Micromachined cascade virtual impactor for aerodynamic size classification of airborne particles

We report design, fabrication and experimental results of a micromachined cascade virtual impactor with flow rate distributor for classifying airborne particles according to their sizes. The fabricated device consists of two components: a cascade virtual impactor for classifying particles according to their own inertia, and a flow rate distributor to maintain specific flow rates at each channel. Proposed device is fabricated using polymer-based micromachining. Due to the flow rate distributor, only one external pump was used for controlling major flow rates and minor flow rates. DOS particles ranged from 100 to 600 nm and carbon particles from 0.6 to 10 mum were used for the classification experiments. Particle size distribution at the inlet and each minor flow were measured by SMPS for DOS particles and APS for carbon particles. Classification of airborne particles with 3 cut-off diameters is successfully demonstrated. The measured cut-off diameters were 135 nm, 1.9 mum, and 4.8 mum.