Chip-Scale Implementation and Cascade Assembly of Particulate Matter Collectors With Embedded Resonant Mass Balances

This paper presents design, fabrication, characterization, and cascade assembly of chip-scale aerosol inertial impactors (airborne micro/nanoparticle collector). Microelectromechanical resonant mass balances are integrated within the fabricated chip-scale aerosol impactors for real-time particulate matter (PM) concentration measurement. A microfabrication process including only three-lithography steps has been developed to form the main impactor stage components: mass balance, impactor nozzle, and impaction micro-chamber on a single silicon on insulator (SOI) substrate. This approach enables dramatic miniaturization of the conventional bulky impactors while adding real-time measurement capability. Furthermore, utilization of microfabrication techniques can address some of the existing manufacturing and precision assembly challenges for such devices. Smaller nozzle diameters down to $30 {\boldsymbol \mu }\text{m}$ enabled by micro-lithography minimize the air flow, typically in the few liters per minute range, to milliliters per minute, and consequently the pump capacity and power requirements. Fabricated devices are tested as individual stages as well as cascaded dual-stages. Tests performed in different environments with different particle mass concentrations show an evident correlation between the resonator response and the expected particle concentrations. scanning electron microscopy (SEM) images of the deposited particles for single impactor stages shows particle sizes as small as ~12 nm. For the cascade impactors, the SEM images show particles of ~150 and 41 nm for first and second stage, respectively. This paper demonstrated that segregation of nano-particles was achieved with the proposed dual stage chip-scale aerosol inertial impactor.