Deposition of micrometric particles on a capacitive sensing area

Paul Maierhofer, Marco Carminati, Giorgio Ferrari, Georg Röhrer, Marco Sampietro, Alexander Bergmann

    Research output: Contribution to conferencePoster

    Abstract

    We characterize a novel micro-sensor with pairs of interdigitated combs of microelectrodes designed to detect particles in air. We evaluate the sensor’s response to 1 µm Polystyrene Latex (PSL) particles experimentally and crosscheck the results with simulations. Experiment and simulation show good consistency. Based on the promising results we propose a redesign of the capacitive particle sensor with respect to PM2.5.
    We have built a setup for selective deposition of well-defined spherical particles in order to evaluate the performance of a microsensor for the capacitive detection of particulate matter in air. The deposition setup consists of an atomizer in combination with a diffusion dryer, which disperses PSL particles of defined size, shape, and dielectric constant in air. A nozzle is used to accelerate the particles towards the sensor in order to use impaction as a means of depositing. Particles induce a sudden change in capacitance when deposited on the sensor’s surface. Width and spacing of the electrodes is 1 µm which allows 1 µm particles to be deposited both onto the electrodes as well as in between them. The capacitive change depends on size, shape, dielectric constant, and the exact position of the particles. Since the dispersed particles are uniform within an experiment, the only influence left is the position of the particles relative to the surface structure of the sensor. Deposited particles are detected both optically using a digital microscope, and utilizing the described sensor effect. The experiment is also simulated using Comsol. We observe a relatively broad distribution of capacitive jumps caused by monodisperse 1 µm particles which stems from the exact position of the particles relative to the microelectrodes. A particle on top of the electrodes will lead to a weaker signal compared to a particle in between the combs. Since the electrodes protrude over the SiO2, particles are more likely to be deposited onto the electrodes rather than in between them. Experiment and simulation agree reasonably well.
    As particles of larger diameters than the distance between two electrodes cannot fall between the electrodes, the sensor can operate in two regimes: large particles are detected at the surface, smaller ones are detected in between the electrodes. This can be used as a feature to tune the size range of detectable particles. A redesign of the sensor should focus on this effect in order to optimize e.g. for PM2.5. We propose to reduce the spacing between the electrodes as far as to 0.5 µm, which we assume is the limit for the size of detectable particles on top of the electrodes. Particles smaller than 0.5 µm can then be detected in between the electrodes. Therefore, the microsensor can be used as a sensor for PM2.5.

    This work was funded by FFG grant 86197, Fondazione Cariplo through the projects MINUTE (No. 2011-2118) and ESCHILO (No. 2013-1760), and ams AG.
    Original languageEnglish
    Publication statusPublished - 15 Jun 2018
    Event2018 Cambridge Particle Meeting - Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, Cambridge, United Kingdom
    Duration: 15 Jun 201815 Jun 2018
    http://www.cambridgeparticlemeeting.org/2018

    Conference

    Conference2018 Cambridge Particle Meeting
    CountryUnited Kingdom
    CityCambridge
    Period15/06/1815/06/18
    Internet address

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    Maierhofer, P., Carminati, M., Ferrari, G., Röhrer, G., Sampietro, M., & Bergmann, A. (2018). Deposition of micrometric particles on a capacitive sensing area. Poster session presented at 2018 Cambridge Particle Meeting, Cambridge, United Kingdom.