Thin polymer film based rapid surface acoustic wave humidity sensors

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) thin films, deposited on the surface of glass slides, were studied using transmission FTIR spectroscopy upon varying relative humidity (RH) from 2 to 70%. The obtained data revealed fast dynamics of water vapor adsorption-desorption with responses on the order of several seconds. Based on the fast FTIR signal intensity changes versus RH, it was proposed that a similar rapid response can be achieved for PVA and PVP coated SAW devices due to changes in mass-loading and film viscoelastic properties upon absorption of water vapor in the films. Sub-micron thickness films were spin-coated onto the surface of LiNbO₃ SAW substrates. Both PVA and PVP based humidity sensors revealed prompt reversible response to variations in humidity, although PVP-based device demonstrated better sensor parameters with total insertion loss variation of about 50 dB over the studied RH range and response time 1.5 s for the humidity step 5-95% (recovery time - 2.5 s), representing one of the fastest SAW-based humidity sensors reported to date.     

声表面波温度传感器频率分级扫描方法研究

针对声表面波(SAW)谐振腔体的频率响应单侧单调特征,为提高传感器的温度响应速度,提出了一种频率分级扫描方法,将频率扫描分为粗扫频和精扫频两个阶段,以不同的扫频步长依次进行.利用粗扫频确定中心谐振频率所处的频率区间,再在该频率区间内利用精扫频得到腔体中心谐振频率,可将温度传感器扫频时间降为原来的1/7.利用提出的频率扫描方法开展实验研究,分别研究了单个传感器的温度量测不确定度和多个传感器的温度量测一致性,并分析了实验结果.     

监测挥发性有机物的SAW传感器的研究进展

综述了可以连续操作和用于原位监测有机挥发性化合物的声表面波(SAW)化学传感器的研究进展。不锈钢包装和集成电路板的应用,使SAW传感器可以用于空气、土壤和水等在内的多种环境中监测有机挥发性化合物(VOCs)。介绍了根据常见地下水污染物氯代脂肪烃(如三氯乙烯)选择的高分子膜以及对传感器进行的优化。     

基于声表面波技术探测微量气体的理论分析

声表面波延迟线振荡器的频率对沉积在延迟线表面上的薄膜很敏感,在延迟线路径上覆盖一层具有选择性的吸附薄膜,这层薄膜吸附对其敏感的气体物质后,其质量密度、弹性参数、介电常数、电导率都将发生变化。给出了传感器的理论分析,根据检测需要,设计最优化的气体传感器。     

基于相位检测的声表面波传感器变送电路设计

本文设计了一种利用直接数字频率合成器（DDS）作为频率源,基于相位测量芯片AD8302的气敏传感器测试系统。该测试方法通过获取相同的输出相位差情况下的两次输八频率之差而达到测试目的,整个测试系统自动化程度高,且声表面波SAW谐振器工作于较高的频率,满足了较高精度现场检测的需要。     

基于SAW表面气液相效应和GC分离柱的气敏传感器的研究

限于传统涂敷敏感膜的声表面波（SAW）气敏传感器存在成膜困难和选择性差、重复性差以及再生性差等问题，本研究提出一种基于压电基底表面气体气液相转换效应机理的瑞利波传感器。首先建立了挥发性有机气体(VOCs)液相凝聚体薄层负载下的SAW波传模型，并仿真计算了其波传频散和波传衰减。然后在此基础上开发了一种基于瑞利声表面波传感器和气相色谱（GC）分离柱的便携式气体检测系统。最后实验论证了方案的可行性，初步的实验结果表明该系统具有分析时间短、选择性好、灵敏度高（可检测ppb浓度的混合VOCs）以及成本低等优势，因此其在痕量挥发性有机气体检测和分析应用上有良好的潜力和前景。     

Investigations on excitation and detection methods for Lamb wave sensors

Due to a high potential sensitivity, Lamb wave acoustic sensors have been studied for biochemical applications. Usually, Lamb waves are generated and detected using piezoelectric transducers. This technology involves bilayers structures and causes some problem of induced strain and temperature compensation. In this paper, we have investigated optical and electrostatic excitation methods. The optical excitation of Lamb waves is studied, and the main limitations of such an excitation method are pointed out. Theoretical as well as experimental studies are reported on electrostatic excitation of Lamb waves, and it is shown that this technique can be suitable for biosensors.     

双声路声表面波毒剂传感器的设计

对声表面波（SAW）芯片结构类型、参数条件、覆膜方法及制作工艺流程进行了详细研究,设计了一种新型双声路谐振器型SAW毒剂传感器,并以聚表氯醇PECH为敏感膜材料,测试了该传感器对芥子气（HD）的检测性能,结果表明：该传感器具有稳定性好、灵敏度高、响应快速、适于连续实时检测等特点,为发展毒剂检测器材提供了依据。     

基于FPGA的双声传感器定位系统的设计

针对小体积声探测系统对阵元数量的要求,设计了基于FPGA的双声传感器定位系统。该定位系统利用两个声传感器接收的回波的声压和时延值进行联合定位,可以达到减小阵元数量的目的。同时,利用硬件描述语言和DSP Builder完成了整个系统的构建。仿真和实验结果表明,所设计的定位系统工作频率可以达到94.4 MHz,完成一次定位只需要52μs,定位误差在1%之内。     

Development of high sensitivity tin oxide based sensors for gas/odour detection at room temperature

An effort has been made to develop thick film tin oxide gas sensors which could detect various gases/odours at room temperature. To achieve this, the fabricated sensors were annealed in oxygen plasma for various durations. It was then found that, the room temperature sensitivity of such sensors was increased to about ten times as compared to the sensitivity of the non-annealed sensors. Further, plasma annealed sensors are found to be practically independent of temperature and the room temperature sensitivity of these sensors are found to be about 1.5 times the sensitivity of the conventional sensors at its operating temperature of 300°C. Studies on the variation of d.c. resistance, sensitivity, temporal response, current–temperature characteristics and impedance spectroscopy with the annealing time have also been made. These studies reveal that, with the increase in annealing time, there is a permanent gradual reduction in the d.c. resistance of annealed sensors. Further, it is also observed that with the increase in annealing time, the response time improves, barrier height reduces, barrier capacitance increases and the dependence of the sensitivity with temperature reduces while the sensitivity itself improves many-fold.     

A nitric oxide gas sensor based on Rayleigh surface acoustic wave resonator for room temperature operation

A Rayleigh surface acoustic wave (RSAW) resonator with polyaniline/tungsten oxide nanocomposite thin film is investigated as a gas sensor for detecting the presence of nitric oxide (NO) in air. The sensor developed in this work was sensitive to NO gas at room temperature. It is shown that the sensor had a frequency shift of 1.2 ppm when it was exposed to 138 ppb NO. The negative frequency response increased with NO concentration increasing. The response and recovery times of the NO sensor in this work were about 20-80 s. In addition, this RSAW sensor also exhibited reversibility and repeatability to the presence of NO gas. Especially, the presented sensor showed high selectivity with NO gas to separate from NO₂ and CO₂ gases.     

压阻式高温压力传感器温度补偿与信号调理设计与测试

设计制作了一种集成信号调理电路的高温压阻式压力传感器,包含倒装式的压敏敏片、无源电阻温度补偿电路和信号调理电路组成;压敏芯片的制作采用SOI材料和MEMS标准工艺,温度补偿和信号调理电路采用高温电子元件;试验表明,无源电阻温度补偿具有显著的效果;此外,采用了高温信号调理电路来提高传感器的输出灵敏度,通过温度补偿来降低输出灵敏度;与传统的经验算法相比,所提出的无源电阻温度补偿技术具有更小的温度漂移,在220℃条件下传感器输出灵敏度为4.93 mV/100 kPa,传感器灵敏度为总体测量精度为±2%FS;此外,由于柔性传感器的输出电压可调,因此不需要使用一般的电压转换器随动压力变送器,这大大降低了测试系统的成本,有望在恶劣环境下的压力测量中得到高度应用。     

基于声表面波技术数字微流体基片间输运研究

复杂的生化分析系统往往很难集成于一个微流基片中,而按功能分别集成于两个或多个基片,为此,需要实现质荷在两基片间输运.提出了采用声表面波技术实现数字微流体在压电基片和玻璃基片间输运的新方法,它在128°YX-LiNbO3基片上光刻一个叉指换能器和一个反射栅,经功率放大器放大后频率为27.5 MHz的RF信号加到叉指换能器上,它激发的声表面波驱动其声路径上的数字微流体,使其按声传播方向快速运动,并到达与其相连接且经疏水处理的弧形聚合物表面,数字微流体由于自身重力克服表面张力作用沿弧形聚合物表面滑落到玻璃基片,实现两基片间输运.实验结果表明弧形聚合物曲率半径和微流体体积的大小影响其在两基片间输运.同时,提出了较小体积的微流体采用不相溶的油作为辅助微流体实现目标数字微流体在两基片间输运.     

A shear horizontal surface acoustic wave sensor for the detection of antigen–antibody reactions for medical diagnosis

In this paper we describe the development of a shear horizontal surface acoustic wave immunosensor for medical diagnostics. There exists a strong interest in the rapid detection of antigen–antibody reactions at small concentrations in the g/ml region in plasma, serum, or whole blood. Sensors whose operating principle is based on shear horizontal acoustic surface waves are well suited for this. We have used a spin-on glass film for the guidance of the surface wave as well as for the protection of the aluminum structures of the surface wave transducers from aggressive analyte liquids. This film has proven to considerably enhance the sensitivity of the device, and to simultaneously provide a durable protection of the transducers. Furthermore, polymers based on polyvinylamines have been used for the first time for immobilization of the capture protein. This technique effectively prevents the undesired binding of foreign substances like cells, non-specific antibodies, or other proteins at the sensor surface.     

Influence of intermediate hydrogel layer and amount of binding sites on the signal response of surface acoustic wave biosensors

Surface acoustic wave (SAW) devices based on horizontally polarized surface shear waves allow direct and label-free detection of biomolecules in real time. Binding reactions on SAW sensor surfaces are detected by determining changes in surface wave velocity caused mainly by mass loading or viscoelasticity changes in the sensing layer. In many cases, analyte-specific capture molecules or ligands are covalently bound on the sensor surface via an intermediate hydrogel layer. It is a fact that the SAW signal response strongly depends on the nature of the hydrogel matrix due to different relative changes of its acousto-mechanical parameters such as density and viscoelasticity. We studied the effect of different hydrogels in two affinity assays. One assay used a low amount of immobilized capture molecules, the other a high amount of immobilized ligands as binding sites in the sensing layer. Significant variations of the SAW signal response were observed. However, performing the assay with immobilized capture molecules resulted in decreasing signal height with increasing molar mass of the hydrogel whereas a reverse signal behavior was obtained performing the assay with immobilized ligands. This means that each affinity system requires its specific hydrogel matrix to obtain maximal signal response.     

MEMS热电堆高温测试系统中单晶材料的红外衰减特性研究

在对PerkinElmer公司的MEMS热电堆红外探测器静态和动态特性实验研究的基础上,本文提出了由MEMS热电堆、红外衰减片、靶体和存储模块组成瞬态表面高温测试装置的方案,对拓宽测温上限的关键元件--红外陶瓷衰减片进行了较深八的研究,用MEMS热电堆测量方法测量了氧化锆陶瓷片红外吸收系数,得出了不同厚度氧化锆（熔点为2715℃）陶瓷片红外衰减倍数曲线,为基于MEMS热电堆的表面高温测试装置的设计提供了依据。     

声表面波技术在化学战剂检测中的研究及发展

该文通过对目前世界各国SAW技术检测化学战剂研究发展状况的回顾,系统介绍了SAW传感器中膜材料的选择、灵敏度和温湿度、干扰气体、气体流速等因素对检测的影响,以及阵列式SAW传感器的检测方法,尤其是联合化学战剂检测器JCAD在化学战剂检测中的实际应用,并对今后声表面波技术检测化学战剂的研究发展前景提出了初步看法.     

Low temperature hydrogen detection at high concentrations: comparison of platinum and iridium

A comparison of platinum and iridium in work-function measurements with regard to hydrogen sensitivity is presented. The measurements were performed by means of a Kelvin probe and an ISFET-based measurement setup. They are concentrated towards high concentrations of hydrogen and low temperature in order to develop room temperature operated FET-based sensors which can withstand H₂-concentrations of some percent. With both materials the detection of H₂ up to 2% is possible. However, iridium shows very-slow reactions with adsorption as well as with desorption times of some hours. In contrast, the response times of platinum could be determined to be below 10 s in the case of 0.1% H₂. Therefore, platinum is the most promising candidate with air-gap configurations of FET like hybrid suspended gate FET (HSGFET).     

A sensor array based on mass and capacitance transducers for the detection of adulterated gasolines

The simultaneous use of different sensors technologies is an efficient method to increase the performance of chemical sensors systems. Among the available technologies, mass and capacitance transducers are particularly interesting because they can take advantage also from non-conductive sensing layers, such as most of the more interesting molecular recognition systems. In this paper, an array of quartz microbalance sensors is complemented by an array of capacitors obtained from a commercial biometrics fingerprints detector. The two sets of transducers, properly functionalized by sensitive molecular and polymeric films, are utilized for the estimation of adulteration in gasolines, and in particular to quantify the content of ethanol in gasolines, an application of importance for Brazilian market. Results indicate that the hybrid system outperforms the individual sensor arrays even if the quantification of ethanol in gasoline, due to the variability of gasolines formulation, is affected by a barely acceptable error.     

A new model of gross primary productivity for North American ecosystems based solely on the enhanced vegetation index and land surface temperature from MODIS

Many current models of ecosystem carbon exchange based on remote sensing, such as the MODIS product termed MOD17, still require considerable input from ground based meteorological measurements and look up tables based on vegetation type. Since these data are often not available at the same spatial scale as the remote sensing imagery, they can introduce substantial errors into the carbon exchange estimates. Here we present further development of a gross primary production (GPP) model based entirely on remote sensing data. In contrast to an earlier model based only on the enhanced vegetation index (EVI), this model, termed the Temperature and Greenness (TG) model, also includes the land surface temperature (LST) product from MODIS. In addition to its obvious relationship to vegetation temperature, LST was correlated with vapor pressure deficit and photosynthetically active radiation. Combination of EVI and LST in the model substantially improved the correlation between predicted and measured GPP at 11 eddy correlation flux towers in a wide range of vegetation types across North America. In many cases, the TG model provided substantially better predictions of GPP than did the MODIS GPP product. However, both models resulted in poor predictions for sparse shrub habitats where solar angle effects on remote sensing indices were large. Although it may be possible to improve the MODIS GPP product through improved parameterization, our results suggest that simpler models based entirely on remote sensing can provide equally good predictions of GPP.