基于图案化石墨烯的宽带太赫兹超材料吸收器

Broadband Terahertz Metamaterial Absorber Based on Patterned Graphene

设计了一种基于石墨烯的新型可调谐宽带超材料吸收器。该吸收器采用经典夹层结构,包含一个图案化的单层石墨烯超表面、介电层和金属底板。该石墨烯图案的结构由不同尺寸的石墨烯谐振器组成,确保高吸收率的同时能拓宽吸收带宽。研究结果表明,当费米能级E_(f)为0.9 eV时,吸收器在光源垂直入射条件下能实现2.3~5.2 THz波段90%以上的宽带吸收率,同时通过控制石墨烯的费米能级可以灵活调节吸收器的带宽和吸收性能。此外,基于单元结构的对称设计,吸收器对偏振角度的变化并不敏感,所设计的吸收器结构将促进石墨烯材料在太赫兹波段和新型吸波器件中的广泛应用。

The frequency of terahertz radiation is 0.1~10 THz,which is between microwave and infrared.In terms of energy,it is between electrons and photons.Terahertz,like X-rays and sound waves,can penetrate the surface of objects for imaging.In addition,the terahertz frequency is very high,so its spatial resolution is also very high;it also has very high temporal resolution because of its short pulse(picosecond order).Terahertz radiation has been widely used in safety inspection because different chemicals can absorb terahertz radiation at different frequencies to different degrees,showing unique frequency characteristics.In addition,it shows unique advantages and broad application prospects in many fields such as radar,communication and nondestructive testing.It can be predicted that terahertz technology will be one of the major emerging fields of science and technology in the 21st century.However,there are relatively few functional devices in the terahertz band at present.The fundamental reason is that most natural materials can only exhibit weak electromagnetic response when interacting with Terahertz waves,which limits the further development of terahertz technology.The absorption of terahertz waves,especially the complete absorption,has great potential application value in electromagnetic stealth,thermal sensing and thermal imaging.Therefore,the search for an absorbing material that can perfectly absorb the terahertz band has become a major research topic in the direction of materials science in various countries.Traditional absorbing materials are mostly designed based on the principle of Salisbury absorption screen.Its typical weakness is that it is very thick and bulky.With the increasing demands on the performance of absorbing materials in the fields of communication and stealth,traditional absorbing materials can no longer meet the needs of civil and military applications.Therefore,the development of more lightweight and miniaturized new wave absorbing devices has become an urgent task at present.With the discovery and research of metamaterials,it provides an effective way to realize terahertz functional devices,especially terahertz absorption devices.Metamaterials are artificial electromagnetic structures typically made of subwavelength metals on dielectric or semiconductor substrates.Compared with traditional materials,metamaterials have some special properties,such as changing the normal properties of light or electromagnetic waves,and such effects can not be achieved by traditional materials.The research shows that using the exotic electromagnetic properties of metamaterials can not only improve the performance of antennas and microwave devices,develop new equipment,but also provide a new technical means for the development of new absorbing materials.Most of the metamaterial absorbers proposed so far are composed of precious metals such as gold and silver.Once the size is determined,it is difficult to adjust the resonance frequency and absorption intensity.At present,the research on terahertz metamaterials at home and abroad is more focused on the application of metamaterials in the realization of tunable functional devices in the terahertz band,especially the realization of tunable terahertz functional devices.Therefore,the development of tunable metamaterial absorbers will be of great significance for the application of metamaterials.Fortunately,the medium on which processing is relied also plays a role in the electromagnetic properties of metamaterials.Studies have shown that the control of the optical properties of metamaterials can be achieved very effectively by combining metamaterials with media with tunable optical properties such as graphene,liquid crystal and phase change materials.Among them,graphene,as a band-free semiconductor,has attracted much attention in the field of materials science in recent years due to its unique electrical and optical properties.Graphene also has important applications in the research of optically tunable metamaterials.Through chemical or electrostatic doping,the carrier concentration and Fermi level of graphene can be changed,which is very wide on the terahertz frequency range,effectively change the position of the resonance peak and can be used to implement the infrared to the terahertz frequency range adjustable perfect absorber,polarizer,filters and other optical components.Based on the selected topic background and the research status,this paper aims at the research of tunable dielectric metamaterials and the design and optimization of broadband terahertz metamaterial absorber structures,mainly on the optical properties and tunability of graphene in metasurfaces.The main research content is to take graphene twodimensional planar metasurface as the research object,design a patterned graphene broadband metamaterial absorber model,and conduct simulation analysis through FDTD solutions optical simulation software.The modulation of graphene on the optical properties of metamaterials and the control of the amplitude,polarization and propagation of terahertz waves by metamaterial are studied based on the FDTD method and principle of surface plasmon resonance,and the structural parameters are optimized by progressive simulation.The absorber adopts a classical sandwich structure containing a patterned single-layer graphene metasurface,a dielectric layer,and a metal backplane.The structure of the graphene pattern consists of graphene resonators of different sizes,ensuring a high absorption rate while broadening the absorption bandwidth.The results show that when Ef=0.9 eV,the absorber can achieve a broadband absorption rate of more than 90%in the 2.3~5.2 THz band under the condition of normal incidence of the light source.Meanwhile,the bandwidth and absorption performance of the absorber can be flexibly adjusted by controlling the Fermi energy level of graphene.In addition,based on the symmetrical design of the unit structure,the absorber is not sensitive to the change of the polarization angle,and the designed absorber structure can promote the wide application of graphene materials in the terahertz band and new absorbing devices.