High frequency surface acoustic wave resonator-based sensor for particulate matter detection

•New SAWR based particle sensor, capable of detection of sub-micron size particles with masses below 1ng.•Sensitive, low-cost and robust acoustic sensor for particulate matter (PM10, PM2.5, UFP) detection for air-quality monitoring.•Novel SAWR design with free and shorted sensing areas, used in differential mode of operation.•Potential for low-power monolithic CMOS implementation.•Frequency dependent sensitivity of SAW resonators can be tailored to the size of particles to make them capable for UFPs, PM2.5 and PM10 detection. This paper describes the characterization of high frequency Surface Acoustic Wave Resonator based (SAWR) sensors, for the detection of micron and sub-micron sized particles. The sensor comprises two 262MHz ST-cut quartz based Rayleigh wave SAWRs where one is used for particle detection and the other as reference. Electro-acoustic detection of different sized particles shows a strong relationship between mass sensitivity (Δf/Δm) and particle diameter (Dp). This enables frequency-dependent SAWR sensitivity to be tailored to the size of particles, thus making these types of sensors good candidates for PM10, PM2.5 and ultrafine particle (UFP) sensing. Our initial characterisation demonstrated a typical SAWR frequency shift of 60Hz in response to a deposition of ca. 0.21ng of 0.75μm-sized gold particles (∼50 particles) on the sensor surface. Sensor responses to different sized particles, such as ∼30μm diameter silicon, gold (diameters of ∼0.75μm and ∼20μm), ∼8μm fine sugar, PTFE (∼1μm and ∼15μm), ∼4μm talcum powder, and ∼2μm molybdenum powder were evaluated, and an average mass sensitivity of 275Hz/ng was obtained. Based on the results obtained in this study we believe that acoustic wave technology has great potential for application in airborne particle detection. Moreover, acoustic resonator devices can be integrated with CMOS interface circuitry to obtain sensitive, robust, low-power and low-cost particle detectors for a variety of applications including outdoor environmental monitoring.