Laser Power Beaming for in-Flight Charging of Unmanned Aerial Vehicles - a Viability Study

The rapid development in Unmanned Aerial Vehicle (UAV) technology is revolutionizing many f ields, both in civilian applications such as aerial mapping and surveillance, and military applications such as intelligence gathering and weapon deployment. One of the biggest limitations of battery powered UAVs is the low energy density in batteries, which causes short flight time. A potential approach to extending the flight time is in-flight charging, which this thesis work aims to study by investigating the viability of in-flight charging of a fixed-wing UAV, via laser power beaming. The work consisted of a theoretical analysis of the required power transmission based on experimental data found in literature. As well as an experimental part, where laser power beaming was tested in practice as a method for wireless energy transmission. The theoretical evaluation was based on the Aerovironment RQ-20 Puma UAV, commonly employed in service in militaries around the world. Experiments were conducted with two lasers emitting in the near-infrared spectra, one at 1055 nm and one at 1064 nm. Two different receiver materials were tested, silicon and copper indium gallium selenide. The impact on efficiency was also examined when varying the laser beam’s angle of incidence on the receiver, and with increased receiver temperature. In the theoretical part, a graphical estimation of available area to mount receivers was done, along with estimations of the required energy transmission to achieve different performance thresholds. For the experimental testing, the methodology was developed through iterations of testing the setup performance. The lasers used were two high power continuous wave fiber lasers, both with a maximum output power of 2 kW. The experiments were performed with the laser’s pump current ranging from 20 % to 100 %. It was found that the maximum power transmission was with a wavelength of 1055 nm, resulting in an electrical output of 0.122 W/cm2 cell area with 0.558 W/cm2 incident laser intensity. The highest photoelectric efficiency measured was 27 % when the laser pump current was set to 20 %, the 1055 nm laser was used. Increasing the angle of incidence to 30◦ had negligible impact on the transmission efficiency. The 1064 nm laser provided much lower power transmission efficiencies than the 1055 nm laser, this is in part due to the spectral response of the receiver, but further evaluation is needed to rule out issues with the laser and alignment. The results further suggest that the receiver temperature is the limiting factor for sustained power transmission. Further research is needed on thermal management of the receiver in the UAV’s standard operating conditions to draw an exhaustive conclusion on the viability of laser power beaming for in-flight UAV charging.