Wireless sensor networks (WSNs) have broad application prospects due to having the characteristics of low power, low cost, wide distribution and self-organization. At present, most the WSNs are battery powered, but batteries must be changed frequently in this method. If the changes are not on time, the energy of sensors will be insufficient, leading to node faults or even networks interruptions. In order to solve the problem of poor power supply reliability in WSNs, a novel power supply method, the single-wire power transfer method, is utilized in this paper. This method uses only one wire to connect source and load. According to the characteristics of WSNs, a single-wire power transfer system for WSNs was designed. The characteristics of directivity and multi-loads were analyzed by simulations and experiments to verify the feasibility of this method. The results show that the total efficiency of the multi-load system can reach more than 70% and there is no directivity. Additionally, the efficiencies are higher than wireless power transfer (WPT) systems under the same conductions. The single-wire power transfer method could satisfy the characteristics of WSNs and effectively solve the problem of poor power supply reliability.

In a wireless power transfer (WPT) system based on coupled magnetic resonance, 2-D planar coils are commonly used as coupling structures. As the spatial position between the coupling structures changes, the system transmission efficiency decreases dramatically, seriously reducing the flexibility of power transfer. To solve this problem and achieve a power transfer with a high degree of freedom in a 3-D space, a novel 3-D coil based on a 26-faced polyhedron is proposed as the transmitting coil winding structure, which is wound using the regular monolithic winding method without overlapping. By means of this coil, it is ensured that the winding direction of each planar coil is different from those of the adjacent planes so that the magnetic fields between adjacent coils are mutually reinforced, thus enhancing the spatial magnetic field density of the system and enabling a stable and efficient transmission of power at any position. The transmitting coil can be enlarged by changing the coil structure, thereby enabling omnidirectional WPT in a larger space. Through experimental research, the system can achieve omnidirectional WPT with an efficiency of 60%, and its transmission efficiency can remain stable within a defined range as the receiver moves.

To solve the battery power supply problem with wireless sensor networks (WSNs), a novel bidirectional wireless charging system is proposed, in which an unmanned aerial vehicle (UAV) can fly to the WSNs to charge sensors through high-frequency wireless power transfer (WPT) and also obtain energy for its own battery in the same way. To improve the performance of the UAV bidirectional wireless charging system, a lightweight design is adopted to increase its loading capacity and working time. Moreover, the radii and the numbers of turns and pitches of coupling coils were designed and optimized on the basis of simulations and experiments. Experimental results show that the weight of optimized UAV coil was reduced by 34.45%. The power transfer efficiency (PTE) of the UAV coil to sensor coil increased from 60.2% to 74.4% at a transmission distance of 15 cm, while that of the ground transmitting coil to UAV coil increased from 65.2% to 90.1% at 10 cm.

Wireless power transfer (WPT), as a noncontact power transfer technology, is expected to solve the power supply difficulties faced by ocean power equipment due to the environment's complexity. However, when the magnetically coupled WPT system operates in seawater, eddy current losses (ECL) affected by the resonant frequency are generated, which in turn causes the resonant frequency characteristics of the system to be altered compared to those in air. The resonant frequency characteristics of WPT have been thoroughly researched, and expressions for the relationship between resonant frequency and efficiency have been derived by utilizing the mutual inductance circuit model with equivalent ECL resistance. The influences of resonant frequency variation on transmission efficiency and distance are comparatively analyzed for the system in seawater and in air, respectively, with the differences between the two situations further illustrated. Research has discovered that there is an optimal resonance frequency for WPT. The factors influencing the optimal resonance frequency were analyzed, and it was concluded that the contact area between the coil and seawater was the key factor affecting it. An experimental system for WPT in seawater media was constructed, and theoretical and simulation conclusions were validated through experiments.

In this paper, a novel one-way single-wire power transfer structure is proposed. Different from the traditional single-wire power transfer system, power is one-way transmitted from the power source to the load, and no loop is constituted. The structure of one-way single-wire power transfer is studied in detail, and the influences of its length and shapes on the transmission efficiency are determined. Research shows that the length of the receiving structure plays a key role in improving the system’s efficiency, while the transmitting structure has a little effect. Based on ensuring transmission efficiency, the space volume optimization method is further applied. The expression of electromagnetic field distribution is derived theoretically, and the proposed structure is verified by simulation and experimental results.