Showing papers in "Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems in 2009"

Current micropump technologies and their biomedical applications

Abstract: This paper briefly reviews recent research and developments of micropump designs with a particular emphasis on mechanical micropumps and summarizes their applications in biomedical fields. A comprehensive description of the actuation schemes, flow directing concepts and liquid chamber configurations for micro pumping is provided with illustrative diagrams. Then, a comparative study of current mechanical micropump designs highlighting their advantages and limitations for various applications is presented, based on performance criteria such as actuation voltage and power consumption, ranges of operating frequency and maximum flow rate and backpressure. This study compiles and provides some basic guidelines for selection of the actuation schemes and flow rate requirements in biomedical applications. Different micropumps in biomedical applications, such as blood transport and drug delivery also have been reviewed.

A micro electromagnetic low level vibration energy harvester based on MEMS technology

Abstract: This paper presents a micro electromagnetic energy harvester which can convert low level vibration energy to electrical power. It mainly consists of an electroplated copper planar spring, a permanent magnet and a copper planar coil with high aspect ratio. Mechanical simulation shows that the natural frequency of the magnet-spring system is 94.5 Hz. The resonant vibration amplitude of the magnet is 259.1 μm when the input vibration amplitude is 14 μm and the magnet-spring system is at resonance. Electromagnetic simulation shows that the linewidth and the turns of the coil influence the induced voltage greatly. The optimized electromagnetic vibration energy harvester can generate 0.7 μW of maximal output power with peak–peak voltage of 42.6 mV in an input vibration frequency of 94.5 Hz and input acceleration of 4.94 m/s2 (this vibration is a kind of low level ambient vibration). A prototype (not optimized) has been fabricated using MEMS micromachining technology. The testing results show that the prototype can generate induced voltage (peak–peak) of 18 mV and output power of 0.61 μW for 14.9 m/s2 external acceleration at its resonant frequency of 55 Hz (this vibration is not in a low ambient vibration level).

Dielectric materials for electrowetting-on-dielectric actuation

Abstract: The fundamental building blocks of typical electrowetting-on-dielectric (EWOD) actuation and their importance in the EWOD mechanism are introduced and reviewed, respectively. The emphasis in this experimental study of EWOD is on dielectric materials, upon which the performance of EWOD devices is heavily dependent. Dielectric breakdown of several typical polymeric and inorganic insulators employed as dielectrics for EWOD has been analytically investigated, which is forced to occur between the electrodes and conductive liquids under certain threshold potential. The electric breakdown occurring in both dielectric layer and surrounding medium (air or silicon oil) has been studied to build up a mathematical model of breakdown voltage as a function of dielectric thickness. Contact angle measurement of some polymeric materials and self-assembled monolayer using pure water has been carried out to demonstrate the contact angle tunability and reversibility, respectively, upon EWOD actuation.

Permanent magnet configuration in design of an eddy current damper

Abstract: This paper discusses the design of an eddy current passive damper using different configurations of permanent magnets. Motional eddy current damping effect is used for the development of a passive damper. Eddy currents are generated in a conductor in a time-varying magnetic field. They are induced either by movement of the conductor in a static field or by changing the strength of the magnetic field, initiating motional and transformer electromotive forces, respectively. The conceived eddy current damper consists of a conductor as an outer tube, and an array of axially magnetized, ring-shaped permanent magnets (PMs), separated by iron pole pieces as a mover. The relative movement of the magnets and the conductor causes the conductor to undergo motional eddy currents. Using this concept, damping characteristics of the new damper is obtained through analytical modeling, and verified by experimental analysis. The optimum PMs’ size and configuration are also derived using analytical and finite element analysis, respectively. A damping coefficient as high as 53 kg/s is achievable with the proposed design specifications.

Lifetime modelling for microsystems integration: from nano to systems

Abstract: Due to the rapid development of IC technology the traditional packaging concepts are making a transition into more complex system integration techniques in order to enable the constantly increasing demand for more functionality, performance, miniaturisation and lower cost. These new packaging concepts (as e.g. system in package, 3D integration, MEMS-devices) will have to combine smaller structures and layers made of new materials with even higher reliability. As these structures will more and more display nano-features, a coupled experimental and simulative approach has to account for this development to assure design for reliability in the future. A necessary “nano-reliability” approach as a scientific discipline has to encompass research on the properties and failure behaviour of materials and material interfaces under explicit consideration of their micro- and nano-structure and the effects hereby induced. It uses micro- and nano-analytical methods in simulation and experiment to consistently describe failure mechanisms over these length scales for more accurate and physically motivated lifetime prediction models. This paper deals with the thermo-mechanical reliability of microelectronic components and systems and methods to analyse and predict it. Various methods are presented to enable lifetime prediction on system, component and material level, the latter promoting the field of nano-reliability for future packaging challenges in advanced electronics system integration.

Dynamic characteristics and forced response of an electrostatically-actuated microbeam subjected to fluid loading

Abstract: In this paper flexural vibrations of an electrostatically actuated cantilever microbeam in an incompressible inviscid stationary fluid have been studied. By applying “Three dimensional aerodynamic theory” pressure jump across the microbeam has been investigated and the inertial effects of fluid on microbeam dynamics have been modeled as a mass added to microbeam mass. Magnitude of the added mass has been calculated for various aspect ratios of cantilever microbeams and compared with those of clamped-clamped microbeams. To investigate the dynamic characteristics, it has been considered that the microbeam has been deflected by a DC voltage, V DC and then the dynamic characteristics and forced response of the system have been considered about these conditions. Galerkin-based step by step linearization method (SSLM) and Galerkin-based reduced order model have been applied to solve the nonlinear static and dynamic governing equations, respectively. Water by neglecting viscidity effects, as an instant has been considered as a surrounding fluid and the frequency response of the microbeam has been compared with that of vacuum conditions. It has been shown that because of the added mass effects in watery environment, the natural frequencies of the microbeam decrease. Because of the higher dielectric coefficient and increasing electrical stiffness and decreasing total stiffness consequently, maximum amplitude of the microbeam vibrations increases in watery environment, compared with vacuum. Moreover, it has been shown that increasing the DC voltage, increases the electrical stiffness and maximum amplitude of the microbeam vibrations, consequently, It has been shown that in higher voltages (near pull-in voltage), the rate of variation of resonance frequency and maximum amplitude is stronger than lower voltages.

Design and fabrication of MEMS-based microneedle arrays for medical applications

Abstract: Fabrication results for MEMS-based microneedle arrays are presented in this paper. The microneedle array was fabricated by employing a bi-mask technique to facilitate sharp tips, a cylindrical body and side openings. The presented array has advantages over previously published microneedle arrays in terms of ease of fabrication and bonding; high needle density and robustness; and side openings, which are expected to minimize the potential for clogging from skin debris during insertion. In addition, control over the process via etch-stop markers employed as stop layers, which assure the depth of long blind holes and the structure of the needle top, allows for different needle lengths and needle top structures to be easily implemented. The preliminary fluid flow and insertion experiments were performed to demonstrate the efficiency of the microneedle arrays.

Cross-axis sensitivity reduction of a silicon MEMS piezoresistive accelerometer

Abstract: This paper presents realization of a MEMS piezoresistive single axis accelerometer using dual doped TMAH solution. The silicon micromachined structure consists of a heavy proofmass supported by four thin flexures and sandwiched between top and bottom glass plates. Boron diffused piezoresistors located near fixed points of the flexure are used for sensing the developed stress due to applied acceleration. Based on the initial results an improved design has also been considered to achieve reduced cross-axis sensitivity and nonlinearity. The fabricated sensor tested upto 13 g acceleration shows average sensitivity of 0.556 mV/g along normal to the proofmass plane. The measured cross-axis sensitivity was 3.272 μV/g for X-axis and 3.442 μV/g for Y-axis which is less than 1% of Z-axis sensitivity. Comparing two designs there was an improvement of 63% sensitivity along Y-axis for the design with flexures placed along the proofmass edges.

Hot roller embossing for microfluidics: process and challenges

Abstract: We report an initial study on hot roller embossing as a potential process for the mass production of polymer based microfluidic chips. Measurements conducted on 100 µm features showed that the lateral dimensions could be replicated to within 2% tolerance, while over 85% of mould depth was embossed. Feature sizes down to 50 µm and feature depths up to 30 µm had been achieved. Results revealed that the embossing depth increased with an increase in the nip force or a decrease in the rolling speed. There was an optimum temperature for achieving a high embossing depth; this was due to the reflow effect seen at higher temperatures. One observation included an asymmetric pile up of polymer material outside the embossed regions as a result of the orientation of the microchannel with respect to the rolling direction. This directional effect could be due to the dynamics of the roller setup configuration.

Design and fabrication of a micro Alvarez lens array with a variable focal length

Abstract: A 5 × 5 micro Alvarez lens array mold was fabricated using a 5-axis ultraprecision diamond machine and an Alvarez lens array was manufactured by injection molding process. Unlike conventional processes for asymmetrical element fabrication such as small tool grinding, this research demonstrates slow tool servo broaching process that allows the entire Alvarez lens array to be accurately machined on a metal mold in a single operation. To further reduce manufacturing cost, injection molding was used to fabricate the Alvarez lens arrays. The mold and molded lenses were both measured using an optical profiler. All measured profiles showed a good agreement with design and surface roughness also indicated an optical surface finish. The functionality of the molded polymeric lens arrays was achieved when the focal lengths were varied by laterally translating the molded Alvarez lens array pair. This research is a demonstration of the capability of fabricating complex optics using the same approach.

Comparison of micro-dispensing performance between micro-valve and piezoelectric printhead

Abstract: In micro-dispensing applications, printhead activation mechanism, its design and operating parameters are integrated together to affect the droplet generation process. These factors give each printhead advantages and limitations over the others in specific fabrication. Hence, multiple printheads on micro level fabrication are preferred to perform multi-material dispensing task. In this paper, the mechanisms of two commonly used micro printheads, solenoid actuated micro-valve and piezoelectric printhead are discussed. Comprehensive experiments are conducted to characterize their performance and the results are analyzed so as to explore optimal droplet formation condition. With regards to the operational parameters’ influence on droplet formation, micro-valve is investigated in terms of pressure, and operational on time, and piezoelectric printhead is investigated based on pulse amplitude, and width of driving pulse. Nozzle size, a key design parameter in the two printheads, is also studied according to its influence on dispensing capability. To facilitate dispenser selection, the two printheads are compared based on droplet size, droplet stability, droplet velocity, and dispensing viscosity of successful ejection. Other factors such as chemical compatibility, time consumption in determining optimal condition and reliability of dispensing process are also reported to play an essential role in this selection. Our investigation on the relationship between related parameters and dispensing performance will not only benefit dispenser selection in multi-material dispensing application, but also build a solid background to develop multiple printhead system for fabrication of bioengineering components.

Static and dynamic stabilities of a microbeam actuated by a piezoelectric voltage

Abstract: In this paper, flutter and divergence instabilities of a cantilever, a clamped–clamped, and a cantilever with intermediate simply-support microbeam sandwiched by piezoelectric layers have been studied. By presenting a mathematical formulation and numerical solution, critical piezoelectric force for avoiding of the instability in a cantilever microbeam has been calculated and validated by known buckling capacity of Beck column. By applying a similar mathematical analysis it has been introduced a critical piezoelectric voltage for a clamped–clamped microbeam. It has been shown that for cantilever microbeams, increasing of the follower piezoelectric force leads to: first flutter and then divergence instabilities whereas in the clamped–clamped microbeams only divergence instability can be occurred. Also effects of the intermediate simply support position on the critical piezoelectric voltage of a cantilever microbeam have been investigated. It has been shown that for case when the intermediate simply support is near to the fixed end of the cantilever increasing of the follower piezoelectric force leads to flutter instability but for case when the intermediate simply support is near to the free end of the cantilever it leads to divergence instability.

Micro injection molding of micro gear using nano-sized zirconia powder

Abstract: Powder injection molding (PIM) is well established in macro molding. Scaling down to micro-PIM (μPIM) opens a new arena for cost effective production of micro components. One potential application is the manufacture of cutting tools with sharp edges for machining. However, scaling down to such a level produces challenges in raw material preparation, injection molding and thermal treatment. In this report, near dense (>98% of theoretical density) tensile bars and 3 mm micro gears were produced using 50 nm Yttria Tetragonal Zirconia Polycrystal (Y-TZP). The sintered gear teeth were well defined and visually defect free.

Study of novel electrical routing and integrated packaging on bio-compatible flexible substrates

Abstract: Electrical routing and integrated packaging on bio-compatible flexible substrates have been designed and fabricated. The realized packaging method can integrate electrical circuits, stationary components and moving components on flexible substrates. Chips can be embedded on flexible packages and work on a non-planar surface. In this article, the package specimens are tested and simulated in tensile, bending and sealing experiments. In addition, the density and Young’s Modulus of polydimethylsiloxane (PDMS) is discussed with various curing conditions. A prototype made by the packaging process shows its functional system integration. This flexible packaging technology can be applied to communication or sensing products when flexibility is required.

Dynamic response of a torsional micromirror to electrostatic force and mechanical shock

Abstract: In this paper dynamic characteristics of a capacitive torsional micromirror under electrostatic forces and mechanical shocks have been investigated. A 2DOF model considering the torsion and bending stiffness of the micromirror structure has been presented. A set of nonlinear equations have been derived and solved by Runge–Kutta method. The Static pull-in voltage has been calculated by frequency analyzing method, and the dynamic pull-in voltage of the micromirror imposed to a step DC voltage has been derived for different damping ratios. It has been shown that by increasing the damping ratio the dynamic pull-in voltage converges to static one. The effects of linear and torsional shock forces on the mechanical behavior of the electrostatically deflected and undeflected micromirror have been studied. The results have shown that the combined effect of a shock load and an electrostatic actuation makes the instability threshold much lower than the threshold predicted, considering the effect of shock force or electrostatic actuation alone. It has been shown that the torsional shock force has negligible influence on dynamic response of the micromirror in comparison with the linear one. The results have been calculated for linear shocks with different durations, amplitudes, and input times.

A single chip, double channel thermal flow meter

Abstract: The fabrication and experimental characterization of a thermal flow meter, capable of detecting and measuring two independent gas flows with a single chip, is described. The innovative aspect of the sensor is the use of a plastic adapter, thermally sealed to the chip, to convey the gas flow only to the chip areas where the sensors are located. The packaging approach allowed placing two micrometric differential thermal anemometers, present on 4 × 4 mm2 silicon chips, into distinct flow channels. The reduced spacing between the sensing structures required positioning of the latter on channel bends, introducing sensitivity reduction and response asymmetries with respect to single channel devices presented earlier. These effects are explained using fluid-dynamic simulations.

Fabrication and characterization of a polymethyl methacrylate continuous-flow PCR microfluidic chip using CO 2 laser ablation

Abstract: An improved microfabrication method was used to fabricate a continuous-flow PCR (polymerase chain reaction) microfluidic chip on the PMMA substrate using the low-power CO2 laser ablation technique. The use of the low-power CO2 laser and the PMMA material could reduce the cost and the time of the fabrication process, especially at the step of laboratory research because of the high flexibility of the laser fabrication technique and the low cost of PMMA. A CO2 laser output power of 4.5 W and a laser scanning velocity of 76.2 mm/s were chosen to fabricate the chip in this work. The micromachining quality could satisfy the microfluidic requirement of the PCR mixture within the microchannel. Good temperature distribution and gradient were obtained on the PMMA chip with a home-built integrated heating system. An amplification of DNA template with a 990 base pair fragment of Pseudomonas was successfully performed with this chip to characterize its availability and performance with various flow rates.

Thermal network model for temperature prediction in hard disk drive

Abstract: In this paper, an alternative numerical method has been proposed to predict the temperature distribution in a 1.8-in. hard disk drive (HDD). Comparing it with conventional finite element model, the proposed thermal network model takes lesser time in predicting the HDD temperatures for both steady-state and transient analysis, and with good accuracy. In addition, it has been shown that this method is capable of performing temperature shock analysis.

Microdroplet generation in gaseous and liquid environments

Abstract: As trends in biology, chemistry, medicine and manufacturing have pushed macroscopic processes onto the micro scale, droplet generation has been a key factor in allowing these methods to translate. For both surface-based liquid-in-gas generation and lab-on-a-chip-based liquid-in-liquid generation, the ability to create small monodisperse liquid droplets is critically important in constructing reliable and practical devices. This article reviews liquid microdroplet generation in gaseous and liquid environments, covering the general characteristics of generators and the specific methods and technologies used for generation. Furthermore, this study compiles the issues encountered when operating generators, and the measurements and instrumentation used to characterize generated droplets. Applications of droplet generation in printing, analysis, synthesis and manufacturing are also discussed.

A study of PZT valveless micropump with asymmetric obstacles

Abstract: The results of a study on a new type of PZT valveless micropump with asymmetric obstacles are presented in this paper. The valveless micropump was made through a MEMS fabrication process by using simply only one photo mask. Asymmetric obstacles are used for the flow directing device instead of the diffuser/nozzle elements used in previous studies. In this study, numerical simulations were also carried out to evaluate the design and the performance of the new micropump. The main feature of the present micropump is that it has a uniform cross-section area across the micro-channel, which gives many advantages. The differential pressure head and the pumping flow rate can be adjusted easily by using obstacles of different shapes and changing the PZT operating frequency without changing the dimensions of the micro-channel. In this experiment, the performance of the micropump was evaluated by measuring the pressure head difference and the flow rate as the input voltage ranged from 20 to 40 V, a range much lower than those in previous studies. The pumping pressure can reach a maximum of 1.2 kPa, and the maximum net volume flow rate is 156 μl/min. These test data indicate that this micropump fulfills the demands for most micro-fluidic systems. Moreover, the present device can be easily applied to complex systems with combinations of several pumps and microchannels in the future.

Influence of processing parameters on micro injection molded weld line mechanical properties of polypropylene (PP)

Abstract: As a hot fabrication technology for micro scale parts, micro injection molding is receiving increasing market attention. Improving mechanical properties of micro parts should be an important issue in the micro injection molding process. The relation between weld line strength in micro injection molding parts and processing parameters is investigated. A visual mold with variotherm unit is designed and constructed, in which the micro tensile specimen with weld line are prepared. Polypropylene (PP) is used as the research material in this study, and six processing parameters were chosen as investigating factors, which were melt temperature, mold temperature, injection pressure, packing pressure, ejection temperature and injection speed. In order to achieve optimized processing parameters and their order of significance, Taguchi experiment method was applied in this presented study. The prediction formulation of the strength of micro weld line was built up by multiple regression analysis based on Chebyshev orthogonal polynomial. The results showed the influencing significance order of parameters from strong to week separately are mold temperature, melt temperature, injection speed, ejection temperature, packing pressure and injection pressure. And the tolerance of micro weld line prediction formulation was found to be lower than 21% through confirmation experiments.

Thermal conductivity measurement of submicrometer-scale silicon dioxide films by an extended micro-Raman method

Abstract: The micro-Raman method is a noncontact and nondestructive method for thin film thermal conductivity measurements. To apply the micro-Raman method, however, the thickness of the film must be at least tens of micrometers. An analytical heat transfer model is presented in this work to extend the micro-Raman measurement method to measure the thermal conductivity of thin films with submicrometer- or nanometer-scale thickness. The model describes the heat transfer process in the thin film and substrate considering the effects of thin film thickness, interface thermal resistance, thermal conductivity of the thin film and substrate. From this heat transfer model, an analytical expression for the thermal conductivity of the thin film is derived. Experiments were successfully performed to measure the thermal conductivity of 200, 300 and 500 nm thickness silicon dioxide films using the extended micro-Raman measurement method, with results confirming the accuracy and validity of the extended model.

A cross-junction channel valveless-micropump with PZT actuation

Abstract: A gas-jet micro pump with novel cross-junction channel has been designed and fabricated using a Si micromachining process. The valveless micro pump is composed of a piezoelectric lead zirconate titanate (PZT) diaphragm actuator and fluidic network. The design of the valveless pump focuses on a cross-junction formed by the neck of the pump chamber and one outlet and two opposite inlet channels. The structure of cross-junction allows differences in fluidic resistance and fluidic momentum inside the channels during each PZT diaphragm vibration cycle, which leads to the gas flow being rectified without valves. The flow channels were easily fabricated by using silicon etching process. To investigate the effects of the structure of the cross-junction on the gas flow rate, two types of pump with different cross-junction were studied. The design and simulation were done using ANSYS-Fluent software. The simulations and experimental data revealed that the step-nozzle structure is much more advantageous than the planar structure. A flow rate of 5.2 ml/min was obtained for the pump with step structure when the pump was driven at its resonant frequency of 7.9 kHz by a sinusoidal voltage of 50 Vp–p.

Design and fabrication of a microfluidic device for near-single cell mRNA isolation using a copper hot embossing master

Abstract: We describe investigations toward a disposable polymer-based chip for the isolation of eukaryotic mRNA. This work focuses here on the improvement of the fabrication methods for rapid prototyping and the actual application at lowest RNA concentrations with total channel volumes of 3.5 μL. Messenger RNA isolation was achieved using paramagnetic oligo (dT)25 beads within a microfluidic channel which incorporated a sawtooth microstructured design to aid in mixing. The structures were shown to facilitate mixing beteen two fluids in parallel flow when compared to a channel without structures. The chip was fabricated by means of hot embossing poly(methyl methacrylate) (PMMA) using a copper master. Copper was used as the master material due to its excellent thermal, mechanical, and electroplating properties. Fabrication of the master consisted of the structuring of a polished copper plate using KMPR 1050 as an electroplating mold for forming the microchannel structures. The copper master was found to be much more robust than traditional silicon masters used for prototyping. The use of KMPR enabled the generation of high straight walls in contrast to SU-8 masters. In addition, embossing times were able to be decreased by a factor of 3 due to improved heat conduction and avoidance of a lengthy and delicate de-embossing step.

Fabrication of compliant high aspect ratio silicon microelectrode arrays using micro-wire electrical discharge machining

Abstract: This paper reports on the fabrication of high aspect ratio silicon microelectrode arrays by micro-wire electrical discharge machining (μ-WEDM). Arrays with 144 electrodes on a 400 μm pitch were machined on 6 and 10 mm thick p-type silicon wafers to a length of 5 and 9 mm, respectively. Machining parameters such as voltage and capacitance were varied for different wire types to maximize the machining rate and to obtain uniform electrodes. Finite element analysis was performed to investigate electrode shapes with reduced lateral rigidity. These compliant geometries were machined using μ-WEDM followed by a two step chemical etching process to remove the recast layer and to reduce the cross sections of the electrodes.

Microfluidic devices for sample pretreatment and applications

Abstract: With the fundamentals of microscale flow and species transport well developed, the recent trend in microfluidics has been to work towards the devices capable of dealing with ‘real’ crude samples directly. Before the real samples reaching the analytical step, it nearly requires significant pre-treated steps. Development of these microdevices that perform sample preprocessing steps is now underway for a broad range of application areas from on-chip DNA analysis, immunoassays to cytometry. This article provides an overview of the latest developments in microfluidic devices for sample pretreatment. Many of the microchips are being designed for individual preprocessing steps, but integration of multiple sample preparation steps has been shown, along with integration of sample preprocessing and analytical procedures on single microchips.

An evaluation of process-parameter and part-geometry effects on the quality of filling in micro-injection moulding

Abstract: This paper addresses the use of micro-injection moulding for the fabrication of polymeric parts with microfeatures. Five separate parts with different micro-feature designs are moulded of Polymethylmethacrylate. The design-of-experiments approach is applied to correlate the quality of the parts to the processing parameters. Five processing parameters are investigated using a screening half-factorial experimentation plan to determine their possible effect on the filling quality of the moulded parts. The part mass is used as an output parameter to reflect the filling of the parts. The experiments showed that the holding pressure is the most significant processing parameter for all the different shapes. In addition, the experiments showed that the geometry of the parts plays a role in determining the significant processing parameters. For a more complex part, injection speed and mould temperature became statistically significant. A desirability function approach was successfully used to improve the filling quality of each part.

Mitigation of flow induced vibration of head gimbal assembly

Abstract: The airflow of a 10,000 rpm hard disk drive is simulated using the LES turbulent model. The critical parameters for using LES model to get the correct/reliable result are discussed. The flow induced vibration of the head gimbal assembly is calculated with the obtained fluid force acting on the head gimbal assembly (HGA) and compared with measured results. Good agreement is observed between the measured and simulated results. The optimization of the airflow is further carried out to reduce the flow induced vibration of the HGA. It is found that almost 50% reduction of flow induced vibration of the HGA can be achieved with the proposed modifications for airflow optimization.

Design, fabrication and analysis of micromachined high sensitivity and 0% cross-axis sensitivity capacitive accelerometers

Abstract: This paper presents the design and fabrication of three MEMS based capacitive accelerometers. The first design illustrates the achievement of an accelerometer with 0% cross-axis sensitivity and has been fabricated using PolyMUMPs, a multi-user surface-micromachining process. A unidirectional parallel plate configuration is utilized in this design to illustrate the achievement of 0% cross-axis sensitivity and an acceptable performance range. In addition, a method is introduced to improve the sensitivity of a capacitive sensor employing a transverse configuration based on the relationship of initial gaps setup in comb-finger arrangements. A design based on this technique and the PolyMUMPs fabrication process is illustrated which demonstrates a sensitivity value of 4.07 fF/µm, with a nonlinearity of 2.05% for a ±3 µm sensor operating range. The last design based on this method and the SOIMUMPs fabrication process exhibits a sensitivity of 3.45 pF/µm for ±1 µm operating range of the sensor.

The effect of the microfluidic diodicity on the efficiency of valve-less rectification micropumps using Lattice Boltzmann Method

Abstract: The efficiency of the valve-less rectification micropump depends primarily on the microfluidic diodicity (the ratio of the backward pressure drop to the forward pressure drop). In this study, different rectifying structures, including the conventional structures (nozzle/diffuser and Tesla structures), were investigated at very low Reynolds numbers (between 0.2 and 60). The rectifying structures were characterized with respect to their design, and a numerical approach was illustrated to calculate the diodicity for the rectifying structures. In this study, the microfluidic diodicity was evaluated numerically for different rectifying structures including half circle, semicircle, heart, triangle, bifurcation, nozzle/diffuser, and Tesla structures. The Lattice Boltzmann Method (LBM) was utilized as a numerical method to simulate the fluid flow in the microscale. The results suggest that at very low Reynolds number flow, rectification and multifunction micropumping may be achievable by using a number of the presented structures. The results for the conventional structures agree with the reported results.