Flexible hot-film anemometer arrays on curved structures for active flow control on airplane wings

A set of flexible MEMS sensor arrays for flow measurements in boundary layers is presented. The sensor principle of these anemometers is based on convective heat transfer from a hot-film into the fluid. Each sensor consists of a nickel sensing element between copper supply tracks. The functional layers are attached either on a ready-made polyimide foil or on a spin-on polyimide layer. These variants are designed to meet the requirements of measurements in different environments. Spin-on technology enables the use of very thin polyimide layers, ideally suited for measurements in transient flows. It is a unique characteristic of the presented arrays that their total thickness can be scaled from 7 to 52 μm. This is essential, because the sensor thickness has to be adapted to the varying thickness of the boundary layers in different aerodynamic tests. With these sensors we meet the special requirements of a wide range of fluid mechanic experiments but in particular those of future active flow control on airplane wings. For less critical flow conditions with much thicker boundary layers, thicker sensors might be sufficient and cheaper, so that sensors fabricated on ready-made foils are perfect for these applications. Since the presented sensors are flexible, they can be attached on curved aerodynamic structures without any geometric mismatches. The entire development, starting from theoretical investigations, is described. Further, the micro-fabrication is discussed, including photolithography, sputtering and wet-etching. In particular the wet-etching of the sensing element is found to be critical for the functional characteristics.     

基于微透镜阵列的多通道光寻址电位传感器研

为了提高化学和生物图像传感器的成像速度和简化成像系统,提出了一种基于微透镜阵列的多通道光寻址电位传感器.利用微透镜阵列把单束激光转化成点阵,通过多频率斩波器,得到不同频率的光点阵列用作光寻址电位传感器的光源,从而实现多点同时检测.实验结果表明该系统具有良好的频域分辨率,通过数字补偿技术可获得各个检测点的电流电压特性曲线,证明可实现多点同时检测.该系统可以用于光寻址电位传感器和扫描光感阻抗传感器的快速成像,以及多通道化学生物图像检测.     

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。     

基于波矢可调谐对称结构的条波导型SPR传感系统研究

针对目前波导型SPR传感器波矢匹配条件受限及较难与光纤实现固化对接进而实现在线传感的缺点,研究由条波导激励对称结构的SPR传感系统。通过对由金属——介质——金属构成的对称结构进行模式分析,研究可在该结构内激发SPW的可能性及其波矢可调谐机制。实验制备单模条波导并激励对称传感结构,对比了条波导激励传统结构与对称结构的检测折射率范围,研究了对称结构中金属材质,金属膜厚及介质厚度对测量结果的影响,给出了折射率测量的结果,实验证明,采用对称结构实现传感,可通过镀金属膜的厚度来改善传感特性,调节两金属膜之间介质的厚度可以实现波矢匹配的调节,进而使得被测范围具有一定的可调性,具有较好的线性。     

The optimisation of a paired emitter-detector diode optical pH sensing device

With recent improvements in wireless sensor network hardware there has been a concurrent push to develop sensors that are suitable in terms of price and performance. In this paper a low-cost gas sensor is detailed, and significant improvements in sensor characteristics have been achieved compared to previously published results. A chemical sensor is presented based on the use of low-cost LEDs as both the light source and photodetector, coupled with a sensor slide coated with a pH sensitive colorimetric dye to create a simple gas sensor. Similar setups have been successfully used to detect both acetic acid and ammonia. The goal of this work was to optimise the system performance by integration of the sensing technique into a purposely deigned flowcell platform that holds the colorimetric slide and optical detector in position. The reproducibility of the sensor has been improved through this arrangement and careful control of deposited film thickness. The enhanced reproducibility between sensors opens the potential of calibration-free measurement, in that calibration of one sensor can be used to model the characteristics of all sensors in a particular batch.     

无线传感器网络技术环境应用进展

随着时代的发展,无线传感器网络技术也迅速的被人们熟知与使用,已经成为了现在的一门主要应用技术.无线传感器网络技术的前身是遥感技术,也就是说无线传感器网络技术是由遥感技术发展而来的.本文主要对无线传感器技术在环境应用上的进展展开了简要的论述,希望可以对无线传感器网络技术在环境应用上起到促进的作用,推动相关事业的发展.     

Sensing Assessment in Unknown Environments: A Survey

This paper surveys sensing assessment solutions from the literature with a particular focus on techniques which can be used in unknown environments, including the following: sensor fault detection and identification (FDI), sensor or source evaluation, and isolating poorly sensed regions. Each approach is evaluated in terms of its ability to perform sensing assessment tasks in unknown environments and its coverage of the range of potential sensing problems. These tasks include sensing problem detection and characterization, as well as performance evaluation (e.g., estimating accuracy or reliability), for a sensor or group of sensors. This survey shows that over 40 existing approaches are focused on either detection and identification of traditional sensor faults (e.g., drift or physical damage) in known environments or evaluation of the reliability of a source (e.g., sensor or agent). Only eight approaches surveyed have tackled environment-dependent problems (e.g., exteroceptive sensor FDI, miscalibration, or use of an inappropriate sensor) in a useful manner for unknown environments. Even less work (two studies) appears to have been done on isolating poorly sensed regions. The survey concludes with a list of opportunities for future research, including developing methods for detecting and characterizing environment-dependent problems and creating comprehensive sensing assessment systems.     

Hydrogen sensing characteristics of vertical type hydrogen sensors based on porous 3C-SiC with catalyst materials

The hydrogen-sensing characteristics of porous 3C-SiC (p-SiC) with different catalyst metals were investigated. The scanning electron microscopy results confirm that the 3C-SiC film has a porous structure with a pore size of 20–30 nm. Hydrogen sensing behavior of Pd/p-SiC was analyzed as a function of hydrogen concentration by current–voltage (I–V) and ?I-t methods under steady state and transient conditions. The Pd was used as a Schottky contact and detection material. The Pt and Au catalyst metals were deposited on Pd layer to increase the hydrogen sensing characteristics. The change in current was monitored in the range of 210–610 ppm hydrogen concentrations. The deposited Pt was more sensitive to hydrogen gas than the Pd and Au catalyst metals. It is evaluated that the hydrogen sensing properties of porous 3C-SiC Schottky-diode can be improved by Pt and Pd catalytic metals.     

A simulation program for the sensitivity and linearity ofpiezoresistive pressure sensors

A simulation program is developed which is capable of calculating the output responses of piezoresistive pressure sensors as a function of pressure and temperature. Analytical models based on small and large deflection theories have been applied to predict the sensitivity and linearity of pressure sensors. Surface-micromachined diaphragms with square or circular shapes, fabricated by a low pressure chemical vapor deposition sealing process, are designed and tested to verify the program. They are made of polysilicon and have a standard width (diameter) of 100 μm and thickness from 1.5 to 2.2 μm. Various parameters of the piezoresistive sensing resistors, including length, orientation, and dopant concentration, have been derived and constructed on top of the diaphragms. For a 100-μm-wide 2-μm-thick square-shape pressure sensor, calculated and experimental results show that int sensitivity of 0.24 mV/V/(Ibf/in²) is achieved. Experimentally, non a maximum linearity error of ±0.1% full-scale span) is found out on a 100-μm-wide 2.2-μm-thick square-shape pressure sensor. Both sensitivity and linearity are characterized by the diaphragm thickness and the length of the sensing resistors     

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。     

敏感电极厚度对NO_X传感器特性影响规律的研究

为快速准确地检测柴油机NOX排放值,提出了以NiO为敏感电极、YSZ为固体电解质的混合电位型NOX传感器。通过分析NOX传感器的气敏、温度、阻抗和响应等特性曲线的变化规律,得到了NOX传感器敏感电极厚度的最佳参数。试验结果表明,优化后的NOX传感器能够满足柴油机选择性催化还原(SCR)系统在线实时检测要求。     

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。     

SnO2-based R134a gas sensor: Sensing materials preparation, gas response and sensing mechanism

Undoped SnO₂ and porous Al₂O₃ powders were obtained through a simple chemical precipitation process. SnO₂-based gas sensing materials and Al₂O₃ catalytic coating loaded with a noble metal were prepared by impregnation. The SnO₂ and Al₂O₃ powders were characterized by TEM, SEM, nitrogen adsorption-desorption experiment, FT-IR and in situ XRD. Gas responses of the SnO₂-based gas sensors were measured in a static state. The experimental results indicated that the response towards R134a of the SnO₂-based gas sensor can be significantly enhanced by loading noble metal and using catalytic coating. The sensor based on a double layer film SnO₂ (Au)/Al₂O₃ (Au) showed satisfactory results including large response, good selectivity, high long-term stability, fast response and recovery, revealing its potential application in the detection of refrigerants and the maintenance of air condition systems. Finally, a gas sensing mechanism for R134a is suggested and proved by bond energy data, FT-IR spectrum and in situ XRD.     

The quartz crystal microbalance: mass sensitivity, viscoelasticity and acoustic amplification

Quartz crystal resonators (QCR) respond to surface mass and material properties of a film coated on their surface. The acoustic load acting at the surface of the resonator is a more general parameter to describe this dependence. It can be represented by a mass factor and an acoustic factor. The quotient of resistance increase and frequency shift can be used for the determination of the acoustic factor, if the loss tangent of the coating is known. Viscoelastic properties of sensitive coatings can enhance the mass sensitivity of quartz crystal microbalance (QCM) sensors. Acoustic factor and acoustic amplification effective during chemical sensing are not the same.

We further suggest a sensor concept, which is based on a bilayer arrangement. Acoustic amplification with a viscoelastic film and chemical sensitivity is separated. With a proper selection of materials, the first layer realizes acoustic amplification while the (chemical) sensitive layer acts as a pure mass detector. Major sensor design parameters are the shear modulus and the thickness of the first layer; major challenge is the preparation of a homogeneous and uniform first film.     

MEMS光纤法珀压力传感器的设计及解调方法实现

基于外界压力引起敏感膜片形变导致腔长变化来实现压力信号传感的原理,提出了一种MEMS光纤法珀压力传感器的设计,建立了传感器敏感膜片的挠度变化与膜厚、半径及施加压力的关系理论模型,并在此基础上进行了膜片的MATLAB二维数值仿真和Comsol Multiphysics三维数值仿真,并完成了FP压力敏感头的制作,进而设计了能够应用于光纤传感的解调方法,搭建了光纤传感的压力测试系统并进行了相关实验,利用所设计的解调方法对实验数据进行处理,进而对压力传感器的性能及特性进行了测试和验证。实验结果表明,传感器测试曲线线性度良好,与数值仿真结果基本一致,在100 kPa的量程范围内其灵敏度可达62.3 nm/kPa,温度敏感系数为0.023μm/℃,测量精度3.93%,且最小压强分辨率为1.29 kPa,证实了该MEMS光纤法珀压力传感系统具有一定的可行性。     

Silicon micro-cantilever chemical sensors fabricated in double-layer silicon-on-insulator (SOI) wafer

Micro-cantilever piezoresistive sensors are optimally designed and fabricated in a double-layer silicon-on-insulator (SOI) wafer. The sensor geometry is optimized by placing the sensing piezoresistor at the cantilever root region to increase effective piezoreisistive sensing area. According to finite-element simulation results, high sensitivity can be obtained by design the cantilever into a wide and short shape. In order to use single-crystalling silicon to fabricate both the cantilever and the piezoresistor for high sensitivity, double-layer SOI wafer, which has two active layers and two insulating layers, is proposed to fabricate the self-sensing micro-cantilever sensor. The piezoresistor is made of the top active-layer single-crystalline silicon. Without p–n junction isolation, such a piezoresistor can be free from leakage-current relative noise that helps to achieve fine sensing resolution. The bottom active-layer is used to form the cantilever, with well controlled cantilever thickness and high fabrication yield. With the top surface of the micro-cantilever is modified with the functionalized self-assembled monolayer, detection of trace-concentration Trinitrotoluene (TNT) vapor is experimentally carried out, with reproducible sensing response to 7.6 ppb TNT.     

Searching for optimal sensitivity of single-mode D-type optical fiber sensor in the phase measurement

To improve the sensitivity of a single-mode D-type optical fiber sensor, we selected a D-type optical fiber sensor with 4 mm long and 4 μm core thickness made of a single-mode fiber, a Au-coating on the sensor with a thickness range of 15–32 nm, a light wavelength of 632.8 nm, and an incident angle of 86.5–89.5° for different refractive index (1.33–1.40) sensing. These simulations are based on the surface plasmon resonance (SPR) theory using the phase method which shows that the sensitivity is proportional to the refractive index, Au film thickness and lower incident angle on the sensing interface. The sensitivity is higher than 4000 (degree/RIU), and the resolution is better than 2.5 × 10⁻⁶(RIU) as the minimum phase variation is 0.01°. This device is used to detect the refractive index or gas or liquid concentration in real-time. The proposed sensor is small, simple, inexpensive, and provides an in vivo test.     

Terahertz sensing application by using planar split-ring-resonator structures

This numerical study investigates terahertz sensing applications of metamaterials based on planar split-ring-resonators. In order to keep the manufacturing process of the sensor simple, arrays of single split-ring-resonators are used. Two types of resonators, square and circular, are designed to cover different frequency ranges. An unknown material is then added as an overlayer to the metamaterial in order to explore the performance of the entire system in terms of sensing phenomenon. The changes in the transmission resonances are monitored upon variation of the thickness, the dielectric constant, and the coverage (distribution of the unknown material within each unit cell) of the overlayer. The results show good sensitivity of the sensors suggesting they can be used for a myriad of terahertz sensing applications in biology and chemistry.     

四电极电化学MEMS加速度传感器仿真

基于溶液相对于电极的运动会使电极附近因电势差作用而产生的离子浓度梯度发生改变,从而使电极电流发生变化等电化学原理,建立一种置于碘(I2)和碘化钾(KI)混合水溶液环境中的阳极—阴极—阴极—阳极(ACCA)四电极阵列传感单元模型。通过理论分析,该传感单元可以局部电解液为惯性质量,利用电解液中带电离子相对于电极的运动来产生并输出附加电流;进一步的建模仿真证明:在一定的加速度范围内(0a x0.149 m/s2),附加电流的大小同加速度呈正比关系,故可以将此电流放大输出,从而实现对加速度大小的表征。可利用MEMS工艺制作,并封装此传感单元成为加速度传感器。     

Design considerations for plasmonic-excitation based optical detection of liquid and gas media in infrared

Surface plasmon resonance (SPR) sensor schemes based on silicon (Si) and chalcogenide glass are evaluated and compared for chemical as well as gas detection in a wide range of infrared (IR) wavelengths. The plasmonic characteristics in IR are critically dependent on the dispersive behavior of the coupling substrate material. The performance of sensor has been evaluated in terms of its intrinsic sensitivity (IS) that includes the FWHM and angular shift of SPR curve for a given change in refractive index of sensing medium. Both these materials are potential candidates for opening up new routes for detection in near- and mid-IR due to their strong dispersion capabilities as compared to normal silica-based glass. The IS of chalcogenide glass-based SPR sensor is found to be larger than Si-based one for a broad wavelength range of 700–2500 nm indicating that chalcogenide glass-based probe provides more sensitive as well as accurate sensing procedure than Si-based probe. Further, for both glasses, the single probe can be used for both aqueous as well as gaseous sensing. Furthermore, for both glasses, it is found that the values of IS are much larger for gaseous sensing in comparison to liquid sensing.