Sensors and Actuators最新文献

A prototype optical fibre thermometer suitable for gas turbine engines has been developed. The working principle of the sensor is based on the detection of black-body radiation from a cavity. A sensor has been designed and constructed. In order to establish the structural intergrity of the sensor before it is exposed to engine environments, a series of vibration and temperature tests has been carried out. These tests are made to conform to the standard environmental specifications for equipment to be used in military applications. The results of these tests are presented, together with the accuracy and resolution of the sensor.

A simple but effective method for the fabrication of reusable dual-microband electrodes for use as gas sensors based on electrochemically polymerized conducting polymers is described. The electrodes are made by sputtering gold onto both sides of thin (12 μm) Mylar films and then encapsulating the resulting gold/Mylar/gold sandwich so that only the edge is exposed. The resulting electrodes are characterized using cyclic voltammetry, a.c. impedance and chronoamperometry.

Following the electrochemical deposition of polypyrrole onto the dual-microband electrodes, they can be used as gas-sensitive chemiresistors. Preliminary results for the change of resistance of such a device on exposure to methanol vapour are presented.

Infrared spectra of Pt/ZnO in vacuum, in H₂ and O₂ are discussed in comparison with those of pure ZnO, Cu/ZnO and Ru/ZnO. An electron transfer from the ZnO donor centres is put in evidence. The growth of a strong absorption band in H₂ is due to the repopulation of the ZnO donor levels as a consequence of the spill-over of H atoms from the metal particles to ZnO, where they are adsorbed in protonic form. The rate of production and depletion of this absorption in H₂ and O₂ atmospheres indicates that the rate-determining steps in the room-temperature sensing are the dissociations of the molecules on the metal catalysts.

With advanced micromechanical devices the ability to form, with highly reproducible results, useful etch-stop layers is becoming increasingly important. A novel etch-stop method of fabricating thin silicon structures is proposed. The approach is based on the use of buried compound layers produced by the implantation of reactive O⁺ and N⁺ ions into single-crystal silicon. The etch-stop properties of these layers are assessed and a conceivable mechanism for the decrease of etch rate for ethylenediamine—pyrocatechol—water(EPW) solution is outlined. It is demonstrated that such substrates incorporating implantation-synthesized oxide or nitride layers have relevance to the micromachining of silicon.

Results are reported for the ultra-high-vacuum (UHV) preparation of PbPc thin-film samples (d < 1000 nm) on single-crystal SiO₂ and Al₂O₃ substrates. During the first exposure of the UHV-prepared thin-films to air, their conductivities increase by orders to magnitude due to incorporation of O₂ in the bulk. In addition, small amounts of surface OH groups are formed, which are a prerequisite for subsequent reversible conductivity changes in sensor applications. The elemental composition and changes in the valence-band structure are characterized by XPS and UPS. Corresponding conductivity measurements show reverible changes upon O₂ exposure at temperatures between 423 and 473 K. Optimized measuring conditions for the use of these thin-film structures for quantitative O₂ and NO₂ monitoring are reported.

A new ammonia-sensitive MOSFET based on the use of a sputtered PdIr alloy gate has been developed. The sensitivity and selectivity of this device are compared with the data reported by others. It is shown that the PdIr alloy-gate MOSFETs have a good selectivity for ammonia.

An i.r. study is made of the room-temperature adsorption of pure CO, H₂ and successive O₂ interaction on SnO₂ powder at different degrees of hydroxylation. Both sharp bands, due to different adsorbed carbonate-like species produced by surface reactions, and a very broad absorption, due to electron transition from the second level of oxygen vacancies to the conduction band, are measured in the case of the CO interaction. A wider variety (bicarbonates, unidentate and bidentate carbonates) and larger amounts of such intermediates are measured on highly-hydroxylated surfaces (h.h.s.) than on less-hydroxylated (l.h.) ones. At the same time, the intensity of the electronic transition is higher for h.h.s. than l.h. ones. A very broad absorption due to the same electronic transition can be detected for H₂ admission; however, no increase in the band intensities due to the vibrations of surface hydroxyls can be measured.

Conducting films of polypyrrole deposited across a narrow gap between two gold electrodes can be used to sense methanol vapour by following changes in the resistance of the polymer. The response is rapid and reversible at room temperature. The effects of the concentration of methanol, the operating temperature and the film thickness on the response have been investigated. The data are consistent with a model in which the methanol interacts with sites either on, or within, the polymer. Simple gas sensors of this type are promising candidates for use in an ‘intelligent’ gas sensor based on an array of gas-sensing elements.

The angle of deflection from the horizontal position can be detected by a sensor that consists of two phototransistors placed symmetrically near a light-emitting diode and immersed in a suitable liquid. In this arrangement the transistors are illuminated by the light reflected from the air-liquid interface. When the sensor is in the horizontal position, both transistors receive equal fluxes, causing the net electrical signal to be zero. In any other position the symmetry is interrupted and the signal becomes dependent upon the tilt angle. The characteristics of the sensor is S-shaped, but has a nearly linear part around the origin. The sensor response there is about 42 m V/degree.