MEMS particle sensor based on resonant frequency shifting

Woo-Tae Park,Ji-Seob Choi

doi:10.1186/s40486-020-00118-9

Woo-Tae Park, Ji-Seob Choi

Open Access

https://doi.org/10.1186/s40486-020-00118-9

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Abstract

Recently, as the concentration of fine dust in the atmosphere has increased due to an increase in the use of fossil fuel power plants, automobiles, and factories, it has been increasingly important to measure fine dust in the atmosphere. This is because exposure to fine dust is closely related to the incidence of respiratory and cardiovascular diseases and eventually affects mortality. In this paper, we introduce a MEMS particle sensor based on the resonance frequency shift according to added particle mass. The actuation is driven by Aluminum nitride (AlN), and the total thickness is 2.8 μm. A laser doppler vibrometer (LDV), an optical measuring instrument, was used to measure the resonance frequency of the sensor. Airborne particles naturally were deposited on the sensor. To show the frequency shift according to the particle mass, the frequency shift was measured by dividing the case where the deposited particle mass was small and large. In each case, the frequency shift according to the deposited particle mass was predicted and compared with the frequency shift measured by LDV. It was shown that the deposited particle mass and frequency shift are proportional. The deposition of particulate mass was estimated by image analysis. The frequency shift caused by the particle mass deposited on the sensor was defined as the sensitivity of the sensor. The estimated sensitivity of the sensor is 0.219 to 0.354 kHz/pg.

Highlights

Fine dust is a mixture of solid particles and liquid drops in the air
Because it is difficult to measure the particle mass deposited on the sensor surface directly [13], the mass of the deposited fine particles was estimated through image analysis through the photo of the sensor surface where the particles were deposited
ΔFm is the measured resonant frequency shift, and ΔFp is the calculated resonant frequency shift by the estimated particle mass from image analysis. In both ΔFm and ΔFp, we can see that the higher the resonant frequency, the higher the resonant frequency shift, which is consistent with the theory [16]

Summary

Introduction

Fine dust is a mixture of solid particles and liquid drops in the air. The exposure to fine dust is closely related to the occurrence of respiratory and cardiovascular diseases and is reported to increase mortality. We developed a high-precision sensor that is cheaper and more portable than an optical particle counter and TEOMs. It is possible to precisely measure the concentration of dust in the air by using frequency shift according to mass change on a micromachined mass, and because it is manufactured by semiconductor process, mass production is possible and product cost can be reduced in high volume [7, 8].

Results

Conclusion