| Metamaterials are artificially designed composite structures that have many electromagnetic characteristics not available in natural materials.Due to the excellent ability in manipulating electromagnetic wave,it have attracted enormous international attention in the past decades.Metamaterial absorber,being different from many other metamaterial devices,utilizes the loss of metamaterial to achieve absorption rather than avoid it.Compared to other absorbers,metamaterial absorber is extremely thin and can realize near 100% absorptivity,shows great potential in many domains.However,the resonant characteristics lead to narrow absorption bandwidth of the current metamaterial absorber.And most of metamaterial absorber is two-dimensional planar structure,which is difficult to realize omnidirectional wave absorption.Metamaterial fiber is a new type of metamaterial structure,while with few related application.So far,it is limited to super lens and waveguide structure.However,it is expected to realize applications in more fields through rational structural design,such as omnidirectional high absorption of electromagnetic waves.Based on the impedance matching theory,a variety of metamaterial absorbers were designed in this study.And the absorption characteristics were simulated.Besides,innovatively,metamaterial fiber with wave absorbing ability was designed and investigated.The main contents are as follow:Based on the existing research results of metamaterial absorber,combined effect of different resonant units was studied.Broadband metamaterial absorbers with novel structural units were further innovatively designed.And the influence of coupling between different resonant elements on absorption was analyzed.At first,square resonator and gap-ring resonator were combined in a unit cell.But it is difficult to obtain broadband high absorption due to the coupling between two resonant elements.The square resonator was modified to release the coupling so that a metamaterial absorber with broadband high absorption was achieved.Then,another metamaterial absorber with broadband high absorption was realized through arranging the cross resonator in the lattice gap of square resonantor.Finally,the above three resonators,modified square resonantor,gap-ring resonator and cross resonator were combined together and reached a broader absorption bandwidth.The results indicated that combining different resonant structures in a unit cell is an effective approach to broaden the absorption bandwidth of metamaterial absorber.But the influence of coupling between different resonant elements should be reduced as much as possible.Metamaterial fiber with wave absorbing ability was designed and investigated innovatively.Based on this,metamaterial fiber structures with broadband wave absorbing ability were achieved.First,cylinder resonator was chosen for it is easy to achieve in fiber structure.And a large diameter metal cylinder was used to replace the bottom metal layer of planar metamaterial absorber,so that the whole planar structure was transformed to fiber structure.Then,arranged the fiber become fiber array and simulated the absorption of the fiber array.The fiber array showed near 1 absorptivity at resonant frequency.Besides,fiber structure with different dimension was combined in a unit cell and achieved a metamaterial fiber array with broadband wave absorbing ability.Finally,fiber structures which can produce multiple ring currents were design and contributed to broadband absorption.The greater the number of ring currents,the broader absorption bandwidth.Compared with planar metamaterial absorber,the metamaterial fiber structure is easier to realize broadband high absorption.Metamaterial fiber structure unit,which can absorb electromagnetic wave incident from omnidirectional was designed and investigated.Utilizing the symmetry of the fiber,fully symmetrical fiber structures with 4-fold symmetry,6-fold symmetry and 8-fold symmetry were designed.And the simulated results showed that as the symmetry of the fiber structure increases,the absorption stability of the structure unit to omnidirectional incident electromagnetic waves is better.Based on above,a fiber structure unit with broadband absorbing ability to omnidirectional incident electromagnetic waves was also achieved. |
