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.