿电压下击穿电流也不断增大。对不同浓度的水蒸气的实验中也得到相类似的结果。     

MEMS神经元微探针研究

制作了一种神经元多电极微探针,采用阻抗分析仪对微探针进行了表征,测量了该探针单个电极在生理盐水中100～1 kHz范围内的交流阻抗.1 kHz工作频率下,探针的交流电阻和交流容抗分别为100 kΩ和10 kΩ,时漂小于1%.作为微探针的初步应用,测量了两个电极之间在不同浓度的NaCl溶液中的交流阻抗.结果表明该探针基本符合神经元探针的要求,为下一步进行生物实验奠定基础.     

Experimental characterization of electrical current leakage in poly(dimethylsiloxane) microfluidic devices

Poly(dimethylsiloxane) (PDMS) is usually considered as a dielectric material and the PDMS microchannel wall can be treated as an electrically insulated boundary in an applied electric field. However, in certain layouts of microfluidic networks, electrical leakage through the PDMS microfluidic channel walls may not be negligible, which must be carefully considered in the microfluidic circuit design. In this paper, we report on the experimental characterization of the electrical leakage current through PDMS microfluidic channel walls of different configurations. Our numerical and experimental studies indicate that for tens of microns thick PDMS channel walls, electrical leakage through the PDMS wall could significantly alter the electrical field in the main channel. We further show that we can use the electrical leakage through the PDMS microfluidic channel wall to control the electrolyte flow inside the microfluidic channel and manipulate the particle motion inside the microfluidic channel. More specifically, we can trap individual particles at different locations inside the microfluidic channel by balancing the electroosmotic flow and the electrophoretic migration of the particle.     

半电极含金属芯压电纤维的动态微力传感器

半电极含金属芯压电纤维(HMPF)是一种新型压电传感器.建立了HMPF的动态微力传感理论模型.根据第一类压电方程,基于振动理论,用平均电荷方法,推导出悬臂梁结构HMPF自由端受到垂直动态微力作用后,产生电荷的解析表达式;分析了长度和半径比对产生电荷的影响.实验结果表明,HMPF可以测量动态微力的频率和幅值,具有较高的动...     

Field analysis and electrical models of multi-electrode impedance sensors

Two types of multi-electrode sensors (with conducting and insulating walls), used in the impedance tomography systems, have been considered theoretically using finite element analysis (FEA). The distribution of potentials and current densities (field analysis) has been studied, assuming that sensors were supplied from current source. Potential differences between the adjacent electrodes and between electrodes and conducting wall, for sensors with insulating or conducting wall, respectively, were determined as a function of distance of measuring electrodes from supplying ones. Analysis of the influence of inhomogeneity location, for both types of the sensors, on measured potential differences has been carried out. On the basis of FEA results, semi-distributed, and then lumped parameter models of the sensors have been proposed. Character of variations of measured potential differences, caused by an inhomogeneity, is intelligible very well in terms of the derived models. Furthermore, the models allow estimation of the influence of frequency of measuring signal on the measured potential differences. Results of the theoretical analysis have been evaluated experimentally and a good agreement between theory and experiment has been obtained.