In this study, a highly sensitive and portable surface acoustic wave (SAW)-based PM2.5 sensor and its interface electronics were developed for real-time monitoring of air quality. Two 2-port SAW resonators were employed for the sensor system to eliminate any environmental disturbance (temperature and humidity variations) on the output of the sensor. The overall system comprised a 2-port SAW resonator for a particulate matter (PM) sensor, a reference sensor covered with polydimethylsiloxane (PDMS) on the top surface, two self-oscillators, an RF mixer, a low-pass filter, a comparator, a field-programmable gate array, and a personal computer. All electronic components were integrated into a single printed circuit board assembly. COMSOL simulations were performed to determine the optimal center frequency for the operation of the PM2.5-based SAW sensor. Based on COMSOL simulation, the sensors were fabricated and their characteristics categorized using a custom-built testbed. We experimentally observed the effect of the center frequency on the frequency response of PM2.5. The experimental data showed that the sensor operating at a center frequency of 180 MHz exhibited the largest frequency shift when exposed to PM2.5, suggesting that 180 MHz is the optimal center frequency for operating a PM2.5-based SAW sensor. Herein, a simple mechanism is proposed to understand the working principle of the PM2.5 sensor. Our results suggest that for the effective detection of PM2.5 particles, it is necessary to use different center frequencies of the SAW sensor with optimal penetration depth to match the size of PM2.5.
