Sensors with very low power consumption are required so that they can last a long time without the need to replace the batteries very often. Low power sensors can save significant cost and time incurred in battery replacement, especially in establishments and organizations that span over several buildings, floors and rooms. In this thesis, we investigate the use of the low-power wireless protocol Z-wave for sensors solutions that can last for approximately 10 years. An algorithm was created and we concluded that 10 years on a 480 mAh battery is not possible and the expected years need to be lowered or we need to increase the battery capacity.

abstract: Precursors of carbon fibers include rayon, pitch, and polyacrylonitrile fibers that can be heat-treated for high-strength or high-modulus carbon fibers. Among them, polyacrylonitrile has been used most frequently due to its low viscosity for easy processing and excellent performance for high-end applications. To further explore polyacrylonitrile-based fibers for better precursors, in this study, carbon nanofillers were introduced in the polymer matrix to examine their reinforcement effects and influences on carbon fiber performance. Two-dimensional graphene nanoplatelets were mainly used for the polymer reinforcement and one-dimensional carbon nanotubes were also incorporated in polyacrylonitrile as a comparison. Dry-jet wet spinning was used to fabricate the composite fibers. Hot-stage drawing and heat-treatment were used to evolve the physical microstructures and molecular morphologies of precursor and carbon fibers. As compared to traditionally used random dispersions, selective placement of nanofillers was effective in improving composite fiber properties and enhancing mechanical and functional behaviors of carbon fibers. The particular position of reinforcement fillers with polymer layers was enabled by the in-house developed spinneret used for fiber spinning. The preferential alignment of graphitic planes contributed to the enhanced mechanical and functional behaviors than those of dispersed nanoparticles in polyacrylonitrile composites. The high in-plane modulus of graphene and the induction to polyacrylonitrile molecular carbonization/graphitization were the motivation for selectively placing graphene nanoplatelets between polyacrylonitrile layers. Mechanical tests, scanning electron microscopy, thermal, and electrical properties were characterized. Applications such as volatile organic compound sensing and pressure sensing were demonstrated. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2020

Die kürzliche globale COVID-19-Pandemie hat deutlich gezeigt, dass hohe medizinische Kosten eine große Herausforderung für unser Gesundheitssystem darstellen. Daher besteht eine wachsende Nachfrage nach personalisierten tragbaren Geräten zur kontinuierlichen Überwachung des Gesundheitszustands von Menschen durch nicht-invasive Erfassung physiologischer Signale. Diese Dissertation fasst die Forschung zur Laserkarbonisierung als Werkzeug für die Synthese flexibler Gassensoren zusammen und präsentiert die Arbeit in vier Teilen. Der erste Teil stellt ein integriertes zweistufiges Verfahren zur Herstellung von laserstrukturiertem (Stickstoff-dotiertem) Kohlenstoff (LP-NC) ausgehend von molekularen Vorstufen vor. Der zweite Teil demonstriert die Herstellung eines flexiblen Sensors für die Kohlendioxid Erfassung basierend auf der Laserumwandlung einer Adenin-basierten Primärtinte. Die unidirektionale Energieeinwirkung kombiniert mit der tiefenabhängigen Abschwächung des Laserstrahls ergibt eine neuartige geschichtete Sensorheterostruktur mit porösen Transducer- und aktiven Sensorschichten. Dieser auf molekularen Vorläufern basierende Laserkarbonisierungsprozess ermöglicht eine selektive Modifikation der Eigenschaften von gedruckten Kohlenstoffmaterialien. Im dritten Teil wird gezeigt, dass die Imprägnierung von LP-NC mit Molybdäncarbid Nanopartikeln die Ladungsträgerdichte verändert, was wiederum die Empfindlichkeit von LP-NC gegenüber gasförmigen Analyten erhöht. Der letzte Teil erläutert, dass die Leitfähigkeit und die Oberflächeneigenschaften von LP-NC verändert werden können, indem der Originaltinte unterschiedliche Konzentrationen von Zinknitrat zugesetzt werden, um die selektiven Elemente des Sensormaterials zu verändern. Basierend auf diesen Faktoren zeigte die hergestellte LP-NC-basierte Sensorplattform in dieser Studie eine hohe Empfindlichkeit und Selektivität für verschiedene flüchtige organische Verbindungen. / The recent global COVID-19 pandemic clearly displayed that the high costs of medical care on top of an aging population bring great challenges to our health systems. As a result, the demand for personalized wearable devices to continuously monitor the health status of individuals by non-invasive detection of physiological signals, thereby providing sufficient information for health monitoring and even preliminary medical diagnosis, is growing. This dissertation summarizes my research on laser-carbonization as a tool for the synthesis of functional materials for flexible gas sensors. The whole work is divided into four parts. The first part presents an integrated two-step approach starting from molecular precursor to prepare laser-patterned (nitrogen-doped) carbon (LP-NC). The second part shows the fabrication of a flexible LP-NC sensor architecture for room-temperature sensing of carbon dioxide via laser conversion of an adenine-based primary ink. By the unidirectional energy impact in conjunction with depth-dependent attenuation of the laser beam, a novel layered sensor heterostructure with a porous transducer and an active sensor layer is formed. This molecular precursor-based laser carbonization method enables the modification of printed carbon materials. In the third part, it is shown that impregnation of LP-NC with molybdenum carbide nanoparticle alters the charge carrier density, which, in turn, increases the sensitivity of LP-NC towards gaseous analytes. The last part explains that the electrical conductivity and surface properties of LP-NC can be modified by adding different concentrations of zinc nitrate into the primary ink to add selectivity elements to the sensor materials. Based on these factors, the LP-NC-based sensor platforms prepared in this study exhibited high sensitivity and selectivity for different volatile organic compounds.

Volatile Organic Compounds (VOCs) are commonly used as indicators of an organism's health, among other factors. Traditionally, gas chromatographs (GC) are used to classify these but are prohibitively expensive and impractical for field use. This thesis outlines the motivations, design, construction, and characterization of a portable GC. This proof-of-concept uses off-the-shelf components to show that the production of a device is feasible. It was able to successfully generate carrier gas from the surrounding air via filtration by activated carbon fiber filters. It was also able to reliably produce distinguishable peaks for acetone and hexane at retention times that were reasonable for a prototype system. With some modifications, this system has the strong potential for long-term implementation in the field.