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Sensors 2019, 19(3), 724; https://doi.org/10.3390/s19030724

Resonant Photoacoustic Spectroscopy of NO2 with a UV-LED Based Sensor

1
Department of Microsystems Engineering—IMTEK, University of Freiburg, 79110 Freiburg, Germany
2
Fraunhofer Institute for Physical Measurement Techniques IPM, 79110 Freiburg, Germany
This paper is an extended version of “Resonant Photoacoustic Detection of NO2 with an LED Based Sensor” published in the Proceedings of the Eurosensors 2018 Conference, Graz, Austria, 9–12 September 2018.
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Received: 31 December 2018 / Revised: 6 February 2019 / Accepted: 8 February 2019 / Published: 11 February 2019
(This article belongs to the Collection Gas Sensors)
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Abstract

Nitrogen dioxide (NO2) is a poisonous trace gas that requires monitoring in urban areas. Accurate measurement in sub-ppm concentrations represents a wide application field for suitable economical sensors. We present a novel approach to measure NO2 with a photoacoustic sensor using a T-shaped resonance cell. An inexpensive UV-LED with a peak wavelength of 405 nm as radiation source as well as a commercial MEMS microphone for acoustic detection were used. In this work, a cell has been developed that enables a “non-contact” feedthrough of the divergent LED beam. Thus, unwanted background noise due to absorption on the inside walls is minimized. As part of the development, an acoustic simulation has been carried out to find the resonance frequencies and to visualize the resulting standing wave patterns in various geometries. The pressure amplitude was calculated for different shapes and sizes. A model iteratively optimized in this way forms the basis of a construction that was built for gas measurement by rapid prototyping methods. The real resonance frequencies were compared to the ones found in simulation. The limit of detection was determined in a nitrogen dioxide measurement to be 200 ppb (6 σ) for a cell made of aluminum. View Full-Text
Keywords: resonant photoacoustic spectroscopy; LED; nitrogen dioxide (NO2) detection; T-cell resonant photoacoustic spectroscopy; LED; nitrogen dioxide (NO2) detection; T-cell
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Kapp, J.; Weber, C.; Schmitt, K.; Pernau, H.-F.; Wöllenstein, J. Resonant Photoacoustic Spectroscopy of NO2 with a UV-LED Based Sensor. Sensors 2019, 19, 724.

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