Search

The precise detection of volatile organic compounds plays a pivotal role in addressing environmental concerns, industrial safety, and medical diagnostics. The accurate identification and quantification of these compounds because of their ubiquity and potential health hazards has fueled the development of advanced sensing technologies. This work presents a sensing system in the realm of long-wavelength infrared spectroscopy for achieving enhanced selectivity and sensitivity of benzene, toluene, and propane detection through quartz-enhanced photoacoustic spectroscopy. High-resolution gas spectroscopy is made possible by the use of specially designed InAs/AlSb-based quantum cascade lasers, emitting in the wavelength range 13–15 μm, and quartz tuning forks. The sensor system, characterized by its robustness and precision, demonstrates exceptional capabilities in benzene, toluene, and propane detection. The system's capacity for practical applications in environmental monitoring and medical diagnostics is demonstrated by its ability to distinguish these volatile organic compounds with a minimum detection limit of 113 ppb, 3 ppb, and 3 ppm for toluene, benzene, and propane at an integration time of 10 s, even in complex gas matrices. This work advances gas sensing technology while also offering insightful information on spectral interferences, a persistent problem in the field. The results usher in a new era of sophisticated and reliable gas sensing techniques meeting the growing demand for precise volatile organic compounds detectors for environmental monitoring purposes. [ABSTRACT FROM AUTHOR]

In this work we report on an innovative sensor box employing two acoustic detection modules connected in series for quartz-enhanced photoacoustic multi-gas detection. One detection module is coupled with an internal distributed-feedback quantum cascade laser (DFB-QCL) emitting at -7.719 µm for methane (CH4) sensing, while the second module has been designed to be coupled with an external laser source targeting the absorption features of a specific gas molecule Mx in the infrared spectral range. The sensor box can thus be employed for any application, depending on the CH4/Mx gas combination to be detected. The -7.719 µm DFB-QCL also allowed water vapor monitoring. To demonstrate the sensor versatility, we report on the QEPAS-box environmental monitoring application by simultaneously detecting in air methane, which is a greenhouse gas, nitric oxide (NO), an ozone depleting substance, and water vapor. Sensitivity levels of 4.30 mV ppm1 and 17.51 mV ppm-1 and minimum detection limits of 48 ppb and 11 ppb for methane and nitric oxide detection were achieved, respectively. The sensor box operation was tested by analysing ambient air. Average concentrations of -1.73 ppm of CH4, -0.134 ppm of NO and 1.8% of H2O were measured. [ABSTRACT FROM AUTHOR]

The development of innovative gas-sensing systems is fundamental in diverse research fields such as physics, chemistry, biology, medicine and environmental science [[1], [3]]. 32672192 7 Ma Y., He Y., Patimisco P., Sampaolo A., Qiao S., Yu X., Tittel F.K., Spagnolo V. Ultra-high sensitive trace gas detection based on light-induced thermoelastic spectroscopy and a custom quartz tuning fork. The second article, submitted by H. Zheng et al., reports on an original approach for trace-gas detection, by combining photo-thermal and photo-acoustic spectroscopy, and relying on a quartz tuning fork as a light-intensity and sound-wave detector, simultaneously [[11]]. [Extracted from the article]

Highlights • We realized a quartz-enhanced photoacoustic (QEPAS) sensor for methane, ethane and propane detection using a single intercascade laser source. • We achieved for ethane a QEPAS record sensitivity of 7 ppb in 1-second integration time. • Detection of propane with QEPAS technique is reported for the first time. • We demonstrated methane, ethane and propane detection at atmospheric pressure avoiding the use of pump and pressure controller systems. Abstract Hydrocarbon detection in the gas phase represents a powerful tool to guide oil exploration and production operations for the oil & gas industry. This application requires highly sensitive, selective and robust spectroscopic techniques. In this work, a quartz-enhanced photoacoustic sensor system designed to detect methane (C1), ethane (C2) and propane (C3), employing a single interband cascade laser emitting in the spectral range 3.342–3.349 μm, is reported. Detection levels in the part-per billion concentration range for C1 and C2 and a few parts per million for C3 were achieved. Measurements at both low and atmospheric pressures were carried out for mixtures simulating typical downhole hydrocarbon concentrations. [ABSTRACT FROM AUTHOR]

We report single-mode midinfrared laser beam delivery through a 50-cm-long tapered hollow-core waveguide (HCW) having bore diameter linearly increasing from 200 to 260 µm. We performed theoretical calculations to identify the best HCW-laser coupling conditions in terms of optical losses and single-mode fiber output. To validate our modeling, we coupled the HCW with an interband cascade laser and four quantum cascade lasers with their emission wavelengths spanning 3.5 to 7.8 µm, using focusing lenses with different focal lengths. With the best coupling conditions, we achieved single-mode output in the investigated 3.5 to 7.8 µm spectral range, with minimum transmission losses of 1.27 dB at 6.2 µm. [ABSTRACT FROM AUTHOR]

We report on a quartz-enhanced photoacoustic (QEPAS) sensor for methanol (CH3OH) detection employing a novel quartz tuning fork (QTF), specifically designed to enhance the QEPAS sensing performance in the terahertz (THz) spectral range. A discussion of the QTF properties in terms of resonance frequency, quality factor and acousto-electric transduction efficiency as a function of prong sizes and spacing between the QTF prongs is presented. The QTF was employed in a QEPAS sensor system using a 3.93 THz quantum cascade laser as the excitation source in resonance with a CH3OH rotational absorption line located at 131.054 cm-1. A minimum detection limit of 160 ppb in 30 s integration time, corresponding to a normalized noise equivalent absorption NNEA = 3.75 10-11 cm-1W/Hz, was achieved, representing a nearly one-order-of-magnitude improvement with respect to previous reports. [ABSTRACT FROM AUTHOR]

We report here on the use of the Allan deviation plot to analyze the long-term stability of a quartz-enhanced photoacoustic (QEPAS) gas sensor. The Allan plot provides information about the optimum averaging time for the QEPAS signal and allows the prediction of its ultimate detection limit. The Allan deviation can also be used to determine the main sources of noise coming from the individual components of the sensor. Quartz tuning fork thermal noise dominates for integration times up to 275 s, whereas at longer averaging times, the main contribution to the sensor noise originates from laser power instabilities. [ABSTRACT FROM AUTHOR]

An innovative quartz enhanced photoacoustic (QEPAS) gas sensing system operating in the THz spectral range and employing a custom quartz tuning fork (QTF) is described. The QTF dimensions are 3.3 cm × 0.4 cm × 0.8 cm, with the two prongs spaced by ∼800 μm. To test our sensor we used a quantum cascade laser as the light source and selected a methanol rotational absorption line at 131.054 cm−1 (∼3.93 THz), with line-strength S = 4.28 × 10−21 cm mol−1. The sensor was operated at 10 Torr pressure on the first flexion QTF resonance frequency of 4245 Hz. The corresponding Q-factor was 74 760. Stepwise concentration measurements were performed to verify the linearity of the QEPAS signal as a function of the methanol concentration. The achieved sensitivity of the system is 7 parts per million in 4 seconds, corresponding to a QEPAS normalized noise-equivalent absorption of 2 × 10−10 W cm−1 Hz−1/2, comparable with the best result of mid-IR QEPAS systems. [ABSTRACT FROM AUTHOR]

• Quartz-Enhanced Photoacoustics for sensitive and selective hydrocarbon detection. • Shoe box sized (sizes 30 cm × 10 cm × 20 cm) QEPAS sensors deployable for real-time and in-situ gas analysis. • Methane, ethane minimum detection limit of 90 ppb and 7 ppb at 1 sec of integration time, respectively. • Propane detected down to 3 ppm at 1 sec of integration time. • 13CH4 and 12CH4 isotopes detected with a 13δ <10‰ at 0.1 sec of integration time. Quartz-enhanced photoacoustic spectroscopy represents a valuable candidate for natural gas analysis in the oil & gas field. The core element of this spectroscopy technique is a quartz tuning forks, employed as high quality-factor optoacoustic transducers, capable of operating in a wide range of temperatures and pressures. The robustness and compactness of these sensors, together with the possibility to avoid the use of optical detectors, open the way to the development of a new generation of small-sized gas spectrometers to be potentially employed downhole for source rock characterization and estimation of oil & gas properties. We report here on the realization of a shoe-box sized quartz-enhanced photoacoustic spectroscopy system capable of: i) selective detection of methane and ethane in the parts-per-billion range, and propane in the parts-per-million range, by employing a single interband cascade laser emitting at 3.345 µm; ii) selective detection of 12CH 4 and 13CH 4 isotopes at the parts-per-billion sensitivity level by employing a quantum cascade laser operating around 7.73 µm. [ABSTRACT FROM AUTHOR]

A ppb-level mid-IR quartz-enhanced photoacoustic sensor for the highly sensitive detection of dimethyl methyl phosphonate (DMMP) —the sarin simulant—is developed using a T-shaped tuning fork. The sensor employs a narrow-linewidth mid-IR quantum cascade laser (QCL) to target a strong, interference-free DMMP absorption band. A custom quartz tuning fork with 800-μm prong spacing is employed to avoid significant photothermal noise, thus removing the requirement for an optical spatial filter. The performance of the photoacoustic sensor was optimized in terms of exciting power, modulation frequency, and gas pressure. A minimum detection limit of 6 ppb was achieved at an integration time of 300 ms, which can be further improved to 0.45 ppb at the optimal integration time of 20 s • A ppb-level photoacoustic sensor for the sarin simulant detection was developed. • A large-gap-spacing quartz tuning fork was used to decrease noise. • A minimum detection limit of 0.45 ppb was achieved at an optimal integration time of 20 s. • The high selectivity of the sensor was verified in a real environment. [ABSTRACT FROM AUTHOR]

We demonstrated a 19-inches 6U-rack sensing system based on quartz-enhanced photoacoustic spectroscopy for simultaneous detection of methane, nitrous oxide, and ammonia in atmosphere. The system embeds two detection modules, each one equipped with a quantum cascade laser as light source and a spectrophone composed of a T-shaped quartz tuning fork coupled with acoustic resonator tubes. The sensing system results compact, lightweight, and portable, with a computer interface for an easy end-user operation. The calibration was performed in laboratory environment with certified concentrations. Because of the NH 3 large and permanent dipole moment, ammonia QEPAS signal was used to model and characterize adsorption/desorption processes, for an accurate and reliable sensor calibration. At 0.1 s signal integration time, detection limits of 28 ppb, 9 ppb, and 6 ppb were obtained for CH 4 , N 2 O, and NH 3 , respectively. Since these detection limits were well below the natural abundance of the three analytes in atmosphere, the sensor was employed to monitor CH 4 , N 2 O, and NH 3 concentrations in laboratory air. • Development of a compact 19-inches 6U-rack QEPAS sensor box for simultaneous detection of CH 4 , N 2 O, and NH 3 in atmosphere. • Minimum detection limits of 28.0 ppb, 9 ppb and 6 ppb at 0.1 s integration time for CH 4 , N 2 O and NH 3 detection, respectively. • Sensor tested by analysing ambient air. Mean concentrations of ∼ 1.81 ppm of CH 4 , 329 ppb of N 2 O and 83 ppb of NH 3 measured. [ABSTRACT FROM AUTHOR]

• A QEPAS-based sensor with V-T relaxation self-calibration was developed. • A dual-gas detection was realized based on two-mode combined vibration of a QTF. • A self-calibration method for the CH 4 V-T relaxation was provided. • The ppb-level self-calibration CH 4 sensor has a simple setup and small sensor size. • Continuous measurements near a landfill in Shanxi province, China, were performed. A quartz-enhanced photoacoustic spectroscopy methane (CH 4) sensor with vibrational to translational (V-T) relaxation self-calibration was realized and tested for atmospheric CH 4 detection near a landfill. To normalize the influence of H 2 O vapor on the CH 4 energy relaxation rate, CH 4 and H 2 O concentrations were detected simultaneously by means of a frequency division multiplexing technique, in which a custom quartz tuning fork was operated in the fundamental and first overtone combined vibration mode. A continuous wave, thermoelectrically cooled distributed feedback interband cascade laser emitting at 3.3 μm and a near-infrared DFB laser emitting at 1.37 μm were used as the excitation source for CH 4 and H 2 O detection, respectively. A theoretical model of V-T relaxation and self-calibration method were developed to allow this CH 4 sensor to have a simple setup and a small sensor size. Continuous field measurements were carried out near the largest sanitary landfill in Shanxi province, China, to demonstrate the stability and ruggedness of the realized CH 4 sensor. [ABSTRACT FROM AUTHOR]