Traditional and Advanced Systems
for Electricity Generation for Unmanned Application
Rocco Citroni1, Antonio Agresti 1, Stefano Di Gennaro2, Franco Di Paolo1, Aldo Di Carlo1
1Department of Electronic Engineering, University of Rome Tor Vergata, Italy
2Department of Information Engineering, Computer Science and Mathematics, University of L'Aquila, Italy
*corresponding author, Email: (rocco.citroni@uniroma2.it)
 
Abstract- Supported by the miniaturization and cost reduction of electronic components, a new class of UAVs (unmanned aerial vehicles) called small-air vehicles represent the future technology for indoor and outdoor mission. Today the ability to extend the flight time and range for an aircraft has become a topic for UAVs. Currently the dominant technology to energize these flight robots is the battery. The battery has a limited capacity and therefore must be replenished periodically. Sometimes, the UAV is in a difficult area and it is not possible to replace or recharge the battery. The real viability to extending flight time (FT) is possibly exploring new and more disruptive alternative solution able either to recharge a battery, or even to directly power the small UAVs during the flight. In this paper, different combinations of energy storage (batteries, supercapacitors) and new technologies that can harvest energy from the environment are investigated. In this review, the concepts emerging from this work identify and suggest how these devices can  constantly supply these flying objects for the whole day.
Keywords—VTOL; Solar and Plasmonic Harvester; MIM-MIIM; Novel Battery, Drude Model
 
1.0 Introduction
Initially designed to be the eyes behind the enemy lines today Unmanned Air Vehicles (UAVs) are playing an important role in global society. Several application military, paramilitary and civilian applications, as to combat terrorism and assisting in peacekeeping operations, protecting borders, monitoring civil unrests, monitoring illegal activity and critical infrastructure for better decision making and timely reaction are involving UAVs systems. The number of terms used interchangeably to describe unmanned aircraft nowadays can lead to confusion.  Drones, RPAS (Remotely Piloted Aircraft Systems), UAVs and UAS (Unmanned Aerial Systems) are considered synonymous references therefore this author believes they must be differentiated. Table 1 provides the correct definitions for these flying objects.
Drone
aircraft does not carry a pilot on-board, controlled by ground control station or able to fly autonomously
RPAS
aircraft does not carry a pilot on-board, remotely controlled by a pilot
UAV
UAVs does not carry a human operator, uses aerodynamic forces to provide lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry lethal or nonlethal payloads.
UAS
All system that encapsulates the aircraft or UAV, the ground-based controller, and the system of communications connecting the two.
Table 1: Correct definitions of unmanned applications
 
Thanks to electronics components miniaturization, a new class of unmanned named small air vehicle is emerging. Small air vehicle can operate in areas where larger UAV could not. Compact dimensions of the small-drones allow the operator to use it effectively in the congested and prone to various threats areas as collapsed building, caves, and tunnels. These small UAVs are always ready to take off, and it takes less than few minutes for launch.  They are capable of transferring data, such as live footage, back to base, designed for quick assembly and disassembly during field deployment. The primary criteria used to classify unmanned systems are weight, range and endurance but also, flight altitude. Today for hazardous scenarios, a drone must respect at least two requirements:  a) close proximity inspection of small-scale areas, combined with b) high speed surveillance of wide areas. The point a) require flying speeds low at low altitudes, with hovering capability to perform close proximity inspection.
Helicopters and multirotors although less efficient (thrust/weight ratio>>1) represent only possible solution.  
The point b) require flying speeds higher at high altitudes. Therefore, a fixed wing more efficient (thrust/weight ratio below 1) represent the best solution. Currently it is possible to combine the advantages of both technologies (multirotor and fixed) in a unique hybrid solution named VTOL (Vertical takeoff landing). VTOL simply mixes the efficiency and speed of a fixed wing  aircraft with the landing and takeoff capabilities of an helicopter. The propellers are used for vertical/hover flight operation, while the props rotate forward are used for forward flight. UAV platform is a new technology that has several bottleneck. To improve flight time (endurance) has become a key issue and a target of research. The other key issues are the weight and size of the small drones, which restrict the mounting of larger payloads or extra batteries. The design challenge is to generate and store enough energy to maximize flight time. Currently for unmanned systems, batteries represent the dominant technologies. They represent a significant fraction of the total size and weight of the system. The most important parameters must have a battery for a successful mission are energy and power density.  A higher energy density enables longer flight times instead higher power density enables on maximum speed, load capacity and altitude of flight. However, the batteries are not very efficient in particular mission where recharging them is impossible for example in toxic and radiation environments. Industries has worked hard to optimize battery, to improve part of UAVs from the chassis Carbon fiber at propellers, from engines to flight-controller. Today the flight time for small UAVs is about 30 minute duration, which drops to 20 when the vehicle carries payloads. Unfortunately, 30 minutes flying is a limit for Search and Rescue operation, as the growing of battery capacity also increases weight, until you get that the engines only work to support the batteries. To go further, new technologies are needed. To overcome this problem and to extend the flight time and range this author suggest three possible solution extensively detailed in the following paragraphs.
1) With limited flight time, we need to force some robots to return to change their batteries. Thus, we aim to apply algorithms that allow for removing robots and adding new ones to the network, to increase the total mission duration.
2) To use a swarm of small and low-cost UAVs for Search and Rescue in the area of interest to minimize the time to find the victim.
3) Direct and ongoing capture of energy from the vehicle’s surrounding environment. These forms of energy will allow creating a highly efficient and self-powered system able to provide unlimited energy supply to UAVs. This is a newly emerging field of Nano-energy.
The article is organized as follows: Section I present introduction, possible scenarios of unmanned aerial vehicles and radiation of the Sun and Earth.  Section II presents traditional and Novel Energy storage on board UAVs. Section III Solar Power, Modelling I-V of Solar Cell, Section IV Economical Alternative to PV, Antenna Theory, Efficiency Limits, Drude Model, Several Rectifying element. Finally, Section VI provides concluding remarks.
1.1 Scenarios of Unmanned Aerial Vehicles
Born to be used in D3 (Dangerous, Dull, and Dirty) and ISR (Intelligence, Surveillance and reconnaissance) categories today UAVs can be used in civil operational scenarios where the common requirement is the time. In search and rescue operation, any delay can have dramatic consequences as potentially human losses. This author describes three possible solutions available for drones. So which one is the best? The dominant technology available to recharge the drones are currently the batteries. However, the problem is that they are heavy and must be frequently recharged.  For this motivation the drones will either need to fly only short distances, or they’ll need places to recharge along the way. Short drone ranges can be compensated installing a series of perches on existing streetlights. The perches could be installed also on existing structures such as cell towers, radio towers, and so on.  Another solution could be stations for drones, installed on ground providing recharging stations. Figure 1 shows possible solution  to recharge.