AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Optimization of Air-Microflidic Circuits for Microfabricated Direct-Read Mass PM2.5 Sensors
SEIRAN KHALEDIAN, Dorsa Fahimi, Troy Cados, David Woolsey, Omid Mahdavipour, Paul A. Solomon, Thomas Kirchstetter, Lara Gundel, Richard White, Igor Paprotny, University of Illinois at Chicago
Abstract Number: 573 Working Group: Instrumentation and Methods
Abstract This work continues the development of our small portable particulate matter (PM) sensing platform that can be incorporated into lightweight, low-power devices with PM levels communicated through wireless networks for community-based monitoring of air pollution, as well as other aerosol instrumentation. The micro-electromechanical systems (MEMS)-based direct reading PM mass sensor measures fine (<2.5 micron aerodynamic diameter, [AD]) PM mass concentrations in real-time, with a limit of detection of a few micrograms/m$^3. Microfabrication techniques have reduced the area of the sensor to few cm$^2 and its weight to about 27 gm including its housing, enabling portable (perhaps wearable) real-time monitoring of airborne particles. The sensor consists of two main components: a virtual impactor (VI) that removes coarse (>2.5 micron AD) particles, and a deposition area where a film bulk acoustic resonator (FBAR) measures the mass of the particles that have been driven from the airstream to the surface of the resonator by thermophoresis.
In this work, we present an optimization of the microfluidic circuit with aim to increase the sensitivity of the sensor to PM$_(2.5). Computational Fluid Dynamic (CFD) modeling is used to design the new optimized version while opto-gravimetric and microscopy results from microfabricated test show experimental results in a good agreement with simulation. The characterization of the opto-gravimetric method is presented, enabling highly accurate sampling of the collection efficiencies of the devices at flow rates below 10 L/min. Cut-point analysis for PM$_(2.5), which consists of the convolution of the cut-point due to upstream VI, inertial concentration of particles, particle settling, and the thermophoretic efficiency, is presented, resulting in an optimized microfluidic circuit.