Modification of a piezo-optical gas dosimeter system towards continuous gas sensing: a feasibility study with carbon dioxide

We report a feasibility study of monitoring gases continuously by means of an adapted piezo-optical dosimeter system. The test gas is carbon dioxide whose presence is detected via a pH indicator colour change. Sensing spots consist of m-Cresol Purple supported in a buffered ethyl cellulose matrix and deposited on an indium-tin oxide coated piezoelectric film. The change in absorbance is measured via illumination with an amber LED whose peak emission at 592 nm corresponds to the basic form of the reagent. A sensor was developed and calibrated over the range 0–2.5% CO₂ of interest for personal monitoring. The 90% response times are 3–4 min but the response rates could be used to trigger an alarm in the first few seconds of CO₂ increase.     

An optical IR-source and CO2-chamber system for CO2 measurements

A new silicon IR source and CO₂-chamber system for measurement of CO₂ concentration is presented. The micromachined IR-source, which consists of four groups of polysilicon filaments coated with silicon nitride suspended across a KOH-etched cavity, is used to generate two switched “sample” and “reference” beams. The electrically modulated sources present a modulation time of 10 ms and a power consumption of 1 W. The CO₂ chambers, placed beneath the reference sources, are used to produce a reference beam for long term stability and compensation against cuvette window contamination. They consist of 1-mm-deep micromachined cavities in which CO₂ is encapsulated during an overpressure anodic bonding procedure. Silicon dioxide is used as an antireflective coating to optimize the filter's optical characteristics. Numerical simulations of the filters are presented and show good agreement with the measurements. The IR sources and the CO₂ filters are both fabricated at wafer level. Using the presented IR-sensor system, measurements with a 9-mm-wide test channel show high CO₂-sensitivity for CO₂ concentrations between 0 and 10% confirming that the stringent requirements for this respirator application can be fulfilled     

Production of singlet oxygen by Ru(dpp(SO3)2)3 incorporated in polyacrylamide PEBBLES

Polyacrylamide (PAA) and amine-functionalized PAA (AFPAA) nanoparticles with disulfonated 4,7-diphenyl-1,10-phenantroline ruthenium (Ru(dpp(SO₃)₂)₃) have been prepared. The nanoparticles produced have a hydrodynamic radius of 20–25 nm.

The amount of singlet oxygen (¹O₂) produced by Ru(dpp(SO₃)₂)₃ as been measured using anthracene-9,10-dipropionic acid (ADPA). A kinetic model for the disappearance of ADPA, by steady state irradiation of Ru(dpp(SO₃)₂)₃ at 465 nm, has been developed taking also into account a consumption not mediated by ¹O₂. This direct consumption of ADPA is evaluated by irradiating in the presence of NaN₃ and is about 30% of the total. All the experimental results are very well described by the model developed, both for free Ru(dpp(SO₃)₂)₃ and with this dye incorporated in the nanoparticles.

It is found that the polyacrylamide matrix does not quench the ¹O₂ produced, allowing it to reach the external solution of the nanoparticles and react with ADPA. When the matrix possesses amine groups, AFPAA, the amount of ¹O₂ that reacts with ADPA is slightly reduced, 60%, but most of the ¹O₂ produced can still leave the particles and react with external molecules. The particles produced may therefore be used as sources of ¹O₂ in photodynamic therapy (PTD) of cancers. The fact that those nanoparticles do not quench significantly the ¹O₂ makes possible the future development of ¹O₂ sensors based on PAA nanoparticles with the appropriate sensor molecule enclosed.     

Enhanced oxygen detection using porous polymeric gratings with integrated recognition elements

The development of ordered porous nanostructured materials, such as polymeric Bragg gratings, offers an attractive platform for the encapsulation of chemical and biological recognition elements. To date, various types of polymer gratings have been developed with several demonstrated applications in switching, lasing, and display devices. Here, we focus on a new class of holographically ordered porous polymer (HOPP) gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. We present biochemical sensing using HOPP gratings that include a volatile solvent as the phase separation fluid. The resulting HOPP gratings are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of recognition elements. As a prototype, we developed an oxygen (O₂) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. The resulting O₂ sensors performed across the full-scale range (0–100%) of oxygen in nitrogen, with a response time of less than 1 s. The O₂ sensor system uses a LED excitation source and a silicon photodiode detector. The ability of these HOPP reflection gratings to transmit or reflect a particular wavelength range, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest.     

Distributed detection with consulting sensors and communicationcost

The problem of distributed detection with consulting sensors in the presence of communication cost associated with any exchange of information (consultation) between sensors is considered. The system considered has two sensors, S1 and S2; S1 is the primary sensor responsible for the final decision u₀ , and S2 is a consulting sensor capable of relaying its decision u₂ to S1 when requested by S 1. The final decision u₀ is either based on the raw data available to S1 only, or, under certain request conditions, also takes into account the decision u₂ of sensor S2. Random and nonrandom request schemes are analyzed and numerical results are presented and compared for Gaussian and slow-fading Rayleigh channels. For each decision-making scheme, an associated optimization problem is formulated whose solution is shown to satisfy certain set design criteria that the authors consider essential for sensor fusion     

Preparation of gas sensors via dip-pen nanolithography

In the present work, a conducting polymer, doped polypyrrole, was used to develop a gas sensor by dip-pen nanolithography (DPN). The response time of the sensor to 18 ppm CO₂ was 9 s. The sensor response increased linearly as the CO₂ concentration increased. A possible mechanism for the CO₂ sensing was discussed.     

大气甲烷探测进展与全球甲烷分布分析

甲烷（CH₄）是大气中具有化学活性和辐射活性的气体。随着人类文明的发展,CH₄的总量一直在增加。工业革命前全球CH₄浓度为700 ppbv,到20世纪90年代它的浓度达到1714 ppbv。研究阐述了CH₄地基探测、空基探测、星基探测及反演算法的发展现状。自1979~1983年Nimbus-7卫星上的SAMS探测仪首次实现对平流层CH₄浓度探测以来,国际上已有许多可探测CH₄的卫星探测仪。随着卫星探测技术的发展及反演算法的改进,卫星传感器反演的CH₄精度逐渐提高。其中天底模式下TROPOMI传感器反演的CH₄浓度与地面站点数据的偏差为14 ppbv（0.8%）;临边/掩星模式下ACE-FTS反演的对流层至平流层下部CH₄廓线精度在10%以内。而后,基于AIRS L3产品分析了300 hPa、150 hPa全球CH₄浓度变化趋势和分布特征, 2010~2020年全球CH₄浓度增长了约50 ppbv,年均增长率约为0.29%;全球CH₄浓度北高南低,高值区分布在大西洋中部、非洲北部、中东地区和中国西部。     

Color blindness and a color human visual system model

A physiologically motivated human color visual system model which represents visual information with one brightness component (A) and two chromatic components (C₁ and C₂) is used to create stimuli for testing the color perception of deuteranomalous trichromats. Two experiments are performed. Using simple ramp patterns, the first experiment finds that three deuteranomalous trichromat test subjects can distinguish variations only in the C₂ component of the color vision model. This finding is further tested in the second experiment: a set of paired comparison preference tests. Two altered versions of each of three natural color images are prepared by setting either one of the color components to a constant over the full image. Pairs of an original and a distorted image are presented to the test subjects, and they are asked to indicate which image they prefer. The experimental results indicate that the C₁ channel is severely attenuated in the deuteranomalous trichromat test subjects, and that nearly all their color sensation is mediated by the C₂ channel of the color vision model     

NOx sensing properties of In2O3 nanoparticles prepared by metal organic chemical vapor deposition

In₂O₃ nanoparticles were deposited by low-temperature metal organic chemical vapor deposition. The response of 10-nm thick In₂O₃ particle containing layers to NO_x and O₂ gases is investigated. The lowest detectable NO_x concentration is 200 ppb and the sensor performance is strongly dependent on the gas partial pressure as well as on the operating temperature. The sensor response towards 200 ppm of NO_x is found to be above 10⁴. Furthermore, the cross-sensitivity against O₂ is very low, demonstrating that the In₂O₃ nanoparticles are very suitable for the selective NO_x detection.     

Electrochemical measurement of SO3-SO2 in process gas streams

The two major industrial sources of sulphur dioxide emissions are electrical generation and non-ferrous smelting. While flue-gas scrubbing and acid-plant technology are well established, continuous methods for the determination of SO₂ in these process streams are based on expensive conventional UV or IR spectroscopic instrumentation in which the gases must be conditioned prior to analysis. Additionally, there appears to be no reliable continuous low-maintenance method of analysis for SO₃ in gases. Solid-state sensors for the continuous real-time measurement of concentrations of SO₃ and SO₂ in process gas streams offer the possibility of monitoring the efficiency of flue-gas scrubbing, determining the concentrations of SO₃ in corrosion-susceptible ducting or in acid-plant conversion towers and guarding against excessive releases of SO₃ from acid-plant tail gas. The measurement of SO₂ and SO₃ in gases by solid-state electrochemistry is reviewed. The electrochemical cells are described, and wherever possible, the temperature and concentration ranges of the various solid-state devices reported in the literature are given. We conclude with a summary of the further requirements for a successful inexpensive commercial solid-state sensor for SO₃ and SO₂ measurement in process gas streams.     

Micromachined sol–gel carbon nanotube/SnO2 nanocomposite hydrogen sensor

A novel micromachined single wall carbon nanotube (SWCNT) reinforced nanocrystalline tin dioxide gas sensor has been developed. The presence of SWCNT in SnO₂ matrix was realized by a spin-on sol–gel process. The SWCNT/SnO₂ sensor's sensitivity for hydrogen detection has greatly increased by a factor of three, in comparison to that of pure SnO₂ sensor. The novel sensor also lowers the working temperature, response time and recovery time. The greatly improved performances are mainly attributed to the effective gas accessing nano passes through SWCNT plus the smaller distance between adjacent gas accessing boundaries formed by the distribution of tiny SWCNTs. Therefore, both the spatial requirement (D ≤ 2L, D is the distance between adjacent gas accessing boundaries and L is the space charge layer thickness) and surficial requirement (adequate gas activation area) are met and the maximum inherent sensitivity of SnO₂ is achieved.     

Computational complexity of distributed detection problems with information constraints

For a system consisting of a set of sensors S = {S₁, S₂, …, S_m} and a set of objects O = {O₁, O₂, …, O_n}, there are information constraints given by a relation R S × O such that (S_i, O_j) R if and only if S_i is capable of detecting O_j. Each (S_i, O_j) R is assigned a confidence factor (a positive real number) which is either explicitly given or can be efficiently computed. Given that a subset of sensors have detected obstacles, the detection problem is to identify a subset H O with the maximum confidence value. The computational complexity of the detection problem, which depends on the nature of the confidence factor and the information constraints, is the main focus of this paper. This problem exhibits a myriad of complexity levels ranging from a worst-case exponential (in n) lower bound in a general case to an O(m + n) time solvability. We show that the following simple versions of a detection problem are computationally intractable: (a) deterministic formulation, where confidence factors are either 0 or 1; (b) uniform formulation where (S_i, O_j) R, for all S_i S, O_j O; (c) decomposable systems under multiplication operation. We then show that the following versions are solvable in polynomial (in n) time: (a) single object detection; (b) probabilistically independent detection; (c) decomposable systems under additive and nonfractional multiplicative measures; and (d) matroid systems.     

A fibre-optic oxygen sensor based on contact charge-transfer absorption

A fibre-optic oxygen (O₂) sensor monitoring at a wavelength of 400 nm has been successfully developed for the determination of gaseous O₂. Its working principle is based on the contact charge-transfer absorption of N,N-dimethyl-p-toluidine and O₂. The response to changes in O₂ concentrations is reversible and in good agreement with the Beer-Lambert law. The response and recovery times are 12 and 26 min, respectively. The sensor can detect a wide range of O₂ concentrations, ranging from 4.3 to 100% O₂. The precision is 1.45% (n=5) in a gas mixture of 95% O₂ in N₂ and the limit of detection is 4.3% O₂ (3σ_b). The sensor is stable with a 0.53% change in sensitivity per hour. There is a 0.25% °C⁻¹ decrease of the sensitivity of the sensor to O₂ in the range 20–34°C. Water vapour and nitrogen dioxide interfere slightly, whereas hydrogen sulphide and hydrogen chloride have moderate interference on the sensor. However, chlorine and sulphur dioxide seriously interfere with the sensor.     

Robust Fault Detection and Isolation Based on Finite-frequency H?/H∞ Unknown Input Observers and Zonotopic Threshold Analysis

This work proposes a robust fault detection and isolation scheme for discrete-time systems subject to actuator faults, in which a bank of H_?/H_∞ fault detection unknown input observers (UIOs) and a zonotopic threshold analysis strategy are considered. In observer design, finite-frequency H_? index based on the generalized Kalman-Yakubovich-Popov lemma and H_∞ technique are utilized to evaluate worst-case fault sensitivity and disturbance attenuation performance, respectively. The proposed H_?/H_∞ fault detection observers are designed to be insensitive to the corresponding actuator fault only, but sensitive to others. Then, to overcome the weakness of predefining threshold for FDI decision-making, this work proposes a zonotopic threshold analysis method to evaluate the generated residuals. The FDI decision-making relies on the evaluation with a dynamical zonotopic threshold. Finally, numerical simulations are provided to show the feasibility of the proposed scheme.      

Selective detection of ethanol vapor and hydrogen using Cd-doped SnO2-based sensors

The effect of CdO doping on microstructure, conductance and gas-sensing properties of SnO₂-based sensors has been presented in this study. Precursor powders with Cd/Sn molar ratios ranging from 0 to 0.5 were prepared by chemical coprecipitation. X-ray diffraction (XRD) analysis indicates that the solid-state reaction in the CdO–SnO₂ system occurs and -CdSnO₃ with pervoskite structure is formed between 600 and 650°C. CdO doping suppresses SnO₂ crystallite growth effectively which has been confirmed by means of XRD, transmission electron microscopy (TEM) and BET method. The 10 mol% Cd-doped SnO₂-based sensor shows an excellent ethanol-sensing performance, such as high sensitivity (275 for 100 ppm C₂H₅OH), rapid response rate (12 s for 90% response time) and high selectivity over CO, H₂ and i-C₄H₁₀. On the other hand, this sensor has good H₂-sensing properties in the absence of ethanol vapor. The sensor operates at 300°C, the sensitivity to 1000 ppm H₂ is up to 98, but only 16 and 7 for 1000 ppm CO and i-C₄H₁₀, respectively.     

Comprehensive study of hydrogen sensing characteristics of Pd metal–oxide–semiconductor (MOS) transistors with Al0.24Ga0.76As and In0.49Ga0.51P Schottky contact layers

The interesting hydrogen sensing characteristics of two transistors with an Al_0.24Ga_0.76As (device A) and In_0.49Ga_0.51P (device B) Schottky layer are demonstrated and studied. Experimentally, device A shows a lower hydrogen detection limit of 4.3 ppm H₂/air, a higher current variation of 7.79 mA and a shorter adsorption time of 10.95 s in a 9970 ppm H₂/air at room temperature. On the other hand, device B exhibits more stable hydrogen-sensing characteristics at high temperatures. Even at a low concentration of 14 ppm H₂/air the hydrogen sensing properties of device B can be obtained as the temperature increases from 30 to 160 °C. Because the Al_0.24Ga_0.76As and In_0.49Ga_0.51P materials are lattice-matched to the GaAs substrate, the studied devices can be integrated as sensor arrays to obtain superior hydrogen sensing characteristics including higher sensing signals, lower detection limit, shorter response time, and widespread detection and temperature regimes.     

基于特征气体SO2F2的SF6气体绝缘设备的过热性故障诊断

利用SF₆分解产物检测来判断GIS故障发展程度已成为一种有效手段,在搭建的实验平台上展开200℃~360℃局部过热模拟实验,研究SF₆热分解特性。当实验温度较高时(320℃~360℃),新增SO₂F₂、H₂S、COS三种产物。在绝缘设备充满大量SF₆子的背景下,分解产生的H₂和COS的含量极少,给气体检测带来了困难。文中提出将SO₂F₂作为设备故障进入严重状态的标志气体,同时用量子化学计算法在B3LYP/6-311G(+d,p)水平下对SO₂F₂生成机理和能量条件进行研究。发现SO₂F₂通过F₂碎片与气室内SO₂反应、F原子与SO₂F结合、SOF 4水解反应这三条途径得到,其中SO₂与F₂反应是SO₂F₂的主要来源。实验现象与理论计算均表明:SO₂F₂的形成机制与高温息息相关,SO₂F₂出现,标志着设备故障处温度较高,SF₆绝缘能力已遭到严重破坏。     

Hydrogen sensors: Role of palladium thin film morphology

The effect of thin film morphology, carbon monoxide (CO) and resistor geometry on the response of hydrogen sensitive thin film palladium resistors has been investigated. Films with two different morphologies were fabricated by DC magnetron sputtering under different gas pressures. Palladium thin film morphology was found to strongly influence sensor response in terms of hydrogen sensitivity and rate of response. In dense columnar Pd films, CO dramatically increases the time-lag in sensor response to H₂ in H₂/CO mixtures. However, the steady state value of the response remains unchanged. Films with a void filled columnar morphology exhibited shorter time-lag in response to H₂ in presence of CO.     

Performance and geometric interpretation for decision fusion withmemory

A binary distributed detection system comprises a bank of local decision makers (LDMs) and a central information processor or data fusion center (DFC). All LDMs survey a common volume for a binary {H₀, H₁} phenomenon. Each LDM forms a binary decision: it either accepts H₁ (target-present) or H₀ (target-absent). The LDM is fully characterized by its performance probabilities. The decisions are transmitted to the DFC through noiseless communication channels. The DFC then optimally combines the local decisions to obtain a global decision which minimizes a Bayesian objective function. The DFC remembers and uses its most recent decision in synthesizing each new decision. When operating in a stationary environment, our architecture converges to a steady-state decision LDM in finite time with probability one, and its detection performance during convergence and in steady state is strictly determined. Once convergence is proven, we apply the results to the detection of signals with random phase and amplitude. We further provide a geometric interpretation for the behaviour of the system     

Development of a bienzyme system based on sugar–lectin biospecific interactions for amperometric determination of phenols and aromatic amines

Bienzyme electrode with horseradish peroxidase (HRP) and glucose oxidase (GOD) multilayers was constructed based on sugar–lectin biospecific interactions for amperometric determination of phenolic compounds and aromatic amines. Atomic force microscopy (AFM) was applied to monitor the uniform layer-by-layer assembly of concanavalin A (Con A) and HRP or GOD on polyelectrolyte precursor film-modified Au electrode. Substituted phenolic compounds and aromatic amines could be determined with in situ generation of H₂O₂ by GOD-catalyzed oxidation of glucose. The parameters of the biosensor including the number of assembled HRP and GOD layer, and the concentrations of glucose were optimized. The linear range for the determination of catechol and p-phenyldiamine was 6.0–60.0 μmol L⁻¹ and 7.6–68.4 μmol L⁻¹ with detection limit of 0.9 μmol L⁻¹ and 0.4 μmol L⁻¹, respectively. The biosensor possessed high sensitivity and fast response for phenolic compounds and 95% of the maximum response could be reached in about 3 s. Glucose, ascorbic acid, tartaric acid, citric acid and starch exhibited no interference for the detection. The biosensor presented high stability due to the design for in situ generation of H₂O₂ with bienzyme system.