An electrically and optically cooperated QEPAS device for highly integrated gas sensors

Mordmüller, Mario; Köhring, Michael; Schade, Wolfgang; Willer, Ulrike

doi:10.1007/s00340-015-6037-9

Cited by 43 publications

(26 citation statements)

References 7 publications

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“…However, for the microphone-based PAS, the low value of Q factor (<100) and the large size of the photoacoustic cell limit its performance and In the QEPAS technique, a quartz tuning fork (QTF) is used as an acoustic wave transducer. The QTF is a commercially available millimeter-sized piezoelectric element, which is usually used in watches, clocks, and electronic circuits to provide clock rate [10][11][12]. The high Q-factor (~100,000 in a vacuum and~10,000 in a standard atmosphere pressure) and narrow resonance frequency band (<1 Hz) of QTF improve the QEPAS selectivity and immunity to environmental acoustic noise [13][14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Review of Recent Advances in QEPAS-Based Trace Gas Sensing

2018

Applied Sciences

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Quartz-enhanced photoacoustic spectroscopy (QEPAS) is an improvement of the conventional microphone-based photoacoustic spectroscopy. In the QEPAS technique, a commercially available millimeter-sized piezoelectric element quartz tuning fork (QTF) is used as an acoustic wave transducer. With the merits of high sensitivity and selectivity, low cost, compactness, and a large dynamic range, QEPAS sensors have been applied widely in gas detection. In this review, recent developments in state-of-the-art QEPAS-based trace gas sensing technique over the past five years are summarized and discussed. The prospect of QEPAS-based gas sensing is also presented.

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Section: Introductionmentioning

confidence: 99%

Review of Recent Advances in QEPAS-Based Trace Gas Sensing

2018

Applied Sciences

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“…In this paper however, we report on the ability of a continuous phase modulation instead of a fixed setting which yields a steady measurement and additionally separates the photo-acoustically induced amplitude from the offset generated by the oscillator circuit. In [9,10] we already described the ability to incorporate a quartz micro-tuning fork with removed container in an oscillator circuit and to simultaneously focus a laser beam between the tuning fork's prongs to generate acoustic waves upon absorption of the molecule. Since the laser modulation signal is derived from the oscillation circuit that automatically adjusts to the current resonance frequency of the tuning fork, the laser is always modulated with the correct frequency.…”

Section: Methodsmentioning

confidence: 99%

Phase Optimized Photoacoustic Sensing of Gas Mixtures

Mordmueller

Edelmann²,

Knestel³

et al. 2020

Applied Sciences

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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.

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“…This feature differs from other laser absorption spectroscopy such as TDLAS. Diode lasers are usually used in QEPAS based sensing systems due to their compactness and low cost [12][13][14]. However the output power of diode lasers is in the range of several milliwatts which limits the QEPAS detection performance.…”

Section: Introductionmentioning

confidence: 99%

Ppb-level detection of ammonia based on QEPAS using a power amplified laser and a low resonance frequency quartz tuning fork

Tong

et al. 2017

Opt. Express

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Abstract:In this report, an ultra-high sensitive quartz-enhanced photoacoustic spectroscopy (QEPAS) based ammonia (NH 3 ) sensor using a power amplified diode laser and a low resonance frequency quartz tuning fork (QTF) was demonstrated for the first time. A fibercoupled, continuous wave (CW), distributed feedback (DFB) diode laser with a watt level output power boosted by an erbium-doped fiber amplifier (EDFA) was used as the QEPAS excitation source. A QTF with a resonance frequency of 30.72 kHz was employed as an acoustic wave transducer. The modulation depth in the wavelength modulation spectroscopy (WMS) based QEPAS system was optimized theoretically and validated by experimental measurements. For the reported NH 3 sensor system, a 418.4 ppbv (parts per billion by volume) minimum detection limit at a NH 3 absorption line of 6533.4 cm −1 was achieved when the modulation depth was set to the optimum value of 0.188 cm −1 . The ppb-level detection sensitivity verified the design of the reported QEPAS method and makes it suitable for use in environmental monitoring and other applications. Patni, "Atmospheric nitrogen compound II: emissions, transport, transformation, deposition and assessment," Atmos. Environ. 35, 1903Environ. 35, -1911Environ. 35, (2000. 3. K. W. van der Hoek, "Estimating ammonia emission factors in Europe: summary of the work of the UNECE ammonia expert panel," Atmos. Environ. 32, 315-316 (1998). 4. G. P. Wyers, R. P. Otjes, and J. Slanina, "A continuous-flow denuder for the measurement of ambient concentration and surface-exchange fluxes of ammonia," Atmos. Environ. 27a, 2085-2090 (1993).

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An electrically and optically cooperated QEPAS device for highly integrated gas sensors

Cited by 43 publications

References 7 publications

Review of Recent Advances in QEPAS-Based Trace Gas Sensing

Review of Recent Advances in QEPAS-Based Trace Gas Sensing

Phase Optimized Photoacoustic Sensing of Gas Mixtures

Ppb-level detection of ammonia based on QEPAS using a power amplified laser and a low resonance frequency quartz tuning fork

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