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Mirthe mar12


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Mirthe mar12

  1. 1. Modeling and Design Optimization ofQuartz-Enhanced PhotoAcoustic Spectroscopy (QEPAS) Sensors J. Zweck(1) , S. Minkoff(1) , F. Tittel(2) , A. Kosterev(2) , N. Petra(3) , M. Barouti(1) , and J. Doty(2) (1) Department of Mathematics and Statistics, UMBC (2) Department of Electrical and Computer Engineering, Rice U. (3) Institute for Computational and Engineering Sciences, U.T. Austin March 2012 J. Zweck (UMBC) QEPAS March 2012 1/5
  2. 2. Project Motivation Microresonator (MR) tubes amplify the QEPAS signal by a factor of about 30. But alignment cost of laser, MR and quartz tuning fork (QTF) is prohibitive (≈$2,500 per sensor). Possible Solution Omit MR and numerically optimize QEPAS signal strength as a function of QEPAS geometry. Potential for 50% assembly cost savings. More generally, we are developing better models for QEPAS—with or without a MR—and using them to numerically optimize QEPAS design (increase S/N). J. Zweck (UMBC) QEPAS March 2012 2/5
  3. 3. Viscous Damping Model for QEPAS Existing QEPAS models require experimentally measured values of Q-factor (bad for numerical design optimization). The Q-factor is primarily determined by viscous damping due to motion of QTF in air. We propose a viscous damping model for QEPAS that will allow us to numerically optimize QEPAS geometry. Mechanism for Viscous Damping Fluid viscosity attenuates acoustic pressure wave Hence pressure-driven displacement of QTF is damped Model based on a system of partial differential equations that couples acoustic pressure wave and heat diffusion in gas with resonant mechanical deformation of QTF. J. Zweck (UMBC) QEPAS March 2012 3/5
  4. 4. Experimental Validation of Models 7 10 Theory 1 Experiment Normalized signal strength 0.8 Normalized Amplitude 6 10 0.6 0.4 5 10 0.2 4 0 10 0 1 2 3 4 5 0 0.4 0.8 Beam Position (mm) z (mm) Normalized amplitude of piezoelectric signal as a function of vertical position of laser beam. Left: QEPAS without MR tubes or viscous damping Right: ROTADE (Resonant OptoThermoAcoustic DEtection). The discrepancy for z > 0.25 mm is due to QEPAS-ROTADE interaction, which we did not model (yet!) J. Zweck (UMBC) QEPAS March 2012 4/5
  5. 5. Preliminary Design Optimization Result(ROTADE) Left: Standard QTF; Right: Optimized QTF with 20× signal strength Caveat: Optimization proceedure assumed Q-factor independent of QTF geometry (not realistic). Goal: Do more realistic design optimization using new viscous damping model for QEPAS. J. Zweck (UMBC) QEPAS March 2012 5/5