A novel highly sensitive gas ionization sensor for ammonia detection

A novel highly sensitive gas ionization sensor for ammonia detection in ambient air is introduced in this paper. Carbon nanotubes (CNTs) grown on silicon substrate were incorporated to fabricate a gas ionization sensor. Application of a positive bias to the CNTs generates electric fields sufficiently to field-ionize passing gas-phase molecular and initiate a prebreakdown current. When the CNTs film is configured as the cathode, secondary electrons repelled away from the CNTs tips into the gap spacing make more ionizing collisions and also initiate a prebreakdown current. By monitoring the prebreakdown current, the gas ionization sensor was demonstrated to be capable of ionizing and detecting the ammonia and with a linear response over the entire range from 1 to 160 ppm ammonia in air. The sensitivity mechanism of the gas ionization sensor was also discussed in detail. The sensitivity and selectivity of the gas ionization sensor to the gases is not only dependent on its ionization energy but also its electric dipole moment. The novel CNTs-based gas ionization sensor described here exhibits high accuracy, repeatability and stability. The sensor is promising for use in various fields.     

Low cost inductor current sensing for power converters using feedback compensation

One of the key components in the current mode control of power converters is the sensing of inductor current. Traditional low cost implementation is to add a sensing resistor in series with the inductor to sense the inductor current. This will reduce the overall efficiency of the power converter. An alternative is to apply a current transformer to the inductor to sense its current. This however will significantly increase the cost of power converters. One low cost implementation is to add a resistor–capacitor network in parallel with the inductor so that the inductor current can be derived from the capacitor voltage. The problem of this implementation is that the capacitor voltage is very sensitive to temperature variations. In this paper, a simple feedback loop is applied to the sensed capacitor voltage based on the steady state duty ratio of power converters such that the sensed inductor current will be independent of temperature variations. The sensing element with feedback compensation can be applied to inductors fitted to power converters such as buck converters and boost converters. Although experimental studies based on a buck converter were carried out to illustrate the correctness of the new sensing technique, the proposed technique is applicable to other converter topologies.     

Vic-dioximes: A new class of sensitive materials for chemical gas sensing

Vic-dioximes, a class of organic chemical compounds, are proposed and characterized for the first time as sensitive materials for volatile organic compound sensing with sorption based chemical gas sensors. Their peculiar sensing properties described in this work originate in the oxime functional group which is a powerful H bond donor interacting strongly but reversibly with H bond acceptors. These specific interactions result in a high preferential enrichment of analyte molecules with H bonding acceptor capabilities in the sensitive material. Accordingly, sensitivity and selectivity for these compounds of vic-dioxime based sensors are high. The advantageous sensing properties are demonstrated in this work with quartz crystal microbalance sensors using 11 selected volatile organic compounds and a set of vic-dioximes varied in their substituents. Vic-dioximes with short alkylthiol substituents were found highly sensitive to such H bond acceptors as organic amines, alcohols, and esters with partition coefficients up to 26,000. At the same time they showed low affinity for aromatic compounds and chlorocarbons. Vic-dioximes are considered powerful sensing materials and interesting for practical use in chemical gas sensor arrays.     

Phthalocyanines as sensitive coatings for QCM sensors: Comparison of gas and liquid sensing properties

The quartz crystal microbalance (QCM) was used to investigate the liquid sensing properties of a set of phthalocyanines (Pcs) which were systematically varied by attaching the substituent 2,2,3,3-tetrafluoropropyloxy to different positions and by introducing a central metal ion (i.e. Ni²⁺, Zn²⁺, and Cu²⁺). The responses to low concentrations of organic compounds such as hydrocarbons and chlorocarbons dissolved in water were recorded. The materials were very sensitive to the tested compounds with detection limits in the lower parts-per-million range and they exhibited a good sensing performance as the sensors have been working fully reversibly and reliably over long periods of time. Besides, the influence of substitution pattern and choice of central metal ion on the liquid sensing properties of Pcs were studied for the first time. The results show that the responses differ notably from each other depending on the modifications made to the Pc. Finally, it is demonstrated that the gas and liquid sensing responses of the materials are highly correlated and can be linked to each other with the help of a basic physical model.     

柔性高灵敏单壁碳纳米管气体传感器研究

在柔性聚对二甲苯C基底上制作了基于单壁碳纳米管的小型化、高灵敏、反应快速的气体传感器。使用介质电泳集成碳管束,并利用单链脱氧核糖核酸修饰增强器件灵敏度。当传感器暴露在甲醇蒸气中时,会出现明显可重复的反应,它可以检测含量低至4.3×10-6的甲醇,并且在相当宽的体积分数范围有清晰的分辨能力。对于4.3×10-6的含量,未修饰的传感器对应电阻变化率是4.8%;经过脱氧核糖核酸修饰,电阻变化率增加到了12.3%。此外,该传感器还显示了很快的响应速度和很好的测试复验性。研究表明:这种柔性气体传感器在未来环境监测应用中有很好的前景。     

电力调度大数据应用平台系统技术研究

为解决智能电网的发展中电网运行和设备检测或监测数据、电力企业管理数据、电力企业营销等数据海量的增加带来的不同业务系统之间分散地开发、运行和管理,系统数据存储结构独立,带来数据多源、格式不一致,数据准确性、实时性不强,数据质量不高,缺乏统一的数据规范等问题,本文利用Hadoop的分布式文件系统HDFS和并行处理框架MapReduce的工作原理,搭建电网调度大数据应用平台系统,解决了不同业务系统之间的数据不能及时共享、访问、管理与分析挖掘等问题。采用数据清洗数据,解决数据质量不高的问题。搭建电网调度大数据应用平台系统,既能实现跨专业、跨部门的多维度关联分析,又能满足海量的智能电网数据存储和数据处理需求,并具有强大的伸缩性,可扩展为电网实现安全、可靠、经济、高效地运行提供保障。     

An extended functional network model and its application for a gas sensing system

Functional networks (FNs) are a promising numerical scheme that produces accurate solutions for several problems in science and engineering with less computational effort than other conventional numerical techniques such as neural networks. By using domain knowledge in addition to data knowledge, functional networks can be regarded as a generalization of neural networks: they allow to design arbitrary functional models without neglecting possible functional constraints involved by the model. The computational efficiency of functional networks can be improved by combining this scheme with finite differences when highly oscillating systems have to be considered. The main focus of this paper is on the possible questions arising from the application of this combined scheme to an identification problem when non-smooth functions are involved and noisy data are possible. These issues are not covered by the current literature. An extended version, based on a piecewise approach, and a stability criterion are proposed and applied to the quantitative identification problem in a gas sensing system in its transient state. Numerical simulations show that our scheme allows good accuracy, avoiding the error accumulation and the sensitivity to noisy data by means of the stability criterion.     

Low temperature gas sensing applications using copier grade transparency sheets as substrates

Transparency sheets, coated with copper on both sides by means of thermal evaporation in vacuum, are patterned by direct chemical etching to realize sensing platforms having copper heaters on the backside, and resistances having calibrated temperature coefficient on the topside. The mechanical and thermal stability of these structures was demonstrated up to 70 °C. Bending tests also show that the metallic patterns do maintain unaltered performances after more than 10⁴ bending cycles. Resistance measurements show that the resistance on the patterned copper structures linearly increases with the temperature in the range between room temperature and 70 °C, while above this temperature an irreversible damage occurs. Experimental investigations demonstrate that the heaters on the backside of the sensing platforms allow to obtain a quite uniform temperature distribution on the top side over an area larger than 1 cm².Coating the flexible sensing platform by doped polyaniline and carbon nanotubes embedded in a polymer host, a chemoresistive system operating at low temperature is developed, which allows to perform tests at constant temperature, with the temperature being set and monitored by using the heater and the patterned resistance, respectively. The sensing performances of the films are evaluated by means of electrical measurements performed while exposing the samples to different relative humidity levels, and to calibrate ammonia pulses.     

Lithium ferrite for gas sensing applications

Microstructure and gas sensing properties of pure and samarium-substituted lithium ferrites, Li_0.5Sm_xFe_2.5−xO₄ (x = 0, 0.05, 0.1 and 0.2), prepared by sol–gel self-combustion were studied. Ethanol, methanol, LPG and ammonia were used as test gases. SEM investigation evidenced that Sm ions induced microstructural changes of the Li ferrite. The finest granulation (about 100 nm) and highest porosity (44%) were observed in Li_0.5Sm_0.2Fe_2.3O₄. The gas response measurements evidenced that it depended on the working temperature and gas type. All ferrites were sensitive to alcohol (ethyl and methyl) and less sensitive to ammonia and LPG. The best responses, over 85%, were obtained at operating temperatures of 340–355 °C to ethanol and methanol vapour.     

Biomorphic synthesis of ZnSnO3 hollow fibers for gas sensing application

Biomorphic ZnSnO₃ hollow fibers have been fabricated using cotton as biotemplates. Cotton fibers are infiltrated with zinc nitrate and stannic chloride solution and subsequently sintered in air at high temperatures to produce the final ZnSnO₃ hollow fibers. The samples have further distinctions in structure and morphology by X-ray diffraction and scanning electron microscopy. It showed that all the samples present an orthorhombic structure of high crystallinity, and the hollow fibers were composed of numerous ZnSnO₃ nanorods. Furthermore, gas sensors were fabricated and an investigation of ethanol sensing properties has been conducted. The sensor, based on ZnSnO₃ hollow fibers calcined at 500 °C, shows highly sensitive to ethanol with fast response, good selectivity and stability, indicating its potential applications for environment and food or the drinking status of drivers.     

Fabrication of coplanar microheater platform for LPG sensing applications

Microsystem Technologies - The design and fabrication of nichrome based coplanar microheater for LPG sensing applications is presented in this work. Nichrome based coplanar microheater is...     

Rice-like CuO nanostructures for sensitive electrochemical sensing of hydrazine

In this work, a low temperature aqueous chemical growth methodology was used for the fabrication of CuO nanostructures. The as-synthesised nanostructures were then elaborately characterised by number of analytical techniques such as scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The obtained nanostructures were observed to possess interlaced rice-shaped structural features with the length and width of individual rice determined to be in the range of 200–300 nm and 50–100 nm respectively. The unique nanostructures when utilised as electrode material exhibited excellent electro-catalytic potential towards oxidation of hydrazine in alkaline media. The excellent conductive of CuO added by the high surface area of obtained nanorice-like structures enabled development of highly sensitive (3087 µA mM⁻¹ cm⁻²), selective and stable electrochemical sensor for hydrazine. In addition, the successfully application of the developed sensor in spiked tap, bottled and industrial water samples for the detection of hydrazine suggested its feasibility for practical environmental application.

     

Compressive sensing based electronic nose platform

Electronic nose (EN) systems play a significant role for gas monitoring and identification in gas plants. Using an EN system which consists of an array of sensors provides a high performance. Nevertheless, this performance is bottlenecked by the high system complexity incorporated with the high number of sensors. In this paper a new EN system is proposed using data sets collected from an in-house fabricated $4\times 4$ tin-oxide gas array sensor. The system exploits the theory of compressive sensing (CS) and distributed compressive sensing (DCS) to reduce the storage capacity and power consumption. The obtained results have shown that compressing the transmitted data to 20% of its original size will preserve the information by achieving a high reconstruction quality. Moreover, exploiting DCS will maintain the same reconstruction quality for just 15% of the original size. This high quality of reconstruction is explored for classification using several classifiers such as decision tree (DT), K-nearest neighbour (KNN) and extended nearest neighbour (ENN) along with linear discrimination analysis (LDA) as feature reduction technique. CS-based reconstructed data has achieved a 95% classification accuracy. Furthermore, DCS-based reconstructed data achieved a 98.33% classification accuracy which is the same as using original data without compression.     

分段幂函数模型在气敏检测器定量算法中的应用

针对传统半导体气敏检测器电阻直接定量算法误差大、适应性差的问题,利用半导体传感器电导率随气体体积分数变化而变化的特点,提出了新的电路模型。通过对其特性曲线进行深入分析,构建了检测电路输出信号与气体体积分数之间的分段幂函数模型。先通过对不同体积分数气体进行采样,将采样气体体积分数和电路输出信号进行分段幂函数模型拟合,然后用拟合参数去计算未知检测气体的体积分数。实验结果表明：提出的定量模型大大提高了定量分析的准确性,且定量误差不受传感器漂移的影响,具有很强的环境适用性,提高了微量可燃气检测的可靠性和精度。     

有毒有害气体无线监测节点的低功耗设计

为了有效延长有毒有害气体无线监测节点的生命周期,提出了一种具有实用性的低功耗设计方案。该方案首先是对节点硬件实现分区分时的电源管理模式,其次在软件方面通过合理设置MCU的工作模式,通过实验方法确定了最优采样时间,进一步降低节点的功耗。     

矿井瓦斯地质智能预警平台的建设与应用

针对煤矿企业瓦斯地质资料缺乏有效管理、瓦斯地质图更新困难及利用率不高的现状,从瓦斯地质预警原理、数据库、平台结构、功能模块、关键技术、预警保障机制等方面介绍了一种矿井瓦斯地质智能预警平台建设方案。该平台采用GIS技术建立瓦斯地质空间数据库,实现了瓦斯地质相关数据的集中、有效管理及瓦斯地质图的自动更新;采用WCF技术实现了跨图形平台的瓦斯地质相关图件的数据共享;以瓦斯地质学理论为指导,形成了一套完整的瓦斯地质预警指标体系,综合分析工作面前方的瓦斯赋存、地质构造、煤层赋存等情况,实现了瓦斯地质的实时超前预警。应用结果表明,该平台各项预警结果与现场实测情况完全一致,效果良好。     

行业应用软件第三方开发平台的研究与实践

为了改进行业应用软件的开发模式和促进行业应用软件的发展,提出了行业应用软件第三方开发平台的基本框架.在该基本框架中,通过分析行业应用软件的特殊性,设计了一种类OAuth授权协议,以保证数据安全,同时引进了新的依赖分析方法,明确组件以及数据关联,量化组件被依赖程度,利于组件分析优化,利于设计和分类API.根据提出的基本框架,以保险行业为背景,设计和实现了一个第三方开发平台.实验测试结果表明,所设计的行业应用软件第三方开发平台安全可行.     

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。