Methods Of Microwave Wireless Power Transmission In Enclosed Space

In recent years,many research efforts on wireless power transmission in enclosed environment have been reported.A typical application scenario is the wireless charging for electronic devices in the interior of satellite and spacecrafts.Implementation of simultaneous transfer of power and information can effectively reduce the complexity and weight of wiring cables and connectors,and as a result,improve the maintainability and extensibility of the avionic system.The severe multipath effect within enclosed space makes it challenging to transmit signal without distortion,but on the other hand,may be beneficial to wireless power transfer since there is no radiation loss.Furthermore,it is possible to provide wireless charging of multiple devices by utilizing the three dimensional space.Based on the aforementioned background,this thesis investigates methods of microwave power transmission in enclosed space.The characteristics of power transmission based on electromagnetic coupling of cavity resonant modes are analyzed,based on which,the possibility of wireless charging to multiple devices in a three dimensional space is explored.A reconfigurable focusing scheme is proposed for transmitting power to devices that is not fixed in location.Simulation and experimental results are provided,showing that the scheme can be used to adjust the distribution of electromagnetic wave within an enclosed space and thus improve the power transmission efficiency.Specifically,the work accomplished includes the follows:?1?Characteristics of microwave power transmission in enclosed space are studied and compared with that in open space.Power transmission based on electromagnetic coupling of cavity resonant modes are presented.Then modeling of multi-port system for power transmission in enclosed space is provided,based on which,two configurations,multiple-input?MI?and single-input-multiple-reflect?SIMR?,are analyzed.With a three port system example,the maximum power transmission efficiencies under these two configurations are compared.The theory and methods used in this thesis is determined and justified.?2?Power transmission though electromagnetic coupling of fixed cavity resonant modes are studied.Simulation and experiments are conducted for a 1m×1m×1m box resonant at the TM_z220mode.The results show that nearly 100%transmission efficiency can be achieved when the power receiver is located close to the focal point with maximum field intensity.In addition,a wireless channel possesses a relatively large bandwidth that can potentially be used for simultaneous transmission of power and information.Results also demonstrate that high transmission efficiency can be achieved when multiple receivers are distributed close to the electromagnetic focal points.Therefore,it is possible to simultaneously transmit power to multiple electronic devices distributed in a three dimensional space.?3?Based on the SIMR model of the multi-port power transmission system,a reconfigurable electromagnetic focusing scheme is proposed for microwave power transfer in enclosed space.Multiple parasitic elements with tunable reactive load are introduced.By adjusting the impedance of the reactive loads,distribution of electromagnetic fields within an enclosed region can be reconfigured.The method of selecting the optimal impedance to maximize power transmission is presented.Simulation and experimental results are provided showing that this method can effectively control electromagnetic focal position and improve the power transmission efficiency?for example,in particular cases,transmission efficiency can be improved from less than 1%to more than 90%?.?4?Design of reflective load with continuously tunable impedance is presented for the SIMR reconfigurable focusing scheme.The continuous turning of the impedance is realized by employing a diode varactor in parallel with a fixed inductor.With an SPDT switch,two sets of varactor-inductor network with different impedance coverage can be combined to maximize the turning range of the reflective load.Numerical results are provided to validate the impedance turner design.