In this study, we identify and survey energy harvesting technologies for small electrically powered unmanned systems designed for long-term (>1 day) time-on-station missions. An environmental energy harvesting scheme will provide long-term, energy additions to the on-board energy source. We have identified four technologies that cover a broad array of available energy sources: solar, kinetic (wind) flow, autophagous structure-power (both combustible and metal air-battery systems) and electromagnetic (EM) energy scavenging. We present existing conceptual designs, critical system components, performance, constraints and state-of-readiness for each technology. We have concluded that the solar and autophagous technologies are relatively matured for small-scale applications and are capable of moderate power output levels (>1 W). We have identified key components and possible multifunctionalities in each technology. The kinetic flow and EM energy scavenging technologies will require more in-depth study before they can be considered for implementation. We have also realized that all of the harvesting systems require design and integration of various electrical, mechanical and chemical components, which will require modeling and optimization using hybrid mechatronics-circuit simulation tools. This study provides a starting point for detailed investigation into the proposed technologies for unmanned system applications under current development.
Novel autophagous (self-consuming) systems combining structure and power functionalities are under development for improved material utilization and performance enhancement in electric unmanned air vehicles (UAV's). Much of the mass of typical aircraft is devoted separately to the functions of structure and fuel-energy. Several methods are proposed to extract structure function from materials that can also serve as fuel for combustion or as a source of hydrogen. Combustion heat is converted to electrical energy by thermoelectric generation, and hydrogen gas is used in fuel cells to provide electrical energy. The development and implementation of these structure-fuels are discussed in the context of three specific designs of autophagous wing spars. The designs are analyzed with respect to mechanical performance and energy storage. Results indicate a high potential for these systems to provide enhanced performance in electric UAV's.