| Electromagnetic Metamaterial(EM)is a kind of artificial composite structure,and has being drawn great attentions due to its exotic properties.Compared with traditional absorbers,metamaterial absorption has the advantages of light weight,thin thickness and high absorption rate,which is widely used in invisible cloaking,nondestructive detection,terahertz imaging,antenna and other areas.This paper focuses on broadening the absorption bandwidth,and the main works are listed as following:(1)In the microwave region,a pyramid-shaped absorption structure with gradient distribution was proposed by placing four different sizes of pyramid cells in one period.Research results indicated that the absorption exceeds 90% from 8 to 14 GHz for the 9 layers structure(the total thickness is 4.122 mm),and the absorption exceeds 90% from 7 to 21.5 GHz for the 13 layers structure(the total thickness is 4.134 mm).The structure is insensitive to both TE and TM polarizations and the total absorption efficiency remains quasi-constant up to relatively large angles.Further analysis showed that the higher order mode of the larger resonant unit has a great contribution to the broadband absorption,which is different from the conventional absorption mechanism that only considers the fundamental mode.(2)In the infrared region,by embedding four different pentagonal resonant elements in one period,a new ultra-broadband absorption structure was proposed.The absorption of the single layered structure exceeds 90% from 7.8 to 12.1 μm for both TE and TM polarizations,and the absorption of the double layered structure exceeds 90% from 5.17 to 13.73 μm for both TE and TM polarizations.By investigating the surface current and magnetic field distributions of the metallic pattern,it is found that both electric and magnetic resonances exist and the resonant wavelengths are nearly directly proportional to the size of the surface patch.Microwave absorption is very important in the radar stealth,and the infrared absorption is very important in the radiation cooling.Therefore,our research results have important practical value in the two areas. |
