Abstract
To investigate the potential of using a surface acoustic wave sensor to measure both particulate matter (PM) concentration and size distribution, a forced-vibration model of a coupled particle–SAW system with interfacial excitation was built using the finite element method. The model shows different behaviors of the coupled vibration between mass loading and elastic loading regimes. The calculation of the frequency change of a 260 MHz SAW perturbed by different sized starch particles in the elastic regime is in agreement with our previous experiment, proving the validity of the model. The impact of different parameters, including the particle size, contact size, and material, on the particle–SAW interaction was investigated for understanding the perturbation mechanism of real particles. Wheat flour and talcum powder particles were measured by SAW experimentally, resulting in positive and negative frequency change, respectively. The experiment shows that SAW has different sensitivities toward particles with different size distributions and morphologies. The size-related sensitivity property of SAW could be used for building an instrument that is capable of monitoring both PM concentration and size distribution.
Highlights
Particulate matter (PM) has become one of the most concerned substances of air pollutants
The simulation by changing different parameters for the particle–surface acoustic wave (SAW) interaction shows that for SAW measuring starch particles sized over 1 μm, elastic coupling usually takes place, mass loading coupling could happen if the contact size is large enough, and perturbing profiles varies between different materials
Complex real particles with different size distributions and morphologies are measured by SAW experimentally
Summary
Particulate matter (PM) has become one of the most concerned substances of air pollutants. Since QCM operates in the MHz region, its interaction with particles sized below 10 μm is strictly in the mass loading regime, when monitoring PM, only mass concentration could be measured. Another microbalance device, surface acoustic wave (SAW), operating at a much higher frequency, typically between 50 MHz and 500 MHz, could interact with PM-sized objects in both mass loading and elastic loading regime. We present the experiment using two kinds of particles, wheat flour and talcum powder, with different size distributions and morphologies to interact with the SAW device, resulting in overall frequency changes in two different regimes
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