Development And Performance Analysis Of The Multi-band And Cross-band Metamaterial Absorber From 1 GHz To 10 THz

Metamaterials,refer to the artificial composite material or structure,which can be designed by controlling atoms or molecules artificially to prepare periodic or aperiodic artificial micro-structure units,showing extraordinary physical properties different from natural materials.In the information age when microwave and terahertz waves are widely used,metamaterial absorbers have broad application prospects in military and civil fields.This paper summarized the development of metamaterial absorbers,and analyzed problems and shortcomings of the current metamaterial absorber in microwave and terahertz band.In the aspect of microwave multiband absorbers,many things need to be improved,such as the complex resonance structure,the inability of excellent absorption and structural characteristics,and the lack of flexible metamaterial absorbers.In the aspect of terahertz absorbers,the absorption gap of the terahertz broad band has to be settled urgently.In the aspect of cross-band absorbers,how to achieve the multiband absorption of the cross band simultaneously is also a challenge.On the basis of above shortcomings,this paper proposed some sorts of metamaterial absorbers to realize multi-band,broad-band and cross-band absorption in the 1 GHz?10 THz frequency band,which mainly focuses on the following aspects.Firstly,five microwave metamaterial absorbers were designed,which include three multiband absorbers with simple resonator,one flexible four-band absorber and one broadband absorber with perforated frustum of a cone.Based on three surface resonators of ring and cross combination,square ring and double cross combination,rhombus ring with straight angle and double cross combination,three multiband metamaterial absorbers with “metal-dielectric-metal” structure were designed and fabricated.Nearly 100% perfect absorption is achieved by those absorbers at the resonance frequencies of 4.44 GHz and 7.85 GHz,3.80 GHz and 8.63 GHz,7.48 GHz,9.70 GHz,and 11.27 GHz.Based on a hollowed ring and cross resonator,an ultra-thin flexible four-band metamaterial absorber was designed and fabricated,which achieves absorptivity above 90% at the resonance frequencies of 3.25 GHz,6.89 GHz,9.38 GHz,and 10.60 GHz.An ultra-broadband metamaterial absorber with a relative bandwidth of 112.44% from C-band to K-band is designed based on the superposed structure with perforated frustum of a cone.It achieves efficient absorption from 6.65 GHz to 23.73 GHz,and the absorptivity is more than 80% in the whole absorption band.The calculation of the proposed metamaterial absorbers at various polarization and incident angles are carried out,which verify the polarization-insensitivity and wide-angle characteristic of the absorbers.The calculation of the electromagnetic fields and surface currents reveal the absorbing mechanism of electromagnetic resonance,and the individual structure extracted from the triple-band and broadband absorber is analyzed respectively.The preparation and measurement method of the microwave metamaterial absorber are expounded minutely.We have prepared two dual-band,a triple-band,and a four-band absorber,and measured the absorption performance by arch method.The experimental results agreed greatly with the simulation,and the error is analyzed to verify the efficient absorption performance of the absorbers.Secondly,a terahertz broad-band metamaterial absorber is designed based on rhombus ring structure,and it has the non-subwavelength characteristics.In terms of absorption,the proposed absorber achieves absorptivity above 90% from 5.09 THz to6.95 THz,whose absorption bandwidth is 1.86 THz.The absorption performance fills the gap of the absorption in the range of 5?7 THz.The absorption principle is numerically analyzed by the equivalent circuit model and equivalent medium theory.The calculations of the various polarization angle demonstrate the polarizationinsensitivity of the terahertz absorber.The absorptivity and absorption band decreases with the increasing of incident angle,which can maintain efficient broadband absorption under the incident angle less than 60° and 50° in the TE and TM mode respectively.Electromagnetic analysis reveals the absorption essence of the proposed absorber is electromagnetic resonance,and the significant influence of dielectric layer's thickness on absorption performance also verifies that main contribution of absorption is the magnetic resonance in dielectric layer.Finally,in order to realize the design of cross-band metamaterial absorber,a novel design concept of superposed principle is put forward and explained in detail.On the basis of the superposed principle and hollow-cross structure,a cross-band metamaterial absorber is proposed to obtain multi-band absorption in both microwave and terahertz bands simultaneously,which generates absorption bands at 110.20 GHz,162.32 GHz,186.37 GHz,1.18 THz and 1.85 THz,respectively.Theoretically,the equivalent electromagnetic parameters and equivalent impedance of the cross-band absorber are derived by equivalent medium theory,which verifies the impedance matching between the proposed absorber and free space.In the simulation,the electromagnetic responses of the individual absorbing unit cells and superposed absorbing unit cell are analyzed,which reveals that the electromagnetic resonance of individual absorbing parts of the superposed absorbing unit causes the energy loss of the incident microwave and terahertz waves respectively.The absorption properties of the proposed cross-band absorber under various polarization angle,incident angle and structural parameters are analyzed,which prove that the polarization and incident characteristics of the superposed absorbing unit cell are consistent with those of the individual absorbing unit cell.In other word,the design of superposed cross-band metamaterial absorber can be regulated and controlled by designing the individual absorbing unit cell.This design concept based on the superposed principle provides a new idea for the design of crossband metamaterial absorber,and the proposed cross-band metamaterial absorber can also be used in multiband electromagnetic stealth and electronic countermeasures.