Research On Omni-directional Wireless Power Transfer Based On Rotating Magnetic Field

Wireless power transfer (WPT) technology is a kind of new proposed technologywhich could transfer electric energy to the load without electric wire. Since thetechnology of magnetic resonance coupling wireless power transfer (MCR-WPT) wasproposed by MIT in2007, more efforts have been put into the research of near-fieldnon-radiative wireless power transfer (WPT) using magnetic resonant coupling in recentyears. MCR-WPT is less sensitive to surroundings and safer for humans and can beused in implanted medical device, mobile devices and electric vehicle. However, mostof the WPT systems face the restriction that it requires precise alignment betweentransmitting and receiving coils. While the centers of two coils shift a little, theefficiency will be significantly decreased, in this case, it is hard to provide wirelesspower transfer for mobile devices. Thus, a method for omnidirectional wireless powertransfer (OWPT) needs to be proposed.In our investigation, we start from the analysis of the magnetic field distribution ofthe MCR-WPT system, and we find out what kind of magnetic magnetic fielddistribution could provide wireless power to receiver omnidirectionally. Then wepropose a pair of cross coil which consists of two orthogonal loops with90°feedingphase difference to sever as the transmitter. Both theoretical analyses and numericalsimulations show that such transmitter generates rotating magnetic field and can providewireless power to multiple receivers moving around it. In addition, a cylindricalmetamaterial slab with negative permeability is used to improve the efficiency of theOWPT system, for the unique property of enhancing evanescent wave of metamaterials.It is shown that the efficiency of the OWPT can be significantly improved bymetamaterial. Finally, we proved that this proposed system could provide wirelesspower to receiver omnidirectionally by experiment.In this paper, we introduced the history of wireless power transfer at first, we givena brief introduction to other researchers’s work and the advantage or disadvantage ofeach method for wireless power transfer is given by comparison. Secondly, we build amodel of MCR-WPT, and find out the influence on the system of different parameters.By using a magnetic dipol antenna to instead the resonant coil, we given a express to thephenomenon that the efficiency of the WPT system dropped quickly when the two coilmissed precise alignment. Thirdly, we proposed a pair of cross coil which consists oftwo orthogonal loops with90°feeding phase difference, and build an omnidirectionalwireless power transfer system with the cross coil serve as the transmitter to solve thequestion mentioned above, both theoretical analyses and numerical simulations showthat an OWPT system is formed. Fourth, we proposed a metamaterial cylinder toenhance the efficiency of the proposed OWPT system. And finally, we demonstrated that the proposed OWPT system could work as what we have predicted by experiment.The metioned method for omnidirectional wireless power transfer in this paper isnovel and has good completeness and originality which realized the goal of providewireless power to receiver omnidirectionally. The paper not only illustrates the theoryanalysis integrallty, but also complete the design and simulation of OWPT system. Inaddition, the experiment results agree with our theoretical analyses and numericalsimulations well. The investigation offers new thinkings in the field of omnidirectionalwireless power transfer and has much value for researchers.