Seamus Clifford

A review of gas sensors employed in electronic nose applications

This paper reviews the range of sensors used in electronic nose (e‐nose) systems to date. It outlines the operating principles and fabrication methods of each sensor type as well as the applications in which the different sensors have been utilised. It also outlines the advantages and disadvantages of each sensor for application in a cost‐effective low‐power handheld e‐nose system.

A review of digital data acquisition hardware and software for a portable electronic nose

This paper discusses the digital hardware and software that is required for data acquisition in a portable electronic nose (e‐nose) system. A review of current e‐nose systems is presented highlighting the methods employed by these systems to acquire the data from the sensor head.

Front‐end signal conditioning used for resistance‐based sensors in electronic nose systems: a review

The overall performance of an electronic nose system will depend on the individual performance of its constituent elements. Although often overlooked, it is clear that careful design/selection of the front‐end signal conditioning circuit is of critical importance if optimal performance of the odour sensing system is to be achieved. In this paper circuits are reviewed, which have been employed as front‐end signal conditioners for resistance‐based sensors in electronic nose systems, with many of the conclusions drawn being equally applicable to other resistor sensors. The relevant equations governing the behaviour of each circuit methodology are derived and advantages and disadvantages are discussed. The performance of the circuit is then quantitatively assessed in a specific test case, in which the maximum sensitivity of the circuit is calculated in relation to the task of interfacing to a theoretical thin‐film conducting‐polymer sensor.

Influence of the Poly(Vinyl Butyral) Binder in Screen-Printed Thick-Film Gas Sensors Containing

This study investigates gas sensitive resistors fabricated by screen-printing inks created from a mixture of NiO-TiO2 and containing a poly(vinyl butyral) binder for the detection of alcohol vapors at room temperature. It was found that these films exhibited a significant resistance change in response to the vapors, while also displaying an inherent selectivity, proving most sensitive to toluene and propanol vapor; with comparatively low responses exhibited towards ethanol and methanol vapors. It is proposed that swelling of the polymer binder used in the fabrication of the NiO-TiO2 thick-films, rather than oxygen ion induced majority carrier modulation in the oxides, is the significant factor in causing the electrical resistance of the films to increase upon exposure to the organic solvent vapors. Very fast response and recovery times of 9 s and 16 s, respectively were recorded for the devices upon exposure to 4000 ppm step changes in propanol concentration. For comparative analysis, poly(vinyl butyral)/carbon black composites were fabricated from a by a drop-coating technique. The superior sensitivities and response times of the screen-printed sensors were attributed to the (SEM confirmed) highly porous structure attained by the thick-film devices, caused by the excessive free-volume induced in the polymer-binder matrix by the oxide materials. The results suggest that the effects of the polymer binder, even when present in comparatively small amounts, cannot be ignored in certain sensing applications

{\rm NiO}{\hbox{-}}{\rm TiO}_{2}

The response of screen-printed thick-films of NiO/TiO/sub 2/ to organic solvent vapours was studied. It was found that these films displayed a significant resistance change in response to the vapours even at room temperature. The sensors displayed an inherent selectivity, proving most sensitive to toluene and propanol vapour; with comparatively low responses exhibited towards ethanol and methanol vapours. Very fast response and recovery times of 9 s and 16 s respectively were recorded for the devices upon exposure to 4000 ppm step changes in propanol concentration.

Oxides

Abstract In this work, an investigation of the pressure-sensing properties of a silicone rubber was conducted. Small amounts of carbon black were added to the silicone during fabrication and the effect on the sensitivity was explored. A full investigation of the mechanical and electrical properties of each composition shows that adding carbon black to the material greatly increases its sensitivity to pressure. This increase in sensitivity appears to be related to improvements in the material’s permittivity, which increases with carbon loading.

NiO-TiO/sub 2/ thick-films for detection of alcohol vapours at room temperature

The effect of ethanol vapour and temperature was investigated on gas sensors fabricated from poly(vinyl acetate)/carbon black composites based around a predetermined percolation threshold. Samples with 8% carbon black loading displayed the best response to the ethanol vapour. Typical response and recovery times of 140s and 45s respectively were recorded. In addition, bridge structures were fabricated, where all four resistive elements were prepared from the same composite material and in which a novel passivation process was employed. It was observed that these bridge structures were significantly less affected by variations in temperature in comparison to the single sensor structures.

Novel silicone-based capacitive pressure sensors with high sensitivity for biomedical applications

In/sub 2/O/sub 3/ and SiO mixtures, in thick film pn-junction form, were investigated for /spl gamma/-radiation dosimetry purposes. Results show that the current increased with an increase in radiation dose to a certain level, exceeding this level resulted in device damage. The performance parameters of the devices, such as sensitivity to /spl gamma/-radiation exposure and working dose region, were found to be highly dependant on the composition of the materials used. To cover a wider range of radiation, the approach of using sensor arrays was utilized, where the sections of the radiation nose system differ in material composition. A dynamic selection of the multiple sensors of various sensitivity and accuracy range was implemented by applying an error and pattern recognition analysis, which maximizes measurement accuracy. The algorithm was optimized for efficiency, which allows its use it in small devices, like handheld computers.