Search

This paper presents a microfluidic device that can passively reduce fluctuations in an upstream fluid flow and generate a largely steady flow in a microfluidic system. The device features a series of compliant membranes that form deformable walls of a microchannel. F or an incoming pulsatile flow, passive vibrations of the membranes allow the fluid to be accumulated for an overflow and discharged for an underflow, resulting in drastically reduced fluctuations in flow rate and pressure. A lumped-parameter model is developed to simulate the device characteristics, in which the coupling of membrane vibrations and fluid flow in individual channel sections associated with a single membrane is first represented by squeeze-film theory and inertia-free structural dynamics. The entire device is next represented as a system by connecting individual channel sections in series. The model is numerically solved, and the results agree with experiments. The theoretical and experimental results both show that a five-membrane device can stabilize a pulsating flow by a factor of about 20. These results also reveal that smaller average flow rate, smaller fluctuation, and higher fluctuation frequency lead to more effective flow stabilization. With these characteristics, the flow stabilizer can be used to obtain steady flow in microfluidic systems. [2008-0305] Index Terms---Compliant membrane, flow rectification, flow stabilization, fluid-structure interaction, lumped-parameter model.

A new packaging method for microfluidic devices is proposed of polymer overmolding to form a fluidic manifold integrated with the device in a single step. The anticipated advantages of the proposed method of packaging are ease of assembly and low part count, making it suitable for low cost and high volume manufacturing. This paper reports the results of a preliminary investigation into this concept. Glass and silicon inserts of 25 x 20 mm in size, used to represent microfluidic devices, were overmolded in an injection molding process with a range of polymers. The inserts were found to survive the molding process intact. The adhesion between overmold and insert was investigated by subjecting the interface between the overmold and insert surface to a hydrostatic pressure of up to 100 Ibf/[in.sup.2] (6.9 bar). The durability of the interfacial adhesion to hydrolysis was investigated by immersion in water at 50[degrees]C for 24 h before testing. Direct measurements of adhesion strength between polymer and glass were also attempted by tensile tests on lap-jointed samples. The best and most durable adhesion for glass and silicon inserts was found for polyamide (PA) 12, which is a low hygroscopicity PA. The ranking of polymers by their performances in the pressurization tests was consistent with the ranking by the calculated work-of-adhesion values for polymer/glass and polymer/silicon joints. [2006-0211] Index Terms--Bonding, fluidics, interconnections, packaging.

We report a new two-axis active optical fiber manipulator for on-chip optical manipulation and detection in microfluidic environment. The system comprising of air chambers, fiber channels, controllable moving walls, and membrane structures were fabricated by using microelectromechanical systems technology. By adjusting air pressures to control the deflection of the pneumatic chambers placed orthogonal to and underneath the fiber channels, accurate alignment of a pair of approximately coaxial optical fibers, which was indicated by maximizing fiber-to-fiber optical-coupling measured in real time, has been achieved. A maximum displacement of a buried fiber as large as 13 [micro]m at an applied pressure of 40 lb/[in.sup.2] for one air chamber has been demonstrated. It was sufficient to accurately align two approximately coaxial optical fibers to maximize the optical coupling efficiency. The maximum coupling efficiency for two single-mode optical fibers facing each other at a distance of 200 [micro]m was measured to be 4.1%. The following features have been successfully demonstrated with this system: 1) stable optical trapping and stretching of a single red blood cell; 2) stable optical trapping of multiple microparticles; 3) optically driven controlled motion of single and multiple microparticles; and 4) integration of a counterpropagating dual-beam trap with single-beam optical tweezers. In addition to optical trapping and manipulation, the proposed device is promising for applications requiring coaxial input/output fibers for in-line optical analysis. Furthermore, it can be easily integrated with other microfluidic devices such as microcapillary electrophoresis channels or microflow cytometers for DNA, protein, and cell analysis. [2007-0182] Index Terms--Microcoupler, microelectromechanical systems (MEMS), microfluidics chip, moving wall, optical detection, optical trappers.

The formation of microscale single- and double-emulsion droplets with various sizes is crucial for a variety of industrial applications. In this paper, we report a new microfluidic device which can actively fine-tune the size of single- and double-emulsion droplets in liquids by utilizing controllable moving-wall structures. Moreover, various sizes of external and internal droplets for double emulsions are also successfully formed by using this device. Three pneumatic side chambers are placed at a T-junction and flow-focusing channels to construct the controllable moving-wall structures. When compressed air is applied to the pneumatic side chambers, the controllable moving-wall structures are activated, thus physically changing the width of the microchannels. The size of the internal droplets at the intersection of the T-junction channel is then fine-tuned due to the increase in the shear force. Then, the internal droplets are focused into a narrow stream hydrodynamically and finally chopped into double-emulsion droplets using another pair of moving-wall structures downstream. For single emulsions, oil-in-water droplets can be actively fine-tuned from 50.07 to 21.80 [micro]m under applied air pressures from 10 to 25 psi with a variation of less than 3.53%. For a water-in-oil single emulsion, droplets range from 50.32 to 14.76 [micro]m with a variation of less than 4.62% under the same applied air pressures. For double emulsions, the sizes of the external and internal droplets can be fine-tuned with external/ internal droplet diameter ratios ranging from 1.69 to 2.75. The development of this microfluidic device is promising for a variety of applications in the pharmaceutical, cosmetics, and food industries. [2007-0230] Index Terms--Double emulsion, flow focusing, microdroplet, microelectromechanical systems (MEMS), microfluidics, moving wall, T-junction.

This paper reports on liquid (deionized water) microlenses that are intrinsically formed and integrated within microfluidics through pneumatic manipulation of fluids inside microchannels. Such microlenses are formed via liquid-air interfaces of liquid droplets, which are pinned at T-shaped junctions of channels. In addition to being tunable in focal lengths (a few hundreds of micrometers to [infinity]) along the microchannels parallel to the substrate used, these microlenses can uniquely be repositioned, removed, and reformed at predetermined locations of the T-shaped junctions within microchannels on demand under pneumatic controls. The design and formation of a microfluidic channel network for the in situ formation are first described. Then, the pneumatic control of the fluids, including the formation, movement, and size control of a lens droplet, is discussed, and the in situ formation processes for single and multiple liquid microlenses are described. The in situ formation processes for a single microlens and a two-lens combination only take tens of seconds, eliminating various conventional microfabrication processes and multiple layers of materials. Finally, the detail of characterization of these microlenses is given. [2007-0176] Index Terms--Liquid microlens, microfluidics, optofluidics, pneumatic control, tunable.

We describe a microfluidic scheme based on remotely controlled self-assembled containers that allows spatio-temporal control over nanoliter-scale chemical reactions. We discuss finite-element simulations of the inductive coupling of radio-frequency radiation to the containers; this coupling enables remotely triggered release of chemical reactants. We demonstrate on-demand chemical release from stationary and mobile containers patterned with different porosities. We also explore reactions between chemicals released from two containers that form liquid products and deposit solid precipitates. We argue that these remotely controlled metallic containers provide an attractive platform for carrying out reconfigurable microfluidics 'without channels.' [2007-0221] Index Terms--Chemistry, microfluidics, radio frequency (RF), remote control, self-assembly.

This paper presents a new miniature reversetranscription polymerase chain-reaction (RT-PCR) system integrating a sample pretreatment device for fast nucleic-acid amplification and diagnosis of viruses and bacteria. In the system, a two-way serpentine-shape (s-shape) pneumatic micropump and a magnetic bioseparator were developed for separation and enrichment of viruses and bacteria. This new bioseparator can also be used as microheating chambers to perform RT-PCR. Taking advantage of the specific interaction between the antibodies on the surface of magnetic beads and the surface antigens on viruses or bacteria, the target virus and bacteria were recognized and further separated and purified from the biosamples by a magnetic field generated by the bioseparator. The target purified virus/bacteria was then lysed to release ribonucleic acid (RNA) or deoxyribonucleic acid (DNA) for the subsequent RT-PCR processes. Experimental results showed that the target virus/bacteria was successfully separated and enriched by the high specificity and selectivity of antibody-conjugated magnetic beads, and the subsequent amplification of RNA/DNA was automatically completed by utilizing the on-chip microheaters and the micro temperature sensor. The high mixing efficiency of the two-way s-shape pump and the rapid heating/cooling rate of the microheating chambers can significantly shorten the pretreatment and diagnosis processes. As a whole, the developed system may provide a powerful platform for sample pretreatment and fast disease diagnosis. [2007-0089] Index Terms--Enrichment, magnetic bead, microelectromechanical systems (MEMS), microfluidics, pretreatment, reverse-transcription polymerase chain reaction (RT-PCR).

Digital (i.e., droplet-based) microfluidics, by the electrowetting-on-dielectric (EWOD) mechanism, has shown great potential for a wide range of applications, such as lab-on-a-chip. While most reported EWOD chips use a series of electrode pads essentially in 1-D line pattern designed for specific tasks, the desired universal chips allowing user-reconfigurable paths would require the electrode pads in 2-D pattern. However, to electrically access the electrode pads independently, conductive lines need to be fabricated underneath the pads in multiple layers, raising a cost issue particularly for disposable chip applications. In this paper, we report the building of digital microfluidic plates based on a printed circuit board (PCB), in which multilayer electrical access lines were created inexpensively using the mature PCB technology. However, due to its surface topography and roughness and resulting high resistance against droplet movement, the as-fabricated PCB surfaces require high (~500 V) voltages unless coated with or immersed in oil. Our goal is the EWOD operations of droplets not only on oil-covered surfaces but also on dry ones. To meet the varying levels of performances, three types of gradually complex post-PCB microfabrication process are developed and evaluated. By introducing land-grid-array sockets in the packaging, a scalable digital microfluidic system with a reconfigurable and low-cost chip is also demonstrated. [2007-0049] Index Terms--Electrowetting, electrowetting on dielectric (EWOD), lab-on-a-chip, microfluidics, micro total analysis system, printed circuit board (PCB).

This paper reports on the design, fabrication, and characterization of a new class of wideband liquid RF microelectromechanical-system reflective and absorptive switches. A number of different liquids are considered, including mercury, Galinstan, and ultrapure and ionic water. We first briefly review the performance of liquid--metal switches made by mercury and Galinstan. Such switches demonstrate excellent off-state insertion loss of less than 1.3 dB up to 100 GHz (the loss includes a 1500-[micro]m-long line) and on-state isolation of better than 20 dB from 20 to 100 GHz. The main part of this paper, however, focuses on significantly transforming these designs to actually absorb and not reflect the incident power in their on-state, while at the same time maintaining their excellent off-state performance. Absorptive behavior is particularly important for high-power applications. Simpler materials such as water are proven to be very effective for wideband absorptive switches. In particular, three classes of water-based absorptive switches are discussed depending on the level of the signal coupling to water. At 10-40 GHz, the optimal design exhibits off-state insertion loss of less than 1.3 dB, on- and off-state return loss of less than 10 dB, and on-state isolation of 27.5-dB isolation at 40 GHz. Index Terms--Absorptive switch, microfluidics, RF microelectromechanical system (RF MEMS), water, wideband.

In this paper, we present a simple, rapid, and low-cost procedure for fabricating glass microfluidic chips. This procedure uses commercially available microscopic slides as substrates and a thin layer of AZ 4620 positive photoresist (PR) as an etch mask for fabricating glass microfluidic components, rather than using expensive quartz glasses or Pyrex glasses as substrates and depositing an expensive metal or polysilicon/amorphous silicon layer as etch masks in conventional method. A long hard-baking process is proposed to realize the durable PR mask capable of withstanding a long etching process. In order to remove precipitated particles generated during the etching process, a new recipe of buffered oxide etching with addition of 20% HCl is also reported. A smooth surface microchannel with a depth of more than 110 [micro]m is achieved after 2 h of etching. Meanwhile, a simple, fast, but reliable bonding process based on UV-curable glue has been developed which takes only 10 min to accomplish the efficient sealing of glass chips. The result shows that a high bonding yield (~100%) can be easily achieved without the requirement of clean room facilities and programmed high-temperature furnaces. The presented simple fabrication process is suitable for fast prototyping and manufacturing disposable microfluidic devices. [2007-0032] Index Terms--Microfabrication, microfluidic devices, UV bonding, wet etching.

This paper presents a novel microfluidic photomasking strategy. Laminar microfluidic streaming is exploited to achieve photomasking with dynamic spatial control. Two light-absorbing streams hydrodynamically focus a transparent stream to define a line of light transmission. A device incorporating two such microfluidic layers, which are aligned orthogonally, enables light transmission only where the transparent streams overlap. Control of fluid flow in the microfluidic layers enables dynamic spatial control of the exposed region. The dynamic microfluidic photomasking strategy is tested through transmitted light microscopy and applied to microfabrication via photoresist patterning. When applied to microfabrication in a frontal photopolymerization mode, this method affords both planar and depthwise control of feature geometry. [2006-0088] Index Terms--Focusing, hydrodynamics, microfluidics, optofluidics, photomasking.

This paper presents a sequential dielectroliboretic field-flow separation method for particle populations using a chip with a 3-D electrode structure. A unique characteristic of our chili is that the walls of the microfluidic channels also constitute the device's electrodes. This property confers the opportunity to use the electrodes' shape to generate not only the electric field gradient required for dielectrophoretic force but also a fluid velocity gradient. This interesting combination gives rise to a new solution for the dielectrophoretic separation of two particle populations. The proposed sequential field-flow separation method consists of four steps. First, the microchannel is hilled with the mixture of the two populations of particle. Second, the particle populations are trapped in different locations of the microfluidic channels. The population, which exhibits positive dielectrophoresis (DEP), is trapped in the area where the distance between the electrodes is the minimum, while the other population that exhibits negative DEP is trapped in locations of maximum distance between electrodes. In the next step, increasing the flow in the microchannels will result in an increased hydrodynamic force that sweeps the cell population trapped by positive DEP out of the chip. In the last step, the electric field is removed, and the second population is swept out and collected at the outlet. For theoretical and experimental exemplification of the separation method, a population of viable and nonviable yeast cells was considered. [2006-0157] Index Terms--Cell separation, dielectrophoresis (DEP), microfluidic device, 3-D silicon electrodes.

In this paper, we present the development of disposable single-use microfluidic pumps entirely based on a straightforward wafer-level fabrication scheme, which allows for precise integrated active dosing in the microliter range. To accomplish stroke-lengths needed for microliter-range applications, we utilize a new method of bending of a unimorph-composite-actuator film. The unimorph composite actuator consists of a temperature-sensitive silicone elastomer composite, i.e., polydimethylsiloxane, with incorporated expandable microspheres. The fabricated micropumps successfully demonstrated precise liquid-volume control, both at low and high flow rates, and show a standard deviation of 6.7% for consecutive pump experiments. Moreover, the method of fluorescent thermometry was used to measure the thermal load on liquid volumes dispensed with the micropumps. The liquid temperature reaches a maximum of 50[degrees]C during the operation. The presented fully integrated single-use micropumps are electrically controllable, do not require external means for liquid actuation, are made of low-cost materials only, and might potentially be used in drug-delivery applications. [2006-0277] Index Terms--Fabrication, fluidics, micropumps, wafer-scale integration.

A contactless microfluidic dosing system based on actuation by an electrochemical reaction has been designed and tested. The device is composed of two chambers separated by a polydimethylsiloxane (PDMS) plate. One chamber is loaded with the liquid sample to be dosed while the electrochemical reaction occurs in the second chamber. Due to the strict separation between the reaction responsible of the actuation and the sample, the latter is preserved from contamination and/or electrochemical modification. Silicon master microstructures were fabricated using cleanroom technologies and subsequently replicated into the PDMS. A full microsystem has been fabricated and tested. Microliter sample solutions can be easily and reproducibly dispensed in a time frame of a few tens of seconds. [2006-0244] Index Terms--Contactless dispensing, dosing, electrochemical actuation, microfluidics, polydimethylsiloxane (PDMS) replication, silicon microfabrication.

To measure a microflow rate and to accelerate the reaction between proteins by an unbalanced impingement of feedback flow, we have proposed and verified the design of a self-flapping microfluidic oscillator. Three specific features--the large aspect ratio of the micronozzle, the structure of the sudden-expansion inlet, and the asymmetric feedback channels--are developed to induce stable oscillation. The large aspect ratio of the micronozzle diminishes the influence of viscous force, and the inlet structure triggers flow instability. The conjunction of both factors promotes the occurrence of the Coanda effect, and initiates oscillation. The asymmetric feedback channels produce an unbalanced impingement of the inlet flow, thus reinforcing the initial oscillation to become stably periodic. Beyond the function of a microflowmeter, the oscillatory characteristics are applicable to accelerate the biochemical reaction between two fluorescent proteins, B-phycoerythrin and an allophycocyanin alpha subunit. With fluorescence induced with a laser, we detected the proteins at a specific wavelength to define the region of interaction caused by the oscillatory motions, which clearly enhances the rate of reaction of these fluids. To focus on the reaction phenomenon of twin fluids, we demonstrated biotin-streptavidin binding that was detected via a fluorescence-resonance-energy-transfer (FRET) pair of fluorescent proteins. The FRET signal demonstrated conclusively that the biochemical reaction was promoted through the oscillatory function. [2006-0233] Index Terms--Fluorescence resonance energy transfer (FRET), microflowmeter, microfluidic oscillator, [mu]-laser-induced-fluorescence (LIF).

This paper describes the design, fabrication, and testing of microfluidic devices enabled by electrodes embedded vertically in the side walls of SU-8 microchannels. With vertical electrodes on the side walls, one can generate higher lateral electrical fields uniform along the vertical direction in the channel (perpendicular to the substrate). By designing the electrode shapes and configurations, uniform and nonuniform electrical fields in the lateral (planar) directions can be applied to manipulate flow or particles in microchannels for switching or sorting applications. The uniform field is demonstrated in a magnetohydrodynamic (MHD) microfluidic device for directing cells to different channel outlets while the nonuniform field is demonstrated in the generation of dielectrophoresis (DEP) forces for microbead focusing. Metal electrodes are fabricated by electroplating to form vertical electrodes aligned with the channel walls. The multilayer SU-8 lithography technique enables the four walls of the channel to he all SU-8. The thin precoated SU-8 layer on the substrate improves structure integrity of the SU-8 microchannels. The mechanical flexibility of PDMS compensates for the surface nonuniformity from the previous patterning steps to conformably call the channel. The ability to integrate versatile electrodes design broadens the realm of electrical control and sensing for microfluidic applications. [2006-0106] Index Terms--Conformably bonding, dielectrophoresis (DEP), electroplating, flexible PDMS, lateral manipulation, magnetohydrodynmic (MHD), microfluidics, multilayer SU-8, surface topology, vertical electrodes.

This paper presents a self-adaptive microfluidic variable resistor that accomplishes passive control of liquid flows by exploiting the large compliance of elastomeric polymers such as polydimethylsiloxane. The device features a compliant microstructure embedded in a microchannel that consists of a flexible thin flap and a stiff stopper located in close proximity. The shape and size of the gap between the flap and stopper vary with the applied pressure, resulting in small resistance with respect to forward flow and large resistance with respect to reverse flow. The variable flow resistor shows an interesting diode behavior because its flow resistance is drastically different for different directions of applied pressures and is self-adaptive in the sense that its flow resistance varies with reverse pressure in such a way that the resulting flow rate remains a constant. That is, the flow resistor can be used as a check valve and, more importantly, a passive flow regulator. Prototype devices have demonstrated regulation of nearly constant water flow rates from 0.21 to 1.2 ml/min, with variations less than 3%, under driving pressures that vary significantly from 100 to over 200 kPa. Three-dimensional fluid-structure interaction simulations have been performed to investigate the interactions between the fluid flow and flap deflection. The simulation results agree with the experimental data and provide insight into the device characteristics. Based on its single-layer planar configuration, passive operation over a large pressure range, and use of a flexible and inexpensive polymer, this self-adaptive variable flow resistor is well suited to flow control in lab-on-a-chip systems. [2006-0129] Index Terms--Flow regulator, fluid structure interaction (FSI), fluidic resistor, microfluidics, valve.

This paper describes a novel composite actuator for controlled liquid actuation in microsystems which is based on a thermally responsive elastomer. The composite actuator consists of expandable microspheres incorporated in a polydimethylsiloxane (PDMS) matrix and entails the merits of both PDMS and expandable microspheres. The main characteristic of the composite actuator is to expand upon heat. The expansion is irreversible and the relative volume increase is measured up to 270% of its original volume after heating to 80 [degrees]C. The composite was used to fabricate single-use microfluidic pumps and valves. We show the displacement of liquids in the range of nanoliters even against counter pressures up to 100 kPa. Moreover, liquid flow in microchannels was entirely blocked by means of the integrated valves. The valves can withstand pressures up to 140 kPa. The devices are fabricated using low-cost materials only, and the composite actuator allows using wafer-level processing. The fluidic components based on the novel composite are highly integrable and do not require external actuators. Index Terms--Fluidics, microactuators, micropumps.

A novel polydimethyl siloxane (PDMS) microfluidic spotter system has been developed for the patterning of surface microarrays that require individually addressing each spot area and high probe density. Microfluidic channels are used to address each spot region, and large spot arrays can be addressed in parallel. Fluorescence intensity measurement of dye-spotted samples compared to control and pipetted drops demonstrated a minimum of three-fold increase in dye surface density compared to pin-spotted dyes. Surface plasmon resonance (SPR) measurement of protein-spotted samples as compared to pin-spotted samples demonstrated an 86-fold increase in protein surface concentration. The spotting system has been applied successfully to protein microarrays for SPR applications, in both a 12-spot linear and 48-spot two-dimensional (2-D) array format. This novel spotter system can be applied to the production of high-throughput arrays in the fields of genomics, proteomics, immunoassays, and fluorescence or luminescence assays. [1565] Index Terms--Microarray, microfluidic, polydimethyl siloxane (PDMS), spotter.

Using silicon microfabrication technology, microchemical devices have been constructed for the purpose of conducting heterogeneously catalyzed multiphase reactions. The motivation behind the design, the fabrication approach, and the experimental characterization are presented for two classes of devices. The first design involves multiple parallel channels with integrated filter structures to incorporate standard catalytic materials. These catalysts are in the form of finely divided porous particles in a packed-bed arrangement. The second device involves the incorporation of porous silicon as a catalyst support, in the form of a thin layer covering microstructured channels. These microstructured channels simulate the structure of a packed bed and enhance mass transfer relative to an open channel. The ability to incorporate features at the tens-of-microns scale can reduce the mass-transfer limitations by promoting mixing and dispersion for the multiple phases. Directly integrating the catalyst support structures into the channels of the microreactor allows the precise definition of the bed properties, including the support's size, shape and arrangement, and the void fraction. Such a design would find broad applicability in enhancing the transport and active surface area for sensing, chemical, and biochemical conversion devices. Reaction rates for the gas--liquid--solid hydrogenation of cyclohexene using the integrated catalyst with porous silicon as a support compare favorably to those rates obtained with the packed-bed approach. In both cases, the mass transfer coefficient is at least 100 times better than conventional laboratory reactors. [743]

Modeling of active control of microparticles is important in a number of different microfluidic applications, including bioflows and self-assembled structures. We present here a fast method for simulating the dynamics of many particles in complex microgeometries. The method is based on a spatial distribution of finite force multipoles and requires much less resolution than full direct numerical simulations. The numerical formulation is summarized, and examples are given for Stokes flow and low Reynolds number flew in smooth and rough microchannels. Comparisons made with full direct numerical simulations and experiments validate the accuracy and efficiency of the proposed approach. [800] Index Terms--Force coupling method, microfluidics, particles, spectral element method.

A thermal-bubble-actuated micropump by the principles of liquid/vapor phase transition and nozzle-diffuser flow regulation is successfully demonstrated. The micropump consists of a resistive heater, a pair of nozzle-diffuser flow controller and a 1 mm in diameter, 50 [micro]m in depth pumping chamber. The actuation mechanism comes from periodically nucleating and collapsing thermal bubbles. A net flow is generated from the nozzle to the diffuser by the nozzle-diffuser flow controller. Two heater designs, single-bubble and dual-bubble actuation mode, have been investigated. In the single-bubble pumping mode, a maximum flow rate of 5 [micro]l/min is measured when the driving pulse is 250 Hz at 10% duty cycle under an average power consumption of 1 W. A similar flow rate of 4.5 [micro]l/min is achieved in the dual-bubble pumping mode, at the driving pulse of 5% duty cycle at 400 Hz with lower average power consumption, 0.5 W. The static pumping pressure is measured at a maximum value of 377 Pascal when the net volume flow rate is zero. As an application example in a microfluidic device, this valve-less micropump is used in a microfluidic system to enhance the fluid mixing by agitating the flows. [742] Index Terms--Bubble, microfluidics, mixing, phase change, pump.

Electroosmotic (EO) micropumps use field-induced ion drag to drive liquids and achieve high pressures in a compact design with no moving parts. An analytical model applicable to planar, etched-structure micropumps has been developed. This model consists of pressure and flow relations in addition to an analytical expression that can be used to estimate the thermodynamic efficiency of planar EO pumps. The analytical model was applied to guide the design of a pump consisting of an etched EO flow chamber for near-optimal hydraulic power performance. To achieve high efficiency, the working fluid used was deionized (DI) water with a conductivity of 3.0 x [10.sup.-4] S/m (pH = 5.7). The EO micropump was fabricated on a soda-lime glass substrate using standard microlithography and chemical wet etching techniques. The active pumping volume of the device consists of a wet-etched flow channel 1-mm long in the flow direction and 0.9 [micro]m by 38-mm in cross section. The pump performance agrees well with the theoretical model. The pump can produce a maximum pressure of 0.33 atm and a maximum flow rate of 15 [micro]L/min min at 1 kV. [791] Index Terms--Electroosmotic (EO) pump, high pressure, Joule heating effects, microfabrication, microfluidics, thermodynamic efficiency.

A study was conducted to examine the use of a microelectromechanical system-based thermopneumatic valve, pressure regulator and mass flow controller technologies to develop ultraclean equipment for electronics specialty gas distribution. Flow models were utilized to determine stead-state behavior of the mass flow controllers. Results indicated that microelectromechanical system-based electronics specialty gas distribution equipment can integrate higher resolution and support better materials compatibility.

A new method for the fabrication of micro structures for fluidic applications, such as channels, cavities, and connector holes in the bulk of silicon wafers, called buried channel technology (BCT), is presented in this paper. The micro structures are constructed by trench etching, coating of the sidewalls of the trench, removal of the coating at the bottom of the trench, and etching into the bulk of the silicon substrate. The structures can be sealed by deposition of a suitable layer that closes the trench. BCT is a process that can be used to fabricate complete micro channels in a single wafer with only one lithographic mask and processing on one side of the wafer, without the need for assembly and bonding. The process leaves a substrate surface with little topography, which easily allows further processing, such as the integration of electronic circuits or solid-state sensors. The essential features of the technology, as well as design rules and feasible process schemes, will be demonstrated on examples from the field of [micro]-fluidics. [482] Index Terms--Lab-on-a-chip, micro channels, [micro]-fluidics, silicon micromachining.

A micrometer resolution particle image velocimetry system has been adapted to measure instantaneous velocity fields in an inkjet printhead. The technique uses 700-nm-diameter fluorescent flow tracing particles, a pulsed Nd: YAG laser, an epi-fluorescent microscope, and a cooled interline transfer charge-coupled device camera to record images of flow tracing particles at two known instances in time. Instantaneous velocity vector fields are obtained with spatial resolutions of 5-10 [micro]m and temporal resolutions of 2-5 [micro]s. The relationship between instantaneous velocity fields is compared to instantaneous shapes of the meniscus. The flow in the nozzle is highly unsteady and characterized by a maximum velocity of 8 [ms.sup.-1], Reynolds numbers of R = 500, and accelerations of up to 70 000 times gravity (i.e., 70 000 g). Since the flow field is periodic for each ejection cycle, the instantaneous measurements can be phased averaged to determine the evolution of the average flow field. The ejection cycle period is 500 [micro]s, and consists of four primary phases: infusion, inversion, ejection, and relaxation. During infusion, the actuator plate is deflected downward creating a low pressure that draws fluid into the inkjet cavity through the orifice and pulls the meniscus into the cavity through the nozzle. The meniscus grows, begins to decrease in size, and then deforms in shape, becoming inverted for approximately 6 [micro]s. The meniscus exits the cavity through the nozzle during droplet ejection. During relaxation, the flow undergoes viscously-damped oscillations, and reaches equilibrium before the next ejection cycle begins. [453] Index Terms--Inkjet, microfluidics, particle image velocimetry, PIV.

A large class of micro pumps consists of a cavity in a substrate, a diaphragm that seals the cavity, and inlets and outlets for the cavity which are controlled by valves. The cavity is initially filled with a fluid. The diaphragm is then actuated by a voltage between the diaphragm and the cavity floor to compress the fluid. When the pressure exceeds a certain value, the fluid is expelled. During actuation, the electrostatic attractive force of the substrate and the pressure rise in the fluid lead to the bending and stretching of the diaphragm. Thus, the prediction of the pump performance (e.g., fluid pressure, diaphragm stresses) requires the solution of a coupled nonlinear elasto-electro-hydrodynamic problem. In this paper, a simplified analytical model is developed to predict the state of an electrostatically actuated micro pump at equilibrium. The state includes the deformed shape and the internal stresses of the diaphragm and the pressure of the fluid when the actuator is subjected to a given applied dc voltage. The model is based on the minimization of the total energy consisting of the capacitive energy, the strain energy of the diaphragm, and the energy of the fluid which is considered to be an ideal gas. The method is employed to study two pumps, one with an axisymmetric single cavity, and the other with an axisymmetric annular cavity (a cavity with an island in the middle). In the former case, upon actuation, the diaphragm contacts the cavity floor from the outer periphery. Thus, energy is a function of the radius of the contact front, and equilibrium configuration is achieved at a radius where the derivative of the energy with respect to the radius vanishes. In the latter case, upon actuation, the diaphragm contacts the cavity from both of the inner and the outer peripheries. Here, equilibrium is reached when the derivatives of the energy with respect to the radii of both of the inner and outer periphery contact points vanish. It is expected that most practical pumps can be analyzed by one of the two formulations presented in the paper. Our analyses of both pumps indicate that the pressure of the gas at equilibrium increases only slightly when the stiffness of the diaphragm is increased, whereas it changes nearly inversely with the thickness of the dielectric between the diaphragm electrode and the cavity floor. Also, as expected, the pressure increases as the initial volume of the cavity (i.e., the volume of the gas to be compressed) is decreased. Furthermore, we find that the calculated stresses in the diaphragm do not exceed the typical yield stress values of many glassy polymers, a candidate material for the diaphragm. Therefore, the assumption of a linear elastic diaphragm employed in the proposed model does not put a limitation on the predictions. Dielectric breakdown may be a limiting factor for the maximum attainable pressure rather than the mechanical strength of the diaphragm material. Although stresses are low, they may be severe enough to cause delamination between different layers in the diaphragm, too. Index Terms - Diaphragm, electrostatic actuator, micro pump, pressure, strain, stress.