Methods for increasing the sensing performance of metal oxide semiconductor gas sensors at ppb concentration levels

Metal oxide semiconductor gas sensors are in general well suited for high volume gas sensing applications, e.g. air quality monitoring, due to their low cost and high sensitivity. However, in many applications, the gases to be detected can occur in very low concentrations, which complicates selective measurement of specific components. In this thesis, several methods are presented which improve the performance of such sensors for the detection of gases at trace concentrations. First, the design and characterization of a gas mixing system is described, which allows generation of test gases in the ppb (parts per billion) concentration range. Several well established techniques are then tested for their applicability at these low concentration levels. Key elements are cyclic modulation of the sensor temperature and signal processing based on methods for pattern recognition, for both single sensors and combined sensor signals. A novel development is an integrated micro system in which gas pre-concentration is realized in combination with the sensor. In addition to the technical developments, the reproducibility of the results has been investigated in an inter-laboratory comparison, where a measurement system for benzene has been characterized in two different setups for test gas generation. The presented methods provide a basis for using low-cost metal oxide semiconductor gas sensors for potential applications in the field of trace gas analysis.Metalloxid-Halbleiter-Gassensoren (MOS) sind aufgrund ihrer hohen Sensitivität und geringen Preises grundsätzlich gut geeignet für Gasdetektion in Anwendungen mit hohen Stückzahlen, zum Beispiel für die Überwachung von Luftqualität. In diesen können die zu detektierenden Gase jedoch in sehr niedrigen Konzentrationen auftreten, was eine gezielte Messung einzelner Komponenten erschwert. In dieser Arbeit werden Verfahren vorgestellt, mit denen die Leistung solcher Sensoren für die Detektion von Gasen in Spuren-Konzentrationen verbessert wird. Zunächst werden das Design und die Charakterisierung einer Gasmischanlage beschrieben, die eine zuverlässige Generierung von Testgasen im ppb-Bereich (parts per billion) ermöglicht. Mehrere etablierte Verfahren werden dann auf ihre Eignung für diesen niedrigen Konzentrationsbereich getestet. Zentrale Elemente sind hierbei eine zyklische Änderung der Sensortemperatur und Signalverarbeitung basierend auf Methoden zu Mustererkennung, sowohl für einzelne Sensoren als auch für kombinierte Signale. Eine neue Entwicklung ist ein integriertes Mikrosystem, in dem zusätzlich zum Sensor eine Gas-Aufkonzentration realisiert ist. Neben den technischen Entwicklungen wurde die Reproduzierbarkeit der Ergebnisse in einer Vergleichsmessung in zwei Labors untersucht; hier wurde ein Messsystem für Benzol in zwei unterschiedlichen Setups zur Gasaufgabe getestet. Die vorgestellten Methoden bieten eine Grundlage zum Einsatz der günstigen MOS-Gassensoren für Anwendungen im Bereich von Spurengasen

Electronic Noses for Biomedical Applications and Environmental Monitoring

This book, titled “Electronic Noses for Biomedical Applications and Environmental Monitoring”, includes original research works and reviews concerning the use of electronic nose technology in two of the more useful and interesting fields related to chemical compounds detection of gases. Authors have explained their latest research work, including different gas sensors and materials based on nanotechnology and novel applications of electronic noses for the detection of diverse diseases. Some reviews related to disease detection through breath analysis, odor monitoring systems standardization, and seawater quality monitoring are also included

Factories of the Future

Engineering; Industrial engineering; Production engineerin

Roadmap on energy harvesting materials

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere

Harvesting Ambient Environmental Energy for Wireless Sensor Networks: A Survey

In recent years, wireless sensor networks (WSNs) have grown dramatically and made a great progress in many applications. But having limited life, batteries, as the power sources of wireless sensor nodes, have restricted the development and application of WSNs which often requires a very long lifespan for better performance. In order to make the WSNs prevalent in our lives, an alternative energy source is required. Environmental energy is an attractive power source, and it provides an approach to make the sensor nodes self-powered with the possibility of an almost infinite lifetime. The goal of this survey is to present a comprehensive review of the recent literature on the various possible energy harvesting technologies from ambient environment for WSNs

Factories of the Future

Engineering; Industrial engineering; Production engineerin

Wearable chemo/bio-sensors for sweat sensing in sports applications: combining micro-fluidics and novel materials

In the last decade, we have witnessed an exponential growth in the area of clinical diagnostic but surprisingly little has been done on the development of wearable chemo/bio-sensors in the field of sports science. In particular, the use of wearable wireless sensors capable of analysing sweat during physical exercise can provide access to new information sources that can be used to optimise and manage athletes’ performance. Lab-on-a-Chip technology provides a fascinating opportunity for the development of such wearable sensors. In this thesis two different colorimetric wearable microfluidic devices for real- time pH sensing were developed and used during athlete training activity. In one case a textile-based microfluidic platform employing cotton capillarity to drive sweat toward the pH sensitive area is presented that avoids the use of bulky fluid handling apparatus, i.e. pumps. The second case presents a wearable micro-fluidic device based on the use of pH responsive ionogels to obtain real-time sweat pH measurements through photo analysis of their colour variation. The thesis also presents the first example of sweat lactate sensing using an organic electrochemical transistor incorporating an ionogel as solid-state electrolyte. In this chapter, optimization of the lactate oxidase stability when dissolved in number of hydrated ionic liquids is investigated. Finally, a new fabrication protocol for paper-based microfluidic technology is presented, which may have important implications for future applications such as low-cost diagnostics and chemical sensing technologies