Misalignment-tolerant wireless power transfer for high endurance IoT sensors using UAVs and nonlinear resonant circuits

• The paper proposes a novel NRC for misalignment-tolerant charging of WSNs via UAVs. • A new lightweight hexagonal coil structure ensures efficient WPT system operation. • A 200 W prototype UAV at 85 kHz is developed, demonstrating practical application. • The system ensures stable power transfer at 5–10 cm distance with ±35 % misalignment. In recent years, the utilization of wireless sensor networks (WSNs) has drastically increased in various remote monitoring applications. However, designing compact, high-endurance sensors is a major demand in emerging Internet of Things (IoT) and Artificial Intelligence (AI) based applications. The inbuilt battery restricts the duration and size of WSN. Various approaches have been proposed in the literature to increase endurance using additional sources such as solar photovoltaics and thermoelectric generators. However, most of these techniques are not viable alternatives to power tiny WSNs, regardless of sensor location and placement. On the other hand, Unmanned Aerial Vehicles (UAVs) are used for recharging wireless sensor nodes (WSNs) at scheduled intervals, showing practical viability in a wide range of applications. Nevertheless, the misalignment between the transmitter (Tx) and receiver (Rx) coils limits the efficient design of the Wireless Power Transfer (WPT) circuit to power the WSN. Moreover, size and weight restrictions on the Tx and Rx coil structures confine the design flexibility of WSNs and charging systems. In this paper, we propose a simple nonlinear resonant circuit (NRC) at the Rx side, which allows for misalignment-tolerant charging of WSNs without precise positioning of the UAV system. Additionally, a lightweight hexagonal coil structure is proposed to enable the WPT system to operate efficiently without much complex design. A 200 W power capacity experimental prototype UAV has been designed and tested at an 85 kHz operating frequency. The power transfer efficiency remained stable over a coupling distance of 5 cm to 10 cm. Furthermore, the proposed circuit maintains the maximum power transfer rate with up to ±35 % misalignment between the Tx and Rx coils, ensuring a reduced power circuit size for tiny sensor applications.