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Development of Micronozzles for Gas Sensing Applications    Collaborators - Dr. Gary W. Rubloff, Dept. of Materials and Nuclear Eng., Univ. of Maryland - Dr. Christopher Cadou, Dept. of Aerospace Eng., Univ. of Maryland    Research Overview This research work is focused on the development of MEMS-based micronozzles for gas sensing applications. Specifically, this project is an effort to investigate the microscale gas dynamics and to develop reliable, robust and high performance front-end components for generic miniaturized sensors. In the first phase of research, fundamental fluid dynamics of gas flows in microscale nozzles is studied by using linear test structures (i.e., contoured converging- diverging nozzles). Device testing includes the development of a gas flow test setup to measure the pressure distribution and mass flow rate of gas flows and estimation of viscous effects in micronozzles. The second phase of research deals with single-stage separation nozzle systems. Design of separation nozzles is based on the testing results of the linear structures and an analytical model on the equilibrium separation process for a cylindrical gas flow. Wafer -level bonding and deep reactive ion etching (DRIE) techniques are used to fabricate the gas separation devices. The elementary effect of the single-stage separation nozzle is evaluated through testing of the devices and analysis of separated gas samples. The experimental results can be extended to the design of multistage separation nozzle systems which are envisioned for miniaturized chemical sensors.    Thesis S. Li, "Design, Fabrication and Testing of Micronozzles for Gas Sensing Applications," Ph.D. Thesis, University of Maryland, College Park, February 2006.    Journal Papers S. Li, J.C. Day, J.J Park, C. Cadou, and R. Ghodssi, "A Fast-Response Microfluidic Gas Concentrating Device for Environmental Sensing", Sensors and Actuators A: Physical, Vol. 136, pp. 69 - 79, 2007. S. Li, C. B. Freidhoff, R. M. Young  and R. Ghodssi, "Fabrication of Micronozzles Using Low Temperature Wafer-level Bonding with SU-8," Journal of Micromechanics and Microengineering(JMM), Vol. 13, pp. 732 - 738, September 2003.    Conference Papers S. Li, J. J. Park, J. C. Day, G. W. Rubloff, C. P. Cadou, and R. Ghodssi, "Development of a Fast-Response Microfluidic Gas Concentrating Device," EUROSENSORS XIX, Barcelona, Spain, September 11-14, 2005. S. Li, C. B. Freidhoff, R. M. Young, and R. Ghodssi, "Development of MEMS-based Micronozzles for Gas Separation," Proceedings of the Materials Research Society 2004 Spring Meeting, San Francisco, California, April 12-16, 2004. S. Li, C. B. Freidhoff, R. M. Young, and R. Ghodssi, "Fabrication, Packaging and Testing of Micronozzles for Gas Sensing Applications," American Vacuum Society 50th International Symposium, Baltimore, Maryland, November 2-7, 2003. S. Li and R. Ghodssi, "Development of Microfluidic devices for Gas Centrifuge Separation," American Vacuum Society 49th International Symposium, Denver, Colorado, November 3-8, 2002.