Search

The rapid development of photo(redox) catalysis within the last decades is remarkable to the extent that the utilization of light‐driven processes in organic chemistry has become a credible alternative to current thermal processes. Such advances offer tremendous opportunities of collaborations between scientific realms that can have a drastic impact on the development of the field. In this concept article, a special emphasis is placed on spectroscopic techniques that are used, or could be used, for light‐induced transformations and photoredox catalysis applications. These include spectroelectrochemistry, UV‐VIS, IR and X‐Ray transient absorption spectroscopy, laser pulsed radiolysis (PR), photo‐induced chemically induced dynamic nuclear polarization (Photo‐CIDNP), photoacoustic spectroscopy, time‐resolved Raman spectroscopy (TRRS), time‐resolved Electron Paramagnetic Resonance (TREPR) and time‐resolved dielectric loss spectroscopy (TRDL). The theoretical background behind each technique is briefly introduced followed by selected relevant examples from the literature. [ABSTRACT FROM AUTHOR]

[Display omitted] • First demonstration of high-Q and SNR of Helmholtz PA cell for VOC biomarkers in THz domain. • ppbV order Low detection limits (LOD) of methanol, ethanol and isopropanol using UV, Mid-IR and THz sources. • Comparative superior performance of VOC detection in THz range. • Dual phase detection of biomarkers using Tunable resonance frequency Helmholtz photoacoustic spectroscopy system. This paper reports the trace-level detection of volatile organic compounds (VOCs) like methanol, ethanol, and isopropanol, which are biomarkers for various diseases like diabetes, breast cancer, lung cancer, chronic pulmonary diseases, squamous cancer, cystic fibrosis, chronic liver diseases, chronic kidney diseases and so on. Here, the photoacoustic spectroscopy technique was used for the trace-level detection of these biomarkers using an indigenously designed tunable frequency (1.4 to 4 kHz range) Helmholtz photoacoustic (PA) cell. The study was carried out with UV (266 nm), Mid IR (5.4–7.3 µm) and THz (0.11 THz) range sources to explore and compare the PA signal generated by mentioned samples for different electronic vibrational and rotational level excitations. We achieved a low detection limit (LoD) of the order of 39.3 ppbV, 29.7 ppbV, and 11.6 ppbV for methanol, ethanol, and isopropanol, respectively using this non-invasive cost-effective, and fast technique. In addition, THz-based PA signal for these samples is reported for the first time. [ABSTRACT FROM AUTHOR]

This work investigates the behavior of commercial and custom Quartz tuning forkss (QTF) under humidity variations. The QTFs were placed inside a humidity chamber and the parameters were studied with a setup to record the resonance frequency and quality factor by resonance tracking. The variations of these parameters that led to a 1% theoretical error on the Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) signal were defined. At a controlled level of humidity, the commercial and custom QTFs present similar results. Therefore, commercial QTFs appear to be a very good candidates for QEPAS as they are also affordable and small. When the humidity increases from 30 to 90 %RH, the variations in the custom QTFs' parameters remain suitable, while commercial QTFs show unpredictable behavior. [ABSTRACT FROM AUTHOR]

The related regulations for electric power industry stipulate that CO gas is an important component to be detected when analyzing the gas composition of SF6 equipment. In this study, based on the photoacoustic spectroscopy technology, the quantitative gas detection of CO is carried out. First, in order to avoid the cross-interference effects of other component gases on photoacoustic spectroscopy detection of CO, the characteristic absorption spectrum of CO in 4291.5 cm−1 (whose wavelength is 2330.2 nm) is determined. Second, the nonresonant photoacoustic cell is optimized in this study. After that, designing and building a trace gas photoacoustic spectroscopy detection platform around the developed photoacoustic cell, using the built detection platform to perform photoacoustic spectroscopy detection of the concentration of CO, and obtaining photoacoustic signals of different concentrations of CO, the photoacoustic signals increase linearly as the concentration increases. With SF6 as the background gas, the lower detection limit of CO gas reaches 20.5 ppm, and with N2 as the background gas, it reaches 5.6 ppm. After all, the influence mechanism of the background gas on the photoacoustic signal is studied, and based on the influence mechanism, the lower detection limit of CO with the background gas of different mixing ratios of SF6/N2 is predicted. The verified experiment is basically consistent with the predicted results, which proves the accuracy of the forecast. This study provides guidance for the engineering application of CO photoacoustic spectroscopy detection in SF6 equipment. [ABSTRACT FROM AUTHOR]

In this letter, an infrared photoinverter with a GeSe 2-D/ $\alpha $ -PbSe heterostructure and a high detectivity ($5.8\times 10 ^{14}$ Jones) and responsivity ($1.26\times 10$ 6 V/W) has been proposed for applications in spectroscopy detectors and quick chemical gas identification. The design concept is based on three criteria: 1) an enhanced heterostructure constructed from a GeSe 2-D nanomaterial with PbSe and an abrupt PN junction; 2) a photoinverting device that can conveniently perform I-V conversion; and 3) a compatible sensing unit that includes a spectral ppb-level trace gas sensing module. Our work, which used a tunable DFB (Distributed Feedback) laser and retained high spectral sensitivity (1550-1750 nm), presents a novel technical method that meets the various requirements for cost-effective trace gas detection in the infrared region. [ABSTRACT FROM AUTHOR]

A CO sensor based on photoacoustic spectroscopy (PAS) with empirical mode decomposition (EMD) algorithm is investigated and demonstrated in this paper. In the PAS system, the complicated photo-thermal-acoustic conversion is a nonlinear and non-stationary process and contains various noise. In order to compensate the low signal-to-noise ratio (SNR), the EMD is introduced in the PAS system to deal with the photoacoustic signal. The experimental results show that a gain factor of ∼3.0 on the SNR is achieved and the sensor has an excellent linear response to the gas concentration. The minimum detection level (MDL) for CO detection is reduced to 1.14 ppm with a 300 ms integrated time at room temperature and atmospheric pressure. [ABSTRACT FROM AUTHOR]

Lamellar structures of transition metal phosphorus trisulfides possess strong intralayer bonding, albeit adjacent layers are held by weak van der Waals interactions. Those compounds received enormous interest due to their unique combination of optical and long‐range magnetic properties. Among them, iron phosphorus trisulfide (FePS3) gathered special attention for being a semiconductor with an absorption edge in the near‐infrared, as well as showing an Ising‐like anti‐ferromagnetism. A successful growth of centimeter size bulk FePS3 crystals with a chemical yield above 70% is reported, whose crystallographic structure and composition are carefully identified by advanced electron microscopy methodologies, including atomic resolution elemental mapping, along with photoelectron spectroscopy. The knowledge on the optical activity of FePS3 is extended utilizing temperature‐dependent absorption and photoacoustic spectroscopies, while measurements are corroborated with density‐functional theory calculations. Temperature‐dependent experiments show a small and monotonic band‐edge energy shift down to 115 K and expose the interconnected importance of electron‐phonon coupling. Most of all, the correlation between the optical behavior and the magnetic phase transition is revealed, which shows the practical utilization of temperature‐dependent optical absorption to investigate magnetic interactions. [ABSTRACT FROM AUTHOR]

Lamellar structures of transition metal phosphorus trisulfides possess strong intralayer bonding, albeit adjacent layers are held by weak van der Waals interactions. Those compounds received enormous interest due to their unique combination of optical and long‐range magnetic properties. Among them, iron phosphorus trisulfide (FePS3) gathered special attention for being a semiconductor with an absorption edge in the near‐infrared, as well as showing an Ising‐like anti‐ferromagnetism. A successful growth of centimeter size bulk FePS3 crystals with a chemical yield above 70% is reported, whose crystallographic structure and composition are carefully identified by advanced electron microscopy methodologies, including atomic resolution elemental mapping, along with photoelectron spectroscopy. The knowledge on the optical activity of FePS3 is extended utilizing temperature‐dependent absorption and photoacoustic spectroscopies, while measurements are corroborated with density‐functional theory calculations. Temperature‐dependent experiments show a small and monotonic band‐edge energy shift down to 115 K and expose the interconnected importance of electron‐phonon coupling. Most of all, the correlation between the optical behavior and the magnetic phase transition is revealed, which shows the practical utilization of temperature‐dependent optical absorption to investigate magnetic interactions. [ABSTRACT FROM AUTHOR]

Charged particles radiation induces the performances degradation of space polyimide (PI) aerogel, which puts forward the requirement for the accurate quantification of the radiation-induced damage. Photoacoustic spectroscopy (PAS) was proposed with a cantilever for the sensitive resonance detection of the photoacoustic (PA) pressure based on the analysis of cantilever-air dynamic coupling theory and finite element simulation. Wavelength scan PAS inspection of the proton irradiated PI aerogel verified the sensitivity of PA signals to the radiation fluence. Dual-wavelength PAS was first theoretically investigated and performed by measuring the PA signals alternately induced by the 405- and 532-nm lasers. Based on the presented theoretical relation between the PA signals and the radiation characteristics, the derived normalized damage fraction ($f_{a}$) revealed distinct reliance on the proton fluence ($\phi$). The experimental results and the theoretical relations fit well on the goodness of $\chi ^{2} = 8.2 \times 10^{-4}$ , and the fit value of the single-proton damage area ($\sigma$) was $1.4\times 10^{-16}$ cm2. The relative error for the measurement of fluence ($\phi$) was 5%. The research indicates that the presented cantilever-enhanced PAS method is an efficient tool for rapid and accurate quantification of the proton radiation-induced damage in PI aerogel. [ABSTRACT FROM AUTHOR]

Gas detection based on photoacoustic (PA) spectroscopy has attracted extensive attention due to high sensitivity and portability. Herein, to achieve the simultaneously detection of the transformer oil carbide gases, C2H2 and CO, a gas-detection system based on one cantilever beam sensor and single-pass PA cell was proposed. The infrared light beams were coupled by the coarse wavelength division multiplexer (CWDM) and fiber coupler, the vibration of the cantilever beam was measured by the vibration meter, and the gas detection experiment was carried out. The results showed that cantilever could distinguish multiple kinds of acoustic waves, in the frequency domain, the simultaneous detection of C2H2 and CO can be realized by extracting the fast Fourier transform (FFT) values at 20 and 55 Hz. The system exhibits a good repeatability, and a linear relationship between the pure PA signals and gas concentration was confirmed with the correlation coefficient greater than 0.9. In addition, the pure PA signals also show linear trend with the coupling ratio. The minimum detection limit and resolution of C2H2 are 0.27 and 0.12 per part million (ppm), respectively, when the CWDM is used to couple the light beams, whereas they are 23.42 and 14.94 ppm of CO. Especially, it was found that the PA signals have good superposition whether the modulation frequencies of the external lasers are same or not. This article provides an idea for simultaneous detection of multicomponent in gas mixture. [ABSTRACT FROM AUTHOR]

Purpose: Photoacoustics (optoacoustics) is a hybrid technology utilizing light excitation of acoustic responses in targets of interest. It has found numerous applications in biomedicine, including eye research, because of its ability to report both morphological and functional data about the interrogated tissue. This presentation will give an overview of current applications. Methods: Wavelength-dependent absorption of light in a tissue chromophore causes local heating, leading to a thermoelastic expansion-contraction cycle. If nanosecond pulses of light are used to excite this process, the resulting pressure wave is an ultrasound signal propagating through the tissue and detectable at the tissue surface. This is highly advantageous because of the known properties of ultrasound propagation in tissue and the ability to use standard, medical ultrasound equipment for detection. The time of arrival and amplitude of ultrasound signals provide information about the location and nature of the absorber. Results: Due to the wavelength dependence of the photoacoustic response, functional and physiological applications are possible. For example, retinal oximetry can be determined from the different optical absorption properties of oxy- and deoxyhemoglobin. Multispectral imaging of the posterior segment can identify pigments such as melanin or lipofuscin or the nature of foreign bodies. The technique can be combined with other imaging modalities such as ultrasound and optical coherence tomography to produce high-resolution images of retinal structures along with functional information. Conclusion: Photoacoustic technology is a powerful noninvasive tool for ocular research and to study ocular morphology, fundamental physiological parameters, cellular responses, and molecular expression. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China Agricultural University is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Quartz-enhanced photoacoustic spectroscopy (QEPAS) gas sensors have been widely developed over the last decade. This technique takes the advantage of a high quality factor tuning fork to enable high-sensitivity and high-selectivity miniature gas sensors. Lock-in detection is classically used to measure the resonator amplitude, which is proportional to the gas concentration, but this technique is slow and leads to measurement drifts as it does not follow the resonator frequency drifts over temperature and pressure. This article presents a new QEPAS signal processing technique that allows faster and more stable measurements that will enable accurate and fast multigas sensors. [ABSTRACT FROM AUTHOR]

Infrared (IR) optoacoustic spectroscopy can separate a multitude of molecules based on their absorption spectra. However, the technique is limited when measuring target molecules in aqueous solution by strong water absorption at IR wavelengths, which reduces detection sensitivity. Based on the dependence of optoacoustic signal on the temperature of the probed medium, we introduce cooled IR optoacoustic spectroscopy (CIROAS) to mute water contributions in optoacoustic spectroscopy. We showcase that spectral measurements of proteins, lipids, and glucose in the short-wavelength IR region, performed at 4 °C, lead to marked sensitivity improvements over conventional optoacoustic or IR spectroscopy. We elaborate on the dependence of optoacoustic signals on water temperature and demonstrate polarity changes in the recorded signal at temperatures below 4 °C. We further elucidate the dependence of the optoacoustic signal and the muting temperature on sample concentration and demonstrate that changes in these dependences enable quantification of the solute concentration. We discuss how CIROAS may enhance abilities for molecular sensing in the IR. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract In the pulsed laser photoacoustic (PA) detection and spectroscopy applications, the fundamental frequency of the PA signal produced, and the sensor resonance frequency should be as close as possible to each other so that analyzes from the obtained signals can be performed effectively. In order to determine the fundamental frequency of the PA wave, a theoretical model approach based on the development of the frequency domain solution of the PA wave equation is presented for use in the PA pressure sensor designs. For the validation of the theoretical model approach, a PA experimental setup was established, and measurements were made in distilled water. The theoretical and the experimental PA frequency spectra were determined to be very compatible with each other. Thus, the theoretical model approach was experimentally validated. According to the theoretical model approach, fundamental frequency values obtained from the experimental measurement results were determined with an average accuracy of ∓ 4.212%. Furthermore, it has been determined that this value has fallen to ∓0.267% in the measurements. With the obtained results from the theoretical model approach, we propose that the PA pressure sensors with the more selective and narrower band can be designed for the more sensitive detection. Moreover, in this study the effects of different laser parameters such that pulse duration, and laser beam width, on the spectral content of the obtained PA signal are analyzed. These analyses will shed light on the vision of acoustic pressure sensor design by helping to select the most optimum parameters for the PA detection. [ABSTRACT FROM AUTHOR]

Highlights • A proof-of-concept of an innovative PAS gas sensor based on a polyvinylidene fluoride (PVDF) film was introduced. • The photoacoustic signal was detected with a PVDF film, instead of using conventional microphone or quartz tuning fork. • The use of PVDF film as transducer offers good flexibility, water resistance, chemical stability, low cost and simple configuration. Abstract A proof-of-concept gas sensor based on innovative photoacoustic spectrophone was introduced for purpose of developing a low cost and simple configuration photoacoustic spectroscopy gas sensor and demonstrated, in which the photoacoustic signal was detected with a low cost polyvinylidene fluoride (PVDF) film being used as transducer, instead of using conventional microphone or quartz tuning fork. In such a PVDF-based photoacoustic spectroscopy (PVDF-PAS) approach, the PVDF film plays a role both as a cantilever used in cantilever-enhanced photoacoustic spectroscopy and as a piezoelectric quartz tuning fork used in quartz-enhanced photo-acoustic spectroscopy. Feasibility of the introduced PVDF-PAS for trace gas sensing was demonstrated by measuring H 2 O vapor with a minimum detection limit of 40 ppmv using a lock-in time constant of 30 ms, this corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 2.4 × 10−7 cm-1W/Hz1/2. The use of polyvinylidene fluoride film as transducer for photoacoustic signal sensing offers good flexibility, water resistance, chemical stability and low cost for applications under harsh or/and specific environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract Common fertilizers have the oxidizing and the reducing elements on the same molecule; therefore they have an explosiveness nature. Reliable approach for fast recognition of such compounds is an urgent need. Laser induced photoacoustic spectroscopy is an interesting technology as it can offer characteristic thermal, acoustical, and light absorption coefficient. The paper deals with a photoacoustic spectroscopy technique to record the characteristic photoacoustic frequency-response of common explosive-related materials. The proper stimulating light was generated using pulsed Q-switched Nd:YAG laser at 1064 nm. Photoacoustic signature for each investigated material was recorded using high response piezoelectric transducer. The captured signal was processed using novel digital algorithm designed for time and frequency domain analysis to achieve good discrimination between different explosive-related materials. Each investigated material demonstrated a characteristic absorption coefficient as well as frequency response with maximum amplitude at 47.9, 49, and 46 MHz for urea nitrate, ammonium nitrate, and ammonium perchlorate respectively. Graphical abstract Image 1 Highlights • Instant identification of explosive-related compounds. • Novel photoacoustic signal processing using time and frequency domain algorithms. • Original approaches to quantify characteristic absorption coefficient as well as frequency response. • Quantified thermal, optical, and acoustical properties that can act as a fingerprint of the material structure. [ABSTRACT FROM AUTHOR]

Organic hazes formed from methane are present in many planetary and satellite atmospheres and influence surface and atmospheric processes. Here we examine the compositional and optical properties of laboratory generated hazes, or tholins, formed with varying amounts of methane using spark discharge excitation. By studying the optical and chemical properties together as a function of methane precursor concentration, the radiative impact of haze can be better understood. To determine the complex refractive index of tholin, we combine two spectroscopic techniques: photoacoustic spectroscopy and cavity ring-down spectroscopy (PASCaRD). The refractive indices are retrieved at λ = 405 and 532 nm. Quadrupole aerosol mass spectrometry is used along with a technique that utilizes isotopically labeled and unlabeled methane gas to quantify elemental composition. Tholin optical and compositional measurements are performed within a flow system, eliminating the need for tholin collection on a substrate and possible post-collection changes. We observe n values within the range of n values from most previous studies. However, the observed k values, like most others from recent studies, are significantly lower than the values from Khare et al. (1984) (Khare, B.N., Sagan, C., Arakawa, E.T., Suits, F., Callcott, T.A., Williams, M.W. [1984]. Icarus 60, 127–137) that are commonly used in data retrieval programs and models. In addition, comparing the tholin k values to their approximate nitrogen and aromatic content suggests both chemical constituents are important factors for increased aerosol absorption. [ABSTRACT FROM AUTHOR]

Laser photoacoustic spectroscopy (LPAS) is an attractive technology in terms of simplicity, ruggedness, and overall sensitivity; it detects the time dependent heat generated (thermo-elastic effect) in the target via interaction with pulsed optical radiation. This study reports on novel LPAS technique that offers instant and standoff detection capabilities of trace explosives. Over the current study, light is generated using pulsed Q-switched Nd:YAG laser; the generated photoacoustic response in stimulated explosive material offers signature values that depend on the optical, thermal, and acoustical properties. The generated acoustic waves were captured using piezoelectric transducer as well as novel customized optical sensor with remotely laser interferometer probe. A digital signal processing algorithm was employed to identify explosive material signatures via calculation of characteristic optical properties (absorption coefficient), sound velocity, and frequency response of the generated photoacoustic signal. Customized LPAS technique was employed for instantaneous trace detection of three main different high explosive materials including TNT, RDX, and HMX. The main outcome of this study is that the novel customized optical sensor signals were validated with traditional piezoelectric transducer. Furthermore, the customized optical sensor offered standoff detection capabilities (10cm), fast response, high sensitivity, and enhanced signal to noise ratio. This manuscript shaded the light on the instant detection of trace explosive materials from significant standoffs using novel customized LPAS technique. [ABSTRACT FROM AUTHOR]

Although the drug-eluting stent (DES) has dramatically reduced the rate of coronary restenosis, it still occurs in up to 20% of patients with a DES. Monitoring drug delivery could be one way to decrease restenosis rates. We demonstrate real-time photoacoustic imaging and spectroscopy (PAIS) using a wavelength-tunable visible laser and clinical ultrasound scanner to track cardiac drug delivery. The photoacoustic signal was initially calibrated using porcine myocardial samples soaked with a known concentration of a drug surrogate (DiI). Next, an in situ coronary artery was perfused with DiI for 20 min and imaged to monitor dye transport in the tissue. Finally, a partially DiI-coated stent was inserted into the porcine brachiocephalic trunk for imaging. The photoacoustic signal was proportional to the DiI concentration between 2.4 and 120 μg/ml, and the dye was detected over 1.5 mm from the targeted coronary vessel. Photoacoustic imaging was also able to differentiate the DiI-coated portion of the stent from the uncoated region. These results suggest that PAIS can track drug delivery to cardiac tissue and detect drugs loaded onto a stent with sub-mm precision. Future work using PAIS may help improve DES design and reduce the probability of restenosis. [ABSTRACT FROM AUTHOR]

In Quartz Enhanced Photoacoustic Spectroscopy (QEPAS), due to the strained material and piezoelectric effect of the Quartz Tuning Fork (QTF), the in-plane mode of QTF is generally detected, requiring micron-scale precise and stable optical alignment and convergence. It poses a significant challenge for the use of light sources and has become a bottleneck for practical implementations of QEPAS. In this paper, a ppb-level all-optical off-axis QEPAS gas sensor based on dual-wavelength demodulation of out-of-plane mode is proposed and experimentally demonstrated. A dual-wavelength Fabry-Perot (FP) Interferometer with Ellipse Fitting-Differential Cross Multiply (EF-DCM) algorithm is designed and employed to demodulate the out-of-plane mode of off-axis QTF, which is approximately 80 times stronger than the conventional in-plane mode. This work established a novel ultra-sensitive off-axis QEPAS-based hydrogen sulfide (H 2 S) sensor with a 1.5 W fiber-amplified near-infrared diode laser. The minimum detection limit and normalized noise equivalent absorption of the developed H 2 S sensor is 74.19 ppb with 1 s integration time and 2.68 × 10−9 W∙cm−1∙Hz−1/2 respectively, beyond previously reported QEPAS-based H 2 S sensors. This technique effectively utilizes the out-of-plane mode of QTF and realizes the simultaneous enhancement of off-axis location and out-of-plane vibration mode detection in QEPAS, allowing a novel approach for the development of ultra-sensitive QEPAS gas sensors with notable practical application prospects. • An out-of-plane vibration mode based QTF was used for off-axis Quartz Enhanced Photoacoustic Spectroscopy (QEPAS). • The dual-wavelength FPI demodulation and the EF-DCM algorithm was proposed to detect the QTF surface vibration. • The developed QEPAS system has reduced the requirement of light source, which can match imperfect beam. • The performance of the system was evaluated using a 1.5 W fiber amplified near infrared diode laser. • The one order of magnitude sensitivity improvement was realized compared with traditional off-axis QEPAS. [ABSTRACT FROM AUTHOR]

Saliva provides a valuable tool for assessing oral and systemic diseases, but concentrations of salivary components are very small, calling the need for precise analysis methods. In this work, Fourier transform infrared (FT-IR) spectroscopy using transmission and photoacoustic (PA) modes were compared for quantitative analysis of saliva. The performance of these techniques was compared with a calibration series. The linearity of spectrum output was verified by using albumin- thiocyanate (SCN-) solution at different SCN- concentrations. Saliva samples used as a comparison were obtained from healthy subjects. Saliva droplets of 15 μL were applied on the silicon sample substrate, 6 drops for each specimen, and dried at 37 °C overnight. The measurements were carried out using an FT-IR spectrometer in conjunction with an accessory unit for PA measurements. The findings with both transmission and PA modes mirror each other. The major bands presented were 1500-1750 cm-1 for proteins and 1050-1200 cm-1 for carbohydrates. In addition, the distinct spectral band at 2050 cm-1 derives from SCN- anions, which is converted by salivary peroxidases to hypothiocyanate (OSCN-). The correlation between the spectroscopic data with SCN- concentration (r>0.990 for transmission and r = 0.967 for PA mode) was found to be significant (P<0.01), thus promising to be utilized in future applications. [ABSTRACT FROM AUTHOR]

One of the most effective and convenient ways to determine the early stages of potential faults in oil-insulated electrical apparatus and to monitor the development is to routinely detect and analyze the concentrations and fluctuations of potential fault gases [1]?[5]. This method has been widely used in power-grid operations and is effective in preventing the occurrence of catastrophic faults. In the past, the technology to detect mixed gas by electrochemical sensors offered effective early warnings of potential faults in electrical apparatus. Today, gas chromatography is widely used to accurately detect the composition of various gases dissolved in oil. Fault development can accurately be diagnosed by using gas chromatography together with various other means such as the Duval Triangle and key gas methods. After extended use, these techniques have been found to have drawbacks, namely, the need to routinely replace or calibrate chromatographic columns and sensors because their properties change with use, and the consumption of calibration and carrier gases with gas chromatography use [6], [7]. Photoacoustic spectroscopy, developed in the 1970s, is a spectral detection and analysis technology derived from a combination of spectroscopy and calorimetry. The method is powerful in physical chemistry research that involves inorganic or organic compounds, semiconductors, metallic materials, and high-polymer materials. It has found widespread application in various disciplines, such as physics, chemistry, biology, medicine, and geology. The major advantages associated with photoacoustic spectroscopy are that it (1) is characterized by high monitoring sensitivity because it directly measures the energy absorbed by gases without background noise; (2) uses easily available air instead of high-purity inert gases as the carrier gas without consuming the to-be-measured gas; (3) does not require chromatographic columns and sensors, which are easily contaminated, undergo aging, and require frequent replacement; (4) does not require a calibration gas, raising the prospect of realizing true maintenance-free operation; and (5) displays a high level of versatility because it even detects the contents of high-concentration gases in the oil tank of on-load tap changers [8]?[12]. Therefore, photoacoustic spectroscopy can greatly enhance the on-line monitoring of electrical system maintenance owing to its high stability, low drift, and maintenance-free features. Considering these technical characteristics, we devised a test platform by combining the technology with the headspace degassing technique. Thus, we investigated the application of photoacoustic spectroscopy to detecting concentrations of gases dissolved in oil-insulated electrical apparatus. [ABSTRACT FROM PUBLISHER]

A new sensor for methane and carbon dioxide concentration measurements in biogas plants is presented. LEDs in the mid infrared spectral region are implemented as low cost light source. The combination of quartz-enhanced photoacoustic spectroscopy with an absorption path leads to a sensor setup suitable for the harsh application environment. The sensor system contains an electronics unit and the two gas sensors; it was designed to work as standalone device and was tested in a biogas plant for several weeks. Gas concentration dependent measurements show a precision better than 1% in a range between 40% and 60% target gas concentration for both sensors. Concentration dependent measurements with different background gases show a considerable decrease in cross sensitivity against the major components of biogas in direct comparison to common absorption based sensors. [ABSTRACT FROM AUTHOR]