| Electromagnetic metamaterials(MMs)and wireless power transfer(WPT)are cutting-edge technologies at the beginning of the century,which have potential application in military and civilian area.In the paper,the good electromagnetic properties of MMs are widely used into absorber and WPT system in order to improve the working performance.We mainly investigate the metamaterial absorbers(MAs)based on metal and dielectric as well as near-filed metamaterials for WPT system by theory,simulation and experiment.Moreover,some designs of the single-band,triple-band and broadband MAs are proposed,and the electromagnetic influence of near-field planar MMs on WPT system is also investigated.Here,the relevant contents are as follows:(1)Based on the unit cells of sectorial annular structure,a MA is designed.Especially,the absorptivity still keeps above 90% even when 70° oblique incidence,which has polarization and incident-angle insensitive absorbing properties.Based on the sectorial annular structure,wide absorption band is obtained by the stacking resonance.The results reveal that the designed MA has above 90% absorption with 3.2 THz bandwidth in the frequency range from 7.55 THz to 10.75 THz.These results provide a solid foundation for the design of teraherz multi and broad frequency MAs.(2)Based on the gap-ring and cave-ring elements,two kinds of MAs are respectively proposed.They achieve triple-band perfect absorption with nearly 100%,which own the wide-angle absorption stability.Electric field distributions are used to analyze absorption mechanism.The number of absorption band is controlled by incident angle.The single-band absorptivity achieves 92% even when 80° oblique incidence of TE wave.And,the MA based on cave-ring simple structure owns over 80% absorption even when 60° oblique incidence.Then,triple-band and four-band MAs are quickly designed by complement strategy.The design philosophy can offer some helpful reference for developing absorbers in other frequency band.(3)A kind of broadband tunable MA based on dielectric structure is designed.Based on the decoupling and weak-coupling model,the interference theory is firstly used to quantitatively analyze the broadband tunable absorption mechanism.Simulated results reveal that the resonance bandwidth and absorptivity are controlled by the moisture in the MA.Under the condition of 30% moisture,the simulation and experiment verify the broadband absorption with 90% in the frequency range from 5.76 GHz to 17.12 GHz,and its relative bandwidth reaches 99.3%.The designed MA owns polarization-insensitive and wide-angle absorptive properties.To highlight the advantage of the wideband absorption,the water based MA is compared.An absorption peak with above 90% absorptivity is obtained by simulation and experiment.(4)The near-field planar MMs which are applied to WPT system are designed.The square and circular spiral structures are popular in near-field metamaterial cells.Effective circuit is constructed by the geometrical character and the electrical parameters are calculated to accurately get the effective permeability.Then,a 6.78 MHz MMs-WPT system is built,which the electromagnetic impacts of near-field MMs on the performance of WPT system are investigated by theory,simulation and test.It indicates that non-pefect MM lens can better improve the transfer efficiency in WPT system.The multi-reflection interference theory is firstly used to explain the broadband tunable dielectric MA which reveals the influence of dielectric loss on theory model.The design of metal and dielectric based MAs establishes some technical bases for multi-band or broadband absorbers in practice.Based on the strong ability of artificially manipulating electromagnetic field,the near-field MM WPT system is constructed.It reveals that the negative permeability MM can enhance the transfer efficiency,and,especially,the non-perfect MM lens can better improve the efficiency.These results have a guide on how to solve the low efficiency of WPT systm. |
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