The main goal of this Electrical Engineering Bachelor project is to build a solar-power system for a quad-copter that will extend its battery life or rather its flight time. The complete system is comprised of a PV system (PV), a micro-controller (MC) and a DC/DC converter (DC) which was mounted onto the drone. On each subsystem, a separate thesis was written and this paper serves as a general yet complete overview of the design process, simulations and test results of a fully functioning solar drone with the theses attached as appendices for reference. The original (optimistic) aim of an extension of at least 25% of the battery lifetime was set by our supervisors. For the PV part SunPower C60 IBC cells were used (no specific selection was done) together with a (borrowed) custom-built drone (not built by this team, it was borrowed from another research group) as a starting point. After analysing the limitations of the drone and the cells, multiple configurations were designed and a mathematical model that determines power usage, energy costs per solar cell and the optimum amount of cells was developed. %The optimum amount of cells for this specific drone was found to be a total of 28 cells. A SEPIC converter will extract solar energy from a PV-module in order to charge the battery of the drone. The converter will be controlled by the micro-controller subgroup using MPPT (Maximum Power Point Tracker) algorithm and this will be done by supplying a PWM signal to the converter. Since the drone was not specifically designed for the project (thus not optimised when it comes to lift capacity and room for cell placement), the efficiency of the solar cells was not sufficient to extend the fight time by 25% (15.1% in summer, 5.6 in winter). Since these bottlenecks can easily be eliminated by replacing the drone and the cells, these results serve as a proof of concept and are an excellent starting point for future research.

The effect of the contact angle and radius of a microsize droplet on the surface acoustic wave (SAW) response for microfluidic applications is reported. It is studied through the dynamic change of the droplet shape during the evaporation process. An aluminium nitride SAW device, operating at 125.7 MHz, is utilized to investigate the deformation of the droplet shape (contact angle and contact radius) caused by shrinking. The large cavity placed on the propagation path distorts the in-band SAW response one time at the centre frequency. The fractional coefficient of the SAW insertion loss, before and after dropping the liquid on the propagation path, is continuously recorded. The change in the fractional coefficient shows that the radiated acoustic kinetic energy depends on the contact area between the sessile micro-size droplet and the SAW device more than the contact angle of the droplet. Three droplet volumes have been considered, namely 0.05, 0.1 and 0.13 μl, and the electrical results show a better agreement with the theoretical data than the optical image data. The average duration of the fractional coefficient change for these cases is 420, 573 and 760 s, respectively. The effect of the hydrophobicity versus hydrophilicity of the contact surface on the duration of the fractional coefficient change is studied by coating the SAW with a silicon oxide or hexamethyldisilazane (HMDS) thin layer. For the same 0.05 μl sessile droplet on the hydrophobic surface, this duration is on average 110 s longer than that on the hydrophilic surface.