Abstract
To study the sensitivity of the surface acoustic wave (SAW) sensor towards particulate matter (PM), an analytic model has been built based on single particle perturbation theory of full size range and the lognormal size distribution of the PM. The sensitivity of the frequency shift to 1 nanogram of PM has been calculated. The model shows that the frequency shift is a result of the competition between the negative perturbation by mass loading and the positive perturbation by elastic coupling, determined by particle size distribution parameters, material, and SAW frequency. To verify the model, the relationship of the frequency shift of a 315 MHz SAW to the concentration of aerosols generated by two kinds of powders of different sizes was measured. The experiment is in agreement with the model: the sensor has shown negative sensitivity towards aerosols generated by the finer particles of 1 μm, 3 μm polytetrafluoroethylene (PTFE), and A1 Arizona dust and positive sensitivity towards aerosols generated by the coarser particles of 10 μm PTFE and A4 Arizona dust; and the negative sensitivity is about 1 order higher than the positive.
Highlights
Particulate matter (PM), known as atmospheric aerosol particles, is a key air pollutant brought into the air by a variety of natural and anthropogenic sources. e exposure to particulate matter (PM) by human can cause asthma, lung cancer, respiratory diseases, cardiovascular disease, premature delivery, and premature death [1,2,3,4]. e size distribution of PM is important because finer particles are more toxic [5]
Other gravity methods use a piezoelectric oscillation component to measure PM concentration based on the change of the resonance frequency due to the mass loading effect by the sampled PM. e oscillation component includes the tapered element oscillation microbalance (TEOM) and silicon resonant cantilever
Result and Discussion e frequency shift of the surface acoustic wave (SAW) vs. PM concentration measured by the optical sensor to PTFE particles of different nominal sizes measured in the 7L platform is shown in Figure 9. e concentration range was controlled between 200 and 800 μg/m3
Summary
Particulate matter (PM), known as atmospheric aerosol particles, is a key air pollutant brought into the air by a variety of natural and anthropogenic sources. e exposure to PM by human can cause asthma, lung cancer, respiratory diseases, cardiovascular disease, premature delivery, and premature death [1,2,3,4]. e size distribution of PM is important because finer particles are more toxic [5]. Other gravity methods use a piezoelectric oscillation component to measure PM concentration based on the change of the resonance frequency due to the mass loading effect by the sampled PM. We have built a particle-SAW coupled resonance model using the finite element method to study the size-related sensitivity of the 260 MHz SAW in the full particle size range [36]. Where ci, listed, is the coupling coefficient of the ith direction, with the subscripted indices i with values of 1, 2, and 3 refer to the x-, y-, and z-direction, respectively, m is mass of the particle, f is SAW operation frequency, and A is the sensing area of the SAW In this case, the particle is rigidly adhered on the SAW surface and perturbs the sensor by its own mass, leading to a decrease of SAW resonance frequency. For single particle with diameter of dp, equation (1) could be written as Particle
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