High temperature field effect hydrogen and hydrocarbon gas sensors based on SiC MOS devices

The growing need for reliable, efficient, high temperature hydrogen and hydrocarbon monitoring has fueled research into novel structures for gas sensing. Metal oxide semiconductor (MOS) devices employing a catalytic metal layer have emerged as one of the leading sensing platforms for such applications, owing to their high sensitivity and inherent capability for signal amplification. The limited operating temperature of such devices employing silicon as the semiconductor has led research efforts to focus on replacing them with devices based on silicon carbide (SiC). More recently, MOS devices having different oxide layers exhibiting improved sensing performance have emerged. Considering the amount of research that has been carried out in this area in recent times, it is important to elucidate the new findings and the gas interaction mechanisms that have been ascribed to such devices, and bring together several theories proposed by different research groups. In this paper we first highlight the needs which have driven research into SiC based field effect hydrogen and hydrocarbon sensors, illustrate the various structures being investigated, and describe the device evolution and current status. We provide several sensing examples of devices that make use of different oxide layers and demonstrate how their electrical properties change in the presence of the gases, as well as presenting the hydrogen gas interaction mechanisms of these sensors.     

Zeolite cover layer for selectivity enhancement of p-type semiconducting hydrocarbon sensors

Screen-printed thick films of the p-type semiconducting materials family SrTi_1−xFe_xO_3−δ have been investigated for hydrocarbon sensing. Among the different compositions tested, the formulations containing 10 and 20% of iron are found to perform best for this purpose. A pronounced cross-interference of NO persisted at operating temperatures of about 400 °C. In order to eliminate this problem, the application of a zeolite cover layer was studied. The properties of this cover layer were optimized with respect to layer thickness and Pt content. Using initial results of a catalytic study on the zeolite powder in addition to a simple diffusion–reaction model, the effect of the zeolite layer with respect to NO cross-interference could be explained satisfactorily.     

声表面波NO2传感器的研究进展

NO2是一种主要的大气污染物,同时对人体健康也有较大的危害,针对其进行检测的传感器的研究和开发就显得十分重要.声表面波气体传感器具有便携性、快速响应、高灵敏度、高稳定性、低成本等特点,引起了国内外相关研究者的广泛关注.简要介绍了声表面波(SAW)气体传感器工作的基本原理、传感器敏感膜与NO2气体的作用机理以及SAW-NO2气体传感器的两种结构类型,综述了SAW-NO2气体传感器常用的几种敏感膜材料,并对SAW-NO2气体传感器的发展趋势做了展望.     

试论家用燃气报警器用气体传感器检定方法

针对家用燃气报警器用的气体传感器的检定方法,提出了不同于报警器检定的、完全针对传感器本身的特性评价的方案,包括检定用模块的规定、符号的规定等.特别是提出了如何使用传感器输出信号的数据,直接评价传感器的报警性能的方法.在此基础上,提出了如何根据报警器检定标准来评价传感器的合格范围,同时提出了对传感器的响应时间、环境试验、...     

一种压缩待测气体增强气体传感的方法

针对普通气体传感器在低体积分数的气体检测中灵敏度低的问题,提出将待测气体进行压缩以增强气体传感器响应的方法,根据检测压缩后的气体响应的特征,间接得到普通状态下该气体的体积分数。设计了一种小型的样机系统来进行气体压缩和气体传感器检测,描述了系统各个模块的设计,给出了该系统的软件设计和控制流程。以H2S气体为检测对象进行了实验,分析结果表明:该方法提高了现有传感器检测低体积分数气体的能力,尤其是提高了对毒害气体的及时发现和预警防范能力。样机的试制也为该压缩传感系统的进一步小型化和提升检测性能提供了条件,具有较高的应用价值。     

非标准化传感器信号调理的一种新方法

以非标准化热电阻为例,介绍了非标准化传感器如何与标准化传感器信号调理电路相匹配的一种方法。这种匹配方法的实质是充分利用测量系统的数据处理功能,通过软件来补偿非标准化传感器与标准化传感器之间的差异。它有效简化了测量系统的硬件,缩短了开发周期,提高了系统的可靠性和稳定性。     

Modifying the selectivity and gas sensitivity of resistive adsorption sensors by targeted doping

This paper explores the physical and chemical laws of energy variations in adsorption centers and the influence exerted on gas-sensitive properties by the targeted doping of semiconductor resistive sensors. The authors establish that minimization of the degradation processes in multisensors requires making each element of these sensors from a same material. In doping by modifiers, an important role belongs to many factors, particularly, the ratio of the squared charge of an impurity ion and its radius. As this factor takes smaller values than that of the parent-ray material, the number of Bronsted centers on the surface goes down and the influence of Lewis centers grows accordingly. The major impact on the energy of surface centers is introduced by the defect rate of the crystal structure (the degree of deviation from stoichiometry).     

A method for evaluating data-preprocessing techniques for odourclassification with an array of gas sensors

The performance of a pattern recognition system is dependent on, among other things, an appropriate data-preprocessing technique, In this paper, we describe a method to evaluate the performance of a variety of these techniques for the problem of odour classification using an array of gas sensors, also referred to as an electronic nose. Four experimental odour databases with different complexities are used to score the data-preprocessing techniques. The performance measure used is the cross-validation estimate of the classification rate of a K nearest neighbor voting rule operating on Fisher's linear discriminant projection subspace.     

Large nanoparticle-induced enhancement of recognition selectivity for Cu ion

A new fluorescent excited state intramolecular proton transfer compound, 2-(2-hydroxy-4-carbaldehydephenyl)benzoxazole (HCPBO), has been synthesized for the detection of Cu²⁺, based on its fluorescence quenching. In molecular monodispersed solution, the recognition selectivity for Cu²⁺ was poor as Co²⁺ and Ni²⁺ gave similar results in fluorescence quenching. However, the nanoparticles of HCPBO, prepared in ethanol-water (1:4, v/v), greatly enhanced the recognition selectivity for Cu²⁺. The mechanism was discussed as energy transfer (ET), energy migration (EM) and the more quantity of formed HCPBO-Cu²⁺ complex than other metal ions in the nanoparticle conditions enhanced the recognition selectivity for Cu²⁺ together.     

Thin-film polymeric sensors for detection and quantification of multivalent metal ions

Chemical sensors that reversibly respond to multivalent metal ions are described. These sensors consist of a thin polymeric sensing element that changes size upon reversibly binding analyte ions, particularly heavy-metal ions. The polymeric sensing elements have been bonded to thin metal-foil strain gauges to form sensors. In laboratory evaluations these sensors exhibit high sensitivity to Ba(II), Cd(II), Pb(II), Cr(III), and Cr(VI). Sensor response time is fast, ranging from several seconds to a few minutes. The selectivity and repsonse characteristics of these sensors depend on the composition of the polymeric sensing element. This paper describes the sensitivity and selectivity demonstrated by sensors containing three chemically different polymeric sensing elements. Potential applications of these sensors include in situ real-time monitoring of the heavy-metal content of ground and surface water, municipal water supplies, and household tap water.     

New method for quantification of clastic sedimentary sequences in time series analysis

Parameters related to the lithology of a clastic sequence may be used for its quantification. Settling velocity of constituent grains of a bed, which is one such parameter, has been taken as a basis for the numerical characterization of clastic rocks and the construction of a stratigraphic time-series representing the sequence. In order to account for varying bed thickness, one may divide an entire section into subsections of equal thickness, varying from 0.1 to 1.0 m. depending on the problem and the nature of data. For each subsection the proportions of thickness of different constituent clastic beds then are multiplied by modified settling velocity values corresponding to their respective grain size characteristics. The resulting numbers are added for each subsection to form the depth series to be analyzed. The proposed method is explained with the help of a case study based on three sections of clastic sequences obtained from the Gondwana coal fields in India. The depth series constructed from the sections have been analyzed by time-series methods. Results of the analysis have been used to demonstrate the applicability of the method in stratigraphic correlation.     

图像增强方法研究新进展

图像增强是一种重要的图像处理方法,其可以增强图像中的细节信息,抑制噪声,改善图像质量,利于后续图像处理.阐述了图像增强研究的现状,对比分析了常用的图像增强方法的优势和局限性,讨论了近些年新涌现的图像增强方法,分析了图像增强评价指标,指出了图像增强方法值得进行深入研究的方向.     

基于遗传蚁群算法的气田集输管网优化方法

气田集输管网是气田建设过程中一个投资巨大的复杂工程,如果能够对其进行整体优化,将取得良好的经济效益和社会效益。气田集输管网的优化设计,即寻求站址、管网布局以及管径、壁厚等工艺参数的合理分配,属于NP难点问题。文章通过分级优化的方法,在采用kruskal算法确定管网最优布局的基础上,提出结合遗传蚁群算法的优化参数方案,以集输管网干线的最小造价为目标函数,管径和壁厚作为优化变量,建立符合实际工程的数学模型。该模型根据集输管网所处的复杂环境,确定了流量连续性,管道规格,节点压力等一系列约束方程。根据模型的结构特点,在遗传蚁群算法的求解过程中,给出了符合实际数据的染色体选择、交叉、变异方式,并且在最佳时刻通过遗传算法与蚁群算法的衔接,将两种算法进行融合,形成了一种时间效率和求解效率都比较好的启发式算法。仿真计算表明,应用遗传蚁群算法的设计方案在求解速度和求解精度上都明显优于单一的遗传算法或蚁群算法,更加节省管网的投资费用。     

Preparation, characterisation and applications of thin films for gas sensors prepared by cheap chemical method

The physical properties of pure and doped (Ni, Os, Pd and Pt) SnO₂ thin films, prepared by using a chloride-based inorganic sol–gel route, have been reported. These properties were investigated by using differential scanning calorimetry and thermogravimetric (DSC/TG), FTIR, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. Microsensors for gas detection were also fabricated and tested in various atmospheres (nitrogen oxide, carbon monoxide, ethanol, methanol and methane). The dopants affected the coating properties depending on the formation of nanoparticles. Furthermore the gas-sensing properties towards reducing and oxidising gases were found to be dependent on the nature of doping element. An array consisting of the manufactured sensors has been arranged and examples of applications for “electronic nose” are given.     

Characterization of protective coatings for planar automotive gas sensors

Alumina support material suitable for use as a planar automotive gas sensor support was coated in thin films of yttria-stabilised zirconia (YSZ) and titania. The morphology, composition, thickness and homogeneity of the coating was measured. The coating was applied to the ‘green’ form of a tape cast alumina substrate which was subsequently fired at 1500 °C to produce the final form of the coated alumina. The YSZ coating gave a continuous 5 μm thick coating with no evidence of mixed oxide formation between the YSZ and the alumina substrate. XRD indicated a face centred cubic Y doped ZrO₂ or primitive tetragonal Zr_0.9Y_0.1O_1.95 phase. The titania coatings were much thinner (<1 μm) with signs of trace amounts of aluminium titanium oxide (Al₂TiO₅) as well as rutile titania in XRD. Spot analysis using X-ray photoelectron spectroscopy showed a fairly regular titania coverage. Atomic force microscopy analysis showed a particle size of 1–3 μm for the YSZ coating and 0.5 μm for titania.     

Self-assembling of micro-patterned titanium oxide films for gas sensors

Metal oxide nanoparticles are interesting building blocks for realizing films for a number of applications that include bio- and -chemical sensing. In the present work TiO₂ nanoparticles have been used for a self-assembling procedure to realize lined-up micro-patterned titanium oxide films. The high surface-to-volume ratio makes these structures suitable to adsorb gases. Morphological, compositional and structural characterization have been performed in order to determine the features of the assembling. The analysis of electrical behaviour of the ordered films in controlled atmosphere allowed us to test the gas sensing properties.     

A numerical method for optimizing the gas flow field in a centrifuge

The performance of a centrifuge which is used in the uranium enrichment industry depends strongly on the gas flow field inside the device. The flow, governed by linearized hydrodynamic equations, is activated by proper boundary conditions which are controllable functions. A numerical method is developed to determine these functions on the boundaries in order to optimize the separative performance. By expanding the control functions in a finite base, the problem is reduced to minimizing a function with respect to a finite number of variables and solved by the simplex method.     

用气体传感器数据求解煤制气报警器的设定浓度

本文详细介绍了如何根据气体传感器的气体特性数据来计算混合气浓度特性的方法.并以TGS822TF型传感器为例,详细介绍了以氢气设定、以CO浓度规定报警点的人工煤制气报警器设定浓度的计算方法.通过使用EXCEL对H2和CO的气体浓度特性数据进行处理,根据不同地区的人工煤制气的组分含量,即可计算当地煤制气报警器的设定浓度.     

New analytical method for gas dynamics equation arising in shock fronts

This work suggests a new analytical technique called the fractional homotopy analysis transform method (FHATM) for solving nonlinear homogeneous and nonhomogeneous time-fractional gas dynamics equations. The FHATM is an innovative adjustment in Laplace transform algorithm (LTA) and makes the calculation much simpler. The proposed technique solves the nonlinear problems without using Adomian polynomials and He’s polynomials which can be considered as a clear advantage of this new algorithm over decomposition and the homotopy perturbation transform method. In this paper, it can be observed that the auxiliary parameter ?$?$, which controls the convergence of the HATM approximate series solutions, also can be used in predicting and calculating multiple solutions. This is a basic and more qualitative difference in analysis between HATM and other methods. The solutions obtained by the proposed method indicate that the approach is easy to implement and computationally very attractive. The proposed method is illustrated by solving some numerical examples.