• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1783-1788
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• 2004

In the present paper, a micro flow sensor, which can be used at bio-delivery systems and micro heat pumps, is developed. For this, the micro flow sensor is integrated on a quartz wafer ($SiO_2$) and is manufactured by simple and convenient microfabrication processes. The micro flow sensor aims for measuring mass flow rates in the low range of about $0{\sim}20$ SCCM. The micro flow sensor is composed of temperature sensors, a heater, and a flow microchannel. The temperature sensors and the heater are manufactured by the sputtering processes in this study. In the microfabrication processes, stainless steel masks with different patterns are used to deposit alumel and chromel for temperature sensors and nichrome for the heater on the quartz wafer. The microchannel is made of Polydimethylsiloxane(PDMS) easily. A deposited quartz wafer is bonded to the PDMS microchannel by using the air plasma. Finally, we confirmed the good operation of the present micro flow sensor by measuring flow rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.7
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• pp.542-548
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• 2008

A thermal mass air flow sensor (MAFS), which consists of a micro-heater and thermo-resistive sensors on the silicon-nitride ($Si_3N_4$) thin membrane structure, is micro-fabricated by MEMS processes. Two thermo-resistive temperature sensors are located at $100{\mu}m$ upstream and downstream from the micro-heater respectively. The thermal characteristics are measured to find the best measurement indicator. The micro-heater is operated under constant power condition, and four flow indicators are investigated. The normalized temperature indicator shows good physical meaning and is easy to use in practice. It is found that the configurations and heating power of thermal-resistive elements are the dominant factors to determine the range of the flow measurement in the MAFS with higher sensitivity and accuracy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.17-20
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• 2000

This paper describes on the fabrication and characteristics of hot-film type micro-flowsensors integrated with Pt-RTD's and micro-heaters on the Si substrate, in which MgO thin-films were used as medium layer in order to improve adhesion of Pt thin-films to $SiO_2$ layer, The MgO layer improved adhesion of Pt thin-films to $SiO_2$ layer without any chemical reactions to Pt thin-films under high annealing temperatures. In investigating output characteristics of the fabricated micro-flowsensors, the output voltages increased as gas flow rate and its conductivity increased due to increase of heat-loss from sensor to external. Output voltage was 82 mV at $N_2$ flow rate of 2000 seem/min, heating power of 1.2W.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.3
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• pp.595-600
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• 2005

A micro flow sensor on silicon substrate allows the fabrication of small components where many different functions can be integrated so that the functionality of the sensors can be increased. Further more, the small size of the elements these sensors can be quite fast. A thermal mass flow sensor measures the asymmetry of temperature profile around the heater which is modulated by the fluid flow. In normal, a mass flow sensor is composed of a central heater and a pair of temperature sensing elements around the heater A new 2-D wide range micro flow sensor structure with three pairs of temperature sensors and a central heater was proposed and numerically simulated by Finite Difference formulation to confirm the feasibility of the flow sensor structure in time domain.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.363-366
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• 2005

A micro flow sensor on silicon substrate allows the fabrication of small components where many different functions can be integrated so that the functionality of the sensors can be increased. Further more, due to the small size of the elements the sensors can be quite fast. A thermal mass flow sensor measures the asymmetry of temperature profile around the heater which is modulated by the fluid flow. In normal, a mass flow sensor is composed of a central heater and a pair of temperature sensing elements around the heater. A new 2-D wide range micro flow sensor structure with three pairs of temperature sensors and a central heater was proposed and numerically simulated by the Finite difference formulation to confirm the feasibility of the flow sensor structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.8
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• pp.573-579
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• 2009

A thermal mass air flow sensor, which consists of a micro-heater and thermal sensors on the silicon-nitride thin membrane structure, is micro-fabricated by MEMS processes. Three thermo-resistive sensors, one for the measurement of microheater temperature, the others for the measurement of membrane temperature upstream and downstream of the micro-heater respectively, are used. The micro-heater is operated under the constant temperature difference mode via a real time controller, based on inlet air temperature. Two design models for microfabricated flow sensor are compared with experimental results and confirmed their applicabilities and limitations. The thermal characteristics are measured to find the best flow indicator. It is found that two normalized temperature indicators can be adopted with some advantages in practice. The flow sensor with this control mode can be adopted for wide capability of high speed and sensitivity in the very low and medium velocity ranges.

• Journal of Mechanical Science and Technology
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• v.20 no.4
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• pp.554-560
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• 2006

This paper describes the demonstration of successful fabrication and initial characterization of micromachined pressure sensors and micromachined jets (microjets) fabricated for use in macro flow control and other applications. In this work, the microfabrication technology was investigated to create a micromachined fluidic control system with a goal of application in practical fluids problems, such as UAV (Unmanned Aerial Vehicle)-scale aerodynamic control. Approaches of this work include: (1) the development of suitable micromachined synthetic jets (microjets) as actuators, which obviate the need to physically extend micromachined structures into an external flow; and (2) a non-silicon alternative micromachining fabrication technology based on metallic substrates and lamination (in addition to traditional MEMS technologies) which will allow the realization of larger scale, more robust structures and larger array active areas for fluidic systems. As an initial study, an array of MEMS pressure sensors and an array of MEMS modulators for orifice-based control of microjets have been fabricated, and characterized. Both pressure sensors and modulators have been built using stainless steel as a substrate and a combination of lamination and traditional micromachining processes as fabrication technologies.

• Journal of Sensor Science and Technology
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• v.11 no.4
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• pp.191-199
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• 2002

This paper presents the design concept, theoretical investigation, and fabrication of a six-degree of freedom (6-DOF) turbulent flow micro sensor utilizing the piezoresistive effect in silicon. Unlike other flow sensors, which typically measure just one component of wall shear stress, the proposed sensor can independently detect six components of force and moment on a test particle in a turbulent flow. By combining conventional and four-terminal piezoresistors in Si (111), and arranging them suitably on the sensing area, the total number of piezoresistors used in this sensing chip is only eighteen, much fewer than the forty eight piezoresistors of the prior art piezoresistive 6-DOF force sensor.

• Journal of Sensor Science and Technology
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• v.20 no.6
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• pp.363-367
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• 2011

This paper proposes a highly-sensitive gas flow sensor with a simple structure. The sensor is composed of a micro-heater for heating the gas medium and a pair of temperature sensors for detecting temperature differences due to gas flow in a sealed chamber on one axis. Operation of the gas flow sensor depends on the transfer of heat through the air medium. The proposed gas flow sensor has the capability to measure gas flow rates <5 $cm^3$/min with a resolution of approximately 0.01 $cm^3$/min. Furthermore, this paper reports some additional experiment results, including the sensitivity of the proposed gas flow sensor as a function of operating current and the flow of different types of gas(oxygen, carbon dioxide, and nitrogen). The fabrication process of the proposed sensor is very simple, making it a good candidate for mass production.

• Journal of Sensor Science and Technology
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• v.9 no.5
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• pp.334-340
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• 2000

This paper presents the fabrication of a micro electromagnetic flow sensor for the liquid flow rate measurement. The micro electromagnetic flow sensor has some advantages such as a simple structure, no heat generation, a rapid response and no pressure loss. The principle of the micro electromagnetic flow sensor is based on Faraday's law. If conductive fluid passes through a magnetic field, the electromotive force is generated and detected by two electrodes on the wall of the flow channel. The flow sensor consists of two permanent magnets and a silicon flow channel with two electrodes. The dimension of the flow sensor is $9\;mm\;{\times}\;9\;mm\;{\times}\;1\;mm$. The micro flow channel is mainly fabricated by anisotropic etching of two silicon wafers, and the detection electrodes are fabricated by metal evaporation process. The characteristic of the fabricated flow sensor is obtained experimentally. When the flow rates of water with the conductance of $100-200\;{\mu}S/cm$ are 9.1 ml/min and 62 ml/min, the generated electromotive forces are $261\;{\mu}V$ and 7.3 mV, respectively.