Investigation on formaldehyde gas sensor with ZnO thick film prepared through microwave heating method

ZnO nanopowders were prepared through microwave heating method. ZnO thick film sensors were fabricated by using ZnO nanopowders as sensing materials. The phase composition and morphology of the material particles were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The gas-sensing properties of the sensors based on ZnO nano-materials were investigated. It was found that the sensor based on ZnO nano-materials (low power, 10× 10 min) exhibited very high responses to benzene and toluene when operating at 440 and 370 °C, respectively; but the sensor based on ZnO (low power, 10× 10 min) showed very low responses to benzene and toluene when operating at 205–215 °C. The sensor based on ZnO (low power, 10× 10 min) showed high response and good selectivity to dilute formaldehyde when operating at 210 °C; especially, the response to 0.001 ppm HCHO attained 7.4 when operating at 210 °C.     

采用脉冲供电的催化传感器的工作性能研究

针对煤矿瓦斯监测系统中催化传感器功耗高的问题,提出了采用脉冲供电方式对传统供电方式进行改进的方法.分析了载体催化元件的工作特性和脉冲供电原理;通过实验研究了不同CH4浓度的标准气样下,供电脉冲频率、脉宽（即占空比）与传感器灵敏度之间的关系.实验结果表明：和普通催化传感器相比,采用脉冲供电的将会很大程度上降低催化传感器的功耗,延长便携式设备的生命周期;同时,分析得到采用脉冲供电的可行性和最佳频率.     

High-sensitive SPR sensing with Indium Nitride as a dielectric overlay of optical fibers

In this work, an Indium Nitride (InN) dielectric overlay has been used to develop a surface plasmon resonance optical fiber sensor. Although InN is a very promising material in electronics industry, this is the first time that this kind of material is used for optical sensing. The obtained results show an improvement of the reliability and long term stability with respect to previous devices made with the same technology. More remarkably, the sensitivity increases up to 11,800 nm/RIU in the range of outer refractive indices between 1.415 and 1.429, the highest sensitivity achieved with this kind of devices. Therefore, a novel application of the InN to optical fiber sensors is demonstrated. The use of this material would be of great interest to produce new SPR-based devices for chemical and biological sensing.     

Thin film SnO2-based gas sensors: Film thickness influence

The influence of the thickness of SnO₂ films deposited by a spray pyrolysis method on the operating characteristics of gas sensors is analyzed in this paper. It outlines how the thickness of metal oxides is an important parameter for gas sensors in determining the main operating parameters, such as the magnitude and rate of the sensor response and the optimal operating temperature. It is also shown that the optimal film thickness of a gas sensing layer depends on the required sensor parameters.     

Effect of thermal and mechanical properties variations on microcantilever mass sensor performance

Ensuring desirable performance for piezoelectric microcantilever sensors constitutes a crucial research subject particularly for the applications such as detection of biochemical entities, virus particles or human biomarkers. However, these sensors’ performance may be affected by the environmental conditions such as temperature variation, and/or the uncertainty in the material properties. The objective of this study is to explore Young modulus uncertainty of microcantilever’s structural layer, thermo-mechanical and geometrical temperature dependency effects, on the natural frequency, bias and sensitivity of microcantilever mass sensors. These effects have been investigated for different sensor lengths and resonant modes. Also, a temperature compensation method which omits the need for bulky non-contact thermometers or fabrication of built-in temperature sensor has been proposed. As theoretical model, Euler–Bernoulli beam theory has been employed and solved by Galerkin expansion procedure. Using this model, it is demonstrated that the sensitivity of microcantilever sensor decreases with increasing the added mass. The microcantilever sensor sensitivity operating at the second resonant mode has been improved almost five times comparing to the first mode sensitivity regardless of microcantilever length. The simulation results show that temperature variation causes thermal frequency shift which in turn introduces a significant mass bias far beyond the sensors’ minimum detectable mass. This mass bias is constant for a given microcantilever in its first and second resonant mode. Additionally, the effect of temperature variation on the sensitivity of the given mass sensors is negligible. However, it has been shown that the variations in sensors sensitivity due to uncertainty of Young modulus remain constant for different lengths and two resonant modes of the microcantilever sensor.     

Ethanol sensing using CuO/MWNT thin film

Copper (II) oxide (CuO)/multiwall carbon nanotube (MWNT) thin film based ethanol-sensors were fabricated by dispersing CVD-prepared MWNTs in varying concentration over DC magnetron sputtered-CuO films. The responses of these sensors as a function of MWNT concentrations and temperatures were measured, and compared. The sensing response was the maximum at an operating temperature near 400 °C for all the samples irrespective of the MWNTs dispersed over them. At optimum operating temperature (T_opt) of 407 ± 1 °C, the response is linear for 100-700 ppm range and tends to saturate at higher concentrations. In comparison with bare CuO sample, the response of CuO/MWNT sensing films increased up to 50% in the linear range. The response improvement for 2500 ppm of ethanol was up to 90% compared to bare CuO sample. In addition, the sensing response time also reduced to around 23% for lowest ethanol concentration at T_opt. However, a decrease in the sensor response was observed on films with very high concentrations of MWNTs.     

氧化锌气体传感器的制备及甲烷检测特性研究

甲烷(CH4)是电力变压器油纸绝缘中溶解的主要故障特征气体,能有效反映运行变压器油纸绝缘故障.气体传感检测是油中气体在线监测、分析的关键.基于水热法,制备了氧化锌(ZnO)纳米片和纳米球气敏材料及传感元件,基于实验室搭建的微量气体检测平台测试了其对CH4的检测特性.研究表明:基于ZnO纳米片制作的气体传感器比纳米球传感器对CH4表现出更好的气敏性能,对50μL/L CH4的最佳工作温度降低了约60℃,同时对低浓度(1μL/L～20μL/L)CH4表现出较高的线性度和长期稳定性.本研究对研制高性能的ZnO基CH4气体传感器奠定了基础.     

退火处理对Ti-WO_3薄膜的结构和气敏特性的影响

用X射线衍射和透射电镜表征了直流磁控溅射法制得的Ti-WO3薄膜的晶型、晶格常数、粒径等。研究了退火对Ti-WO3薄膜气敏性质和微结构的影响,找出了最佳退火温度和工作温度;并对机理进行了分析。结果表明:450℃退火的薄膜的气敏效应很好,最佳工作温度在150℃左右;     

WO_3气敏薄膜的膜厚对气体响应时间的影响

用简单的模型分析了薄膜气体传感器敏感材料的膜厚对气体响应时间的影响,该模型适用于分析WO3薄膜气体传感器的敏感特性。薄膜气体传感器的敏感特性依赖于气体原子在薄膜内的扩散和与气敏材料的响应;而气体原子在薄膜内的扩散是由薄膜厚度决定的。经过推导得出理论上WO3薄膜对NH3的敏感特性,并将其与实验所得的数据进行比较。最后,给出了WO3薄膜气体传感器的气敏特性与气体在其膜内扩散和膜厚的关系。     

Micromachined thermal shear-stress sensor for underwater applications

This paper reports the development of micromachined thermal shear-stress sensors for underwater applications. The thermal shear-stress sensor is a polysilicon resistor sitting atop a vacuum-insulated nitride diaphragm. Special challenges for underwater measurements, such as the waterproof coating and minimization of pressure crosstalk, have been addressed. More rigid diaphragms than the aerial sensors are implemented to increase the operating range and reduce pressure crosstalk, with the cost of larger power consumption and lower sensitivity. Sensors with different diaphragm dimensions and resistor lengths have been fabricated and tested. Nearly zero pressure sensitivity has been achieved by either reducing the diaphragm width or adjusting the sensing element length. The effects of overheat ratio and operating mode on the sensor's pressure crosstalk have been discussed. Parylene C is chosen as the waterproof material for the underwater shear-stress sensors. The primary failure mode is identified as the corrosion of the soldering pads.     

Au-doped WO3-based sensor for NO2 detection at low operating temperature

Pure and Au-doped WO₃ powders for NO₂ gas detection were prepared by a colloidal chemical method, and characterized via X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The NO₂ sensing properties of the sensors based on pure and Au-doped WO₃ powders were investigated by HW-30A gas sensing measurement. The results showed that the gas sensing properties of the doped WO₃ sensors were superior to those of the undoped one. Especially, the 1.0 wt% Au-doped WO₃ sensor possessed larger response, better selectivity, faster response/recovery and better longer term stability to NO₂ than the others at relatively low operating temperature (150 °C).     

Photon stimulated sensor based on indium oxide nanoparticles I: Wide-concentration-range ozone monitoring in air

Ozone sensors are of great demand for monitoring high-concentration ozone for industrial applications and low-concentration ozone for protecting people's health, although commercial ozone sensors are limited in their detection range. In this work, it is demonstrated that compact energy-saving photostimulated ozone sensors based on indium oxide nanoparticles can detect ozone with a dynamical range over four orders of magnitude at room temperature. The photostimulated ozone sensor shows a very low cross response to NO₂, CO, and CO₂. Furthermore, the sensing signal is very reproducible, and no hysteresis effects were found in repeated measurements.     

Highly stable and sensitive humidity sensors based on quartz crystal microbalance coated with bacterial cellulose membrane

A novel highly stable and sensitive humidity sensor based on bacterial cellulose (BC) coated quartz crystal microbalance (QCM) has been successfully fabricated. The results showed that the sensors possessed good sensing characteristics by increasing more than two orders of magnitude with increasing relative humidity (RH) from 5 to 97%, and the Log(Δf) showed good linearity (20-97% RH). The sensitivity of sensors coated with BC membranes was four times higher than that of the corresponding cellulose membranes at 97% RH. In addition, the sensor sensitivity is greatly enhanced by increasing the coating load of the BC membranes with more absorption sites in the sensing membranes. Moreover, the experimental results prove that the resultant sensors exhibited a good reversible behavior and good long term stability. Herein, not only a novel and low-cost humidity sensor material was exploited, but also a new application area for BC nanofibrous membranes was opened up.     

海上溢油遥感探测技术及其应用进展

介绍了海上溢油遥感探测常用的可见光、红外、紫外光学遥感器、微波辐射计、雷达、激光荧光器和油层厚度探测器等几种溢油遥感探测器的探测原理、能力及应用状况。可见光仪器的溢油探测能力非常有限；红外遥感器是有一定探测能力的最为实用的探测器；微波遥感具有全天候的特点，但空间分辨率低，识别能力也有一定的限制；而激光荧光器和油层厚度探测器等激光遥感器则是最有发展前景的一类溢油探测器。通过性能等方面的对比分析以及当前实际应用情况，分析了未来溢油遥感技术的发展趋势。     

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.     

MOS气敏传感器阵列优化与工作温度选择

通过对金属氧化物半导体(MOS)气敏传感器阵列进行阵列优化和工作温度的选择,达到提高阵列选择性、降低其功耗的目的。实验采用10个MOS传感器组成阵列,在不同加热电压下,对不同浓度的苯、甲苯、甲醇、乙醇进行测试;利用四种特征选择方法进行阵列优化,同时对优化后的特征子集做Fisher线性判别(DFA)分析。结果表明,优化的阵列在比通用加热电压(5.0V)低的加热电压(4.4V)下工作,对四种物质的正确识别率由91.7%提高到100%。     

Development of high sensitivity potentiometric NOx sensor and its application to breath analysis

Using a combination of similar potentiometric sensors connected in series, a strategy for measuring NO at ppb concentrations has been demonstrated. Sensors numbering from 2 to 20 were fabricated, with each sensor based on YSZ electrolyte with WO₃ sensing electrode and Pt-zeolite/Pt as the reference electrode. Use of a catalytic filter allows for the cancellation of interferences due to oxidizable gases, such as CO. The optimum operating temperature of the filter and sensor was determined to be 250 and 425 °C, respectively. For human breath samples, the interference from water was acute enough that only scrubbing through a dry ice/acetone bath led to adequate performance for detection of NO in the 5-80 ppb range with a 20-sensor array. A more practical strategy suitable for clinical analysis was demonstrated by using water saturated air as the background gas. A linear calibration curve in the range suitable for use in clinical analysis is demonstrated.     

SnO2超微粒子薄膜的气敏特性研究

作者用自行设计的直流气体放电活化反应蒸发装置制备出平均粒径约为40nm的SnO_2超微粒子薄膜.研究了不同氧分压下所得SnO_2超微粒膜的形貌、结构和组成等特性,以及不同样品对各种易燃气体的气敏特性,得出了灵敏度随氧分压及灵敏度随工作温度的变化曲线.     

热催化气体传感器的特性分析及其设计原则

热催化气体传感器的输出受诸多因素的影响,从理论上分析其输出特性有助于传感器的优化设计和性能评估。从一个热催化气体传感器的典型结构和热催化气体敏感机理出发,应用热平衡方程和热敏电阻的电阻温度关系推导了传感器输出与被测气体浓度、催化反应速度、工作温度以及传感器结构尺寸等之间的定量关系。从推导过程中的诸多假设,得出了热催化气体传感器设计时应遵循的一般原则。     

Ultra-low-power components for an RFID Tag with physical and chemical sensors

In this work the development and optimization of the main components for a multisensing flexible Tag with RFID communication capabilities and integrated physical and chemical sensors for logistic datalogging applications will be reported. For this specific scenario, several constraints must be considered: power consumption must be limited for long-term operation, reliable ISO compliant RFID communication must be implemented, and special encapsulation issues must be faced for reliable sensor integration. In this work, the developments on application specific electronic interfaces and on ultra-low-power Metal OXdide semiconductor (MOX) gas sensors will be reported. The electronics for sensor control and readout as well as for RFID communication are based on an ultra-low-power MSP430 microcontroller from Texas Instruments together with a custom RFID front-end based on analog circuitry and a CPLD digital device, and are designed to guarantee a passive ISO15693 compliant RFID communication in a range up to 6 cm. A thin film battery for sensor operation is included, thus data acquisition and storage can be accomplished when no reader field is present. This design allows the user to access both the traceability and sensor information even when the on-board battery is exhausted. The physical sensors for light, temperature and humidity are commercially available devices, while for chemical gas sensing innovative MOX sensors are developed, based on ultra-low-power micromachined hotplate arrays specifically designed for flexible Tag integration purposes. A single MOX sensor requires only 8.9 mW for continuous operation, while temperature modulation and discontinuous sensor operation modes are implemented to further reduce the overall power consumption. The development of the custom control and RFID front-end electronics, together with innovative ultra-low-power MOX sensor arrays with flexible circuit encapsulation techniques will be described.