| The plasmonic metamaterial is a new type of artificial electromagnetic structural material composed of metal and dielectric unit structure.It presents the extraordinary physical properties that natural materials do not possess,which breaks the limitations of traditional materials design ideas and greatly improves the overall performance of materials.Since the first microwave frequency band of electromagnetic supermaterials was successfully implemented at the beginning of the 21st century,metamaterials has developed into a cross-cutting discipline involving many disciplines such as physics,materials science,chemistry,biology,and energy,and in recent years metamaterials It has also become a research hotspot in the academia and industry at home and abroad and has received sustained and extensive attention.In this paper,two commonly used electromagnetic simulation methods-Finite Element Method(FEM)and Finite Difference Time Domain(FDTD)-are used to study the negative refraction,electromagnetic induction transparency,and broadband electromagnetic waves of metamaterials.The new physical phenomena such as absorption,etc.,are taken into account.Based on the deep analysis of the relevant metamaterials physical mechanisms,their applications in solar thermal utilization,passive radiation cooling,electromagnetic stealth,and refractive index sensing have been systematically studied.The main research work and innovation contributions are as follows:(1)Fistrly,a dual-band double negative(each band possesses simultaneously negative permittivity and permeability)metamaterial is designed and demonstrated with broad NRI bands in mid-infrared region(3-30um).The broad band of NRI is contributed to the strong magnetic resonance caused by the excitation of surface plasmon polaritons.The influence of the number of square-shaped holes on the properties of the designed structures are also investigated by analyzing and comparing the transmission,permeability,permittivity,refractive index and figure of merit.Then,by optimizing the structural parameters,the proposed structure exhibits a negative band with a figure of merit of 3.3,which is to our knowledge larger than previously reported plasmonic metamaterial in mid-infrared region(M-IR).The value of negative refractive index(NRI)reaches-6 and the bandwidth of NRI can reach up to 4.2 THz in the low-frequency band of M-IR region,which is the widest NRI band in M-IR spectrum at present as far as we know.(2)Next,we propose and numerically investigate a novel perfect ultra-narrow band absorber based on a metal-dielectric-metal-dielectric-metal(MDMDM)periodic structure working at near-infrared region,which consists of a dielectric layer sandwiched by a metallic nanobar array and a thin gold film over a dielectric layer supported by a metallic film.The absorption efficiency and ultra-narrow band of the absorber are about 98%and 0.5nm respectively.The ultra-narrow band absorber shows an excellent sensing performance with a high sensitivity of 2400nm/RIU and an ultra-high figure of merit(FOM)of 4800.The FOM of refractive index sensor are significantly improved,compared with previously any reported plasmonic sensor.Besides,a novel optically tunable plasmonic metasurface is also proposed based on the hybridization of in-plane near-field coupling and out-of-plane near-field coupling.At the same time,ultra-sharp perfect absorption peaks with ultra-high Q-factor(221.43)is achieved around 1550 nm,which can lead to an ultra-high FOM(214.29)in sensing application.Particularly,by using indium-doped CdO,this metasurface is also firstly demonstrated to be a femtosecond optical reflective polarizer in near-infrared region,possessing an ultra-high polarization extinction ratio.Meanwhile,operating as nanoantennas,this metasurface achieves simultaneously strong local electric FE(|Eloc|/|EO|>100)and a near-perfect absorption above 99.9%for the first time,which will benefit a wide range of applications including photocatalytic water splitting and surface-enhanced infrared absorption.(3)Then,a novel way is proposed and numerically demonstrated to achieve electromagnetically induced transparency(EIT)phenomenon in the reflection spectrum by stacking two different types of coupling effect among different elements of the designed metamaterial.Compared with the conventional EIT-like analogues coming from only one type of coupling effect between bright and dark meta-atoms on the same plane,to our knowledge the novel approach is the first to realize the optically active and precise control of the wavelength position of EIT-like phenomenon using optical metamaterials.An on-to-off dynamic control of the EIT-like phenomenon also can be achieved by changing the refractive index of the dielectric substrate via adjusting an optical pump pulse.The novel approach realizing EIT-like spectral shape with easy adjustment to the working wavelengths will open up new avenues for future research and practical application of active plasmonic switch,ultra-high resolution sensors and active slow-light devices.(4)Then,a novel ultra-broadband solar absorber with applying iron in a 2-D simple metamaterial structure is proposed and numerically investigated to achieve the perfect absorption above 95%covering the wavelength range from 400 to 1500 nm.The broadband perfect absorption is caused by the excitation of localized surface plasmon resonance and propagating surface plasmon resonance.We firstly propose and demonstrate that the iron is obviously beneficial to achieve impedance matching between the metamaterial structure and the free space over an ultra-broad frequency band in the visible and near-infrared region,which play an extremely important role to generate an ultra-broadband perfect absorption.Besides,we also propose an ultra-broadband selective solar absorber with an extremely high absorption efficiency above 99%within the range of 435nm-1520nm.And meanwhile the emissivity of the nanostructure is below 20%in mid-infrared region.The total photothermal conversion efficiency of the proposed solar absorber can reach 91.53%,which is very close to the photothermal conversion efficiency(95.6%)of the ideal cut-off absorber.Owing to the characteristics such as polarization and angle independence,broadband operation,near-perfect absorption and strong spectral selectivity,the solar absorbers are promising candidates for solar energy harvesting,stealth technology,and thermo-photovoltaic energy conversion.(5)Finally,a near-ideal radiative cooler operating below the ambient temperature,is designed and numerically demonstrated to achieve both broadband selective emissivity in the infrared atmospheric window and extremely low absorption in the entire solar spectrum,realizing a net cooling power exceeding 122 W/m2 at ambient temperature.The cooling effect can still persist under significant nonradiative heat exchange conditions.The design of multi-layer all-dielectric micropyramid structure in this work not only solves the shortcoming of poor mid-infrared selectivity in planar photonics device,but also overcomes the disadvantage of high solar absorption in metal/dielectric metamaterials.The comparisons of physics mechanism between this multi-layer all-dielectric structure and previously reported multi-layer metal/dielectric structure also are investigated clearly.Thus,this study can help pave the way for designing ideal daytime radiative coolers. |
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