Research On Metamaterials Applied In Wireless Power Transfer

Wireless power transfer has gained extensive interest in the past decades with the surge in the use of electronic devices.Among all the different methods,resonant inductive coupling has been studied and used most wildly in consumer electronic devices.The main concern of this technique is to improve the transmission efficiency while maintaining a satisfying transmission distance.Most existing researches focused on the topology of the electronic converters,the controlling method and the structure of the transmitting and receiving coils.This paper proposes a new solution to the problem — to increase the efficiency of a wireless power transfer system with metamaterials.Metamaterials are artificially engineered materials with negative permittivity or permeability.They can be designed to manipulate the electromagnetic fields at will.This paper studies the application of metamaterial devices in a wireless power transfer system and experimentally validates the effects of metamaterials.First,the transformation optics method is explained in both cartesian coordinate system and orthogonal coordinate system.Three metamaterial devices that are suitable for wireless power transfer are designed by transformation optics,including the magnetic concentrator,the shifting medium and the superscatterer.Their effects are validated through simulation.The aforementioned devices have complicated electromagnetic parameters,thus difficult to manufacture.To avoid this difficulty,this paper proposes a pair of shifting slabs,constituted by a positive magnetic slab and a negative magnetic slab.The shifting slabs can be used in a wireless power transfer system to cover the transmitting coil or the receiving coil.Numerical simulations validate that the shifting slabs can approximately shift the electromagnetic fields generated by the transmitting coil,thus enhancing the magnetic coupling as well as the efficiency of the system while remaining the transmission distance unchanged.Moreover,the special case of a magnetic metamaterial slab — a magnetic metamaterial plane is studied in this paper.The magnetic metamaterial plane can be regarded as a slab with peculiar permeability at one direction and unity permeability at other directions.The performance of the metamaterial plane of different permeabilities is studied with both theory and simulation in a wireless power transfer system.The derived conclusions are validated with experiments on a wireless power transfer platform whose working frequency can be adjusted by matching capacitors.Finally,a 7.2MHz wireless power transfer platform is established to further study the performance of metamaterial devices in a practical system.Experiments are conducted to compare the efficiency of the wireless power transfer system with a metamaterial plane and that of the non-metamaterial system with the same effective transmission distance.It suggests that a metamaterial plane can effectively improve the whole system's efficiency when the required transmission distance is larger than the size of the transmitting coil and the receiving coil.The performance of a metamaterial plane and a metamaterial hemisphere is also compared.