Flow Microsensor Research Articles

Soft microflow sensors

We present a rapid prototyping method for integrating functional components in conventional PDMS microfluidic devices. We take advantage of stop-flow lithography (D. Dendukuri, S. S. Gu, D. C. Pregibon, T. A. Hatton and P. S. Doyle, Lab Chip, 2007, 7, 818)(1) to achieve the in situ fabrication of mobile and deformable elements with a controlled mechanical response. This strategy is applied to the fabrication of microflow sensors based on a deformable spring-like structure. We show that these sensors have a large dynamic range, typically 3 to 4 orders of magnitude, and that they can be scaled down to measure flows in the nl per min range. We prepared sensors with different geometries, and their flow-elongation characteristics were modeled with a simple hydrodynamic model, with good agreement between model and experiments.

Biomimetic Cilia Based on MEMS Technology

A review on the research of Micro Electromechanical Systems (MEMS) technology based biomimetic cilia is presented. Biomimetic cilia, enabled by the advancement of MEMS technology, have been under dynamic development for the past decade. After a brief description of the background of cilia and MEMS technology, different biomimetic cilia applications are reviewed. Biomimetic cilia micro-actuators, including micromachined polyimide bimorph biomimetic cilia micro-actuator, electro-statically actuated polymer biomimetic cilia micro-actuator, and magnetically actuated nanorod array biomimetic cilia micro-actuator, are presented. Subsequently micromachined underwater flow biomimetic cilia micro-sensor is studied, followed by acoustic flow micro-sensor. The fabrication of these MEMS-based biomimetic cilia devices, characterization of their physical properties, and the results of their application experiments are discussed.

Time-of-Flight Flow Sensor Microstructure Using Free-Standing Polysilicon Filaments

In this work we present a time-of-flight flow microsensor implemented using surface micromachining in combination with sacrificial layer technology. This approach allows obtaining free-standing polysilicon microfilaments that can be used as heaters or temperature sensors. The obtained microstructure can find applications in many important areas as process and environmental control, biomedicine and instrumentation. Numerical simulation showed a compromise between the size of the device (distance heater to sensor) and the range of volumetric flow to be detected. Also, the proposed structure is suitable for the detection of low volumetric flows and presents a response time of the order of milliseconds. Experimental results demonstrate that the heater can be operated at a temperature of the order of 100{degree sign}C with a power dissipation of ~ 30 mW. Also, tests with the implemented flow sensor structure and characterization apparatus revealed a good agreement with respect to the numerical simulation, confirming the predicted behavior.

Coupled Electro-Thermal Analysis of the Micro Flow Sensor with Control Circuit using SPICE

This paper reports an electro-thermal analysis of two-element Micro Flow Sensor (MFS). The measurement principle is based on temperature difference between upstream and downstream part of electrically connected heating-sensing elements. The two-heater MFS, the thermal fluid flow around MFS and the electric circuit were modeled together using a commercial general-purpose circuit simulator based on SPICE (Simulation Program with Integrated Circuit Emphasis). The model has a partial three-dimensional lumped thermal network model involved in a two-dimensional one. Two-dimensional laminar Poiseuille channel flow was assumed as the flow field in the model, and the forced convective heat transfer was calculated by energy balance at each node in the fluid flow. The tendency on the sensor characteristics was in good agreement between the simulation and experiment.

Hydrogel‐Encapsulated Microfabricated Haircells Mimicking Fish Cupula Neuromast

A hydrogel-capped hair-cell flow microsensor, which closely mimics a superficial neuromast of a fish, is introduced. By encapsulating the hair sensor into the artificial hydrogel cupula a dramatic increase in hair-sensor sensitivity to the oscillating and the steady flow is achieved. It opens the way toward the remote monitoring of the underwater environment by autonomous, unmanned microvehicles with self-navigating capability.

Study on an injection quantity sensor. II: Evaluation of the sensing element

For further optimization of the combustion process, the information about the actually injected fuel quantity is desirable, especially in diesel engines equipped with direct injection technology. A miniaturized hot-film anemometer with a titanium/platinum metallization on a low-temperature co-fired ceramics substrate was developed and integrated into a Common Rail injection nozzle. The micro-flow sensor proved its high performance and its capability over the complete fuel quantity map of a high pressure hydraulic injection system where drive pulses for the operation of the injector range between 0.3 ms and 1.5 ms at injection pressures up to 135 MPa (1350 bar). In correspondence with measurements of an injection amount indicator integrated into the hydraulic test bench, the injected fuel quantity and the opening behaviour of the orifice were derived from the sensor signals as a function of injection parameters. Assuming a power law dependence on the fluid velocity for the flow-sensitive portion of the heat-transfer coefficient, a value of 0.5 for the exponent was determined experimentally, in excellent agreement with theoretical predictions.

Evaluation of an amperometric glucose biosensor based on a ruthenium complex mediator of low redox potential

An amperometric glucose ring-disk biosensor based on a ruthenium complex mediator of low redox potential was fabricated and evaluated. This thin-layer radial flow microsensor (10 μl) with ring-disk working electrode displayed remarkable amperometric sensitivity. For Ru 3(μ 3-O)(AcO) 6(Py) 3(ClO 4) (Ru-Py), a trinuclear oxo-acetate bridged cluster, a reversible redox curve of low redox potential and narrow potential window (redox potentials were −0.190 and −0.106 V versus Ag/AgCl wire, respectively) was observed, which is comparable to many reported mediators such as ferrocene derivatives and other ruthenium complexes. The glucose and hydrogen peroxide assays were carried out with this complex-modified electrode Ru-Py-HRP-GOx/Nafion. The sensitivity was obtained 24 nA (15.4 mA M −1 cm −2) for 10 μM glucose and 126 nA (160 mA M −1 cm −2) for 5 μM H 2O 2, respectively with a working potential at 0 V versus Ag/AgCl. Ascorbic acid was studied as interference to the glucose assay. The application of 0 V potential versus Ag/AgCl did not avoid the occurrence of the oxidation of ascorbic acid, however, the pre-coating of ascorbate oxidase on the disk part of the ring-disk working electrode efficiently pre-oxidized the ascorbic acid and hence eliminated its interference on the glucose response. The practical reliability was also evaluated by assaying the dialysate from the prefrontal cortex of Wistar rats.

Monolithically integrated micro flow sensor for lab-on-chip applications

A monolithically integrated micro flow sensor (MFS) for lab-on-chip application is presented. The MFS utilizes a miniaturized adaption of the anemometric principle. The combination of an established detection principle with the benefits of microtechnology results in a sensor with very high sensitivity. The temperature distribution in the microfluidic channel is simulated and compared with experimental results. The experimental investigation confirms that the micro MFS is able to detect flow rates as low as 10 nl/min.

Distributed microflow sensor arrays and networks: design of architectures and communication protocols

Distributed microflow sensor arrays and networks are built from collections of spatially scattered, intelligent microflow sensor nodes. They can enhance the reliability and fault tolerance of the system. A new cluster network architecture and two original alternatives of fault-tolerant time-out communication protocol are described. Teamwork integration evaluator/micro-electromechanical system, a micro-electromechanical system sensor network simulation tool, was developed to evaluate the effectiveness of the network architectures and communication protocols.

Simulation for Velocity Measurement with Thermal Micro-flow Sensors

The measurement technology of fluid flow for micro-flow sensors has been applied in biomedicine, aerospace, the automobile industry and heat exchangers. A numerical study has been conducted to investigate the laminar flow and heat transfer behaviors of micro-channels for velocity measurement of micro-flow sensors. In this study, one method is used to calculate the heat transfer of the fluid flow in the micro-channels, and the difference of temperatures on the upper and bottom walls, which can be used to determine the velocity of fluid in the micro-channels. Another method consists of heating the bottom wall of the micro-channels, to observe the buoyancy effect induced by the difference in temperature or the secondary flow phenomenon, which can also result in very low fluid flow. We used the commercial code CFX4.1C as a numerical arithmetic unit with the finite volume method is used to simulate the equations for the three-dimensional, compressible and laminar flow.

On-Line Monitoring of Formaldehyde In Water and Air Using Chemiluminescence Detection

A rapid and sensitive chemiluminescence flow sensor for the determination of formaldehyde was proposed in this article. The analytical reagents involved in chemiluminescence (CL) reaction, luminol and KIO4, were both immobilized on an anion-exchange column. The CL signal produced by the reaction between luminol and KIO4, which were eluted from the column through water injection, was decreased in the presence of formaldehyde. Formaldehyde was sensed by measuring the decrement of CL intensity, which was observed linear over the logarithm of formaldehyde concentration range of 5.0-1000.0 ng mL−1, and the limit of detection is 1.8 ng mL−1 (3σ). At a flow rate of 2.0 mL min−1, including sampling and washing, could be performed in 0.5 min with a relative standard deviation of less than 3.0%. The flow sensor offered reagentless procedures and remarkable stability in determination of formaldehyde, and could be easily re-used over 80 h. The proposed flow microsensor was applied successfully in the determination of formaldehyde in artificial water samples and air.

A novel micromachined flow sensor using periodic flapping motion of a planar jet impinging on a V-shaped plate

Here we present a novel micromachined flow sensor capable of detecting small amounts of volumetric flow rates (down to 2 nl/s) and extra-low flow velocities (down to 0.15 mm/s). The innovative flow sensor detects a periodic flapping motion of a planar jet impinging on a V-shaped plate downstream. Instead of sensing DC current or voltage signals induced by small volumes of the flow, the microflow sensor detects the oscillating frequency of the periodic flapping jet, resulting in a higher sensitivity and a larger dynamic range than that of the existing products. The microflow sensor is fabricated on a quartz substrate using wet chemical etching and metal masks. It is composed of a planar convergent nozzle, a V-shaped plate downstream and a pair of sensing resistors. The microflow sensor is characterized both optically and electrically. First, a dye-containing sample flow is used to visualize the flapping motion of the impinging jet under a microscope. Flapping motion is confirmed experimentally even at a low flow velocity (0.15 mm/s). Then, the flapping frequency is detected using built-in microsensing resistors driven by a constant-current circuit. Data from microscopic flow visualization and electrical sensing are highly consistent. It indicates that even in microscale the flow velocity is still linearly proportional to the frequency of the jet flapping motion. Therefore, the velocity or volumetric flow rate of small amounts of the flow can be measured by detecting the flapping frequency. Note that the test Reynolds number ranges from 0.2 to 5.4 in the present study. It is the first time that low-Reynolds-number flow is reported with a flapping motion for flow impinging on a V-shaped plate. The microflow sensor can be applied in various fields, including biomedical detection, micrototal analysis system, smart fluidics etc.

Optimization of two-element flow microsensors using quasi 3-D numerical electrothermal analysis

Simulation and measurement results are presented for a two-element boundary layer flow sensor fabricated using integrated circuit and micromachining technologies. The sensor is located on a thermally isolated membrane and utilizes platinum-based resistive heating and sensing elements. Device optimization is based on quasi three-dimensional (3-D) numerical solutions of the electrothermal equations governing heat transport. Here, we investigate the effects of geometrical non-idealities, and in particular, thermal isolation (between elements and between elements and substrate) on output response and offset. The results corroborate well with measurement data for a large range of operating voltages and flow velocities.

Behavior of Thermal and Fluid Flow around a Micro-Sensor. The Experiment by Enlarged Model and Numerical Analysis.

Micro-Flow-Sensor (MFS) equipped with a heater at its center can measure temperature difference up and downstream of the heater. MFS is a suitable sensor for determining separation point, since it can detect flow speed and direction near the wall. The sensor is so small that it is difficult to measure directly heat and fluid flow around it by other instruments. In the stage of micro sensor development the mutual guarantee is needed between the experiment of an enlarged sensor model and its numerical analysis. In this paper, a problem of micro sensor is described from a point of micro experimental fluid dynamics by numerical analysis with convection heat transfer around the micro sensor and experiment of the enlarged MFS model.

K-1336 低レイノルズ数における後方ステップ再付着流れの研究(S15-11 ステップのはく離)(S15 噴流・はく離流れの計測と制御)

A study on flow around the micro device is strongly required in MEMS development. The objective of this paper is to study dependence of Reynolds number on reattachment process over a backward-facing step in low Reynolds number flow. The Reynolds number based on step height H is 190-5730 and reattachment length was measured by Micro Flow Sensor (MFS) in a Micro Sensing Wind Tunnel which was constructed in the present research program. The reattachment length from 8H to 21H is observed depending on Reynolds number.

Development and Characterization of Microfluidic Devices and Systems for Magnetic Bead-Based Biochemical Detection

This paper presents the development and characterization of a generic microfluidic system for magnetic bead-based biochemical detection. Microfluidic and electrochemical detection devices such as microvalves, flow sensors, biofilters, and immunosensors have been successfully developed and individually characterized in this work. Magnetically driven microvalves, pulsed-mode microflow sensors, magnetic particle separators as biofilters, and electrochemical immunosensors have been sep-arately fabricated and tested. The fabricated microfluidic components have been surface-mounted on the microfluidic motherboard for fully integrated microfluidic biochemical detection system. A magnetic bio-bead approach has been adopted for both sampling and manipulating target biological molecules. Magnetic beads were used as both substrate of antibodies and carriers of target antigens for magnetic bead-based immunoassay, which was chosen as a proof-of-concept for the generic microfluidic bio-chemical detection system. The microfluidic and electrochemical immunosensing experiment results obtained from this work have shown that the biochemical sensing capability of the complete microfluidic subsystem is suitable for portable biochemical detection of bio-molecules. The methodology and system, which has been developed in this work, can be extended to generic bio-molecule detection and analysis systems by replacing antibody/antigen with appropriate bio receptors/reagents such as DNA fragments or oligonucleotides for application towards DNA analysis and/or high throughput protein analysis.

A novel open flow microflow sensor for reduced fouling of chemical sensors in physiological sampling environments

A method of reducing fouling/biofouling on the active surface of sensors in unclean environments is presented. The technique depends on differences in the diffusion coefficients of the analytes and foulants. Details of the fabrication and testing are given. Results of experiments with a micromachined flow cell are presented and contrasted with those of a computational fluid dynamics model. Modelling shows effective repulsion of foulants and predicts a signal strength consistent with experimental results.

Design issues for membrane-based, gas phase microchemical systems

The use of finite element simulations to characterize the operating behavior of a microchemical reactor and enhance its design is described. Important design issues for a microreactor, specifically heat and mass transfer, are explored with the design of a micro-flow sensor and the redesign of the reactor heater. The impact of the design choices for a flow sensor is quantitatively evaluated and an optimal design is proposed. This design was fabricated and testing confirmed the simulation work. The reaction channel heater was redesigned to improve thermal uniformity in the reaction zone. Simulations showed that before ignition significant non-uniformity still existed, but this was dramatically reduced after ignition. The use of previously reported kinetic models for ammonia oxidation in microreactor simulations is also discussed. It was found that kinetic models evaluated in conventional reactor experiments are inadequate for use in microreactor simulations because of the lower operating temperature and broader range of temperatures of the microreactor.

An Analysis of the Heat Transfer for a Micro-Flow Sensor

An Analysis of the Heat Transfer for a Micro-Flow Sensor

Finite-element modeling of the transient response of MEMS sensors

The finite-element method of analysis is unrestricted by size considerations and is well suited for the study of very small structures such as MEMS devices embedded in structures. This paper presents the numerical approach and results for a silicon-based micro-flow sensor for pulsed-flow sensing. The new approach presented here is the treatment of transient problems. A finite-element formulation is presented for modeling the dynamic response of piezoelectric ceramic sensors embedded in a micro-cantilever subjected to mechanical loading resulting from fluid flow. An unconditionally stable method (called the -method) is used for the direct integration of the equations of motion and implicit - explicit procedures are used for the transient analysis of the linear system of equations. For verification of the code, the device is tested for step, rectangular pulse and sinusoidal loading. For the case of the micro-fluid flow sensor, numerical results are in good agreement with the available experimental data based on a piezoresistive sensor. The numerical approach presented here may be used in CAE models for microsensors under more realistic, transient excitation.