(1)
T= Time to Locate Target (minutes), S=Search Area (Square kilometers), V=Area Searched by Vehicle in one minute, N=Number of Vehicles. The solutions presented above have several drawbacks. The charging stations presented will be useful if the mission time is shorter than the discharge time of the battery (currently Lithium Polymer battery). In fact, during recharging time UAVs cannot carry out its mission. Therefore, extra time is required and the mission will be delayed which is undesirable. The swarm approach decreases the time to achieve specific tasks, however the systems is very complex (different energy levels, varying storage, novel protocol communication, between UAV-UAV and UAV-ground control station, sensing and processing capabilities). Moreover also for Swarm UAV the energy limitation is dominating. The last solution proposed is to extract (harvest) energy from the environment converting ambient energy into electrical energy, which can be used to power the aircraft. These forms of energy will allow creating a highly efficient and self-powered system. This is a newly emerging field of Nano-energy. Two possible energy sources for enhancing flight time are traditional photovoltaic (solar cells generators) and a novel alternative, the nanoantennas derived by plasmonics field. The choice of these technologies is because both have the highest energy density. The combination of solar cells and batteries provide a hybrid source that can be used for powering small UAVs. For unmanned applications, thin film solar cells are more flexible, lightweight, and efficient. By placing solar panels on the wings of a drone, solar powered drones can get more airtime. Energy harvesting can, however add a significant amount of mass to the aircraft, to the detriment of payload capacities and endurance. In contrast to PVs, which are quantum devices limited by material bandgaps, the novel technique employs Nano-Antennas (NA) that absorb the incident IR radiation treating it as electromagnetic waves. Rectennas (Nano antennas coupled to a tunneling diode) that use excited localized surface plasmons can harvest Mid-IR energy from the sun at night and day and convert it into DC electricity to energize any device all day. Unlike solar cells, NA can operate round the clock, independently of weather conditions such as humidity and cloud cover, without restriction of orientation towards the sun and the most important the size of batteries decreased.
1.2 Radiation of the Sun and Earth
Electromagnetic radiation originating from the sun reaching the earth in both the visible and IR regions subsequently it is reradiated from earth’s surface in the mid-IR range (7–14