Design of a Frequency Counter for Mass-sensing Film-Bulk Acoustic Resonators

Particulate matter (PM) is a category of air-borne pollutant that includes dust, smoke, diesel exhaust and smog. Fine particle (PM2.5) pollution is especially damaging to our health. Due to their small size these particles penetrate the body’s natural filtration systems and lodge deep within the lungs, contribute to several health problems such as reduced lung functionality, bronchitis, and heart attacks. While there is increasing demand for PM2.5 monitoring, the prevailing equipment is fairly bulky and expensive, which limits the possibilities for widespread, fine granularity sensing. Portable PM sensors are needed to allow for better identification of pollution sources, health awareness, and pollution control. In order to achieve this goal a MEMS air-microfluidic sensor is used, which measures the concentration of the particulates by the rate of the frequency shift of a mass-loaded film bulk acoustic resonator (FBAR). As particles are deposited onto the exposed surface of the resonator, the additional mass lowers its resonant frequency[1]. The main goal of this dissertation thesis is to design and realize a very low power portable RF frequency counter which operates with the MEMS air-microfluidic sensor in order to correctly measure the concentrations of airborne PM. The whole design is realized on a PCB board and it is specifically designed for small form factor and low power so that it can be seamlessly integrated with a mobile device such as a smartphone or a laptop.