SnO2 thin film sensor with enhanced response for NO2 gas at lower temperatures

Semiconducting SnO₂ thin films having higher value of electrical conductivity have been deposited using RF sputtering technique in the reactive gas environment (30% O₂ + 70% Ar) using a metallic tin (Sn) target for detection of oxidizing NO₂ gas. The effect of growth pressure (12-18 mTorr) on the surface morphology and structural property of SnO₂ film was studied using Atomic force microscopy (AFM), Scanning electron microscopy (SEM) and X-ray Diffraction (XRD) respectively. Film deposited at 16 mTorr sputtering pressure was porous with rough microstructure and exhibits high sensor response (∼2.9 × 10⁴) towards 50 ppm NO₂ gas at a comparatively low operating temperature (∼100 °C). The sensor response was found to increase linearly from 1.31 × 10² to 2.9 × 10⁴ while the response time decrease from 12.4 to 1.6 min with increase in the concentration of NO₂ gas from 1 to 50 ppm. The reaction kinetics of target NO₂ gas on the surface of SnO₂ thin film at the Sn sites play important role in enhancing the response characteristics at lower operating temperature (∼100 °C). The results obtained in the present study are encouraging for realization of SnO₂ thin film based sensor for efficient detection of NO₂ gas with low power consumption.     

Frequency characteristics of the one-layer anisotropic magnetoresistive sensitive nanoelements

The high-frequency characteristics of the one-layer anisotropic magnetoresistive strip—the magnetosensitive nanoelement of the magnetic field sensor—were analyzed on the basis of the Landau-Livshits-Hilbert equation. The results of this study were shown to coincide completely with the linear microwave theory. The strip frequency characteristics were analyzed for low-anisotropy and high-anisotropy FeNiCo ferromagnetic films of various thickness, strip width, easy magnetization direction, and fixed external magnetic field.     

Analog-to-digital interfaces for microcontroller-based adaptive cyclic regulating devices for electrical plants

A principle of designing realizable precision interfaces between sensors and digital ports of microcontrollers and microconverters which enable one not only to measure a physical variable but also to estimate its derivative was proposed. These analog-to-digital interfaces were shown to feature higher precision of conversion without additional precision reference power supplies. The basic requirements on the active analog elements are in good agreement with the “system on chip” VLSI circuit technology.     

组合结构半导体气体传感器的研究进展

综合介绍了基于气体传感器互补反馈和互补增强原理的新型组合结构半导体气体传感器的研究进展,着重对传感器的原理、结构、材料及性能作了介绍,并分析了组合结构半导体气体传感器的发展趋势。     

Au/SnO2 an excellent material for room temperature carbon monoxide sensing

Tin dioxide synthesized by the hydrothermal method, impregnated with Au has been used for the room temperature carbon monoxide sensing in air. Incorporation of poly ethylene glycol (PEG-6000) as a modifier during the synthesis procedure results in well dispersed nanosized particles of SnO₂ which influence the sensing capability dramatically. This tailored morphology leads to development of a material with improved sensor response. Incorporation of gold resulted in a composition that was capable of selectively sensing low concentrations (upto 10 ppm CO in air) at temperatures below 50 °C. The mechanism of improved sensing has been explained based on the gas sensing characteristics with support from TEM, UV-DRS, XPS and FTIR.     

SiC气体传感器

SiC肖特基二极管气体传感器可以广泛应用于检测气体排放物和气体泄露。通过采用PdCr合金 ,可以提高Pd/SiC气体传感器的灵敏度。同时 ,在Pd层和SiC之间引入SnO2 作为界面层也是提高其灵敏度的一种有效途径。进一步的研究表明 ,SnO2 层的大小也对传感器的性能有着重要影响。     

Analysis of the aging characteristics of SnO2 gas sensors

Two types of tin oxide (SnO₂) gas sensors were synthesized, which consist of spherical SnO₂ nanoparticles and SnO₂ nanorods mixed at different ratio, and their aging processes were studied. Using the Complex Impedance Spectroscopy method the electrical properties that are related to the microscopic structure of the samples were investigated. The evolution of absorption current was measured to analyze the ionic conductance that reflects the charging states of the samples. The results indicate that devices of optimal long-term stability can be obtained by sintering the mixture of SnO₂ nanorods and spherical nanoparticles (1:1 weight ratio) at 850 °C. In the samples’ impedance data considerable fluctuation could be seen during the early stage of the aging process, which gradually disappeared after several days. The aging process, which is revealed by the changes in both grain-boundary resistance and capacitance, indicates the corresponding changes in the grain-boundary barrier height and the width of depletion layer. We suggest the DC-field-induced migration of ions within the grain boundaries as the probable cause of the phenomenon.     

MEMS-based gas flow sensors

Micro-electro-mechanical system (MEMS) devices integrate various mechanical elements, sensors, actuators, and electronics on a single silicon substrate in order to accomplish a multitude of different tasks in a diverse range of fields. The potential for device miniaturization made possible by MEMS micro-fabrication techniques has facilitated the development of many new applications, such as highly compact, non-invasive pressure sensors, accelerometers, gas sensors, etc. Besides their small physical footprint, such devices possess many other advantages compared to their macro-scale counterparts, including greater precision, lower power consumption, more rapid response, and the potential for low-cost batch production. One area in which MEMS technology has attracted particular attention is that of flow measurement. Broadly speaking, existing micro-flow sensors can be categorized as either thermal or non-thermal, depending upon their mode of operation. This paper commences by providing a high level overview of the MEMS field and then describes some of the fundamental thermal and non-thermal micro-flow sensors presented in the literature over the past 30 years or so.     

Fitting sparse multidimensional data with low-dimensional terms

An algorithm that fits a continuous function to sparse multidimensional data is presented. The algorithm uses a representation in terms of lower-dimensional component functions of coordinates defined in an automated way and also permits dimensionality reduction. Neural networks are used to construct the component functions.

Program summary

Program title: RS_HDMR_NNCatalogue identifier: AEEI_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEEI_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 19 566No. of bytes in distributed program, including test data, etc.: 327 856Distribution format: tar.gzProgramming language: MatLab R2007bComputer: any computer running MatLabOperating system: Windows XP, Windows Vista, UNIX, LinuxClassification: 4.9External routines: Neural Network Toolbox Version 5.1 (R2007b)Nature of problem: Fitting a smooth, easily integratable and differentiatable, function to a very sparse (∼2-3 points per dimension) multidimensional (D?6) large (∼¹⁰⁴-¹⁰⁵ data) dataset.Solution method: A multivariate function is represented as a sum of a small number of terms each of which is a low-dimensional function of optimised coordinates. The optimal coordinates reduce both the dimensionality and the number of the terms. Neural networks (including exponential neurons) are used to obtain a general and robust method and a functional form which is easily differentiated and integrated (in the case of exponential neurons).Running time: Depends strongly on the dataset to be modelled and the chosen structure of the approximating function, ranges from about a minute for ∼¹⁰³ data in 3-D to about a day for ∼¹⁰⁵ data in 15-D.     

气体传感器试验分析系统

在分析研究了电子鼻的基本原理和系统组成的基础上,建立了气体传感器(7ST/F,7NDH)流量静态数学模型和试验分析测试系统,对其输入-输出特性进行了试验测试,并用Matlab对试验数据进行了分析与研究。通过试验,验证了模型的正确性及分析测试系统的通用性,获得了具有应用价值的结果,为后续的模式识别技术和人工神经网络技术的应用打下了基础。     

Measurement system for metal-oxide gas sensors

A study on smell sensing and classification has been developed for a long time by many ways. Most of these have been focused on bad smells, when factors of bad smells were known chemically. Many gas sensors have been developed to detect specific chemicals. Our purpose is to make a new measurement system of smell gases and to apply it to classification of many gases. The proposed system has many sensors in a chamber and detects some chemicals at the same time. Smells data are transmitted to an A/D converter in a host PC which can be used to analyze data to classify the smells. The system must classify not only kinds of smells but also densities of them. In this paper, we develop the measurement system for multi-channel sensors made of metal-oxide semiconductors with power supply circuits.     

Micromachined gas sensors for environmental pollutants

An Au doped tin oxide thin film was deposited as base material for carbon monoxide detection over a micromachined substrate. The performances of a recent technique to heat the device, named fast pulsed temperature supply, are presented. This technique exploits the property that, due to the very low thermal mass of the membrane, the term required to reach steady state conditions is very short (about 40 ms). The sensor heater is periodically supplied for very short terms, hundred of milliseconds, and kept off for long ones, seconds or more. Besides a strong reduction of power consumption compared with isothermal characterization, an increase of sensitivity is observed. Different shapes of the heating wave were examined and results are summarized and compared. Received: 1 June 1999 / Accepted: 2 June 1999     

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.     

半导体式气体传感器信号的非线性修正

探讨了使用反对数放大器,并与查表法相结合的半导体式气体传感器信号的非线性修正方法,实验表明:这种方法能够满足高体积分数甲烷检测的需要。基于这种方法非线性修正的仪器,甲烷检测体积分数范围为0%~1.0%,检测精度可以达到±5.0%。     

FracMAP: A user-interactive package for performing simulation and orientation-specific morphology analysis of fractal-like solid nano-agglomerates

Computer simulation techniques have found extensive use in establishing empirical relationships between three-dimensional (3d) and two-dimensional (2d) projected properties of particles produced by the process of growth through the agglomeration of smaller particles (monomers). In this paper, we describe a package, FracMAP, that has been written to simulate 3d quasi-fractal agglomerates and create their 2d pixelated projection images by restricting them to stable orientations as commonly encountered for quasi-fractal agglomerates collected on filter media for electron microscopy. Resulting 2d images are analyzed for their projected morphological properties.

Program summary

Program title: FracMAPCatalogue identifier: AEDD_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDD_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 4722No. of bytes in distributed program, including test data, etc.: 27 229Distribution format: tar.gzProgramming language: C++Computer: PCOperating system: Windows, LinuxRAM: 2.0 MegabytesClassification: 7.7Nature of problem: Solving for a suitable fractal agglomerate construction under constraints of typical morphological parameters.Solution method: Monte Carlo approximation.Restrictions: Problem complexity is not representative of run-time, since Monte Carlo iterations are of a constant complexity.Additional comments: The distribution file contains two versions of the FracMAP code, one for Windows and one for Linux.Running time: 1 hour for a fractal agglomerate of size 25 on a single processor.     

The effect of scintillation on the active microwave remote-sensing sensors

Recently, space-borne radar systems have been used to collect data for many different remote sensing applications. Some of the applications demand very high accuracy in the measured backscattering cross-sections. Microwave signals passing through the ionosphere may be, at times, affected by the scintillation effect, thus the backscattering cross-section. It is the purpose of this paper to discuss the gigahertz scintillation phenomenon and to assess the potential impact on active microwave observations.     

FBG温度传感器在微波场的应用

微波作为一种新型热源已被广泛用于化学研究、食品加工、医疗仪器以及材料热处理等行业中,发展极为迅速。在这些应用中,温度显然是个重要的参数,但处于强电磁场的环境下,在微波场中温度的测量依然是一个技术难题。阐述了光纤光栅温度传感器的原理,以及分析了光纤光栅温度传感器在微波场中测温的前景及应用。     

SnO_2纳米结构气体传感器制备与气敏特性研究

由于二氧化锡(SnO_2)稳定的理化性质与优越的导电性能,制备的气体传感器具有灵敏度高、寿命长、稳定性好等特点。利用水热法制备了纳米结构SnO_2材料,进而制作旁热式气体传感器。通过调节氢氧化钠(Na OH)的量,研究不同浓度下纳米结构SnO_2材料的形貌,搭建实验平台,测试不同形貌下敏感材料的灵敏度、选择性、重复性,并分析其敏感机理。     

微悬臂梁谐振式气体传感器研究进展

微机械谐振式传感器已经成为微型机电系统(MEMS)领域的研究热点。讨论了微悬臂梁谐振式气体传感器的工作原理,介绍微悬臂梁表面修饰的关键技术、主要方法和基于微悬臂梁的谐振式气体传感器领域的研究状况以及近五年以来该领域的研究进展,并对基于微悬臂梁的谐振式气体传感器的发展方向和应用前景做了展望。