R.-H. Ma

Hargrave Military Academy, Rochester, New York, United States

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Publications (7)0.45 Total impact

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    ABSTRACT: The purpose of this paper is to propose two types of airflow velocity measurement modules, double-chip and single-chip, of MEMS-based flow sensors that consisting of heating resistors and sensing resistors on alumina films. In this study, MEMS techniques are used to deposit a platinum layer on the substrate to form resistors which is to regard as heater and sensing elements. As air flows through the heater and sensor, the temperature of the sensing resistor on the hot film decreases and the changes of the local temperature determine the airflow rate. The experimental results show the resistance variations as airflow velocity changes from 0 to 28 ms-1. Finally the experimental data indicate that sensing performance of the single-chip type is better than that of the double-chip type with due to its faster response and higher sensitivity.
    No preview · Article · Jan 2010
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    ABSTRACT: In realizing Lab-on-a-Chip systems, micro pumps play an essential role in manipulating small, precise volumes of solution and driving them through the various components of the micro chip. The current study proposes a micro pump comprising four major components, namely a lower glass substrate containing a copper micro coil, a microchannel, an upper glass cover plate, and a PDMS-based magnetic diaphragm. A Co-Ni magnet is electroplated on the PDMS diaphragm with sufficient thickness to produce a magnetic force of the intensity required to achieve the required diaphragm deflection. When a current is passed through the micro coil, an electromagnetic force is established between the coil and the magnet on the diaphragm. The resulting deflection of the PDMS diaphragm creates an acoustic impedance mismatch within the microchannel, which results in a net flow. The performance of the micro pump is characterized experimentally. A deflection of 30 ìm is obtained by supplying the micro coil with an input current of 0.6A, and results in a flow rate of 1.5 μl/sec when the PDMS membrane is driven by an actuating frequency of 240 Hz.
    No preview · Article · Jan 2009 · IFMBE proceedings
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    ABSTRACT: In this study, the proposed sensor integrates a sensing layer, a heating device, and electrodes on the substrate. The micro heater is integrated in the sensor to provide instantaneous and precise temperature control capability. The electrodes are fabricated to connect resistance meter for measuring variation of electrical conductibility of the sensing layer. The grain size of the NiO thin film is almost to be nanometer level, and therefore both the sensitivity and the lowest sensing limit of the device are enhanced due to the enlarged area of the catalyst grains contacting with the surrounding gas. The experimental data show that decreasing thickness of sensing layer in the sputtering process significantly increases the sensitivities of the gas sensor and improves its lowest detection limit capability (0.7 ppm). Although we can further improve lowest detection limit by co-sputtering with NiO/Al2O3 (40 ppb), it needs to consider that selectivity will be reduced. The integrated micro heater simplifies the experimental set-up and can be realized using a simple fabrication process. The presented microfabricated formaldehyde gas sensor with a self-heating NiO/Al2O3 thin film is suitable not only for industrial process monitoring but for safeguarding the human health in buildings.
    Full-text · Article · Jan 2008
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    ABSTRACT: The current study develops a new process for the fabrication of Pt resistor temperature detectors (RTD), cantilevers covered with a water-absorbent polyimide layer for humidity measurement and bending-up cantilevers to determining the wind velocity. Pt RTD's are fabricated on the silicon substrate. The temperature measurement is based on the linear resistance variations when temperature changes. The polyimide layer is spun on the cantilever to form a humidity sensing layer. A variation in humidity causes moisture-dependent bending of the microcantilever, which changes the measured resistance of the resistor on the microcantilever. The same type of microcantilever without spinning on polyimide is used to form an anemometer. It is found the cantilever slightly bends upward as a result of the released residual stress induced in the beam during the fabrication. When wind passes over the cantilever beam, a small deformation occurs. Variations in the wind velocity can therefore be determined by measuring the changes in resistance caused by the beam deflection using a LCR meter.
    Full-text · Article · Apr 2007
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    ABSTRACT: This paper proposes a numerical and experimental investigation of mixing behaviors of two liquid samples in microchannels that are shaped into different geometric barriers. The micro-mixers utilized in this study are fabricated on low-cost glass slides using a simple and reliable fabrication process. Samples are driven by a hydrodynamic pump to lead them into the mixing section of the microchannels. The effects of mixing performance of various kinds of barrier shape are discussed in this study. The numerical and experimental results show that a better mixing efficiency can be obtained in the microchannels while using the elliptic-shape barriers in compare with the leaking side-channels. In this study, the simulated and experimental results are in good agreement. The investigation of mixing efficiency in microchannels with different geometric barriers could be crucial for microfluidic systems.
    Full-text · Article · Jan 2006 · Materials Science Forum
  • R.-H. Ma · M.-C. Ho · C.-Y. Lee · Y.-H. Wang · L.-M. Fu
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    ABSTRACT: In this study, we exploit the bending-up of a cantilever paddle caused by residual stress to manufacture a micro-gas-flow-sensor for high-flow-rate sensing. Microsensors not only have a smaller physical size than their traditional counterparts, but also provide greater measurement accuracy and a higher sensitivity in the high gas flow velocity range. In this study, micro-electro-mechanical system (MEMS) techniques are used to deposit a silicon nitride layer on a silicon wafer to create a cantilever structure. A platinum layer is deposited on the silicon nitride layer to form a resistor and the structure is then etched to form a freestanding microcantilever. It is found that the cantilever slightly bends upward as a result of the released residual stress induced in the beam during the fabrication process. When airflow passes over the cantilever beam, a small deformation occurs. Variations in the airflow velocity can therefore be determined by measuring the changes in resistance caused by the beam deflection using an inductance-capacitance-resistance (LCR) meter. The experimental data indicate that the proposed gas flow sensor has a high sensitivity (0.0533 Ω/ms -1), a high measurement limit (45 ms -1) and a short response time (1.38 s).
    No preview · Article · Jan 2006 · Sensors and Materials
  • Y. Feng · X.H. Zhao · Y.H. Wang · R.H. Ma · Z.G. Zhou

    No preview · Article ·