Wireless Power Transfer System Based On Magnetic Resonances For Wireless Sensor Networks

21st century is the times of rapid development for information and communication technology. As a new information-accessing technology, Wireless Sensor Networks (WSNs) has broad application prospects and potential in the areas of national defense science and technology, environmental monitoring, etc with its characteristics such as large scale, avoid wiring, flexible network etc, and has become a research focus in IT field. In all of the factors that affect the life span of WSNs, the power supply of sensor nodes is a bottleneck problem restricting the development of WSNs. Realizing wireless power transfer for sensor nodes is one of the fundamental ways to extend service life of WSNs.To solve the problem above, this paper designed a wireless power transfer system to power multiple sensor nodes by using magnetic-resonant wireless power transfer technology. The design steps were based on the principles of maximizing power transfer efficiency and minimizing receiver size.This paper firstly analyzed the mechanism of wireless power transfer based on magnetic resonances. An equivalent circuit model for magnetic-resonant system was built from the angle of circuit theory. The key factors affecting power transfer efficiency were outlined, and the drawback of traditional two-resonator system was put forward. To compensate defect of two-resonator system, a four-resonator system and its improved structure were proposed and the power transfer efficiency formula was obtained, based on which, four coils were optimized according to power transfer performance index. The receiver area was greatly reduced to only 30.25 cm2, while transfer power and distance kept at the same level.By using the optimized four coils, an experimental platform for wireless power transfer system based on magnetic resonances was completed. The frequency response of the system, load variation characteristics and position transmission characteristics (including axial distance, radial migration and angle misalignment transmission characteristics) were studied. By analyzing multiple receivers system, the basic conditions for receivers not interfering with each others was concluded. Experimental results showed that multiple receivers system could transfer more power and was more efficient and practical than single receiver system.Finally, power of the receiver was exchanged from AC to DC according to the needs of sensor nodes. The space range for guaranteeing sensor node working normally was studied. The experiment results showed that the designed power transfer system could ensure at least 90mW transfer power within the range of 50cm axial distance.