Design, Fabrication and Testing of Micronozzles for Gas Sensing Applications

Real-time identification and quantitative analysis of volatile and semi-volatile chemical vapors are critical for environmental monitoring. Currently available portable instruments lack the sensitivity for routine air quality monitoring, so preconcentrators are employed as front-ends for miniaturized chemical sensors. However, commonly used techniques for sensitivity enhancement have a time constant associated with adsorption/desorption or permeation of gas molecules being concentrated. Little work has been reported on fast-response concentrating techniques for gas sensing applications. This research is devoted to the development of a fast-response microfluidic gas concentrating device with appropriate flow dynamic shapes and pressure gradients based on the separation nozzle method. It is capable of concentrating heavy gas molecules diluted in light ones when they are flowing at high speeds, thus maintaining the measurement system response time. This is promising for developing real-…

Author: Li, Sheng

Source: University of Maryland

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Contents
CHAPTER 1
INTRODUCTION
1.1 Introduction
1.2 Motivation and Background
1.3 Literature Review
1.3.1 Common Sensitivity Enhancement Techniques
1.3.2 Separation Nozzle Method for Isotope Separation
1.4 Objectives
1.5 Contributions
1.6 This Organization
CHAPTER 2
LINEAR TEST STRUCTURES
2.1 Introduction
2.2 Design of Linear Nozzles
2.2.1 One-dimensional Isentropic Model
2.2.2 Finite Element Analysis
2.3 Device Fabrication and Packaging
2.3.1 SU-8 Bonding Process
2.3.2 Anodic Bonding Process
2.3 Fluidic Interconnection
2.4 Gas Flow Test
2.5 Results and Discussion
2.6 Summary
CHAPTER 3
DEVICE DESIGN AND MODELING
3.1 Introduction
3.2 Theory: Separation Nozzle Method
3.2.1 Equilibrium Separation
3.2.2 Diffusion Processes
3.3 Design of Separation Element
3.4 Computational Fluid Dynamics Modeling
3.4.1 Governing Equations
3.4.2 Boundary Conditions
3.4.3 Solution Method
3.4.4 Results
3.5 Summary
CHAPTER 4
DEVICE FABRICATION
4.1 Introduction
4.2 Processing
4.2.1 Wafer Cleaning
4.2.2 Photolithography
4.2.3 Reactive Ion Etching
4.2.4 Deep Reactive Ion Etching
4.2.5 Anodic Bonding
4.2.6 Packaging and Mounting
4.3 Summary
CHAPTER 5
DEVICE CHARACTERIZATION
5.1 Introduction
5.2 Gas Separation Experiment
5.2.1 Experimental Setup
5.2.2 Mass Flow Test
5.3 Mass Spectrometric Gas Analysis
5.3.1 Principle of Mass Spectrometry
5.3.2 Evaluation of Mass Spectra
5.3.3 Experimental Setup
5.4 Results and Discussion
5.4.1 Characterization of Separation Effect
5.4.2 Evaluation of Device Performance
5.5 Summary
CHAPTER 6
CONCLUSION
6.1 Introduction
6.2 Summary of Current Research
6.3 Future Work
APPENDIX A
BASIC THEORY OF COMPRESSIBLE FLUID FLOW
A.1 Introduction
A.2 Compressibility
A.3 Fundamental Principles and Aspects of Compressible Flow
A.4 Convergent-Divergent Nozzle
A.5 Summary
APPENDIX B
EQUILIBRIUM SEPARATION NOZZLE FLOW
B.1 Introduction
B.2 Equilibrium Separation Process
B.3 Equilibrium Bifractional Splitting
B.4 Summary
APPENDIX C
AUTOMATED PRESSURE MEASUREMENT SETUP
C.1 Introduction
C.2 Computer Setup
C.3 LabVIEW
C.4 Summary
APPENDIX D
ELECTRONIC NOSE TECHNOLOGY
D.1 Introduction
D.2 Caltech Electronic Nose
D.3 Comments and Summary
BIBLIOGRAPHY