Sensors and Actuators最新文献

A thin-film zinc oxide chemical sensor with integrated heater and temperature sensor for the measurement of oxygen in water is described. The principle of operation and the fabrication steps are given. The sensor operates at a temperature near 300 °C. A simple reaction model explains the linear increase of the sensor resistivity with increasing oxygen concentration and the logarithmic time response. The measurement of the oxygen concentration in water is demonstrated with an arrangement incorporating a membrane and a low nitrogen flow.

A study is carried out to evaluate the ability of boron nitride thin films to act as ultraviolet - sensitive semiconductors. Boron nitride thin films are sputter deposited from a BN target in Ar, Ar/N₂ and N₂ discharges. Inter-digital electrodes of various geometries and varying spacing are laid out photolithographically. Results of I(dark) verus voltage and I(u.v.) versus V in the temperature range −40 °C to 80°C are presented here. Preliminary studies on the effect of doping boron nitride films with aluminum and zinc impurities do not yield significant results.

A silicon chip fabricated with standard IC technology has been used to monitor air flow in a pipe in a non-invasive way through the pipe wall. Flow detection is based on the measurement of a temperature difference on the chip, which is heated with respect to the flow. The device is direction sensitive and has a zero output in the absence of flow. In the experiment the detection threshold for air flow is approximately 0.1 m/s.

The gas-sensing characteristics of Li⁺-doped and undoped ZnO whiskers were investigated for 1% carbon monoxide, 1% hydrogen and 1% methane in air as a function of the operating temperature between 200 °C and 700 °C. The gas sensitivities of undoped ZnO whiskers were negligibly small to the sample gases because of their extremely low resistivities in air. However, the sensitivity was significantly enhanced by Li⁺-doping of the whiskers. The values of the enhanced sensitivities were comparable to those of the as-grown [101] SnO₂ whiskers. But there was no definite correlation between the sensitivity and the morphology of the Li⁺-doped ZnO whiskers.

A batch-fabricated non-reverse valve has been manufactured in silicon with micromachining tools, i.e., electrochemical doping-selective etching in KOH and anisotropic etching in EDP. The valve simply consists of a cantilever beam that can take two positions, one letting a gas or a fluid through the valve, the other forced by the pressure to close on of the two inlet holes.

The valve features fast response, small size, batch manufacturing and small dead volumes, and also shows an application of the mechanical strength of silicon. A simple theory is used to predict the basic characteristics of the valve.

A passive optical linear displacement transducer for aerospace applications has been developed. The principle of operation is the wavelength encoding of the position of a reflective Gray code. The design allows the sensor to be passively interrogated using only two optical fibres. The example described here has a 38 mm stroke with a 38 μm resolution. The same principle can be applied to longer stroke linear sensors and rotary displacement sensors.

The optical design is based on the wavelength division of a broad-band source into 11 spectral bands, which are directed onto a reflective Gray code. The reflected light is decoded by a second wavelength division multi-plexer in the electronics housing and the position of the Gray code is determined by the respective on/off states of the channels. The transducer has been designed to operate in the harsh aerospace environment. The housing is of rugged construction to withstand the standard range of temperature, vibration, pressure and contamination conditions.

General analyses of the piezoresistance, taking into consideration the effect of shear stress, have been made for circular, square and rectangular silicon diaphragms. The analyses can lead to the design of a full-bridge pressure transducer on a (110) circular diaphragm with 30% higher sensitivity than previous designs. Experimental results showing the dependence of the piezoresistive sensitivity on the inclination angle agree well with the results of general analyses. Experiments show that the information obtained might also be useful in a new application where the non-linearity of transverse voltage of a four-terminal resistor can be compensated for by its own piezoresistive sensitivity of resistance.

The gas-sensing properties of metal-oxide semiconductors have been studied extensively over the past twenty years. There has been renewed interest recently in their application in differential gas sensor arrays and the association with cellular automata and neural networking methods. A diffusion-based analytical model is considered that relates the electrical conductance of a porous thick-film semiconductor gas sensor to its physical and geometrical properties. The theoretical responses of sensing elements with several configurations have been derived, and compared with experimental data on tin-oxide sensors exposed to simple alcohols. The results obtained broadly agree with the predictions of the basic model at low gas concentrations (<50 ppm); but, at higher gas concentrations (>50 ppm), the model needs to incorporate a dependence of the gas diffusivity upon concentration.

The effect of changes in sensor design on the response is considered, and the optimum coplanar electrode configuration is obtained when the electrodes lie a distance equal to the electrode separation below the semiconductor surface. Thus, the use of a fully-developed analytical model may well lead to improvements in sensor design and to modifications in the decision criteria currently utilized in pattern recognition techniques.

The effects of H₂ adsorption on the conductivity of pressed pellets of a Rh/TiO₂ polycrystalline material are studied as a function of the degree of hydroxylation and reduction of the TiO₂ support.

The process involved in the enhancement of conductivity induced by the adsorption of H₂ at 295 K is examined in detail with the aid of different techniques including e.p.r., n.m.r. and i.r. spectroscopies. The results show that this material can be an efficient sensor for H₂ at 295 K in ambient atmosphere. A mechanism is proposed for the behaviour of this H₂ sensor, which involves electron and proton transfer from the Rh metal to the TiO₂ semiconductor in the presence of H₂.

Both numerical analysis using the finite differential method and experimental measurements are performed for varius geometric designs of rectangular four-terminal pressure gauges to assess the short-circuiting effect of current contacts and sensor contacts on the sensitivity of the sensor. The agreement between the calculated and experimental results is quite good. Based on the results obtained, geometric design rules are suggested: the length:width ratio of the body should be 1:1 to 1:2 and the length:width ratio for the signal conducting arms should be around 1:1.