Metalloporphyrins as sensing material for quartz-crystal microbalance nitroaromatics sensors

Five octaethylporphyrins (OEP) and tetraphenylporphyrins (TPP): (OEP)InCl, (OEP)MnCl, (OEP)GaCl, (TPP)Pd, and (TPP)RhI have been deposited as sensitive coating onto quartz-crystal microbalances. The sensitivities of the resulting sensors have been measured with respect to 2,4-dinitrotrifluoromethoxybenzene vapors. When exposed to the nitroaromatic compound, a large and significative response is recorded for every tested porphyrin, the detection process being slightly reversible. Along with a good sensitivity, the sensors exhibit an excellent selectivity when common solvents are used as interfering vapors. Among all the studied derivatives, (OEP)MnCl appears as the most sensitive and selective coating.     

New spark-test device for material characterization

An automated spark test system based on combining field emission and spark measurements, exploiting a discharging capacitor is investigated. In particular, the remaining charge on the capacitor is analytically solved assuming the field emitted current to follow the Fowler Nordheim expression. The latter allows for field emission measurements from pA to A currents, and spark detection by complete discharge of the capacitor. The measurement theory and experiments on Cu and W are discussed.     

Polymer nanocomposite nanomechanical cantilever sensors: material characterization, device development and application in explosive vapour detection

This paper reports an optimized and highly sensitive piezoresistive SU-8 nanocomposite microcantilever sensor and its application for detection of explosives in vapour phase. The optimization has been in improving its electrical, mechanical and transduction characteristics. We have achieved a better dispersion of carbon black (CB) in the SU-8/CB nanocomposite piezoresistor and arrived at an optimal range of 8-9 vol% CB concentration by performing a systematic mechanical and electrical characterization of polymer nanocomposites. Mechanical characterization of SU-8/CB nanocomposite thin films was performed using the nanoindentation technique with an appropriate substrate effect analysis. Piezoresistive microcantilevers having an optimum carbon black concentration were fabricated using a design aimed at surface stress measurements with reduced fabrication process complexity. The optimal range of 8-9 vol% CB concentration has resulted in an improved sensitivity, low device variability and low noise level. The resonant frequency and spring constant of the microcantilever were found to be 22 kHz and 0.4 N m(-1) respectively. The devices exhibited a surface stress sensitivity of 7.6 ppm (mN m(-1))(-1) and the noise characterization results support their suitability for biochemical sensing applications. This paper also reports the ability of the sensor in detecting TNT vapour concentration down to less than six parts per billion with a sensitivity of 1 mV/ppb.     

Improvements of optical tactile sensors for robotic system by gold nanocomposite material

In this work we propose the evolution of a new class of optical pressure sensors suitable for robot tactile sensing. The sensors are based on a tapered optical fiber, where optical signals travel embedded into a PDMS-gold nanocomposite material. By applying different pressure forces on the PDMS-based nanocomposite we measure in real time the change of the optical transmitted intensity due to the coupling between the gold nanocomposite material and the tapered fiber region. The intensity reduction of the transmitted light intensity is correlated with the pressure force magnitude.     

应力自感知水泥基复合材料及其传感器的研究进展

应力自感知水泥基复合材料是在传统的水泥或砂浆中添加特定导电材料或纳米材料复合而成的具有压阻效应的材料。利用这类材料的电阻率与其自身压应力存在一定对应关系的特性, 可以制成性能独特的应力自感知水泥基复合材料传感器。此类传感器因具有造价低、耐久性好、埋设工艺简单以及与混凝土材料相容性好等特性, 有望成为混凝土结构长期健康监测的新一代传感装置。本文作者从原材料选择、搅拌工艺、电阻测试方法以及传感器测试系统等多方面综合评述了应力自感知水泥基复合材料的研究进展。同时指出, 为促进其在工程中的应用, 对碳纤维水泥石电阻率的离散性、稳定性以及多向约束受力下电阻率的变化曲线等问题都必须进一步深入研究。      

Fuzzy modeling of measurement data acquired from physical sensors

The measurement uncertainty in physical sensors is often represented by a probabilistic approach, but such a representation is not always adapted to new intelligent systems. Therefore, a fuzzy representation, based on the possibility theory, can sometimes be preferred. We previously proposed a truncated triangular probability-possibility transformation to be applied to any unimodal and symmetric probability distribution which can be assimilated to one of the four most encountered probability laws (Gaussian, double-exponential, triangular, uniform). In this paper, we propose to build a fuzzy model of data acquired from physical sensors by applying this transformation. For this purpose, a minimum of knowledge about the probabilistic modeling of sensors is required. Three main situations are considered and for each situation, an adapted fuzzy modeling is proposed. Examples of these three situations are based on FM-chirped ultrasonic sensors     

以SnO_2纳米颗粒为敏感电极的阻抗型氢气传感器的研究

采用浸渍法在Ce0.9Gd0.1O1.95(CGO)固体电解质骨架中制备敏感材料SnO2,并组装成氢气传感器。利用XRD、SEM对氢气传感器的相组成及微观形貌进行表征,采用IM6e型电化学工作站对传感器气敏性能进行测试。结果表明浸渍法制备的敏感材料SnO2颗粒细小,约为400nm左右;在400~550℃时,传感器阻抗值随氢浓度的增加而减小,且传感器信号与氢气浓度表现出非常良好的线性关系。随着温度升高,传感器的信号响应速度逐渐增加,在550℃、氢浓度为1.0×10-3时,其90%的响应时间为170s。     

Dielectric studies of barium bismuth titanate as a material for application in temperature sensors

Ceramic nanocrystalline samples with composition Ba_1?3aBi_2aTiO₃ were synthesized by sol–gel method, for different values of parameter a (for a = 0.0165, 0.033, 0.050). In order to determine whether barium bismuth titanate is suitable for application in temperature sensors, dielectric properties measurements were conducted on the prepared samples, as a function of both temperature (from room temperature up to 190 °C) and frequency (from 50 kHz to 1 MHz). Real and imaginary parts of dielectric constant were determined using an Impedance Analyzer HP-4194A. Depending on parameter a two different behavior were determined: (1) classical ferroelectric behavior, for the sample with low a value and (2) relaxor behavior for the samples with higher a values. Thus, a typical characteristic of relaxor ferroelectrics with a broad and dispersive dielectric maximum was observed for the samples Ba_0.85Bi_0.1TiO₃ and Ba_0.90Bi_0.066TiO₃. Temperature dependence (for real part of dielectric constant ε_r′) is almost linear, for lower temperatures than peak value (slope +1.3 1/ °C), and higher than this value (slope ?1 1/ °C). The feature of linearity is very important from practical aspects of application of this material in wireless temperature sensors. The temperature coefficient of dielectric constant for the sample with the best linearity (Ba_0.95Bi_0.033TiO₃ at 1 MHz) was found to vary from positive one +3.72 × 10^?3 1/ °C to negative value ?2.85 × 10^?3 1/ °C, in the temperature range 25–190 °C.     

Method of optimum compacting of control material in moisture sensors

A theoretical analysis of the methods of packing loose medium in humidity sensors is given and their experimental investigations are presented. Power packing is recommended for continuous moisture sensors, while inertial-power packing is recommended for discrete sensors.     

基于光纤光栅传感器的复合材料层合板冲击能量研究

复合材料结构较容易产生结构表面无法探测到的低速冲击损伤。试验利用光纤复合材料结构中布拉格光纤光栅传感器受到低速冲击后光栅中心波长随应力变化这一特性,在恒温下用布拉格光纤光栅传感器对复合材料智能结构受到的低速冲击能量给出判别,并对通过光纤光栅解调仪采集下来的低速冲击信号进行频谱分析。在计算冲击信号所有能量等级的频谱峰值后,给出可以界定能量等级的频谱峰值临界值,利用其来判别低速冲击能量等级。试验表明布拉格光纤光栅传感器可以监测复合材料受到冲击的信号,能够对复合材料结构低速冲击进行能量等级判断研究     

Fabrication and characterization of microwell array chemical sensors

Microwell arrays have been fabricated on the distal face of coherent fiber-optic bundles. A typical microwell array comprises approximately 3,000 individual optical fibers that were etched chemically. Individual microwells were 1 to 14-microm deep with approximately 22-microm widths and were filled partially with a chemical sensing (polymer + dye) layer to produce a microwell array sensor (MWAS). MWASs were fabricated using a technically expedient, photoinitiated polymerization reaction whereby a approximately 2 to 10-microm thick pH-sensitive or O2-sensitive sensing layer was immobilized inside each microwell. The pH-sensing layer comprised fluorescein isothiocyanate-dextran conjugate immobilized in a photopolymerizable poly(vinyl alcohol) membrane. The O2-sensing layer comprised a ruthenium metal complex entrapped in a gas-permeable photopolymerizable siloxane membrane. pH and PO2 were quantitated by acquiring luminescence images using an epifluorescence microscope/charge-coupled device imaging system. The pH-sensitive MWAS displayed a pKa of approximately 6.4 and a response time of approximately 2.5 s. The O2-sensitive MWAS behaved according to a nonlinear Stern-Volmer model with a maximum I0/I of approximately 4 and a response time of approximately 2.5 s. MWASs are advantageous in that suitably sized samples such as single biological cells can be co-localized with the sensing matrix in individual microwells.     

New characterization method for macrostructures of ceramics hybrid material

This paper presents new powerful characterization tools for ceramic and hybrid materials based on optical microscopy. Specimens are made transparent by thinning or the immersion liquid and the structure is observed in transmission mode. The tools can reveal detrimental defects, which are characteristically very few in number but large in size. Comfocal laser scanning fluorescent microscopy and infrared microscopy are also applied to extend the potential of the tool.     

Computational design of multiaxial tests for anisotropic material characterization

Although anisotropic materials provide more capabilities for mission‐ and application‐tailored design and functional flexibility to final structures than regular isotropic materials, the directional behavior of the anisotropic materials further complicates their inelastic and damage behavior. Such a non‐linear behavior can be effectively observed and characterized by multiaxial testing, but how to design a multiaxial test for material characterization given a specimen remains an untouched issue. This paper presents a methodology that numerically designs the loading path of a multiaxial testing machine to characterize anisotropic materials. The multiaxial test must be able to exhibit quantities used to characterize materials as distinctly as possible. The proposed methodology formulates distinguishability and uniqueness as such quantities by first analyzing the specimen on a continuum basis with finite element method and then applying singular value decomposition. Associating the distinguishability and uniqueness with the informativeness of the loading path, the design problem is formulated such that an effective loading path can be found efficiently by a standard optimization method. Numerical examples first investigate the validity of the distinguishability and the uniqueness as performance measures to evaluate loading paths. The efficacy of the proposed methodology has been then confirmed by analyzing it with and applying it to design problems. Copyright © 2007 John Wiley & Sons, Ltd.     

Electrical characterization of functionalized platinum electrodes and ISFET sensors for metal ion detection

This paper reports the application of functionalized platinum (Pt) electrodes and ChemFETs sensors for metal ion detection. The sensitive part of the sensors consists in a film of ethyl 2-thienylglyoxalate (ETGO) deposited by a spin-coating process. Electrochemical impedance spectroscopy was used to investigate the electrical properties of functionalized Pt electrodes. The optimized working conditions of the sensors have been studied with regard to the sensitivity performances, in particular, the polarization was adjusted to − 0.85 V/ESC in order to neglect the Warburg effects at low frequencies. The functionalized Pt electrodes have shown a good sensitivity towards Cu(II) ions, whereas low response towards Ca(II) ions was observed. The ETGO/ISFET devices have shown good sensitivity (14 mV/decade) and linear responses over at least two decades of Cu(II) activity compared to (0.5 mV/decade) for Ca(II) ions.     

Realization and characterization of porous gold for increased protein coverage on acoustic sensors

Immunosensors show great potential for the direct detection of biological molecules. The sensitivity of these affinity-based biosensors is dictated by the amount of receptor molecules immobilized on the sensor surface. An enlargement of the sensor area would allow for an increase of the binding capacity, hence a larger amount of immobilized receptor molecules. To this end, we use electrochemically deposited "gold black" as a porous sensor surface for the immobilization of proteins. In this paper, we have analyzed the different parameters that define the electrochemical growth of porous gold, starting from flat gold surfaces, using different characterization techniques. Applied potentials of -0.5 V versus a reference electrode were found to constitute the most adequate conditions to grow porous gold surfaces. Using cyclic voltammetry, a 16 times increase of the surface area was observed under these electrochemical deposition conditions. In addition, we have assessed the immobilization degree of alkanethiols and of proteins on these different porous surfaces. The optimized deposition conditions for realizing porous gold substrates lead to a 11.4-fold increase of thiol adsorption and a 3.3-fold increase of protein adsorption, using the quartz crystal microbalance (QCM-D) as a biological transducer system. Hence, it follows that the high specific area of the porous gold can amplify the final sensitivity of the original flat surface device.     

Simultaneous measurements of multiple flow parameters for scramjet characterization using tunable diode-laser sensors

This paper reports the simultaneous measurements of multiple flow parameters in a scramjet facility operating at a nominal Mach number of 2.5 using a sensing system based on tunable diode-laser absorption spectroscopy (TDLAS). The TDLAS system measures velocity, temperature, and water vapor partial pressure at three different locations of the scramjet: the inlet, the combustion region near the flame stabilization cavity, and the exit of the combustor. These measurements enable the determination of the variation of the Mach number and the combustion mode in the scramjet engine, which are critical for evaluating the combustion efficiency and optimizing engine performance. The results obtained in this work clearly demonstrated the applicability of TDLAS sensors in harsh and high-speed environments. The TDLAS system, due to its unique virtues, is expected to play an important role in the development of scramjet engines.