Research On Efficiency Of Indoor Wireless Power Transfer Based On Time Reversal Multi-spot Focusing Method

In the 5G era,massive sensors are utilized to achieve intelligent control of the indoor scene,such as smart factory and smart home,which greatly facilitates our work and life.Due to limited battery capacity and life cycle of sensors,how to provide power for massive sensors must be considered to maintain its permanent work.Traditional techniques of wired charging rely on cables and interfaces,which increases the difficulty of wiring and limits movement of sensors.Therefore,exploring technique of wireless power transfer(WPT)for indoor sensors is an urgent issue which determines whether smart factory and smart home can be realized.Time reversal spot focusing wireless power transfer refers to a technique that utilizes antenna array to generate spatial focusing of electromagnetic field to transmit power which is promising for powering multiple users over moderate distance safely and suitable for power supplement for indoor sensors.However,TR spot focusing WPT is hard to achieve the specified power distribution;in addition,how to improve the efficiency on the basis of specifying the power distribution of multiple users is also one of the difficulties.To achieve high efficiency under the specified power distribution of multiple users,in this dissertation,the TR multi-spot focusing method and efficiency improvement scheme are studied.The details of main contribution are as follows.First,the advantages about efficiency of TR for multi-spot focusing WPT is proved through the theoretical derivation,and further a multi-spot focusing method that optimizes the phase of the received signal is proposed.Compared with one that is based on linear superposition of weighted TR vectors,the proposed method has the advantages of less optimization variables and accurate power distribution.Secondly,according to the proposed multi-spot focusing method,the key factors of efficiency are analyzed through formula derivation and quantitative analysis.The influence of the channel and the received signal on efficiency is clarified in detail,which lays a theoretical foundation for efficiency improvement.Next,the novel scheme of efficiency improvement is proposed.Optimization design method of time reversal mirror(TRM)based on co-feed antenna unit is first proposed to improve the channel characteristics.In addition,efficiency can also be improved through perturbing power distribution owing to the constraint between efficiency and power distribution.Finally,experiment system of TR multi-spot focusing is designed and built for powering indoor users wirelessly.Through the comparison of experimental data,the effectiveness of the proposed efficiency improvement scheme is proved.By selectively driving LEDs wirelessly,the feasibility of TR multi-spot focusing WPT to supply power for multiple indoor sensors is verified.