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.

Wireless power transfer (WPT) techniques are being popular currently with the development of midrange wireless powering and charging technology to gradually substitute the need for wired devices during charging. Unmanned Aerial Vehicles (UAVs) are also being used with many practical purposes for agriculture, surveillance, and healthcare, etc. There is a trade-off between the weight of the UAVs or their batteries and their flying time. In order to support those UAVs perform better in their tasks, WPT is applied in UAVs to recharge batteries which help to increase their working time. This paper highlights up-to-date studies that are specific to near-field WPT deploying into UAVs. The charging distances, the transfer efficiency, and transfer power, etc. are considered to provide an overview of all common problems in using and charging UAVs, especially for autonomous landing and charging. By classification and suggestions in specific problems will be provided opportunities and challenges with respect to apply near-field WPT techniques for charging the battery of UAVs and other applications in the real world.

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The recent use of rotary-wing unmanned aerial vehicles (UAVs) has gained significant interest and continuously been implemented since they are used across the world for civilian, commercial, as well as military applications. The drawback of UAVs is the fight-time due to the limited battery capacity. Therefore, energy harvesting (EH), captured energy from the ambient environment is one of the effective measures to prolong the flight time for UAVs. This paper proposes the hybrid EH system, which can simultaneously harvest power from solar and radio frequency (RF) energy sources to significantly improve the energy issues for endurance longer flight UAVs. A 7-stage voltage multiplier circuit of the stand-alone RF-EH system is designed and simulated in this work. The stand-alone solar harvester is a solar panel. The DC output voltage from both of two energy sources is passed through a DC-DC boost converter and stabilizer. Simulation results can be deployed to power for the battery of UAVs in practice.