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Fisher, Brian. "Surface Acoustic Wave (SAW) Cryogenic Liquid and Hydrogen Gas Sensors." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5208.
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This research was born from NASA Kennedy Space Center's (KSC) need for passive, wireless and individually distinguishable cryogenic liquid and H2 gas sensors in various facilities. The risks of catastrophic accidents, associated with the storage and use of cryogenic fluids may be minimized by constant monitoring. Accidents involving the release of H2 gas or LH2 were responsible for 81% of total accidents in the aerospace industry. These problems may be mitigated by the implementation of a passive (or low-power), wireless, gas detection system, which continuously monitors multiple nodes and reports temperature and H2 gas presence. Passive, wireless, cryogenic liquid level and hydrogen (H2) gas sensors were developed on a platform technology called Orthogonal Frequency Coded (OFC) surface acoustic wave (SAW) radio frequency identification (RFID) tag sensors. The OFC-SAW was shown to be mechanically resistant to failure due to thermal shock from repeated cycles between room to liquid nitrogen temperature. This suggests that these tags are ideal for integration into cryogenic Dewar environments for the purposes of cryogenic liquid level detection. Three OFC-SAW H2 gas sensors were simultaneously wirelessly interrogated while being exposed to various flow rates of H2 gas. Rapid H2 detection was achieved for flow rates as low as 1ccm of a 2% H2, 98% N2 mixture. A novel method and theory to extract the electrical and mechanical properties of a semiconducting and high conductivity thin-film using SAW amplitude and velocity dispersion measurements were also developed. The SAW device was shown to be a useful tool in analysis and characterization of ultrathin and thin films and physical phenomena such as gas adsorption and desorption mechanisms.?Ph.D.
Doctorate
Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering
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Drake, Philip. "The development of quartz crystal microbalance based chemical sensors." Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323573.
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Mao, Youxin. "Liquid phase epitaxial growth of InAsâ†0â†.â†9â†1Sbâ†0â†.â†0â†9 and fabrication of 4.2#mu#m light emitting diodes for carbon dioxide detection." Thesis, Lancaster University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296888.
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Sharaf, Safa. "Testing and application of wire mesh sensors in vertical gas liquid two-phase flow." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/14252/.
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The behaviour of gas-liquid two-phase flow has been studied extensively in the past at near atmospheric pressure in small diameter pipes. However, the industrial reality is the utilisation of large diameter pipes at elevated pressures and there is significantly less information available in this area due principally to the cost of investigating large diameter pipes. This research relied on using large-scale laboratory facilities at the University of Nottingham, and on using newly developed state of the art multiphase instrumentation. This study tested and applied the wire mesh sensor (WMS). The work included in this thesis utilised the two variants of the WMS; the already established Conductivity WMS and the recently developed Capacitance WMS and the two sensors were compared against each other. The Capacitance WMS was recently supplied by HZDR (Research Institution, Germany) to the University of Nottingham. Extensive experimental campaigns were carried out with this novel sensor. The WMS was initially tested and validated against several other instruments such as high speed camera and gamma densitometry. It was subsequently applied to a large diameter bubble column and large diameter pipe with two phase flow. The aims of this project was to gain a better understanding of the flow patterns and their transitions in large diameter pipes and to provide real experimental data to assist researchers and engineers in producing relevant and physically sound models for use in larger diameter pipes. As a result of this study, novel and interesting structures which have been labelled as wisps were discovered in large diameter pipes. In addition the WMS was used extensively for the first time on bubble columns in order to assess its suitability for such an application.
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Zhang, Jian. "Zeolite Thin Film-Fiber Integrated Optical Sensors for Highly Sensitive Detection of Chemicals in Gas and Liquid Phases." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1195680520.
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Xiong, Linhongjia. "Amperometric gas sensing." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:a8dcbf36-14b6-4627-b380-3b81e83d446c.
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Amperometric gas sensors are widely used for environmental and industrial monitoring. They are sensitive and cheap but suffer from some significant limitations. The aim of the work undertaken in this thesis is the development of ‘intelligent’ gas sensors to overcome some of these limitations. Overall the thesis shows the value of ionic liquids as potential solvents for gas sensors, overcoming issues of solvent volatility and providing a wide potential range for electrochemical measurements. Methods have been developed for sensitive amperometry, the tuning of potentials and especially proof-of-concept (patents Publication numbers: WO2013140140 A3 and WO2014020347 A1) in respect of the intelligent self-monitoring of temperature and humidity by RTIL based sensors. Designs for practical electrodes are also proposed. The specific content is as follows. Chapter 1 outlines the fundamental principles of electrochemistry which are of importance for the reading of this thesis. Chapter 2 reviews the history and modern amperometric gas sensors. Limitations of present electrochemical approaches are critically established. Micro-electrodes and Room Temperature Ionic Liquids (RTILs) are also introduced in this chapter. Chapter 4 is focused on the study of analysing chronoamperometry using the Shoup and Szabo equation to simultaneously determine the values of concentration and diffusion coefficient of dissolved analytes in both non-aqueous and RTIL media. A method to optimise the chronoamperometric conditions is demonstrated. This provides an essential experimental basis for IL based gas sensor. Chapter 5 demonstrates how the oxidation potential of ferrocene can be tuned by changing the anionic component of room temperature ionic liquids. This ability to tune redox potentials has genetic value in gas sensing. Chapters 6 and 7 describe two novel patented approaches to monitor the local environment for amperometric gas detection. In Chapter 6, an in-situ voltammetric ‘thermometer’ is incorporated into an amperometric oxygen sensing system. The local temperature is measured by the formal potential difference of two redox couples. A simultaneous temperature and humidity sensor is reported in Chapter 7. This sensor shows advantageous features where the temperature sensor is humidity independent and vice versa. The Shoup and Szabo analysis (Chapter 4) requires ‘simple’ electron transfer and as such the reduction of oxygen in wet RTILs can be complicated by dissolved water. Chapter 8 proposes a method to stop oxygen reduction at the one electron transfer stage under humid conditions by using phosphonium based RTILs to ‘trap’ the intermediate superoxide ions. Chapters 9 and 10 report the fabrication of low cost disposable electrodes of various geometries and of different materials. The suitability of these electrode for use as working electrodes for electrochemical experiments in aqueous, non-aqueous and RTIL media is demonstrated. Their capability to be used as working probes for amperometric gas sensing systems is discussed.
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Becari, Wesley. "Desenvolvimento de sensores em frequências de micro-ondas para caracterização de etanol combustível." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-28062017-144309/.
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Etanol é um dos principais combustíveis na matriz energética brasileira. Embora tenha uma fiscalização rigorosa, é comum sua adulteração com água. Este trabalho propõe o desenvolvimento de sensores planares de micro-ondas para a qualificação de etanol combustível. São apresentados dois conjuntos de sensores, sendo um voltado para a análise da fase vapor e outro para a fase líquida do etanol combustível. Foram projetados dois sensores para a fase vapor, sendo um deles uma antena de microfita e o outro uma antena de fenda em cavidade de guia de ondas integrada ao substrato, ambos recobertos com nanotubos de carbono e operando em 5,8 GHz. As antenas foram utilizadas como ressoadores e não como elementos radiantes. Os dois sensores para a fase líquida foram projetados em tecnologia de guia de ondas integrado ao substrato, sendo um deles a antena de fenda em cavidade, sem cobertura de nanotubos de carbono, e o outro um guia de ondas operando na faixa de 3,95 a 6 GHz contendo uma seção no substrato. Foram implementadas as técnicas de perturbação da cavidade ressonante e de transmissão/reflexão para a extração dos valores de permissividade elétrica complexa dos materiais sob teste, a partir da resposta em frequência dos sensores propostos. Foram caracterizadas amostras de álcool etílico absoluto 99,5%, água deionizada e misturas desses materiais em diferentes frações. Todos os sensores propostos demonstraram capacidade de discriminação de frações volumétricas de etanol em água de 2% (v/v) na faixa especificada pela legislação. Os nanotubos de carbono viabilizaram o desenvolvimento dos sensores de fase vapor, sendo que o sensor empregando a antena com fenda apresentou sensibilidade 5,1 vezes maior comparado ao sensor com antena de microfita. O sensor de fase líquida usando a antena com fenda apresentou a maior sensibilidade entre os sensores ressonantes -- 30,9 vezes maior do que o obtido com a antena de microfita com nanotubos de carbono. O sensor com guia de ondas integrado ao substrato apresentou incerteza máxima de 3,4% para medidas de etanol em água nas frações permitidas pela legislação. Dessa forma, este trabalho contribui de forma original no desenvolvimento de sensores para caracterização eletromagnética de materiais e para qualificação de etanol combustível.Ethanol is one of the main fuels in the Brazilian energy matrix. Despite going through rigorous inspection, it is usually altered with water. This work proposes different planar microwave sensors for qualifying ethanol fuel. Two sets of sensors are presented: one for analyzing the vapor phase of ethanol and the other for the liquid phase of ethanol. Two sensors were designed for the vapor phase: a microstrip antenna and a cavity-backed slot antenna based on the substrate integrated waveguide technology, both coated with carbon nanotubes and operating at 5.8 GHz. The antennas were used as resonators and not as radiation elements. The sensors for the liquid phase were also designed based on the substrate integrated waveguide technology. The first sensor is a cavity-backed slot antenna, without carbon nanotubes, and the second sensor is a waveguide containing a section in the substrate, which operates at frequencies from 3.95 to 6 GHz. The cavity perturbation technique and the transmission/reflection method were implemented to extract the complex permittivity values from the materials under test, from the frequency response of the sensors. Samples of ethanol 99,5% pure, deionized water, and mixture with different proportions of these two materials were characterized. All the proposed sensors demonstrated capacity to differentiate 2% (v/v) of volumetric fraction of ethanol in water within the range specified by the legislation. Carbon nanotubes allowed the development of the vapor phase sensors. The vapor phase sensor using the cavitybacked slot antenna presented 5.1 times higher sensitivity compared to the sensor employing the microstrip antenna. The liquid phase sensor using the cavity-backed slot antenna presented the highest sensitivity among the resonant sensors -- 30.9 times higher than the microstrip antenna with carbon nanotubes. The sensor with substrate integrated waveguide presented uncertainty 3.4% for fractions of ethanol in water allowed by the legislation. Thus, this work provides an original contribution to the development of electromagnetic sensors for the characterization of materials and for qualifying ethanol fuel.
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Antelius, Mikael. "Wafer-scale Vacuum and Liquid Packaging Concepts for an Optical Thin-film Gas Sensor." Doctoral thesis, KTH, Mikro- och nanosystemteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119839.
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This thesis treats the development of packaging and integration methods for the cost-efficient encapsulation and packaging of microelectromechanical (MEMS) devices. The packaging of MEMS devices is often more costly than the device itself, partly because the packaging can be crucial for the performance of the device. For devices which contain liquids or needs to be enclosed in a vacuum, the packaging can account for up to 80% of the total cost of the device. The first part of this thesis presents the integration scheme for an optical dye thin film NO2-gas sensor, designed using cost-efficient implementations of wafer-scale methods. This work includes design and fabrication of photonic subcomponents in addition to the main effort of integration and packaging of the dye-film. A specific proof of concept target was for NO2 monitoring in a car tunnel. The second part of this thesis deals with the wafer-scale packaging methods developed for the sensing device. The developed packaging method, based on low-temperature plastic deformation of gold sealing structures, is further demonstrated as a generic method for other hermetic liquid and vacuum packaging applications. In the developed packaging methods, the mechanically squeezed gold sealing material is both electroplated microstruc- tures and wire bonded stud bumps. The electroplated rings act like a more hermetic version of rubber sealing rings while compressed in conjunction with a cavity forming wafer bonding process. The stud bump sealing processes is on the other hand applied on completed cavities with narrow access ports, to seal either a vacuum or liquid inside the cavities at room temperature. Additionally, the resulting hermeticity of primarily the vacuum sealing methods is thoroughly investigated. Two of the sealing methods presented require permanent mechanical fixation in order to complete the packaging process. Two solutions to this problem are presented in this thesis. First, a more traditional wafer bonding method using tin-soldering is demonstrated. Second, a novel full-wafer epoxy underfill-process using a microfluidic distribution network is demonstrated using a room temperature process.QC 20130325
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Piras, Simone. "Volatile and sensory characterization of white wines from minority grapes varieties." Master's thesis, ISA, 2019. http://hdl.handle.net/10400.5/19567.
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Powell, Jodi. "The Sensory and Analytical Analyses of Nonfat Milk Formulations: Stability to Light Oxidation and Pasteurization." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/35114.
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Sweet cream liquid buttermilk and skimmed milk ingredients were heat processed and/or exposed to fluorescent light to determine changes in potential flavor compounds. Solid phase microextraction-gas chromatography/flame ionization detection was used to analyze the concentrations of the volatile compounds (2-butanone, 2-pentanone, acetaldehyde, diacetyl, hexanal, methyl sulfide) found in the two components.
Pasteurized unoxidized skimmed milk had measurable levels of 2-butanone, acetaldehyde, and diacetyl. Pasteurization of skimmed milk increased concentration of 2-pentanone and methyl sulfide to measurable levels. However only 2-butanone and acetaldehyde were detectable in oxidized skimmed milk. All liquid buttermilk ingredient treatments had measurable concentrations of 2-butanone, 2-pentanone, and acetaldehyde. Pasteurization of unoxidized liquid buttermilk increased the concentration of diacetyl and hexanal to measurable levels whereas oxidized buttermilk, both pasteurized and unpasteurized, had measurable levels of hexanal and methyl sulfide.
Nonfat (.3%) dairy beverages were formulated using the same components to determine if the volatiles in liquid buttermilk might enhance the flavor of nonfat milk. Triangle tests and hedonic tests were performed on the nonfat formulations to determine their overall difference and overall acceptance. There was no significant difference between formulations.Master of Science
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Conteau, Delphine. "Développement d’outils pour l’étude des écoulements diphasiques dans les canaux d’une pile à combustible de type PEM." Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL036N/document.
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Parmi les nombreuses problématiques liées à la PEMFC, l'eau est un point crucial car elle est à la fois indispensable et indésirable dans le coeur de pile. En effet, les flux gazeux qui alimentent le système en réactifs sont humidifiés pour que la membrane soit convenablement hydratée afin de faciliter le transport des protons de l'anode vers la cathode. Mais à cet apport initial vient s'ajouter l'eau produite par la réaction électrochimique. Des gouttes d'eau liquide peuvent alors se former dans les pores des couches actives et peuvent grossir jusqu'à boucher les canaux des plaques d'alimentation en gaz. Ce travail de thèse est centré sur l'étude des écoulements gaz-liquide dans ces canaux, dont le diamètre hydraulique est de l'ordre du millimètre. Dans un premier temps, des micro-capteurs ont été mis au point pour détecter la présence d'eau liquide. Après une phase de tests en maquette froide, ces micro-capteurs ont été insérés dans une cellule de 25 cm2 de surface active, identique à celles étudiées au LRGP. Ceci a permis de montrer que dans une pile en fonctionnement, les fluctuations de tension sont liées à la présence d'eau liquide. Par ailleurs, des corrélations existantes ont été utilisées pour prédire les pertes de charge engendrées par la présence de deux phases dans les mini-canaux. Ces calculs ont été comparés aux mesures expérimentales, mettant en évidence l'influence de la couche de diffusion des gaz, située entre les canaux et la membrane, et l'importance des conditions opératoires.Ces méthodes originales viennent compléter les outils de diagnostic existants sans demander d'appareillage complexe et coûteux, ni nécessiter le développement de matériel spécifique, non optimisé pour une utilisation commercialeWater management is a critical issue in the operation of proton exchange fuel cells (PEMFC). On one hand, the membrane must be sufficiently hydrated to allow the transport of protons from the anode side to the cathode side. But on the other hand, supersaturation of water vapour in the gas phase results in liquid water formation, which can be detrimental to the fuel cell operation. Liquid water can clog up the porous structure of the gas diffusion layer (GDL) and hinder the transport of gases in the catalyst layer. Liquid accumulation can also lead to the formation of water columns inside the gas flow channels, thus preventing the fuel gas from flowing into the reaction area.Micro-sensors have been designed to detect the presence of liquid water. Three of them were inserted inside the gas distribution channels of a 25 cm2 cell. The tests run with this equipped cell highlighted the link between the presence of liquid water and the variations of the cell voltage. Besides, existing correlations were used to calculate the pressure drop between the inlet and the outlet of the cathode channel due to two-phase flow during the cell operation. The results of this calculation were compared with experimental results. This part of the study highlighted the influence of the GDL and of the operating conditions on the flows inside the channels
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Ryan, Benjamin Thomas. "Polymeric gas sensors." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531149.
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Archer, P. B. M. "Organometallic gas sensors." Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379015.
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Belghachi, Abderrahmane. "Metal phthalocyanine gas sensors." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293280.
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Rigby, Geraldine Patricia. "NOâ†x gas sensors." Thesis, University of Kent, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333520.
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Martínez, Hurtado Juan Leonardo. "Gas-sensitive holographic sensors." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244643.
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Holographic sensors are photonic layered structures contained in analyte sensitive lms that upon illumination produce monochromatic reflections (λ). The present work reports the fabrication of oxygen and ammonia sensors in Nafi on membranes and hydrocarbon and volatile organic compound sensors in poly(dimethylsiloxane) (PDMS) films. A holographic recording technique was developed to suit these materials consisting of the in situ formation of nanoparticles of 18nm average diameter and their subsequent ordered ablation with a 300mJ laser. The wavelength of the monochromatic reflections depends principally on the refractive index of the resulting layers (n) and the separation between them (Λ). Changes in these parameters are generated by the analyte-sensor interactions and their magnitude can be correlated to the analyte concentration. The strength of these interactions is determined by the thermodynamic properties of the analytes, such as the cohesive energy density (δ^2), and this, was coupled with a photonic model for the prediction of the holographic response. After exposure to different concentrations of the analytes, the kinetics of the responses were determined and the lowest detection limits (LDL) established as follows: Hydrocarbons in PDMS holograms 1% (v/v) in 3s for a range of concentrations from 0-100%; ammonia in Nafi on holograms 0.16% in 100s in the 0-12.5% range; the LDL for oxygen sensing could not be determined although the response was recorded down to 12.5% and up to 100% in 100s. Holographic sensors show competitive responses comparable to commercially available gas sensors for biomedical diagnostics and industrial process monitoring because of their facile fabrication and their shared sensing platform allowing multiplexing.
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Wallgrén, Kirsi. "Novel amperometric gas sensors." Thesis, University of Nottingham, 2005. http://eprints.nottingham.ac.uk/49484/.
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The electrochemistry of oxygen and methanol at solid polymer electrolyte (SPE)-based amperometric sensors, fabricated according to an all-planar design concept, has been investigated. The solid protonic conductors used were Nafion®-117 membranes and Polybenzimidazole (PBI) films. The working and counter electrodes were non-porous gold and/or platinum layers (300-1500 nm thick), sputtered on the same face of the solid electrolyte, separated by a gap of the ionic conductor (10-1 mm wide) and in contact with the gas sample. Such all-planar solid-state devices could offer potential advantages over sandwich-type gas sensors namely, reduction in precious metal electrode area and simplified fabrication. Sensors based on both materials exhibited near-linear response to oxygen concentration changes (in the 0.1-21% v/v range) and response times comparable to those of commercially available sensors, irrespective to sample relative humidity, but the magnitude of the signal did depend on the latter even after ohmic correction or at low currents. A systematic study of the effect of humidity on oxygen reduction and gold surface electrochemistry reveals, that the fall in the oxygen signal with decreasing humidity cannot be explained simply in terms of decreasing membrane conductivity and increased ohmic losses, but is related to the effect of water on the number of electro active sites, their catalytic activity and oxygen reduction mechanism in general. The latter is further supported by the unusually high Tafel slopes obtained both on gold and platinum electrodes with decreasing levels of test gas humidification. The shape of the oxygen reduction current-potential curves observed at open all-planar gold-based devices and the magnitude of current at both gold-and platinum-based ones, when compared to those of sandwich-and capillary-type arrangements, point to high mass transport rates and a thin or porous mass transport barrier. Current distribution considerations supported by surface electrochemistry estimates suggest that parts of the deposit closer to the reference and counter electrodes contribute more to the observed currents. Further experimentation by varying the deposit thickness and progressive masking of working electrode areas, revealed that the test gas reacted both at the line formed by the gas/solid electrolyte/metal layer interface (diffusion from the gas phase) and underneath the deposit (diffusion from the back of the sensor and through the Nafion® membrane), but not through the metal layer. For monitoring of dissolved methanol (0.5-3 M) in acidic solutions using bare platinum micro disc electrodes and of methanol vapours (in eqUilibrium with 2-10% w/w or ca. 0.6-3 M aqueous solutions of methanol) using Nafion®-based all-planar platinum sensors, a simple amperometric method was developed. For both types of sensors a clear voltarnmetric picture was obtained with a good separation of methanol oxidation and oxygen reduction curves. The amperometric response could be correlated to the variations in methanol concentration, demonstrating the suitability of the method for crude monitoring of dissolved methanol levels in a range applicable to the feed of direct methanol fuel cells.
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Maráčková, Lucie. "Studium elektrických a dielektrických vlastností plynových senzorů na bázi iontových kapalin." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2017. http://www.nusl.cz/ntk/nusl-316154.
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This diploma´s thesis is focused on a study of electrical and dielectric properties of gas sensors based on ionic liquids. Measurements were done on two different types of OECT substrates (0099 and 0160). Three ionic liquids and physiological solution PBS were chosen as electrolytes. Direct current current-voltage characteristic was measured. Switching rations of transistors with this electrolyte were determined by current-voltage characteristic. Alternating resistivity dependence on frequency were measured as well. Better properties showed OECT 0099 substrates.
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Haque, M. S. "Gas sensors using carbon nanotubes." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603677.
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A novel approach has been adopted for in-situ growth of CNTs on CMOS Silicon on Insulator (SOI) devices. The growth and deposition of CNTs on SOI CMOS has been successfully implemented at high temperature (>700°C) using tungsten as an interconnect. A detailed study of the nanotubes growth dependence on a number of parameters has been carried out on fully processed SOI CMOS substrates. A novel growth process of depositing CNTs using the very low power CMOS microhotplate acting as the thermal source has also been carried out. One of the key advantages of this process is the confinement of high temperature to the heater region only during the CNT growth, thereby, keeping the electronic circuitry unaffected. The results of the growth were highly repeatable with no degradation of the CMOS devices. High quality multi walled CNTs were locally grown, self-aligned onto the pre-formed sensing metal interdigitated electrodes. A low temperature process (<450°C) for single walled and multi walled CNTs was also developed using a hot filament stage. This process is suitable for devices with aluminium interconnect and is CMOS compatible. The locally growth CNTs on the sensor devices were tested with NO2 extensively and showed response at room temperature which was an improvement on the present gas sensing technologies. The sensor was found to offer reasonable sensitivity to 100 ppb of NO2 and faster chemical response time at elevated temperatures (tens of seconds). The smart CNT micro-sensor also showed responses to ammonia, methanol and ethanol. The ultra-low power consumption of the hotplates on ultra-thin CMOS compatible membranes and the growth of CNTs on multi-chips at the same time, in parallel, show great potential for high volume manufacturability and is a potential way forward for the next generation nanostructured material sensors.
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Watt, Esther Jane. "Poly(pyrrole) based gas sensors." Thesis, Birkbeck (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338770.
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Prasser, Horst-Michael. "3. Workshop "Meßtechnik für stationäre und transiente Mehrphasenströmungen", 14. Oktober 1999 in Rossendorf." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-30118.
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Am 14. Oktober 1999 wurde in Rossendorf die dritte Veranstaltung in einer Serie von Workshops über Meßtechnik für stationäre und transiente Mehrphasenströmungen durchgeführt. Dieses Jahr kann auf auf 11 interessante Vorträge zurückgeblickt werden. Besonders hervorzuheben sind die beiden Hauptvorträge, die von Herrn Professor Hetsroni aus Haifa und Herrn Dr. Sengpiel aus Karlsruhe gehalten wurden. Erneut lag ein wichtiger Schwerpunkt auf Meßverfahren, die räumliche Verteilungen von Phasenanteilen und Geschwindigkeiten sowie die Größe von Partikeln bzw. Blasen der dispersen Phase zugänglich machen. So wurde über einen dreidimensional arbeitenden Röntgentomographen, ein Verfahren zur Messung von Geschwindigkeitsprofilen mit Gittersensoren und eine Methode zur simultanen Messung von Blasengrößen sowie Feldern von Gas- und Flüssigkeitsgeschwindigkeit mit einer optischen Partikelverfolgungstechnik vorgetragen. Daneben wurden interessante Entwicklungen auf dem Gebiet der lokalen Sonden vorgestellt, wie z.B. eine Elektrodiffusionssonde. Neue meßtechnische Ansätze waren ebenfalls vertreten; hervorzuheben ist der Versuch, die Methode der optischen Tomographie für die Untersuchung von Zweiphasenströmungen nutzbar zu machen. Der Tagungsband enthält die folgenden Beiträge: S. John, R. Wilfer, N. Räbiger, Universität Bremen, Messung hydrodynamischer Parameter in Mehrphasenströmungen bei hohen Dispersphasengehalten mit Hilfe der Elektrodiffusionsmeßtechnik E. Krepper, A. Aszodi, Forschungszentrum Rossendorf, Temperatur- und Dampfgehaltsverteilungen bei Sieden in seitlich beheizten Tanks D. Hoppe, Forschungszentrum Rossendorf, Ein akustisches Resonanzverfahren zur Klassifizierung von Füllständen W. Sengpiel, V. Heinzel, M. Simon, Forschungszentrum Karlsruhe, Messungen der Eigenschaften von kontinuierlicher und disperser Phase in Luft-Wasser-Blasenströmungen R. Eschrich, VDI, Die Probestromentnahme zur Bestimmung der dispersen Phase einer Zweiphasenströmung U. Hampel, TU Dresden, Optische Tomographie O. Borchers, C. Busch, G. Eigenberger, Universität Stuttgart, Analyse der Hydrodynamik in Blasenströmungen mit einer Bildverarbeitungsmethode C. Zippe, Forschungszentrum Rossendorf, Beobachtung der Wechselwirkung von Blasen mit Gittersensoren mit einer Hochgeschwindigkeits-Videokamera H.-M. Prasser, Forschungszentrum Rossendorf, Geschwindigkeits- und Durchflußmessung mit Gittersensoren
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Prasser, Horst-Michael. "3. Workshop "Meßtechnik für stationäre und transiente Mehrphasenströmungen", 14. Oktober 1999 in Rossendorf." Forschungszentrum Rossendorf, 1999. https://hzdr.qucosa.de/id/qucosa%3A21838.
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Am 14. Oktober 1999 wurde in Rossendorf die dritte Veranstaltung in einer Serie von Workshops über Meßtechnik für stationäre und transiente Mehrphasenströmungen durchgeführt. Dieses Jahr kann auf auf 11 interessante Vorträge zurückgeblickt werden. Besonders hervorzuheben sind die beiden Hauptvorträge, die von Herrn Professor Hetsroni aus Haifa und Herrn Dr. Sengpiel aus Karlsruhe gehalten wurden. Erneut lag ein wichtiger Schwerpunkt auf Meßverfahren, die räumliche Verteilungen von Phasenanteilen und Geschwindigkeiten sowie die Größe von Partikeln bzw. Blasen der dispersen Phase zugänglich machen. So wurde über einen dreidimensional arbeitenden Röntgentomographen, ein Verfahren zur Messung von Geschwindigkeitsprofilen mit Gittersensoren und eine Methode zur simultanen Messung von Blasengrößen sowie Feldern von Gas- und Flüssigkeitsgeschwindigkeit mit einer optischen Partikelverfolgungstechnik vorgetragen. Daneben wurden interessante Entwicklungen auf dem Gebiet der lokalen Sonden vorgestellt, wie z.B. eine Elektrodiffusionssonde. Neue meßtechnische Ansätze waren ebenfalls vertreten; hervorzuheben ist der Versuch, die Methode der optischen Tomographie für die Untersuchung von Zweiphasenströmungen nutzbar zu machen. Der Tagungsband enthält die folgenden Beiträge: S. John, R. Wilfer, N. Räbiger, Universität Bremen, Messung hydrodynamischer Parameter in Mehrphasenströmungen bei hohen Dispersphasengehalten mit Hilfe der Elektrodiffusionsmeßtechnik E. Krepper, A. Aszodi, Forschungszentrum Rossendorf, Temperatur- und Dampfgehaltsverteilungen bei Sieden in seitlich beheizten Tanks D. Hoppe, Forschungszentrum Rossendorf, Ein akustisches Resonanzverfahren zur Klassifizierung von Füllständen W. Sengpiel, V. Heinzel, M. Simon, Forschungszentrum Karlsruhe, Messungen der Eigenschaften von kontinuierlicher und disperser Phase in Luft-Wasser-Blasenströmungen R. Eschrich, VDI, Die Probestromentnahme zur Bestimmung der dispersen Phase einer Zweiphasenströmung U. Hampel, TU Dresden, Optische Tomographie O. Borchers, C. Busch, G. Eigenberger, Universität Stuttgart, Analyse der Hydrodynamik in Blasenströmungen mit einer Bildverarbeitungsmethode C. Zippe, Forschungszentrum Rossendorf, Beobachtung der Wechselwirkung von Blasen mit Gittersensoren mit einer Hochgeschwindigkeits-Videokamera H.-M. Prasser, Forschungszentrum Rossendorf, Geschwindigkeits- und Durchflußmessung mit Gittersensoren
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Jean, Rong-Her. "Hydrodynamics and gas-liquid mass transfer in liquid-solid and gas-liquid-solid fluidized beds /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487596807822292.
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Odozi, Utomi Ayodele. "Three-phase gas/liquid/liquid slug flow." Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/8444.
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Zidan, M. D. "Gas-liquid surface interactions." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333478.
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Besnard, Isabelle. "Improvement of conducting polymer gas sensors." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341716.
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Gautam, Madhav. "Development of Graphene Based Gas Sensors." University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1365030920.
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Weisser, Karl. "Gas monitoring system using ultrasound sensors." Thesis, KTH, Mikrosystemteknik (Bytt namn 20121201), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91814.
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This thesis reports a collaboration between KTH Microsystem Technology Labs and Maquet critical care. Maquet is a company that produces medical ventilators and anesthesia machines. In an anesthesia machine it is important to monitor the anesthesia concentration that is delivered so that the delivered anesthesia concentration does not deviate from the desired concentration. Furthermore, in case of fail function there is a need to stop the delivery of anesthesia to the patient and flush the system. The anesthetic agent concentration is presently monitored with an infrared spectrometer. By using ultrasound technology it is possible to determine the volume concentration of a gas mixture by knowing the sound speed in the gases. Maquet has an ultrasound sensor that is developed to measure the oxygen concentration in air. This sensor was modified in order to measure nitrous oxide and anesthesia. The anesthesia concentration was measured by placing sensors upstream and downstream from the vaporizer. Using this ultrasound sensor system one can observe that the average discrepancy of the entire concentration range is ±0.84 % for Desflurane and 0.17 % for Isoflurane in relation to the infraredspectrometer sensor that is presently used in the anesthesia machine to monitor the anesthetic agent. Measurements show that the rise time of the ultrasound sensor varies when placing the sensor in different orientations with respect to the airway flow. It also show that by placing a flow restrictor that is used to force the airway flow in to the sensors measurement chamber reduces the rise time to a tenth of its previous value.
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Pearce, Ruth Elizabeth. "Carbon nanotubes as fire gas sensors." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/5551.
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Multi walled carbon nanotubes (MWCNTs) possess properties that make them particularly relevant for sensing applications in both the gas and liquid phase. This study presents an evaluation of cheap readily available CVD grown MWCNTs for use as fire gas sensors. Current fire detectors exploit heat and smoke detectors and it is hoped that the inclusion of gas detectors will increase the speed and reliability of detection. In order to prepare a variety of different MWCNTs a range of CVD synthesis were employed including an injected catalyst method where MWCNTs grew in dense mats from quartz substrates, MWCNTs were also synthesised using a sputtered Fe catalyst layer with acetylene as the carbon source which enabled control over the positioning of the growth. In each case, the growth parameters were varied until aligned growth was achieved. Doping of MWCNTs was also carried out as this may enhance and enable some control over the electrical properties of the CNTs; nitrogen was also added as a dopant by including 1,4-diazine as a precursor, and the effects on morphology of the MWCNTs produced were studied. The chemistry of the surface is also known to affect the sensing properties of CNTs. A batch of MWCNTs produced via the injected catalyst method were purifed by acid reflux, base washing and high temperature vacuum annealing, then modified with platinum or palladium metal nanoparticles via a reduction of the metal salts under hydrogen. MWCNTs were also coated with the polymer polyethyleneimine and with copperphthalocyanine. Prototype sensor devices were fabricated by electrophoretic deposition of these modified MWCNTs, and gas testing was carried out with the gases NO2, NH3, CO, H2 and C3H6. The mechanisms of sensing were investigated by repeating the tests at different temperatures, which revealed which sensing mechanisms were dominant and responses were compared between the differently modified MWCNTs. Sensor response was also investigated with a series of vapours to probe the dispersive and polar interactions on the MWCNT walls.
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Song, Gyung-Ho. "Hydrodynamics and interfacial gas-liquid mass transfer of gas-liquid-solid fluidized beds /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487599963590971.
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Ash, Peter William. "Studies of tin oxide gas sensors for gas chromatographic detection." Thesis, University of Plymouth, 1990. http://hdl.handle.net/10026.1/2066.
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Gas sensitive semiconductors have been known for many years and applied in static gas alarm systems for the monitoring of hazardous gases, however, their application has been limited by a lack of selectivity. In this work a semiconducting gas sensor has been configured for use as a gas chromatographic detector thus combining the sensitivity of semiconductor sensors with the selectivity of gas chromatography. The study has been confined to tin oxide devices, more specifically the Taguchi gas sensor (TGS) . The majority of this work has concentrated on the TGS 813 although the use of other TGS is described. The development of suitable instrumentation is described and rigorous optimisation of the operating parameters e.g. heater voltage and column temperature has been performed using the variable step size simplex technique. Attention was concentrated on the response of the TGS 813 to hydrogen which was used as a test gas. A novel figure of merit, response multiplied by retention time and divided by skew factor was designed so that optimum response was obtained whilst maintaining adequate chromatographic separation. Optimum conditions were verified by univariate searches and the response was observed to be most dependant upon heater voltage. A limit of detection of 20 ppb v/v of hydrogen in a 1 ml sample was obtained at optimal conditions. Illustrative analyses of hydrogen were performed in human breath and laboratory air with results found to be in close agreement with literature values. Calibration was found to be linear over at least three orders of magnitude. The response of the TGS 813 to low molecular weight alkanes has also been investigated. It was observed that different heater voltage optima existed for each of the C1-C5 alkanes and that the sensor was relatively more sensitive to the higher molecular weight compounds. As with hydrogen linear response was obtained over at least three orders of magnitude and an illustrative analysis of natural gas showed excellent agreement with known levels. A compromise optimum heater voltage was used to study the response of the TGS 813 to alcohols, aldehydes, ketones and some Cs hydrocarbons. Capillary columns were used in this investigation and it was noted that they had potentially wider application than packed columns due to the use of an inert carrier with an air make-up flow to the detector. This replaced the air carrier gas used previously which might degrade certain stationary phases. Three different types of TGS: the 813; 822 and 831 were used in a study of the response and skew factor for the detection of halogen-containing compounds. Very high skew factors were often observed, although, for some compounds it appeared that symmetrical peaks could be obtained within narrow heater voltage ranges. Skewed response was observed to be dependant upon sensor type, heater voltage and halogen proportion and type. Analysis of the three sensor types was performed and differences in potential surface area and tin oxide additives observed. The presence of additives was observed to adversely affect sensor recovery.
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Zhang, Chen. "Piezoelectric-Based Gas Sensors for Harsh Environment Gas Component Monitoring." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538769/.
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In this study, gas sensing systems that are based on piezoelectric smart material and structures are proposed, designed, developed, and tested, which are mainly aimed to address the temperature dependent CO2 gas sensing in a real environment. The state-of-the-art of gas sensing technologies are firstly reviewed and discussed for their pros and cons. The adsorption mechanisms including physisorption and chemisorption are subsequently investigated to characterize and provide solutions to various gas sensors. Particularly, a QCM based gas sensor and a C-axis inclined zigzag ZnO FBAR gas sensor are designed and analyzed for their performance on room temperature CO2 gas sensing, which fall into the scope of physisorption. In contrast, a Langasite (LGS) surface acoustic wave (SAW) based acetone vapor sensor is designed, developed, and tested, which is based on the chemisorption analysis of the LGS substrate. Moreover, solid state gas sensors are characterized and analyzed for chemisorption-based sensitive sensing thin film development, which can be further applied to piezoelectric-based gas sensors (i.e. Ca doped ZnO LGS SAW gas sensors) for performance enhanced CO2 gas sensing. Additionally, an innovative MEMS micro cantilever beam is proposed based on the LGS nanofabrication, which can be potentially applied for gas sensing, when combined with ZnO nanorods deposition. Principal component analysis (PCA) is employed for cross-sensitivity analysis, by which high temperature gas sensing in a real environment can be achieved. The proposed gas sensing systems are designated to work in a high temperature environment by taking advantage of the high temperature stability of the piezoelectric substrates.
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Lei, Pan. "High pressure three-phase (gas/liquid/liquid) flow." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/7204.
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Lu, Jiahui. "Designing wavefront sensors from liquid crystal microlenses." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707989.
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Finnemeyer, Valerie A. "Development of Liquid Crystal Infrared Imaging Sensors." Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1463139065.
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Dungey, S. J. "Modelling of gas transport in porous zeolite-modified discriminating gas sensors." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1310248/.
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The ability to distinguish effectively between a range of gases in a reliable, repeatable manner is of major interest with both scientific and commercial relevance. Semiconducting metal oxide gas sensors have a long life-span, are inexpensive and are highly sensitive; however, they are generally found to lack a desired level of selectivity. One highly viable approach for enhancing the selective power of such devices is the addition of a transformation layer. This will typically be a micro- or meso-porous, solid which will act to transform the analyte gas stream by some means. Here the use of zeolite compounds for this purpose is investigated. Different theoretical models are used to probe the dependency of the response of a porous metal oxide sensor on the transport properties of gas through the device, including through an additional zeolite layer. Through the use of a force-field based method, shape and size selective adsorption is predicted and used to justify experimental results of zeolite modified sensors, for example, the reduction of response to linear hydrocarbons as the chain-length is increased. However, the limit of such calculations is also realised such that this approach is unlikely to provide an adequate predictive tool for selecting a suitable zeolite for a particular gas sensing task. Following this, a model based on the method of diffusion eigenstates has been developed to calculate bulk effective diffusivities and rate constants for porous systems representing both the sensor and zeolite porous layers. The effective properties are found to depend strongly on the microstructure, the partitioning between phases and diffusion coefficients of the different phases. The effective parameters are then interpreted in terms of sensor response by solving the one-dimensional diffusionreaction equation for a simple two-layered macroscopic geometry. The method of finite differences is used to find the concentration profile which generates a response on interaction with an electric field established between two electrodes. The concentration profile and hence the response depends on the balance of diffusion and reaction of the analyte gas within both the sensor and zeolite layers. It is shown how the response can be explored to expose such differences by firstly looking at both the steady state response and response time and also by varying the positioning of the electrodes used to measure the response. Good correlation with experimental response data is demonstrated, supporting the importance of the diffusion-reaction properties modelled to the sensing mechanism, and the potential of developing a predictive tool based on the models presented is discussed.
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Singh, Jaswant. "Gas entrainment by liquid sprays." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432173.
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Jensen, Anne-Lise B. "Models of gas-liquid solubilities." Thesis, Aston University, 1996. http://publications.aston.ac.uk/9616/.
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A recent method for phase equilibria, the AGAPE method, has been used to predict activity coefficients and excess Gibbs energy for binary mixtures with good accuracy. The theory, based on a generalised London potential (GLP), accounts for intermolecular attractive forces. Unlike existing prediction methods, for example UNIFAC, the AGAPE method uses only information derived from accessible experimental data and molecular information for pure components. Presently, the AGAPE method has some limitations, namely that the mixtures must consist of small, non-polar compounds with no hydrogen bonding, at low moderate pressures and at conditions below the critical conditions of the components. Distinction between vapour-liquid equilibria and gas-liquid solubility is rather arbitrary and it seems reasonable to extend these ideas to solubility. The AGAPE model uses a molecular lattice-based mixing rule. By judicious use of computer programs a methodology was created to examine a body of experimental gas-liquid solubility data for gases such as carbon dioxide, propane, n-butane or sulphur hexafluoride which all have critical temperatures a little above 298 K dissolved in benzene, cyclo-hexane and methanol. Within this methodology the value of the GLP as an ab initio combining rule for such solutes in very dilute solutions in a variety of liquids has been tested. Using the GLP as a mixing rule involves the computation of rotationally averaged interactions between the constituent atoms, and new calculations have had to be made to discover the magnitude of the unlike pair interactions. These numbers have been seen as significant in their own right in the context of the behaviour of infinitely-dilute solutions. A method for extending this treatment to "permanent" gases has also been developed. The findings from the GLP method and from the more general AGAPE approach have been examined in the context of other models for gas-liquid solubility, both "classical" and contemporary, in particular those derived from equations-of-state methods and from reference solvent methods.
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DeBoer, John Raymond. "Evaluation Methods for Porous Silicon Gas Sensors." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4971.
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This study investigated the behavior of porous silicon gas sensors under exposure to CO, NO, and NH3 gas at the part per million level. Parameters of interest in this study included the electrical, environmental, and chemi-resistive performance associated with various porous silicon morphologies. Based upon the variability of preliminary results, a gas pulsing method was combined with signal processing in order to analyze small impedance changes in an environment of substantial noise. With this technique, sensors could be effectively screened and characterized. Finally this method was combined with various post-treatments in order to improve the sensitivity and selectivity of individual sensors.
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Díaz, Delgado Raül. "Tin Oxide Gas Sensors: An Electrochemical Approach." Doctoral thesis, Universitat de Barcelona, 2002. http://hdl.handle.net/10803/2743.
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En la actualidad existe una preocupación creciente en lo concerniente a los problemas medioambientales provocados por la actividad humana y en cómo estos problemas pueden afectar a nuestra salud. Uno de los problemas medioambientales más acuciantes es la creciente presencia de gases contaminantes en la atmósfera, y la investigación en este campo trata de determinar tanto las especies que son perjudiciales como las concentraciones a partir de las cuales son nocivas. Por lo que a este último punto se refiere, las legislaciones medioambientales son cada vez más restrictivas respecto a las concentraciones máximas permitidas, por lo que se necesitan materiales capaces de detectar concentraciones de gases contaminantes cada vez más pequeñas. Y no tan sólo eso sino que, además, sean de coste moderado para permitir un uso particular de ellos. Es en este contexto en el que se enmarca esta tesis, que trata del estudio de nuevos materiales que permitan la detección de gases nocivos como el monóxido de carbono o el metano a bajas concentraciones y a un coste menor que los actuales materiales, permitiendo la comercialización de estos detectores a escala masiva.Uno de los materiales más estudiado por lo que a este tipo de materiales se refiere es el SnO2. Para optimizar la detección de este tipo de gases por parte de este material, uno de los procesos cruciales consiste en la adición de pequeñas cantidades de metales. Esta adición y, por tanto, las características de estos materiales como detectores de gases depende del método usado. En este trabajo se estudia un nuevo método de adición de metales sobre SnO2 basado en una reacción electroquímica espontánea que añade estos metales en forma de partículas nanométricas sobre este material, lo que constituye una característica fundamental para optimizar la detección de gases. El método constituye, por tanto, una interesante alternativa a otros métodos usados en la actualidad, con el importante añadido de ser un método de bajo coste y fácilmente implementable a escala industrial.
Por otro lado, en este trabajo también se ha empezado el estudio electroquímico de las reacciones de oxidación y reducción del estaño. El objetivo final de este estudio es la formación electroquímica de una capa de SnO2 de propiedades perfectamente controlables de manera que, al poner esta capa en contacto con un cierto gas, se pueda medir la influencia del gas en estas propiedades y, por tanto, desarrollar sensores electroquímicos de gases. Más aún, lo que se pretende es estudiar en condiciones realistas los mecanismos de intercambio electrónico implicados en la detección de gases para entender estos procesos. Es por ello que se ha empezado el estudio electroquímico del monocristal de Sn (100) y, como primer paso de este estudio, se ha desarrollado un proceso químico de preparación de la superficie de este monocristal que también se puede aplicar al policristal de estaño. Este proceso mejora sensiblemente los procesos usados hasta la fecha ya que disminuye considerablemente la contaminación en la superficie y, además, es capaz, en el caso del monocristal, de preparar superfies atómicamente planas siendo, por su sencillez y resultados, un método ideal para preparar estas superficies y efectuar estudios mecanísticos en este sistema.
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Cavanaugh, Curtis. "AN ADAPTIVE ELECTRONIC INTERFACE FOR GAS SENSORS." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-20020108-121219.
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CAVANAUGH, CURTIS C. An Adaptive Electronic Interface for Gas Sensors (Under the direction of H. Troy Nagle).This thesis focuses on the development of an adaptive electronic interface for gas sensors that are used in the NC State electronic nose. We present an adaptive electronic interface that allows for the accurate mapping of the sensor?s voltage output to sensor resistance profiles. The adaptive interface uses a linearized Wheatstone bridge in a constant current configuration. The balancing of the bridge and the adjustment of the subsequent gain stage is performed using programmable variable resistors. The programmable resistors are controlled by a LabVIEW® program. The same control program also determines and records all the resistor values in the interface circuit. The resistance of each sensor is accurately computed by LabVIEW® using the interface-circuit, resistor values, and the voltage output of the circuit. Compensating for sensor drift can be done in LabVIEW® by adjusting the programmable resistor values so that a zero-voltage output is produced during the reference cycle. By doing this zero adjustment between each ?sniff? of an odorant, the baseline drift can be minimized.A single channel of the adaptive electronic interface has been designed and tested. The interface can be calibrated so that it is 99% accurate when performing sensor resistance measurements.A new conducting polymer sensor chamber has also been designed and tested. The new radial flow sensor chamber was minimizes the dead volume in the chamber and also deliver the odorant to each sensor at the same time. Two operating modes were compared: continuous-flow and sniff-and-hold. Both modes gave good classification performance while testing four different coffee samples. Experimental testing indicates that sensor response is highly correlated with the sample flow rate. Future work to more fully characterize this correlation is recommended.
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Khawaja, Jaleed Ejaz. "Asic gas sensors based on ratiometric principles." Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/2230/.
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The wide-scale usage of VOCs in industrial processes requires monitoring the concentrations of these vapours to keep a safe operating environment. Most combustible hydrocarbons can be ignited as a gas-air mixture in the range of 0.5% to 15% by volume. This has led to the development of several portable air quality monitoring instruments. However, the high costs and lack of durability of these instruments has remained an issue to be addressed. This PhD thesis reports on the development and characterization of a novel low cost smart gas sensor technology adaptable for use in a portable instrument. The smart gas sensor devices have been developed to target four different VOCs in air. The smart gas sensor device combines a smart ASIC (SRL 194 designed at SRL, Warwick University) fabricated in standard 0.7 μm CMOS technology and two alkyl-dithiol based self-assembled gold nanoparticle chemoresistive sensors (fabricated at Sony Deutschland GmbH) in a ratiometric array to offer a robust system which can address the common mode variations found in polymer based gas sensor systems. The ratiometric ASIC sensor array architecture allows for the reduction of the baseline value’s dependence on environmental variations and the elimination of baseline drift due to long term application of DC voltage. Three ratiometric array arrangements - mono-type uni-variate with only one chemosensor per device, mono-type bi-variate with two chemosensors of the same film material per device and duo-type with a polar and a non-polar chemosensor per device and their variations were characterized in an automated FIA test station against exposure to methanol, ethanol, propan-1-ol, and toluene at 30°C and 0-5% rh. It was determined that the devices’ response output to VOC analytes was entirely dependent on the variation of the resistance ratio of the chemoresistive sensors in the ratiometric sensor array. The effects of variations of the temperature and rh on the smart sensor output were calibrated. The mono-type devices gave a high magnitude response to the vapours whereas the duo-type arrangement offered a high degree of discrimination between the test analytes with little post-processing steps. Three different alkyl-dithiol chemoresistive sensor films on gold electrodes were successfully used as the VOC vapour sensitive elements in each arrangement. The effects of using a silicone sealant gel as a partitioning layer were characterized and it was observed that at vapour concentrations less than 3000 ppm the silicone encapsulated chemosensor devices reported a larger response to the VOC analytes as compared to those without the silicone. The test devices reported promising response repeatability and reproducibility with excellent return to baseline properties, a negligible hysteresis and an error margin of under 10%. Ideal operating temperature was determined to be 40°C at which rh variations were found to be minimal. The test devices were found to be robust with little variation in the quality of the device output over the course of 18 months. The novel research demonstrated that it is possible to get high level of diversification between analytes from a low cost and robust gas sensor system for monitoring VOCs. The work carried out here has opened the opportunity to develop highly integrated programmable hand-held gas sensor and e-nose systems for environmental monitoring use in health and safety applications.
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Chan-Henry, Robert Yatshein. "Design and development of electrochemical gas sensors." Thesis, City University London, 1992. http://openaccess.city.ac.uk/7730/.
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Historically, electrochemical gas sensors had suffered from several drawbacks such as poor temperature coefficient, leakage, susceptibility to shock and vibration and orientation sensitivity, which led to poor field reliability. In the present work these problems have largely been overcome by superior design, drawing on field experience in fuel cell and battery technology. The culmination of a sensor design embodying a number of unique concepts has revolutionised electrochemical gas sensor analysis and has pioneered the way for many new and hitherto difficult applications. The main features are: (a) A capillary diffusion-limiting barrier, based on gas-through-gas diffusion, with a theoretical temperature coefficient of 0.17% of signal per °C (at 20°C). (b) Very active fuel cell-type Pt black electrodes with large activity reserves giving rise to low span temperature coefficients, wide dynamic measurement ranges and enhanced long-term stability. (c) A close-wick sandwich arrangement of the electrodes conferring very good stability, to the extent that the sensors are substantially immune to shock and orientation problems. The sandwich design also enables the sensors to be very compact. (d) Use of strong sulphuric acid electrolyte in balance with ambient relative humidity (RH) - about 65% on average in temperate climates - in conjunction with a wick dipping into an expansion reservoir, giving maintenance-free, continuous dynamic range of operation between 20% and 90% RH and very long residence times outside these limits -several weeks in zero RH and several months in 100% RH at 20°C. (e) Extensive use of porous polytetrafluoroethylene (PTFE) membrane sealing techniques, which have dramatically improved cell integrity to the extent that leakage is virtually eliminated.(f) Matched sensing and reference electrodes in conjunction with zero bias cell operation, which allows the sensing and reference electrodes to be shorted out when the instrument is switched off; this gives almost instant warm-up when the instrument is switched on and the cell has excellent (NULL) stability under all conditions. (g) Since the sensor does not need to be powered-up when the instrument is switched off, there is a considerable saving on battery power in portable, hand-held instruments. (h) Inclusion of a second sensing (auxiliary) electrode, which enables the cancellation of partially reacting cross-interfering gases such as hydrogen. The auxiliary electrode can also substantially offset baselines; this is especially beneficial in biased sensors which generate large baselines. (i) Use of inboard chemical filters, which can remove cross interfering gases such as NO, N02, SO2, C12, NH3 and C2H4 by chemical reaction/adsorption.
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Darby, John Edward. "Semiconducting Langmuir-Blodgett films as gas sensors." Thesis, University of Kent, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293551.
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Steele, J. M. "Metal oxide single crystals as gas sensors." Thesis, University of Kent, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233273.
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Morris, Ljuibov. "Surface modification of solid state gas sensors." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392366.
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Wales, Dominic. "Planar integrated optical Bragg grating gas sensors." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/366987/.
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This thesis reports the development and modification of direct ultraviolet (UV) written planar integrated optical Bragg grating refractometers for detection of gases and vapours. The technique of direct UV writing utilises the localised refractive index increase within a UV-photosensitive silica layer, when the layer is exposed to a tightly focussed UV beam, to fabricate a wide range of optical waveguides and optical components. One such component, the Bragg grating, is used as an optical sensor for changes in refractive index. This thesis reports on the development of practical planar integrated optical Bragg grating gas sensors. This has been achieved through the use of two approaches. The first approach was to increase the number of gas molecules that can interact with the evanescent wave through the use of films of material that extended normally to the surface of the sensor device. Upon functionalisation of a planar Bragg grating sensor device with sol-gel thin films, a response between relative humidity and Bragg wavelength shift was revealed. Functionalisation of the Bragg grating sensor device with a polysiloxane polymer imparted sensitivity to solvent vapours. A quantitative structure-activity relationship (QSAR) approach was used to develop a linear regression model, between Bragg wavelength shift and solvent properties, which had good predicting power. The second approach was to utilise the associated change in refractive index of a material, when the material changed colour upon exposure to a gas, to create a measurable Bragg wavelength shift. This method was successfully achieved upon interrogation of a Bragg grating sensor device, which had been modified with an encapsulated pH sensitive organic dye upon exposure to hydrogen chloride fumes.
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Kukkola, J. (Jarmo). "Gas sensors based on nanostructured tungsten oxides." Doctoral thesis, Oulun yliopisto, 2013. http://urn.fi/urn:isbn:9789526202082.
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Abstract The aim of this thesis is to study whether nanostructured particles of WO3 could be competitive counterparts of traditional, more bulky materials in resistive gas sensor applications. Pristine and various surface decorated derivatives of three different types of WO3 nanoparticles applied on the surface of lithographically defined Si chips were used in the work to analyse the electrical behaviour of thin films when exposed to different gas atmospheres. Nanosized particles of WO3, obtained by capillary force-induced collapse of porous anodic tungsten oxide in water, were demonstrated as a sensing medium for the detection of H2 and NO analytes. Commercially available nanoparticles of WO3 were also studied. After decorating their surface with metal/metal oxide nanoparticles (Ag, PdOx and PtOx), stable aqueous dispersions were made and used for the inkjet printing of conductive patterns on test chips. Surface decoration was found to affect substantially the gas response behaviour of the materials with the largest differences in response to H2 and NO. The third type of tungsten oxide applied consisted of hydrothermally synthesized nanowires that were also surface decorated with PdO as well as with PtOx. The nanowires were suspended in water and drop cast on test chips for gas sensing measurements. The nanowire based devices allowed ultrasensitive detection of H2 even at room temperature. The results summarized in this thesis indicate that resistive gas sensors based on nanostructured tungsten oxides are excellent alternatives to existing devices utilizing porous thick films or bulky thin films. Their high sensitivity, low operating temperature and low electrical power consumption may enable the construction of portable sensors, for example by inkjet printing, thus having great potential for fast prototyping but also for large scale production at low costTiivistelmä Väitöstyön tavoitteena on tutkia nanorakenteisten WO3 hiukkasten kilpailukykyä suhteessa perinteisiin suuremman kidekoon materiaaleihin resistiivisissä kaasusensorisovelluksissa. Työssä tutkittiin kolmella eri tekniikalla valmistettujen WO3 nanopartikkeleiden alkuperäisistä ja pintakäsitellyistä versioista muodostettujen ohutkalvojen sähköisiä ominaisuuksia erilaisten kaasukehien funktiona. Veden kapillaarivoimien aikaan saaman huokoisen anodisen volframioksidirakenteen romahduksen kautta saatujen WO3 nanopartikkeleiden osoitettiin toimivan havaintoväliaineena H2 ja NO kaasuille. Myös kaupallisia WO3 nanopartikkeleita tutkittiin. Partikkelien pinta päällystettiin metalli- ja metallioksidinanopartikkeleilla (Ag, PdOx and PtOx), jonka jälkeen niistä muodostettiin vakaita vesipohjaisia seoksia johtavien kuvioiden mustesuihkutulostukseen testisubstraateille. Pintakäsittelyn havaittiin vaikuttavan merkittävästi materiaalien kaasuvasteisiin erityisesti H2:n ja NO:n tapauksessa. Kolmannen tyyppinen väitöskirjassa tutkittu volframioksidimateriaali koostuu hydrotermisesti syntetisoiduista nanojohdoista, jotka ovat pintakäsitelty PdO tai PtOx nanopartikkeleilla. Nanojohdot sekoitettiin veteen ja pipetoitiin testisubstraateille kaasumittauksia varten. Tämän tyyppiset kaasusensorit olivat erityisen herkkiä H2 kaasulle jopa huoneenlämmössä. Väistökirjan tulosten mukaan nanorakenteiset volframioksidimateriaalit ovat erinomainen vaihtoehto perinteisille huokoisille paksukalvoille ja suhteellisen paksuille ohutkalvoille kaasusensorisovelluksissa. Niiden suuri herkkyys, alhainen toimintalämpötila ja matala sähkönkulutus voivat mahdollistaa kannettavien kaasusensorien valmistuksen, esimerkiksi mustesuihkuteknologilla, nopeaan testaukseen ja suuren mittakaavan tuotantoon alhaisin kustannuksin
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Weglicki, Peter Stanislaw. "MOCVD of tin oxide for gas sensors." Thesis, University of Salford, 1990. http://usir.salford.ac.uk/26961/.
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Thin films of a wide variety of materials can be produced using an assortment of physical and chemical techniques. Such techniques are reviewed and compared, with particular reference to the deposition of tin oxide films. In the present study, MOCVD (Metal organic chemical vapour deposition) was used to grow thin films of tin oxide from dibutyltin diacetate precursor on a variety of substrates. A series of reactor prototypes were developed in accordance with specific requirements of reproducibility and process control. The evolution of the designs leading to the final working system is detailed. The theory of MOCVD is given with particular reference to the reactor used in this project. The effects of various deposition parameters on tin oxide film growth rates were investigated, and the results are discussed with reference to the deposition kinetics in the system. Films were characterised by optical interferometry, optical and electron microscopy, X-ray diffraction, Rutherford backscattering and electrical measurements. The films were generally uniform, conducting and polycrystalline, and were comprised of very small grains, resulting in a high density. A specific application of metal oxide materials is in solid state gas sensors, which are available in various forms and operate according to different mechanisms. These are compared and a detailed account is given on the theory of operation of surface conductivity modulated devices. The application of such devices based on tin oxide in thin film form was investigated in the present work. The prepared sensor samples were comprised of very small grains, resulting in a high density. The observation that preferred (310) orientation occurred in thicker films, can be attributed to dendritic growth. The sensors generally showed response to numerous reducing gas ambients, although there was evidence of a degree of selectivity against methane. Sensor response times due to changes in gas ambients between hydrogen and dried air were related to sensor thickness in terms of a grain surface defect diffusion process. This is driven by the equilibrium requirement between the exposed, gas modulated film surface states and inter-grain surface defects which are not subject to direct interaction with the gas ambient, owing to low structural porosity.
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Khor, Siew Hiang. "Three-phase liquid-liquid-gas stratified flow in pipelines." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8714.
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