Fire detection with low power fet gas sensors

Gas sensors based on hybrid suspended gate field effect devices are used for the detection of specific gases occurring in test fires. This sensor type can be operated with a power consumption < 1 mW and is therefore best suited for the use in fire detectors. Different floating gate FET (FGFET) sensors designed for the detection of CO, CO₂ and NO₂ were tested in standard test fires regarding EN54. Significant sensor signals were obtained for all test fires enabling a reliable and fast detection of fires. In addition, a separation of fire types is possible by signal evaluation combining signals of different sensors.     

An optical IR-source and CO2-chamber system for CO2 measurements

A new silicon IR source and CO₂-chamber system for measurement of CO₂ concentration is presented. The micromachined IR-source, which consists of four groups of polysilicon filaments coated with silicon nitride suspended across a KOH-etched cavity, is used to generate two switched “sample” and “reference” beams. The electrically modulated sources present a modulation time of 10 ms and a power consumption of 1 W. The CO₂ chambers, placed beneath the reference sources, are used to produce a reference beam for long term stability and compensation against cuvette window contamination. They consist of 1-mm-deep micromachined cavities in which CO₂ is encapsulated during an overpressure anodic bonding procedure. Silicon dioxide is used as an antireflective coating to optimize the filter's optical characteristics. Numerical simulations of the filters are presented and show good agreement with the measurements. The IR sources and the CO₂ filters are both fabricated at wafer level. Using the presented IR-sensor system, measurements with a 9-mm-wide test channel show high CO₂-sensitivity for CO₂ concentrations between 0 and 10% confirming that the stringent requirements for this respirator application can be fulfilled     

High-performance solid-electrolyte SOx sensor using MgO-stabilized zirconia tube and Li2SO4---CaSO4---SiO2 auxiliary phase

Solid-electrolyte-based electrochemical SO_x sensors fabricated with MgO-stabilized zirconia and Li₂SO₄---CaSO₄---SiO₂ (4:4:2 in molar ratio) exhibit fairly good sensing characteristics for 2–200 ppm SO₂ in air at 600–750 °C, with the e.m.f. responses following the Nernst equation for the two-electron reduction of SO₂. The 90% response and 90% recovery times to 20 ppm SO₂ are 10 s and 7 min at 650 °C, and 10 s and 3 min at 700 °C, respectively. It is further found that the sensor exhibits excellent selectivity to SO_x in the coexistence of CO₂ and NO_x, and good long-term stability. The sensor is simple in structure, easy to prepare, and quite tough chemically and mechanically. These features should ensure practical use for this SO_x sensor.     

Potentiometric CO2 gas sensor with lithium phosphorous oxynitride electrolyte

Potentiometric cell, Au/LiCoO₂ 5 m/o Co₃O₄/Li_2.88PO_3.73N_0.14/Li₂CO₃/Au, has been fabricated and investigated for monitoring CO₂ gas. A LiCoO₂–Co₃O₄ mixture was used as the solid-state reference electrode instead of a reference gas. The idea is to keep the lithium activity constant on the reference side using thermodynamic equilibrium at a given temperature. The thermodynamic stability of the reference electrode was studied from the phase stability diagram of Li–Co–C–O system. The Gibb’s free energy of formation of LiCoO₂ was estimated at 500°C from the measured value of the cell emf. The sensors showed good reversibility and fast response toward changing CO₂ concentrations from 200 to 3000 ppm. The emf values were found to follow a logarithmic Nernstian behavior in the 400–500°C temperature range. CH₄ gas did not show any interference effect. Humidity and CO gas decreased the emf values of the sensor slightly. NO and NO₂ gases affect this sensor significantly at low temperatures. However, increased operating temperature seems to reduce the interference.     

Preparation of gas sensors via dip-pen nanolithography

In the present work, a conducting polymer, doped polypyrrole, was used to develop a gas sensor by dip-pen nanolithography (DPN). The response time of the sensor to 18 ppm CO₂ was 9 s. The sensor response increased linearly as the CO₂ concentration increased. A possible mechanism for the CO₂ sensing was discussed.     

Calculation of phase diagrams of the reciprocal quaternary systems Li, Na, K/CO3, SO4; Li, Na/CO3, SO4, OH; Li, K/CO3, SO4, OH and Na, K/CO3, SO4, OH

Phase diagrams of the quaternary reciprocal salt systems Li, Na, K/CO₃, SO₄; Li, Na/CO₃, SO₄, OH; Li, K/CO₃, SO₄, OH; and Na, K/CO₃, SO₄, OH (the last three up to 10 mol % hydroxide) were calculated from the optimised thermodynamic properties of their sub-systems via the Conformal Ionic Solution Theory by means of a computer program designed for the purpose.     

MEA-AMP混合醇胺捕集烟气二氧化碳过程分析

本文根据焦化烟道气实际数据,应用流程模拟软件Aspen Plus模拟分析了MEA吸收剂以及MEA和空间位阻胺AMP混合吸收剂捕集烟道气中CO₂的吸收解吸效果。结果表明,混合胺浓度30 wt%（摩尔比MEA:AMP=1:1）吸收剂的吸收效果较好,为了进一步考察该种配比混合胺吸收剂的吸收、解吸特性,对其进行了灵敏度分析,并选取了25 wt%MEA为基准吸收剂,对比分析了进料温度、解吸塔再沸器热负荷和解吸塔压力对吸收解吸效果的影响,当吸收剂进料温度40℃时,单一MEA吸收剂吸收CO₂效率86.8%,混合胺的吸收率89.6%:2种吸收剂达到55%的解吸率,单一MEA吸收剂工艺再沸器热负荷为4500 kW,混合胺吸收剂工艺再沸器热负荷为3000 kW;当解吸塔压力1.5 bar时,单一MEA吸收剂对CO₂解吸率52.4%,混合胺吸收剂的解吸率55.8%,由对比结果得出混合胺（摩尔比MEA:AMP=1:1）的吸收、解吸效果均优于单一25 wt%MEA吸收剂。     

Continuous flow polymerase chain reaction using a hybrid PMMA-PC microchip with improved heat tolerance

Recently, polymeric materials have been explored as more versatile alternatives for the fabrication of polymerase chain reaction (PCR) microchips. Poly(methyl methacrylate) (PMMA) is a popular substrate material due to its high mechanical stability, good chemical properties and most importantly, its suitability for cheap and simple CO₂ laser ablation. However, it has a low glass transition temperature (T_g) of 105 °C, which is just above the denaturation temperature for PCR, thus the bond integrity is compromised. Polycarbonate (PC) is preferred as a substrate for PCR microchip as it has a higher T_g of 150 °C; but since its thermal properties are not suitable for CO₂ laser light, the more expensive excimer laser has to be employed. Here we report a novel hybrid PMMA-PC microchip by bonding a PC cover plate with a PMMA substrate containing microchannel which is fabricated by CO₂ laser ablation. This hybrid microchip has improved heat tolerance, such that the bonding integrity is sustained at the denaturation temperature. DNA amplification is found to be more efficiently performed in a PMMA-PC microchip than in a PMMA-PMMA microchip.     

Characterization of ozone sensors based on WO3 reactively sputtered films: influence of O2 concentration in the sputtering gas, and working temperature

We report on electrical responses of tungsten oxide thin film ozone sensors based on a tungsten trioxide (WO₃)/tin oxide (SiO₂)/Si structure with interdigitated Pt electrodes. The influence of O₂ concentration in the sputtering gas and working temperature of the sensor are investigated. Sensitivity to ozone increases with O₂ content in the sputtering gas. It reaches its highest value for sensors fabricated with 50% O₂. For these sensors, the best ozone sensitivity and shortest response and recovery times are obtained at a working temperature of 523 K. Ozone sensitivity is compared to other ozone sensors.     

Performance of GaAs microbridge thermocouple infrared detectors

GaAs microbridge thermocouples with lengths ranging from 40 to 650 μm and operating at room temperature have been fabricated for the detection of infrared radiation. A CO₂ laser of a 10.6 μm wavelength was used to characterize the performance of the detectors in air and in vacuum. A responsivity of 4.2 V/W with a corresponding detectivity D*=8×10⁶ cm Hz^1/2/W and a time constant of 2.2 ms have been measured in vacuum for 650-μm-long bridges, and a shorter time constant of 50 μs was obtained for 40-μm-long bridges. An analytic thermal transport model has been used to simulate the operation of the sensors. The heat-transfer coefficient has been evaluated by comparing the data from air and vacuum measurements. The spectral response and the absorbance of the microbridge have also been presented