AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Characterization of an Air-Microfluidic Direct-Reading MEMS PM Mass Sensor
IGOR PAPROTNY, Paul A. Solomon, Richard White, Lara Gundel, University of California, Berkeley
Abstract Number: 298 Working Group: Portable and Inexpensive Sensor Technology for Air Quality Monitoring
Abstract This work continues the development of a small portable particulate matter (PM) sensor 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 Microelectromechanical Systems (MEMS) - based PM sensor directly measures fine (< 2.5 micrometer aerodynamic diameter, AD) PM mass concentrations in real-time, with a limit of detection of a few microgram/m$^3. Microfabrication techniques have reduced the area of the sensor to few cm$^2 and about 27 g with 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 micrometer 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. As the PM loading on the FBAR increases, the resonating frequency (600 MHz) decreases.
In this work, we show how the PM sensor performs in the field under ambient conditions as temperature and relative humidity change, affecting the sensitivity of the FBAR to the deposited PM mass. We also investigate the performance of the VI by comparing PM size cutpoints and size-dependent wall losses through its microfabricated channels. Several different designs of the microfabricated VI are investigated and discussed. The results are used to verify the numerical model used to design a nominal cutpoint of 2.5 micrometer AD at a flow-rate of 6 mL/min. Finally, we discuss improvements to key steps of the microfabrication process to improve the sensitivity of MEMS scale particle mass measurements.