E. Moore

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.

Custom electronic nose with potential homeland security applications

Detailed in this work is the design and development of a handheld electronic nose nose with an array of conducting polymer composite film sensors interfaced to a Compaq iPAQ. The device has potential applications in homeland security, such as screening people packages, luggage and vehicles at key locations such as airports or government buildings, for the prevention of terrorist attacks. The overall system design consisted of a Compaq iPAQ used for the main computing and controlling of the device, connected to the custom built electronic nose interface. The electronic nose interface was designed to fit into the iPAQ expansion case providing a fully integrated system. An array of eight conducting polymer composites were inserted into the modular sensing head for the detection of organic solvents.

A novel approach to electronic nose-head design, using a copper thin film electrode patterning technique

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 arrays ability to discriminate between different solvents was carried out with promising results

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— This paper describes the effect of hypermer PS3 surfactant on the response of PEA \ CB sensors to 20000 ppm of propanol. The surfactant was varied from 10-50 mg and its effect on the response and properties of the sensor material were examined. It was found that increasing the amount of surfactant in the sensors significantly improved batch-to-batch reproducibility in addition to the sensitivity of each device. This is due to a more homogenous dispersion of the carbon black (CB) filler particles achieved by the addition of surfactant. It is concluded that this approach can be used to optimize the sensitivity and reproducibility of conducting polymer composite (CPC) sensor devices. Keywords—Conducting polymer composites, surfactant, drop coating, alcohol vapour detection

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

This paper details results obtained from an array of drop coated room temperature carbon filled polymer composite sensors showing anomalies in the initial responses of the devices. The paper details the construction of the sensors, and the theory of their operation. The manufacture techniques are introduced along with the experimental configuration used to acquire the results.

Surfactant treated drop-coated polyethylene adipate \ carbon black nanocomposite sensor for alcohol vapour detection

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.

Anomalous Behavior of Carbon Filled Polymer Composites Based Chemical and Biological Sensors

Detection of bacteria such as Ralstonia pickettii in high purity water (HPW) has gained increasing interest for researchers. Contamination problems in HPW in both pharmaceutical and semiconductor applications can lead to a reduction in performance and inefficiency in production chains leading to huge expense. Real time detection of these bacteria in HPW prior to use can allow corrective action to be taken sooner, by reallocating the water for repurification or utilization elsewhere thereby reducing industrial costs The aim of this study was to evaluate the responses of polymer nanocomposite sensors to increasing concentrations of Ralstonia pickettii bacteria. M9 minimal growth medium was used to grow the bacteria and three different concentrations were prepared by taking samples after 2 hours, 4 hours and 6 hours of growth. The sensors showed large sensitivity to each concentration of bacteria and produced a decrease in response over the growth cycle of the bacteria. These sensors demonstrated the ability to detect early stage actively growing cells in real time, which is of large benefit to HPW applications. This work has shown that these sensors can be used to detect both lag phase and late exponential and stationary phase growing cells in a minimal nutrient environment.

Response of poly(vinyl acetate)/carbon black composites to ethanol vapour and temperature

This study presents an analysis of electrode patterns suitable for use with drop coated conducting polymer gas sensors. A thin-film technique was used to efficiently fabricate the copper electrode patterns (Arshack, 2005). Conducting polymer composite (CPC) materials were deposited using a 500 nano-litre syringe onto the electrode patterns to produce an array of sensors for organic solvent vapour detection. The sensors were exposed to propanol vapour in steps of 3000 ppm from a minimum concentration of 5000 ppm up to a maximum concentration of 20,000 ppm. Empirical results showed that a non-parallel electrode configuration produces a marginally larger response and is also less noisy than the interdigitated or parallel electrode configurations. Results show that increasing the baseline resistance of the sensing material gives a larger response