Ying Dong

Characterization of the gas sensors based on polymer-coated resonant microcantilevers for the detection of volatile organic compounds.

The gas sensors based on polymer-coated resonant microcantilevers for volatile organic compounds (VOCs) detection are investigated. A method to characterize the gas sensors through sensor calibration is proposed. The expressions for the estimation of the characteristic parameters are derived. The effect of the polymer coating location on the sensors sensitivity is investigated and the formula to calculate the polymer-analyte partition coefficient without knowing the polymer coating features is presented for the first time. Three polymers: polyethyleneoxide (PEO), polyethylenevinylacetate (PEVA) and polyvinylalcohol (PVA) are used to perform the experiments. Six organic solvents: toluene, benzene, ethanol, acetone, hexane and octane are used as analytes. The response time, reversibility, hydrophilicity, sensitivity and selectivity of the polymer layers are discussed. According to the results, highly sensitive sensors for each of the analytes are proposed. Based on the characterization method, a convenient and flexible way to the construction of electric nose system by the polymer-coated resonant microcantilevers can be achieved.

Laboratory calibration of star tracker with brightness independent star identification strategy

Star trackers based on charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) sensors, use a brightness independent star identification strategy that requires highly accurate measurements of star spot position. Therefore, precise calibration of the measurement model is crucial. Generally, ground-based real night sky observation is a specific and costly approach. In this work, an optical laboratory method for star tracker calibration is proposed. This method is based on ordinary instruments, laser autocollimation adjustment, and image processing techniques. The calibration issues of the star tracker with a brightness independent star identification strategy are analyzed. A new laboratory calibration method is introduced, and its results on an active pixel sensor (APS) star tracker are discussed. This method proves to be practical and adequate in the development of a star tracker with wide field of view.

Brightness independent 4-Star matching algorithm for lost-in-space 3-Axis attitude acquisition

Abstract A star identification algorithm was developed for a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) autonomous star tracker to acquire 3-axis attitude information for a lost-in-space spacecraft. The algorithm took advantage of an efficient on-board database and an original “4-star matching” pattern recognition strategy to achieve fast and reliable star identification. The on-board database was composed of a brightness independent guide star catalog (mission catalog) and a K-vector star pair catalog. The star pattern recognition method involved direct location of star pair candidates and a simple array matching procedure. Tests of the algorithm with a CMOS active pixel sensor (APS) star tracker result in a 99.9% success rate for star identification for lost-in-space 3-axis attitude acquisition when the angular measurement accuracy of the star tracker is at least 0.01°. The brightness independent algorithm requires relatively higher measurement accuracy of the star apparent positions that can be easily achieved by CCD or CMOS sensors along with subpixel centroiding techniques.

Improvement of a micro-beam in a smart gas sensor with resonating mechanism

A micro-beam of a creative smart resonating gas sensor with a self-actuating and detecting (SAD) system is presented. The smart SAD sensor, in which the resonance frequency shifting of the MEMS cantilever is monitored to probe its mass change caused by adsorption of certain gas molecules, has never need exclusive detection circuits and instruments, and the micro-beam has never need additional detective MEMS structure consequently. Some design rules of the more compact micro-beam has been obtained by computer simulation analysis and related discusses. Some electrostatic driving MEMS beam has been fabricated by surface silicon micromachining and sacrificial layer process with low cost, and tested by laser vibration-meter system. An improvement of the micro-beam is introduced by comparison study of the computer simulation results and testing results of the fabricated beam.

Trace Gas Sensor Based on MEMS Cantilever Resonator

A chemical gas sensor for volatile organic compounds (VOCs) detection at trace level is proposed. In this paper, the development and demonstration of the sensor prototype are presented. The prototype is based on a microcantilever resonator that is fabricated from direct bonding silicon-on-insulator (SOI) wafer. The resonant cantilever employs integrated thermal driving and piezoresistive detecting units, and operates in a self-oscillation system. Polyethylenevinylacetate (PEVA) is deposited on top of the cantilever as gas sensitive layer through a spraying method. The responses of the prototype to relative humidity (RH) and six common VOCs: toluene, benzene, ethanol, acetone, hexane and octane have been tested. The PEVA-coated prototype has trace sensitivity to toluene, benzene, hexane and octane, while is insensitive to humidity. The experimental results provide confirmation that the microcantilever resonator is an excellent platform for chemical gas sensor.

Electrothermal Driving Microcantilever Resonator as a Platform for Chemical Gas Sensing

Abstract In the current research, the use of a micromachined cantilever resonator as a platform for chemical gas sensing was examined. The microcantilever resonator integrates an electrothermal driving unit and a piezoresistive detecting unit, and it is fabricated by direct bonding a silicon-on-insulator (SOI) wafer. With a particular polymer layer coated on the surface of the microcantilever, a gas sensor for volatile organic components (VOCs) detection can be realized. The operation mechanism provides the microcantilever resonator with integrated circuit (IC) compatibility in terms of both the fabrication process and operating voltage. The configuration of the microcantilever resonator can optimize the performance of the gas sensor. The SOI wafer provides a solution for the integrated fabrication of the microstructure, transducers, electronics, and the precise control of the resonator parameters. In this paper, the principles, design, analysis, process, and demonstration of the gas sensor based on the microcantilever resonator are presented. The experimental results provide confirmation that the polymer-coated microcantilever resonator has excellent performance with regard to VOC detection.