Wireless power transfer (WPT) techniques are important in a variety of applications in both civilian and military fields. Unmanned aerial vehicles (UAVs) are being used for many practical purposes, such as monitoring or delivering payloads. There is a trade-off between the weight of the UAVs or their batteries and their flying time. Their working time is expected to be as long as possible. In order to support the UAVs to work effectively, WPT techniques are applied with UAVs to charge secondary energy supply sources in order to increase their working time. This paper reviews common techniques of WPT deployed with UAVs to support them while working for different purposes. Numerous approaches have been considered to illustrate techniques to exploit WPT techniques. The charging distances, energy harvesting techniques, electronic device improvements, transmitting issues, etc., are considered to provide an overview of common problems in utilizing and charging UAVs. Moreover, specific problems are addressed to support suitable solutions with either techniques or applications for UAVs.

Over the decades, with the advancement of science and technology, wheelchairs have undergone remarkable changes, such as controlling an electrical wheelchair by using brain signals. However, existing electrical wheelchairs still need improvements in terms of energy management. This paper proposes an hybrid Solar-Radio frequency (RF) harvesting system able to supply power for the continuous and effective operation of electrically powered wheelchairs. This system can simultaneously harvest power from RF and solar source that are both available in the surrounding environment. A maximum power point tracking (MPPT) and a boost converter are exclusively employed for the standalone solar system while the standalone RF system is equipped with a 9-stage voltage multiplier (VM). The voltage level for the charging process is obtained by adding the output voltage of each source. In addition, a current booster and a stabilizer are used to reach the required level of current and pin the charging voltage to a stable level, respectively. Simulation results show how the hybrid system is better and more stable when the boost current and stabilizer are used in the charging system. Moreover, we also provide some analytic results to prove the advantages of this system.