Calculation Of Wideband Electromagnetic Scattering Based On Equivalent Principle Algorithm

Electromagnetic metamaterials are constructed by artificially designed sub-wavelength unit structure in a certain periodic or aperiodic space,because of its excellent electromagnetic/optical characteristics,such as negative refractive index,super-resolution,and polarization conversion,making them to be the leading field in the areas of quantum communication,nano-optics,material science,and energy exploration.Among them,the study of chiral metamaterials is particularly prominent.Chiral metamaterials which have no geometric symmetry with its mirror image,can't be overlapped with their mirror image by rotation or translation or other operations.Chiral "molecular" modeling based on artificial electromagnetic microstructures greatly promote the development of information communication,nano-optics,materials chemistry and other disciplines.Nevertheless,the realization of chiral resonance largely depends on the size of the cell unit structure and the periodic array arrangement.Not only the absorption bandwidth is narrow,but also the identification of left-handed circularly polarized waves(LCP)and righthanded circularly polarized waves(RCP)(chiral absorption)ability is weak.Therefore,this paper aims to achieve strong absorption circular dichroism,and carry out chiral "molecular" modeling,absorbing mechanism analysis,experimental measurement and other related studies.The main tasks are as follows:Firstly,a dual-band chiral metamaterial absorber(CSMA)in the microwave region is designed and experimentally verified.The structure of CSMA is composed of an asymmetric 'Ishaped' resonator on the top,a bottom metal shield,and an intermediate dielectric(FR-4).The absorption of LCP waves can reach 95.18% and 91.77% at the frequencies of 12.04 and 14.22 GHz.The power loss of the RCP wave is very small,which results in significant absorption circular dichroism.Research shows that the structure also realizes the circular polarization conversion of RCP reflected waves in a wide frequency band,and the bandwidth of circular polarization conversion rate(PCR)greater than 0.7 is as high as 5.2 GHz.By calculating the surface current,electric/magnetic field distribution,energy flow distribution,and optimization of different parameters,it is proved that this chiral absorption mechanism is mainly derived from the differential dielectric loss caused by the asymmetric resonance structure on the surface.Secondly,a mid-infrared dual-band chiral metamaterial absorber is proposed.Based on the structure of the microwave band chiral absorber,the surface resonance unit is simulated and calculated by the Drude model through parameter optimization.Finally,circularly polarized differential absorption in the mid-infrared band is realized.The calculation results show that,at the frequencies of 65.96 THz and 97.30 THz,super-absorption circular dichroism with an intensity of0.86 and 0.73 is achieved,respectively.Different from the absorption mechanism of the microwave band model,the mechanism of chiral absorption in the mid-infrared band is mainly derived from surface plasmon resonance.Thirdly,two models are proposed by combining method to study the effect of different periodic arrangement on chiral absorption.The longitudinal periodic chiral metamaterial absorber consists of two sets of asymmetric ' ?-shaped' resonators arranged upside down and the opening direction is reversed.At the frequency of 8.98 GHz,it achieves efficient absorption of LCP incident waves with an absorption rate of 91%.In the frequency range of 12.22-12.66 GHz,a strong broadband absorption of RCP waves is generated,with a peak value exceeding 84% and a relative bandwidth of about 7.0%.For comparison,the transverse periodic chiral structure consists of two sets of identical asymmetric '?-shaped' resonators arranged in parallel.Through numerical simulation calculations and research on the chiral absorption mechanism,the transverse chiral structure can only efficiently identify LCP waves(strongly absorbing LCP waves)at low frequency of 9.14 GHz,but cannot identify circularly polarized waves at high frequencies.