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Near-Infrared Quartz-Enhanced Photoacoustic Sensor for H2S Detection in Biogas

Phase Optimized Photoacoustic Sensing of Gas Mixtures

Institute for Energy Research and Physical Technology and Research Center Energy Storage Technologies, Clausthal University of Technology, Am Stollen 19B, 38640 Goslar, Germany
KNESTEL Technologie & Elektronik, Osterwalder Straße 12, 87496 Hopferbach, Germany
Fraunhofer Heinrich Hertz Institute, Am Stollen 19H, 38640 Goslar, Germany
Author to whom correspondence should be addressed.
Appl. Sci. 2020, 10(2), 438;
Received: 1 December 2019 / Revised: 23 December 2019 / Accepted: 1 January 2020 / Published: 7 January 2020
(This article belongs to the Special Issue Quartz-Enhanced Photoacoustic and Photothermal Spectroscopy)
In this paper, we report on the progress of the auto-triggered quartz-enhanced photoacoustic spectroscopy (QEPAS) technique which operates without external frequency generators and ensures permanent locking to the current resonance frequency of the tuning fork. This is obtained by incorporating the tuning fork in an oscillator circuit that autonomously oscillates at the present resonance frequency that shifts with changing environmental conditions, e.g., density and viscosity of the surrounding gas, temperature, and pressure. Both, the oscillation amplitude as well as the frequency can be read from the oscillator circuit. The photoacoustic signal appears as an offset of the electrically induced signal amplitude. Since the sum amplitude depends on the phase relation between the electrical and photoacoustic driving forces, the phase is permanently modulated, enabling the extraction of the photoacoustic component by use of a second lock-in amplifier stage which is being referenced with the phase modulation frequency. The functionality of this method is demonstrated for methane detection in a carbon dioxide atmosphere in a concentration range from 0 to 100% and ammonia in synthetic air employing a pulsed mid infrared QCL around 1280 cm−1. The gas mixtures are motivated by the demands in biogas-analysis. View Full-Text
Keywords: photoacoustics; QEPAS; autotrigger photoacoustics; QEPAS; autotrigger
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MDPI and ACS Style

Mordmueller, M.; Edelmann, S.; Knestel, M.; Schade, W.; Willer, U. Phase Optimized Photoacoustic Sensing of Gas Mixtures. Appl. Sci. 2020, 10, 438.

AMA Style

Mordmueller M, Edelmann S, Knestel M, Schade W, Willer U. Phase Optimized Photoacoustic Sensing of Gas Mixtures. Applied Sciences. 2020; 10(2):438.

Chicago/Turabian Style

Mordmueller, Mario, Simon Edelmann, Markus Knestel, Wolfgang Schade, and Ulrike Willer. 2020. "Phase Optimized Photoacoustic Sensing of Gas Mixtures" Applied Sciences 10, no. 2: 438.

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