Diesel engine dynamometer testing of impedancemetric NOx sensors

Prototype solid-state electrochemical sensors using a dense gold sensing electrode, porous yttria-stabilized zirconia (YSZ) electrolyte, and a platinum counter electrode (Au/YSZ/Pt) were evaluated for measuring NO_x (NO and NO₂) in diesel exhaust. Both electrodes were exposed to the test gas (i.e., there was no reference gas for the counter electrode). An impedancemetric method was used for NO_x measurements, where the phase angle was used as the response signal. A portion of the tailpipe exhaust from the dynamometer test stand was extracted and fed into a furnace containing the experimental sensor. The prototype sensor was tested along with a commercially available NO_x sensor. Simultaneous measurements for NO_x, O₂, CO₂, H₂O, CO, and CH₄ in a separate feed stream were made using Fourier transform infrared (FTIR) spectroscopy and an oxygen paramagnetic analyzer. The experimental sensor showed very good measurement capability for NO in the range of 25-250 ppm, with a response paralleling that of the FTIR and commercial sensor. The prototype sensor showed better sensitivity to NO_x at the lower concentration ranges. O₂ is an interferent for the experimental sensor, resulting in decreased sensitivity for measurement of NO_x. Methods to overcome this interference are discussed.     

Carbon dioxide gas sensor using a graphene sheet

In this article, we report on a high-performance graphene carbon dioxide (CO₂) gas sensor fabricated by mechanical cleavage. Unlike other solid-state gas sensors, the graphene sensor can be operated under ambient conditions and at room temperature. Changes in the device conductance are measured for various concentrations of CO₂ gas adsorbed on the surface of graphene. The conductance of the graphene gas sensor increases linearly when the concentration of CO₂ gas is increased from 10 to 100 ppm. The advantages of this sensor are high sensitivity, fast response time, short recovery time, and low power consumption.     

Application of deep reactive ion etching for silicon angular rate sensor

 A new silicon resonant angular rate sensor by deep reactive ion etching was developed. The sensor consists of a glass-silicon-glass structure. To have a sensor of high Q factor, a one-side suspended tuning fork structure was adopted. The silicon resonator structure which has high aspect ratio was machined by reactive ion etching. The etching gas of the RIE was SR₆ and etching rate was 0.8 μm/min. The resonator is driven electromagnetically and the torsional vibration caused by the Coriolis force is detected capacitively. The test device showed a sensitivity of 6 fFsec./deg. and had an output to the angular rate in a range from −360 deg./sec to 240 deg/sec. Received: 30 October 1995/Accepted: 20 May 1996     

固态降水传感器现场核查装置技术研究

针对气象观测台站固态降水传感器现场核查及测试的实际需求,研制了现场核查装置,结合砝码法实现了固态降水传感器的现场核查和测试;现场核查装置由基于ZigBee无线网络的数据获取装置和加重装置构成,数据获取装置具备环境气压、温度、相对湿度的实时检测能力,具备RS232、RS485及通断信号方式3种固态降水传感器接口的数据读取能力;加重装置由三角支架、OPD降水模拟器及砝码托盘组成,其中降水模拟器采用阻挡原有OPD降水发生探测器红外光束,人为给定指定频率脉冲信号的方法实现了降水的模拟,能够兼容多种型号的固态降水传感器;经实验测试,固态降水传感器能够准确识别加入其中的砝码重量,数据获取装置的3种接口数据读取准确度均达到100%;降水量测量值与理论值相关系数为0.9999;表明现场核查装置能够应用于固态降水传感器现场核查及测试业务。     

Microcoil speed and position sensor for automotive applications

 An inductive ABS speed and position sensor has been realized, based on an arrangement of batch-fabricated microcoils in a differential transformer configuration. The position of a metallic toothed wheel is measured with a precision of ±2 μm in a 0 to 3.2 kHz bandwidth and at a distance of 0 to 2 mm, with a transformer power consumption of less than 50 mW. Both the differential sensor approach and the ratiometric analysis allow for position detection that is insensitive to target speed, target distance and sensor temperature. The AC excitation allows the frequency to be adapted to the target material and to measure down to zero speed. Received: 1 November 1996/Accepted: 13 November 1996     

Evaluation of microparticle materials for enhancing the performance of fluorescence lifetime based optrodes

Fiber optic based sensors have many advantages over electrochemical sensors, and as a result have broad application for sensing in agriculture, basic biology, the environment, and medicine. An important component of a fiber optic sensor is the sensing element, usually a solid-state matrix containing the analyte specific fluorescent dye, immobilized on an optical fiber. The fluorescence output of the dye can be calibrated to analyte concentration based on intensity or lifetime. The membrane matrix immobilizes and entraps the fluorescent dye molecules by providing the mechanical support at the optrode tip. The present study used micro- and nanoparticles of TiO₂ and microparticles of different materials (BaSO₄, Cr, CuO, diamond, Au, PbO and ZnS) to investigate the phenomena underlying the role of accessory materials for optrode performance enhancement. We found that 2 μm particles amplified fluorescence intensity better than 10–150 nm particles. Materials with high refractive indexes performed better, provided that they have low absorbance across the visible region. Microparticles with either high refractive indices or high reflectance will amplify the fluorescence output, but microparticles with both properties enhance optrode performance at lower dye concentrations. The results of these experiments have allowed us to engineer membrane microparticle content to optimize a platinum-tetra-fluoro-phenyl-porphyrin (PtTFPP) O₂ optrode.     

The measurement of minimotors and micromotors torque-characteristic using miniaturized cable brake

 A miniaturized torque sensor based on cable brake principle for the measurement of torque-characteristic of minimotors and micromotors has been developed. The first generation torque sensor enables the measurement of torque of minimotors in the range of μNm. Design principles and the production process are described. Experimental results show fair conformity with technical data for minimotors. Received: 30 October 1996 / Accepted: 14 November 1996     

Selective mixed potential ammonia exhaust gas sensor

Novel selective ammonia sensors with high potential for long-term stability in harsh exhaust environments are introduced. The sensor bases on the mixed potential effect. In contrast to common sensors, the electrode functionalities electrical conductivity, selective catalytic activity, and electrochemical activity combined with long-term stability are separated. For that reason, one of the two electrodes is covered by a well-known porous vanadia–tungstenia–titania-based SCR catalyst material, which has been developed for exhaust gas SCR applications. The resulting sensor signal depends semi-logarithmically on ammonia. The NO_x cross-sensitivity is marginal. If enough oxygen is in the exhaust, the sensor signal is independent of the oxygen concentration. Tests downstream of an SCR catalyst show that very small ammonia slips can be determined.     

Microfabricated electrochemical sensors for exhaustive coulometry applications

The development of microfabricated electrochemical systems suitable for deployment in sensor networks that operate with a minimum of operator intervention are of great interest; therefore, a coulometric sensing system for exhaustive coulometry with the potential for calibration-free operation has been designed, fabricated and evaluated to support such development. The sensor chips were microfabricated onto a silicon substrate and contained a variety of specially designed thin-film gold working electrodes (ranging from one to five per chip) and a Ag/AgCl pseudo-reference electrode. A custom flow cell containing fluidic connections and counter electrode chamber was also constructed to integrate the sensor and to create an electrolysis chamber with a fixed volume. Different chip designs were evaluated as exhaustive coulometric sensors in terms of reproducibility and longevity using Fe(CN)₆^3?/4? as model analytes. The relative standard deviation (RSD) for a chip tested over a period of 42 days was 5.5% whereas the sensor-to-sensor reproducibility was within 6.3%.     

A selective room temperature formaldehyde gas sensor using TiO2 nanotube arrays

A new gas sensor using TiO₂ nanotube arrays was fabricated and explored for formaldehyde detection at room temperature. Highly ordered vertically grown TiO₂ nanotube arrays were synthesized by using the conventional electrochemical anodization process. The sensor using the fabricated nanotube arrays as the sensing elements demonstrated a good response to different concentrations of formaldehyde from 10 to 50 ppm and a very good selectivity over other reducing gas species such as ethanol and ammonia at room temperature. While the exact sensing mechanism is unclear, some possibilities are briefly discussed.     

Sensing properties of organised films based on a bithiophene derivative

Highly reproducible optic and electrochemical sensors have been developed using organised films from a polar bithiophene derivative, the 5-(dimethylamino)-5′-nitro-2,2′-bithiophene (Me₂N–T₂–NO₂). The strength of the molecular dipole moment of this push–pull end-capped bithiophene has permitted to obtain highly ordered, homogeneous and reproducible films by using both the Langmuir–Blodgett and the casting techniques. The organisation of the molecules in LB films and cast films has been established by means of UV–vis, infrared and Raman spectroscopy and by AFM.Me₂N–T₂–NO₂ thin films possess appealing optical and electrochemical sensing capabilities. UV–vis spectra can be modified in the presence of a variety of volatile organic compounds and the sensitivity is related to the polarity of the gas analysed. Films can also be used as electrochemical sensors because the characteristics of the current/potential curves are sensitive to the nature of the electrolytic solution. The spectral changes accompanying the applied voltage could be used to produce ionochromic sensor electrodes.The structure of the films has an important impact in the sensing properties of the films and in their stability. The optical and electrochemical sensing properties of Langmuir–Blodgett films are more reproducible than those observed in cast films. This makes films prepared using the LB technique to be preferred as sensing devices. However the casting technique provides a fast method to obtain cheap and highly ordered sensors.     

基于DSP的磁阻传感器导航仪设计

微机电系统的迅猛发展,使得固态传感器具有体积小、重量轻、成本低等特点,研究利用固态传感器来构建低成本、小型化的导航系统成为导航领域的热点之一.通过将捷联惯性导航系统、磁阻/加速度计测姿系统和全球定位系统结合在一起,形成了组合导航系统.静态测试表明,相比单一的导航系统,组合导航系统的性能有了较大的提高.     

Improvement of the NOx selectivity for a planar YSZ sensor

In recent years planar yttria-stabilized zirconia (YSZ) based electrochemical gas sensors for automotive exhaust applications have become a major source of interest. The present work aims to develop a sensor for industrialisation. For this reason planar YSZ-based electrochemical sensors using two metallic electrodes (platinum and gold) were fabricated using screen-printing technology and tested in a laboratory test bench for different concentrations of pollutant gas such as CO, NO, NO₂ and hydrocarbons in oxygen rich atmosphere. It was furthermore shown that the selectivity towards NO_x could be highly reinforced by deposing a catalytic filter consisting of 1.7-4.5 wt.% Pt dispersed on alumina directly on the sensing elements. This filter was characterized by the use of SEM, TPD and XRD.     

Electrochemical sensor for simultaneous detection of ascorbic acid, uric acid and xanthine based on the surface enhancement effect of mesoporous silica

The measurement of ascorbic acid (AA), uric acid (UA) and xanthine (XA) is very important in the clinical diagnosis because many diseases have been found to be associated with their concentrations. Herein, an electrochemical sensor using mesoporous SiO₂ as sensing material was firstly developed for the simultaneous detection of AA, UA and XA. With distinctive properties such as uniform porous networks, large surface area and high sorption ability, the mesoporous SiO₂ sensor exhibits remarkable surface enhancement effect, and greatly increases the response signals of AA, UA and XA. In addition, the electrochemical responses of coexistence of AA, UA and XA were studied, and three well-shaped oxidation peaks were observed at 0.00, 0.25 and 0.63 V. Further studies suggest that their oxidation takes place independently and has no mutual interference. This sensor possesses high sensitivity, and the limit of detections are 3.0 × 10⁻⁶ mol L⁻¹, 1.0 × 10⁻⁷ mol L⁻¹ and 7.5 × 10⁻⁷ mol L⁻¹ for AA, UA and XA. Finally, the mesoporous SiO₂ sensor was successfully employed to detect AA, UA and XA in the urine and blood serum samples.     

Hydrogen sensor based on antimonium pentoxide-phosphoric acid solid electrolyte

A solid composite electrolyte with high proton conductivity based on antimonium pentoxide with additives of phosphoric acid has been obtained. A potentiometric solid-state gas sensor using this electrolyte has been developed for detecting small amounts of hydrogen (10–2000 ppm) in gas mixtures at ambient temperature. The sensor consists of the reference electrode: Ag or Ag/(Ag + Ag₂SO₄), the solid composite electrolyte and H₂-sensitive electrode: Pt or Pd. The electromotive force (e.m.f.) of the sensor varies logarithmically with H₂ concentration for hydrogen partial pressures in the range 100–2000 ppm and depends on the oxygen partial pressure. The slope of e.m.f.-log(pH₂) dependence is 170 and 200 mV for Pt and Pd, respectively, which exceeds the Nernst value, presumably due to the formation of a mixed potential. The sensor can operate at a wide range (20–95%) of a relative humidity.     

Usage of porous Al2O3 layers for RH sensing

Capacitive sensors prepared by microelectronic technology are based on dielectric property changes of thin films upon water vapor uptake, which depends on the surrounding media’s relative humidity content. One of the dielectrics to be used is porous Al₂O₃, obtained by electrochemical oxidation of aluminum under anodic bias. In this paper a sensitive, fast and cheap capacitive sensor has been described and investigated. The work was presented at Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2007, Stresa, Lago Maggiore, Italy, 25–27 April 2007.     

pH sensor based on the crown heteropolyanion K28Li5H7P8W48O184·92H2O immobilized using a layer by layer assembly process

A new sensitive pH sensor based on immobilization of the crown heteropolyanion K₂₈Li₅H₇P₈W₄₈O₁₈₄·92H₂O (P₈W₄₈) on a electrode surface through a layer by layer assembly process is described. The immobilization is based on the electrostatic adsorption of the complex in layers of charged polyelectrolyte poly(allylamine hydrochloride) (PAH). The deposited P₈W₄₈/LBL film was investigated by cyclic voltammetry, potentiometry and electrochemical impedance spectroscopy. Compared to the electrochemical behavior of dissolved P₈W₄₈, a slight shift in the redox peak towards negative potentials is observed, which have been attributed to a slight decrease in the acidity of the interior of the P₈W₄₈/LBL film compared to the testing buffer solution. The relationship between the peak currents of the deposited P₈W₄₈/LBL film and the number of layers is shown to be linear, which demonstrates that equal amounts of P₈W₄₈ are adsorbed in each deposition layer. The P₈W₄₈/LBL modified electrode showed high sensitivities toward pH. Therefore, such electrodes were tested as pH sensors using the titration method. The resulting pH sensor has a detection range of pH 1–13, a sensitivity of 69 ± 2 mV/pH, high repeatability (<3 mV), fast response time (<7 s), low sensitivity toward change in ionic strength and nature of the supporting electrolyte, low internal resistance and a working life time of at least 3 months. Moreover, the sensor is easy to manufacture and can be easily miniaturized for measurements in micro- and nano-systems.     

Tracking control system using image sensor for arc welding

A highly accurate and widely applicable tracking control system which guides a welding torch along a joint line is described. The control system includes a servomechanism, a solid-state image sensor, and an image processor. The solid-state image sensor detects the cross-sectional pattern of the welding groove with a He-Ne gas laser. The image processor, consisting mainly of a microcomputer, processes video information and estimates the position of the welding groove center using a statistical technique. This method of tracking control has been employed in the welding apparatus for penstocks with good practical results.     

智能CO探测器设计

设计了一种基于电化学传感器的CO探测器,探测器使用CO—7G燃料电池型电化学CO传感器,分析了CO电化学传感器的工作原理与探测器的电路组成。其中,探测器的硬件电路由电化学传感器的信号调理电路、数码管显示电路、单片机数据处理与控制电路、4~20mA模拟输出电路、继电器控制电路等组成。对采集的数据采用均值滤波算法,提高了系统的灵敏度,减少了探测器的响应时间,降低了误报警率。实验结果表明:该CO探测器的误差小于0.001 16 mg/L,在1个月的时间内其误差没有超过0.005 82 mg/L。该CO探测器灵敏度高,响应时间短,测量精度高,稳定性好,具有很高的实用价值。     

Ionic liquid thin layer EQCM explosives sensor

An integrated sensor that combines electrochemical and piezoelectric transduction mechanisms into a single miniaturized platform was developed and validated for the detection of nitro aromatic compounds such as ethyl nitrobenzene (ENB) and dinitrotoluene that are analogues of redox active explosives. An ionic liquid (IL) BMIBF₄ was used as both the electrolyte and the sorption solvent for the two-dimensional electrochemical and piezoelectric gas sensors.The electrochemical behaviors of these nitro compounds in BMIBF₄ were studied by cyclic voltammetry, differential pulse voltammetry and square wave voltammetry, in parallel. The electrochemical properties of these compounds resembled the electrochemical reduction processes in their aprotic solutions, showing first a reversible reduction process and then subsequently an irreversible reduction processes. The redox properties of these compounds also depend on the number of nitro groups and the position of the nitro groups on the benzene ring. Square wave voltammetry was used to quantitatively analyze the ENB in BMIBF₄. Reduction peaks in the square wave voltammetric curves could be obtained when the concentrations were at ppm level. A small amount of moisture in the IL electrolyte did not significantly affect the redox behaviors. Piezoelectric quartz crystal microbalance (QCM) electrodes and the electrodes for amperometry were fabricated on a single piece of quartz plate. Detection of the volatile ENB vapor with this integrated EQCM chip was tested with both QCM and amperometric methods. The sensor's signal was related quantitatively to the ENB vapors adsorbed in BMIBF₄ from air. Combining amperometric and QCM detection simultaneously can cross-validate the detection technology, reduce false positives and false negatives and increase the accuracy of the detection.