N-SMARTS: Advanced Sensing

Home
Platform
Data
Advanced Sensing
Participatory Urbanism
Publications
People
Internal Wiki
Source Code
Links

MEMS Particulate Mass sensing

Prototype board demonstrating a GHz Thin Film Bulk Acoustic Wave Resonator (FBAR) Mass Sensor

Optical particle descrimination using IR and UV spectrometry

Airborne particulate matter (PM), or aerosols, are a major public health issue Estimated 65,000 excess U.S. deaths per year
  • Mechanisms not yet established; exposure not well known
  • No affordable population-based exposure assessment tools
  • Existing equipment bulky and expensive
  • Energy link: PM largely due to combustion
  • Broad biodefense applications (weaponized aerosols)
  • Nanoparticles
The N-SMARTS project is working to integrate a MEMS PM2.5 (particulate mass of less than 2.5 microns) mass sensor developed at LBNL and Berkeley into our design. For more technical details, check out the presentation (25MB!) on the original prototype design, done in a collaboration between Berkeley EECS and LBNL, and sponsored by California Air Resources Board and California Energy Commission.

Particulate Mass Sensing

Portable, compact monitor for airborne particulate matter (PM)
  • based on principles established at LBNL, since 2001
  • thermophoretic precipitation of particles on mass monitor
  • size-selective inlet based on competition between viscous flow and gravity
  • mass measurement using thin-film bulk acoustic wave resonator (FBAR) / Pierce oscillator
  • compatible with PM Federal Reference Methods
  • commercializable
Since the sensor mechanism itself is very small (around 100um x 100um), the majority of the prototype pictured to the right is plumbing. We are currently miniaturizing this mechanism and moving from a size-selective inlet based on compettion between viscous flow and gravity to one based on competition between viscous flow and centrifugal force. This change will make the design independent of the orientation of device, while not requiring limited lifetime filters.

Particle Characterization

Deposited particles can be descriminated by observing the absorbtion or scattering of UV and IR light. We plan to integrate this mechanism (previously verified with an independent prototype) into our miniaturized design, and study the sensitivity of this mechanism when using low cost UV and near-IR LEDs.

Previous studies have verified that particles generated by diesel fuel exhaust can be descriminated from cigarrette smoke particles. We plan to study the ability of this mechanism to descriminate between other forms of indoor air pollution, including particles generated by indoor cook stoves buring differnt types of fuel.

Other MEMS sensing possiblities

Source: Kamins, T.I., et al, "Metal Catalyzed Silicon Nanowires: Control and Connection," Proceedings on the 2005 5th IEEE Conference on Nanotechnology, Japan.
First, it might be possible to deposit gasses such as CO and NO2 on a FBAR using a chemical process rather than thermophoresis. In that case, the a design very similar to the one described above could be employed.

Also, there has been some initial consideration at the Berkeley Sensor and Accuator Center (BSAC) into using nanowires grown between two mems cantilever beams, and coated with tin oxide (SnO2). As CO contacts the nanowires, their temperature momentarily increases, and the resistance between the cantilevers changes. This resistance can be measured to give a fast, precise measurement of CO concentration.

We are looking for participants in this investigation!