Biofuel sensors for measuring the ethanol and gasoline concentrations in bio-ethanol blends, have been studied world-wide and currently used in engine management in Flex-Fuel cars fabricated by amongst others, Ford Motor Company. However, water that results from ethanol sugar cane is inevitable present in the ethanol blend and requires a sensor that is capable of measuring the full ternary ethanol/gasoline/water compostion. This thesis presents design of biofuel sensors, which can be used for the determination of compositions of ternary liquid mixtures of ethanol, gasoline and water. Firstly, the technical background and societal relevance of this thesis are given. Subsequently, the different physical domains are introduced that are in principle suitable for liquid composition sensing, such as the electrical, the acoustic, the optical and the thermal domains. As a next step, the thermal domain was selected with injected heat flux, J_h, as the through parameter and the resulting temperature difference, ∆T, as the across parameter. The basic principle of thermal impedance spectroscopy by frequency scanning was presented. Next, the thermal equivalent circuit model was used to simplify the thermal problem by transferring the thermal issue into an electrical topic. The main design challenge is to have the heat injected into the liquid rather than the substrate and to have a temperature-difference measurement not affected by the presence of the thermally conductive substrate. Different design properties such as heater, sensors, doping level, heat efficiency improvement and thermopile optimization, are explained in detail. After the interpretation on design properties, the fabrication process is introduced in detail and followed by the fabrication results. Finally, measurement results were obtained and used for validating the simulations and model and for drawing the final research conclusions.

In this thesis,two essential parts of microspectrometer are designed, fabricated and measured. They are a hot wire of polysilicon with constant temperature profile that used as the IR light source, and the LVOF which is aimed at IR spectral range. In order to have the desired IR source, the hot wire should have temperature distribution as uniform as possible based on black-body emission. Thus, the thermal mechanics inside the hot wire is fully studied including heat generation, conduction, convection and radiation. The thermal energy is electrically generated by voltage and current source. While the heat loss causing non-uniformity on temperature is mainly induced by heat conduction between the hot wire body and substrate, and to surrounding air. For the first one, the geometry including the length, width and thickness, the resistivity profile of hot wire and the meander bridge at the end of hot wire body are designed. The meander bridge works as the connection and interface to substrate which to some extent determines the heat conduction through it. Moreover, it can bear tensile force induced by thermal expansion. Besides, the meander middle bridge is added to hot wire as well in some design plans for stronger mechanical stability. On the other hand, since the temperature on hot wire is significant related to air pressure due to heat conduction to surrounding air, all hot wires are designed to operate in vacuum environment. Finally, a bunch of hot wires with different geometry, resistivity and TCR are designed and fabricated. To design the LVOF aimed at IR band, the working schematics and properties of LVOF are firstly studied in depth. All factors such as reflectance, incident angle, cone angle and so on that might affect its performance which includes the most important transmittance are researched. The LVOF is also designed in different length and tilt angle. The case that the LVOF with the hot wire as IR source is paid special attention to. Eventually, the electrical property and optical performance of hot wire is measured in vacuum chamber by FLIR IR camera. So far, the hot wire that has best performance is the one comprised of array of short hot wires. The result is fully discussed and divergence between actual performance and design plan is analyzed from many aspects.