Compact QEPAS sensor for trace methane and ammonia detection in impure hydrogen

Wright, Jonathon S.; Peters, Brent; Ferguson, B. A.; Tittel, Frank K.; McWhorter, Scott

doi:10.1007/s00340-012-4908-x

Cited by 70 publications

(38 citation statements)

References 21 publications

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“…The signal-to-noise ratios (SNRs) of the two methods were calculated separately since the sensitivity is determined by the SNR. With the general QEPAS method, it was verified in several experimental tests [4,13,14] that the observed QEPAS noise is equal to the theoretical thermal noise of the QTF at its resonance frequency. In this work, the theoretical and experimental thermal noise levels are 420.3 cnts and 450.2 cnts, The normalized noise-equivalent absorption coefficient is 3.3×10 −7 cm −1 ·W·Hz −1/2 .…”

Section: Resultsmentioning

confidence: 96%

Optical Detection Technique Using Quartz-Enhanced Photoacoustic Spectrum

Zhang

Zheng

et al. 2014

Int J Thermophys

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A new optical detection approach based on quartz-enhanced photoacoustic spectroscopy (QEPAS) to detect gases is developed. The new method not only employs a modulated laser to excite acoustic wave, as the general QEPAS does, but also adds an extra laser beam without modulation as the detection source to transform the prong vibration into a laser intensity change. Due to the mechanical vibration of the prongs, the intensity of the reflection laser beam is modulated. Thus, the information of the target gas (composition, concentration, etc.) is obtained by demodulating the reflected light. The achieved sensitivity of 1.13 × 10 −6 cm −1 ·W·Hz −1/2 is inter-compared to the sensitivity of the conventional QEPAS. Further developments of the new optical detection approach are also discussed in detail.

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Section: Resultsmentioning

confidence: 96%

Optical Detection Technique Using Quartz-Enhanced Photoacoustic Spectrum

Zhang

Zheng

et al. 2014

Int J Thermophys

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“…The signal from the fork was passed through another lock in the amplifier and was delivered to a data acquisition card (Adlink PCI9826), and then connected to a personal computer. The photoacoustic signal received by the detector [7] is ： ε αQ…”

Section: Experiments and Resultsmentioning

confidence: 99%

Ammonia sensor based on QEPAS with HC-PBF as reference cell

et al. 2015

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Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors involves with many desirable features, such as being small and portable, with fast continuous in situ measurements possible. In QEPAS systems, reference cells filled with gas mixtures for wavelength locking and calibration are used to improve the precision and stability of the trace gas concentration measurement. For this study, a 5 m length hollow core photonic bandgap fiber (HC-PBF) splicing with single mode fibers at two ends was manufactured as reference cell, which has long absorption path, low transmission loss and easy connectivity. Hollow cores under high pressure (3.0× 10 5 Pa) were filled with a certified mixture of ammonia and nitrogen gas to reach equilibrium rapidly. The experiment results indicated that absorption spectra of reference cell with a low loss <3.5dB maintained stable after 150 days at atmosphere. For trace gas detection, 1.531 μm DFB laser with wavelength modulation technique was demonstrated based on QEPAS. A normalized noise equivalent absorption coefficient (NNEA) of 1.18×10 -7 cm -1 W/√Hz was obtained at room temperature and pressure of 760 Torr. This results in a minimum detection limit of 3.6ppm for noise equivalent concentration within a 1s lock in integration time.

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“…Also the surrounding gas mixture, e.g. humidity 4 influences the signal by promoting or delaying deexcitation and vibrational-translational-transfer. Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Photoacoustic sensing with micro-tuning forks

Willer

Köhring

Mordmüller

et al. 2015

Next-Generation Spectroscopic Technologies VIII

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Different modifications of quartz enhanced photoacoustic spectroscopy (QEPAS) are discussed. An analysis of the signal-to-noise ratio for the generated photoacoustic signal gives hints for an optimized geometry of tuning fork and acoustic resonator. Furthermore, simultaneous or alternate photoacoustic and electrical driving is discussed, leading the way to new detection schemes that are capable of measuring changes in molecular relaxation dynamics

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Compact QEPAS sensor for trace methane and ammonia detection in impure hydrogen

Cited by 70 publications

References 21 publications

Optical Detection Technique Using Quartz-Enhanced Photoacoustic Spectrum

Optical Detection Technique Using Quartz-Enhanced Photoacoustic Spectrum

Ammonia sensor based on QEPAS with HC-PBF as reference cell

Photoacoustic sensing with micro-tuning forks

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