Uğur Soysal
Published: 2019
Total Pages: 0
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Microfabrication methods are an emerging technology which enables to build micro scale airborne particle mass concentration measurement systems. A personal airborne particle monitoring system can be achieved by combining an appropriate sampling method with inertial micro-electromechanical systems (MEMS) mass sensors. While aerosol sampling methods can take airborne particles from ambient air and transport to a detector in the most efficient way, MEMS provide the detection and estimation of the mass based on a shift in the resonance frequency of oscillating sensors.In this context, an extensive literature review is proposed in order to examine the mass concentration measurement methods from past to present. The methodological tendencies for advanced real-time aerosol mass concentration measurement are evaluated. Finally, bulk-mode silicon-based MEMS mass sensor is chosen to be coupled with an appropriate aerosol sampler.Following that the miniaturization possibilities of aerosol sampling methods are discussed and inertial impactor is chosen as a suitable aerosol sampling method. Then, the impactor is designed, fabricated, and characterized based on the classical impaction theory. The latter, the deposition characteristics of monodisperse aerosol (fluorescent) and bioaerosols (Aspergillus niger, Staphylococcus epidermidis, Pseudomonas fluorescens) are explored by inertial impaction on silicon and nanostructured silicon (i.e. black silicon). The empirical results show that the size of airborne particles plays a key role to determine the deposition characteristics of the impaction by the mechanism of rebound and re-entrainment (i.e. bounce effect) of the particles.In the context of developing an inertial mass sensor, sub-μm air gap MEMS mass sensors have been successfully fabricated based on the thick oxide as a mask layer method. This method enables to fabricate high-aspect-ratio air-gap MEMS resonators. Then, the devices are electrically characterized and the mass resolution is investigated. As a result, high-aspect-ratio MEMS sensors are operated in two different bulk modes (Lamé and extensional modes) and the mass resolution of the sensors is found to be as sub-ng.Finally, the fabricated MEMS mass sensors are integrated into the developed impactor and monodisperse fluorescent particles are successively impacted on the sensors. The shift in the resonance frequency of MEMS mass sensors are evaluated based on Sauerbrey's principle. Ultimately, MEMS mass sensors have achieved to detect and perform mass measurements of the impacted fluorescent particles with a promising precision. Although more impactions are needed to calibrate the sensors, the theoretical mass sensitivity of the device is matched with the experimental mass sensitivity obtained from successive impactions. Therefore, the developed airborne particle detection system paves the way for real-time detection and mass measurements of aerosol and bioaerosols.