Maciej Trawka

New approaches for improving selectivity and sensitivity of resistive gas sensors: a review

Purpose – This paper aims to present the methods of improving selectivity and sensitivity of resistance gas sensors. Design/methodology/approach – This paper compares various methods of improving gas sensing by temperature modulation, UV irradiation or fluctuation-enhanced sensing. The authors analyze low-frequency resistance fluctuations in commercial Taguchi gas sensors and the recently developed tungsten trioxide (WO3) gas-sensing layers, exhibiting a photo-catalytic effect. Findings – The efficiency of using low-frequency fluctuations to improve gas detection selectivity and sensitivity was confirmed by numerous experimental studies in commercial and prototype gas sensors. Research limitations/implications – A more advanced measurement setup is required to record noise data but it will reduce the number of gas sensors necessary for identifying the investigated gas mixtures. Practical implications – Fluctuation-enhanced sensing can reduce the energy consumption of gas detection systems and assures bett...

UV-Light-Induced Fluctuation Enhanced Sensing by WO 3 -Based Gas Sensors

WO3-based gas sensors were investigated under UV-light irradiation and at different working temperatures with the object of achieving superior sensitivity and selectivity. Resistance fluctuations in the WO3 layer were studied together with dc resistance measurements. The data were taken in synthetic air, ethanol, nitrogen dioxide, and mixtures of these gases. We conclude that UV irradiation can easily be applied to enhance the gas sensing properties of a WO3 layer.

Nickel oxide thin film sensor for fluctuation-enhanced gas sensing of formaldehyde

Nanocrystalline nickel-oxide-based thin films were prepared by advanced reactive gas deposition, and the response of these films to formaldehyde was studied by fluctuation-enhanced sensing. Morphological and structural analyses showed porous deposits of nickel oxide particles with face-centered cubic structure. Resistance fluctuations were measured upon exposure to ethanol, formaldehyde and methane at 200 °C. Power density spectra were used to quantify the response. The response to formaldehyde was higher than to ethanol at 200 °C, and no significant response was observed for methane thus demonstrating some gas-species selectivity.

Portable measurement system for breath analysis by real-time fluctuation enhanced sensing method

Resistance flicker noise of gas sensors gives a new opportunity to improve gas detection by enhancing selectivity and sensitivity of cheap and popular gas sensors. The improvement at low gas concentrations can be even increased further by UV light irradiating the gas sensing layers exhibiting photocatalytic effect (e.g., WO3 or TiO2 gas sensing layers). A new system has been developed recently to utilize low frequency noise measurement method but controlling a set of sensors applied for breath analysis and medical check-up. The system measures DC resistance and resistance noise in an array of four prototype resistive gas sensors. An operating temperature of each sensor can be set independently by the software controlling the system. Some sensors can be irradiated by the UV light as well. Humidity, temperature and pressure within a miniature gas chamber, of a volume about 40 ml, is monitored to secure repeatable conditions during the measurements and to avoid humidity condensation in the exhaled breath. The setup is controlled by an FPGA circuit performing necessary computations (power spectrum density estimation) and data transmission. Further processing by applying selected detection or gas concentration estimation methods can be done by a smartphone or a PC controlling the measurement setup. The system was prepared for fast and non-invasive medical diagnosis of patients suffering from tropical diseases.