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.

Deep understanding of physical properties of the materials under the influence of radiation is vital for the effective design of dosimeters. Detection of radiation is based on the fact that both the electrical and the optical properties of the materials undergo changes upon the exposure to ionizing radiation. Thin film technology is considered as cost-effective alternative for a broad range of sensors, as a wide range of films with mixed composition call be produced. This paper reports on gamma radiation sensing properties of thermally evaporated NbO(2) thin films. It was experimentally confirmed that the manufacturing parameters of the films affected their gamma radiation sensitivity.

Ozone sensing properties of mixed oxides of In 2 O 3, ZnO , and SnO 2 in the form of thin films are explored. Exposure to ozone causes defects in the materials, and subsequently causes changes in the materials properties. In this work, a cost-effective, room temperature, real-time ozone monitoring device has been developed. The fabricated sensors are capable of detecting threshold ozone safety levels proposed by the World Health Organization (WHO) while operating at room temperature. Room temperature operation offers many advantages over high temperature operation, such as reduced power consumption, reduced fabrication costs, and ease of implementation into portable devices, such as laptops and mobile phones. The fabrication of these sensors was carried out by means of an Edwards E306A Coating System. Various mixtures of In 2 O 3, ZnO , and snO 2 were deposited in a rectangular pattern on top of copper interdigitated electrodes. X-ray Photo Spectroscopy (XPS) analysis showed that there were levels of impurities in the sensor samples, which were dependant on the fabrication process and parameters. XPS analysis also gave a detailed account of the shifts in binding energies of the thin oxide layers. The results presented show that the highest response to environmentally relevant ozone concentrations is achieved with a very thin sensing layer and a high deposition rate. The performance of the sensors has been investigated and compared.

Ozone sensing properties of mixed oxides of In2O3, ZnO, and SnO2 in the form of thin films are explored. Exposure to ozone causes defects in the materials, and subsequently causes changes in the materials properties. In this work, a cost-effective, room temperature, real-time ozone monitoring device has been developed. The fabricated sensors are capable of detecting threshold ozone safety levels proposed by the World Health Organization ( WHO) while operating at room temperature. Room temperature operation offers many advantages over high temperature operation, such as reduced power consumption, reduced fabrication costs, and ease of implementation into portable devices, such as laptops and mobile phones. The fabrication of these sensors was carried out by means of an Edwards E306A Coating System. Various mixtures of In2O3, ZnO, and snO(2) were deposited in a rectangular pattern on top of copper interdigitated electrodes. X-ray Photo Spectroscopy (XPS) analysis showed that there were levels of impurities in the sensor samples, which were dependant on the fabrication process and parameters. XPS analysis also gave a detailed account of the shifts in binding energies of the thin oxide layers. The results presented show that the highest response to environmentally relevant ozone concentrations is achieved with a very thin sensing layer and a high deposition rate. The performance of the sensors has been investigated and compared.

Decomposition of food is caused by microorganisms, which produce odorous gases as a result of metabolic products. The early detection and control of these organisms provides a longer shelf life and prevents food poisoning. The identification of aerobic and anaerobic bacterial cultures in food can take up to 3 days or longer using existing laboratory techniques. Conducting polymer nanocomposite (CPC) materials are of special interest to the gas sensor industry where arrays of polymer composites may be used to detect gases and odours. These composite gas sensors operate at room temperature, which provides an advantage over thick film metal oxide gas sensors. CPC sensors are composed of conducting particles embedded into an insulating polymer matrix. The resistance changes of the sensors in the array are used to produce a pattern that corresponds to the vapour under investigation. This study presents the use of an array of CPC sensors for real time analysis and quantification of the odours given off a selection of food borne pathogens including Salmonella spp., Bacillus cereus and Vibrio parahaemolyticus.

Thin films of Indium-zinc-tin oxide have been prepared by Vacuum Thermal Evaporation (VTE). The sensing characteristics of these films to environmentally relevant ozone concentrations were studied at room temperature. The effects of film thickness, deposition rate and annealing were investigated. The resistance of the thin film was found to be inversely proportional to the deposition rate. The highest sensitivity of the ozone sensors was found at a deposition rate of 1.2 nm/s - 1.4 nm/s. In addition the O 3 sensors were found to perform best with a 40 nm thick sensing layer. ln 2 O 3 , ZnO and SnO 2 were deposited on alumina substrates containing interdigitated electrodes by means of VTE. These results have shown that In 2 O 3 :ZnO:SnO 2 thin films prepared by VTE method are promising for room temperature ozone sensing.

It is important to know the behaviour of materials under the influence of radiation for the effective design of novel sensor systems. Optical properties of bismuth germinate (Bi4Ge3O12-BGO) thin films were investigated in terms of their perception to gamma radiation exposure. An Edwards E306A vacuum thermal coating system was used for thin films deposition. BGO films with a thickness of 200 nm were exposed to a disk-type (CS)-C-137 gamma radiation source with an activity of 370 kBq. Optical properties of the films were investigated using CARY IE U-V-Visible Spectrophotometer. Calculated optical band gap for as-deposited BGO thin film was 1.95 eV. Gamma radiation induced changes in the optical properties of thin films, which could be explained by the variation in the degree of disorder. From the density-of-state model, it is known that optical band gap decreases with an increasing degree of disorder of the amorphous phase.Electrical properties of BGO thin films were recorded in real time using a low power capacitive interface system with a high resolution, which is based on Delta-sigma modulator. At doses from 0 to 1.5 mGy little if any changes in the capacitance were measured. This could be explained by co-existence of two processes, namely creation and annihilation of defects under the influence of radiation. After a threshold dose of 1.5 mGy creation of defects becomes more prevailing and the BGO film capacitance has gradually increased in value from 2.97 pF to 7.09 pF after irradiation with a 2.44 mGy dose. (C) 2007 Elsevier B.V. All rights reserved.

A new type of highly sensitive ozone (O3) metal oxide gas sensor has been developed. Various mixtures of ln2O3, ZnO and SnO2 were deposited on alumina substrates containing indigitated electrodes by means of vacuum thermal evaporation (VTE). Deposition rate of the sensing layer was varied from 0.3 nm/s-1.4 nm/s. The highest sensitivity of the sensors was found at a deposition rate of 1.2 nm/s-1.4 nm/s. In addition the O3 sensors were found to perform best with a 40 nm thick sensing layer. With such sensors, environmentally relevant ozone concentrations can be measured (0-500 ppb (parts per billion)). Different combinations of this material were investigated and compared focusing on the sensitivity and performance when exposed to ozone. Most of the current metal oxide ozone sensors on the market have the disadvantage of requiring operation at elevated temperatures (200degC-600degC). Room temperature operation has some major advantages over elevated temperature operation such as, reduced fabrication costs, reduced operating costs, as well as ease of implementation into portable/handheld devices.

In this work, the pressure sensing properties of polyethylene (PE) and polyvinylidene fluoride (PVDF) polymer films were evaluated by integrating them with a wireless data acquisition system. Each device was connected to an integrated interface circuit, which includes a capacitance to frequency converter (C/F) and an internal voltage regulator to suppress supply voltage fluctuations on the transponder side. The system was tested under hydrostatic pressures ranging from 0 to 17 kPa. Results show PE to be the more sensitive to pressure changes, indicating that it is useful for the accurate measurement of pressure over a small range. On the other hand PVDF devices could be used for measurement over a wider range and should be considered due to the low hysteresis and good repeatability displayed during testing. It is thought that this arrangement could form the basis of a cost-effective wireless monitoring system for the evaluation of environmental or physiological processes.

This work investigates the effects of gamma-rays on the optical properties of pure and mixed-oxide materials, namely MnO and TeO 2 for their possible application as thin film optical gamma radiation sensors. The values of the optical band gap E opt were obtained in view of the Mott and Davis theory. All samples showed a decrease in E opt with an increase in radiation dose to a certain level, which was found to be composition dependent. Films with 100 wt.% MnO exhibited the highest sensitivity to low doses of radiation, showing a strong decline in the optical band gap value from 0.64 eV before irradiation to 0.54 eV after a dose of 1.14 mGy. It was experimentally confirmed that both the sensitivity and the working dose range of radiation sensors can be controlled by the composition of the materials used

The effect of surfactants on the properties of poly(vinyl acetate) (PVAc)/carbon black (CB) composite gas sensors was examined. Percolation curves of the composites with and without surfactant were prepared. The percolation curves of surfactant treated composites showed that the resistivity of the composite was increased due to better dispersion of the CB and also the prevention of the CB from reagglomerating after shear mixing. TEM images were used to investigate the effect of adding surfactant to the composites. These images confirmed that the surfactants significantly improved the level of dispersion of CB in the composites and prevented reagglomeration of the CB. The response (ΔR/R%) was increased by addition of surfactants and implies that increased dispersion increases response to methanol vapour.

Presented in this paper is a process for manufacturing copper electrode patterns on alumina substrates using thin film deposition, spin coating and printed circuit board (PCB) etching techniques. The process was used for the design and manufacture of an array of gas sensors for use in an electronic nose system. This approach was executed in three phases. Firstly a 500nm layer of copper was deposited onto the alumina substrate. Secondly photoresist was applied by spin coating onto the copper layer and finally the PCB etching process was used to achieve the final electrode pattern. Conducting polymer composite materials were deposited onto the resulting electrode patterns producing an array of sensors for vapour detection. The sensor array showed good responses to Propanol at concentrations ranging from 5000ppm to 30000ppm with fast recovery times. The sensor array was slotted into an electronic nose system and an illustrative analysis of the sensor array's ability to discriminate between different solvents was carried out with promising results

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.

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.

This work investigates the effects of /spl gamma/-rays on the optical properties of pure and mixed oxide materials, namely MnO and TeO/sub 2/, for their possible application as thin film optical gamma radiation sensors. The values of the optical band gap E/sub opt/ were obtained in view of the Mott and Davis theory. All samples showed a decrease in E/sub opt/ with an increase in radiation dose to a certain level, which was found to be composition-dependent. Films with 100 wt.% MnO exhibited the highest sensitivity to low doses of radiation, showing a strong decline in the optical band gap value from 0.64 eV before irradiation to 0.54 eV after a dose of 1.14 mSv. It was experimentally confirmed that both the sensitivity and the working dose range of radiation sensors can be controlled by the composition of the materials used.

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.

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.

Thick films of nickel phthalocyanine (NiPc) were fabricated using the screen-printing technique. The effects of gamma- irradiation on the optical and electrical properties of these films were studied in order to establish their suitability for dosimetry applications. The analysis of the optical properties were carried out in view of the models proposed by Mott & Davis. The experimental data have shown the predominance of the direct allowed transition for the as printed NiPc thick film and the indirect allowed for the irradiated samples. The energy values of the optical band gap showed irregular slight decreases when the NiPc thick films were irradiated the as-printed and irradiated Ag/MPc/Ag devices demonstrated a Schottky conduction mechanism. The values of the absorbance and the capacitance of the NiPc thick films showed a highly consistent and continuous linear changes when exposed to various doses of gamma-radiation.

Thermally evaporated thin film PN-junctions with a metal/Sulfur/Copper- phthalocyanine/ metal structure were fabricated and the effects of gamma-radiation on their optical and electrical properties were investigated for the purpose of dosimetry applications. The optical band gap showed slight changes in value when irradiated. The as-deposited and irradiated Al/S/CuPc/Al devices demonstrated Zener diode breakdown under reverse bias voltage and a space-charge-limited conduction mechanism under forward bias. The absorbance, the density of colour centre and Zener break down current exhibited a highly consistent linear response to gamma-radiation exposure. However, the best fit for the experimental data was obtained using the Zener breakdown current for gamma-ray dose assessment.

Cobalt phthalocyanine films were screen-printed on glass substrates using polymer thick film technology (PTF). The films were treated with various doses of gamma-radiation from Cs-137 standard source with a dose rate of 6.0 Gy/min. Measurements for I-V characteristics were performed and the capacitance values were recorded for a numb er of irradiated Ag/CoPc/Ag devices. The electrode-limited conduction mechanism, namely, Schottky effect was shown to be predominant for both the as-printed and irradiated samples. The ultraviolet/visible spectra were recorded for the as-printed and irradiated thick films at room temperature. It was found that the optical, density increased significantly as the dose of gamma-ray was increased The optically induced electronic transitions were analysed in view of the models proposed by Mott & Davis resulting in a predominance of a direct allowed transition for the as-printed CoPc thick film and indirect allowed for the irradiated samples. In addition, there was small and insignificant decrease in the optical band gap. The dosimetric properties were established by two methods: firstly by the continuous linear decrease in the values of the capacitance and secondly by the continuous linear increase in the absorbance over a dose range of 5.4-27.0 kGy.