A resonant cantilever based particle sensor with particle-size selection function

This paper reports on a novel resonant-gravimetric micro-cantilever based particle sensor for detecting particles (e.g. PM2.5) in air. A row of micro-pillars with desired separation-distance are integrated in a micro-channel that is embedded in the cantilever as a filter to select the particles of desired size. When particles containing air are pumped into the micro-channel, the particles with desired diameters are trapped by the micro-pillars near the free-end of the cantilever, which results in a detectable resonant frequency shift of the micro-cantilever. After detection the sensor can be recovered by reversing the direction of the air flow to blow off the trapped particles and the sensor is ready for the next detection. By tuning the spacing between the barrier bars, the diameters of the trapped particles can be customized for specific detection applications. The complicated structure of the resonant sensor is fabricated by using a novel IC-foundry compatible single-sided surface micromachining technique, with single-side-polished (1 1 1) silicon wafers on a low-cost non-SOI substrate. The sensor prototype has experimentally exhibited excellent real-time detection performance to standard polystyrene micro-spheres, with the resolution of the single particle being distinguishable. The sensor is promising in applications of air pollution monitoring and analysis. (paper)