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、...     

Sensitivity and selectivity improvement of rf sputtered WO3 microhotplate gas sensors

Active layers consisting of rf sputtered WO₃ were deposited on microhotplate substrates. The films were doped with seven different materials (Pt, Au, Ag, Ti, SnO₂, ZnO and ITO (indium tin oxide)). The eight types of sensors (including pure tungsten oxide ones) were tested in the presence of ammonia, hydrogen sulphide, nitrogen dioxide, carbon monoxide and methane. It was found that gold improved the sensitivity to H₂S. On the other hand, doping with Ag and Pt led to higher responses to NO₂ and NH₃, respectively. No response to CH₄ was observed. The sensitivity to CO was very low. The influence of the working temperature on the sensor response was also studied. Our study proves that selective gas detection is possible combining a few tungsten oxide sensors with different dopants.     

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。     

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。     

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).     

一种新的材料微结构电磁场效应数值模拟方法

为了定量揭示材料微结构与入射电磁波引起的材料内电磁场效应之间的内在关联性,借助可以表征能量流动方向和大小的Poynting矢量,通过程序设计结合有限元数值模拟的方法实现了材料微结构电磁场效应的计算。建立了材料微结构电磁场效应数值分析有限元模型。在数值计算中,将Poynting矢量正交分解为三个不同方向分量,计算了材料微结构的吸收、透射和波源方向反射效应;根据Poynting矢量在反射方向的分量,计算了任意反射方向的反射效应。研究方法对任意微结构均具有适用性。     

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.     

PPB级锆基安培型NO气体传感器性能的研究

采用丝网印刷技术制备了以In2O3为敏感电极的锆基安培型三电极NO传感器用以探测10-9级NO气体。用X射线衍射仪（XRD）和扫描电镜（SEM）对该传感器进行了理化分析;通过测量其在不同温度和不同NO浓度的气氛中的伏安特性曲线和时间响应曲线,研究了传感器的电流输出信号和NO浓度的关系以及时间响应特性。实验表明：在350℃~500℃测试温度范围内,极化电压为-60 mV,NO浓度变化为0~900×10-9时传感器响应电流的变化值Δcurrent和NO浓度之间存在较好的线性关系并且传感器在400℃时响应值最大。在被测气体总流量为100 cm3/min时,传感器信号90%的响应和恢复时间分别为18 s和12 s。传感器信号不受CO2浓度变化的影响,传感器的响应信号在测试时间里具有较好短期稳定性,但长期稳定性有待进一步提高。本文还采用阻抗谱分析方法对传感器的响应机理进行了初步的探索。     

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.     

高炉料面成像工业内窥镜的视场覆盖增强方法

高炉料面形状信息对调节布料操作具有重要参考作用.针对目前工业内窥镜对高炉料面成像视场覆盖范围较小的问题,提出了一种新的视场覆盖增强方法.首先,基于坐标系变换建立工业内窥镜的感知模型,定量刻画工业内窥镜参数与感知区域面积之间的关系;然后,在感知模型的基础上提出料面成像区域面积的计算方法,并提出基于粒子群优化算法优化感知方向的视场覆盖增强策略,实现最大面积的料面区域感知.最后,的实验和应用结果表明,提出的方法可有效提高视场覆盖的料面面积,具有很好的应用价值.     

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.