A low-cost acoustic microsensor based system in package for air quality monitoring

In this paper we report on the development of a novel hybrid System in Package (SiP) microsensor utilizing high frequency acoustic wave devices for the real time monitoring of airborne fine particulates. The hybrid particle sensing system consists of a zinc oxide (ZnO) based solidly mounted resonator (SMR) device interfaced to a CMOS application-specific integrated circuit (ASIC) chip. Air is drawn into a virtual impactor where PM2.5 particles are separated and then deposited onto the SMR surface. The mass loading due to the fine particles is measured as a shift in the resonant frequency of the SMR working at 894 MHz. Experimental results performed in both laboratory conditions and real outdoor environment showed that the hybrid system is capable of detecting fine particles with a sensitivity of 7.5 kHz per μg/m
³
. This system is used as a basis towards a fully integrated portable smart particle sensor based on CMOS-SMR devices for the continuous, real-time and low-cost monitoring of airborne particulate matter.