梯度折射率超材料透镜  

A review of gradient index metamaterials lenses

作　　者：王丹凤 任致远 庄国志 Danfeng Wang;Zhiyuan Ren;Kuo-Chih Chuang(Istinute of Appied Mechanics,School of Aeronautics and Astronawtics,Zhejiang Universiny,Hangzhou 310058,China)

机构地区：[1]浙江大学航空航天学院,应用力学研究所,杭州310058

出　　处：《科学通报》2022年第12期1279-1289,共11页Chinese Science Bulletin

基　　金：国家自然科学基金(11972318)资助。

摘　　要：超材料是由人工设计的、具有天然材料所不具备的超常物理性质的人工复合结构,有负等效质量密度、负等效弹性模量、负折射率等特性.声子晶体超材料是一种具有周期性结构的超材料,其布拉格带隙或局域共振带隙的存在使处于禁带频率下的声波或弹性波进入声子晶体后无法在其中传播.其能带特性可以通过设计进行调节,使通带频率下的声波或弹性波进入具有特定结构的声子晶体后,实现成像、聚焦以及定向传输等对波传播的极端控制功能.梯度折射率超材料是一种折射率随空间变化而变化的结构.梯度折射率透镜由局部非均匀结构组成,其折射率是空间坐标的函数.波在透镜中会沿着弯曲的轨迹传播,可以通过适当的设计实现对波的弯曲、偏转和聚焦等功能.梯度折射率的设计可以通过改变局部晶体单元的性质实现有效折射率的梯度分布,如改变声子晶体的晶格尺寸、散射体的填充率、散射体的材料等.此外,梯度折射率超材料透镜能够通过设计在宽频率范围内精准聚焦波,从而实现能量采集等工程应用.本文从光学理论原理、透镜设计及其应用三方面展开介绍,首先对理论基础以及目前构建梯度折射率器件的几种方法进行总结,然后从透镜的应用角度介绍几种典型案例,最后对透镜的未来研究作出展望.As a kind of vibration propagation phenomenon existing in nature,waves have been captured and studied by people for a long time.With the concept of metamaterials proposed in recent decades,the manipulation and regulation of waves have reached a new height.Metamaterials are composites with artificially designed structures and supernormal physical properties that natural materials do not have.Generally,most of them have special characteristics such as negative equivalent mass densities,negative equivalent elastic modulus,negative refractive index,and so on.As a kind of metamaterials,phononic crystals are periodic structures whose Bragg band gaps or local resonant band gaps forbid the propagation of sound waves or elastic waves.The band characteristics can be adjusted by elaborate design,so that the acoustic waves or elastic waves under the passband frequency can achieve extreme control functions of wave propagation such as imaging,focusing and directional transmission.Gradient-index metamaterials are composites,whose refractive index varies with space,and have been employed in various applications.Gradient index lenses are composed of locally inhomogeneous materials,in which the refractive index is a function of spatial coordinates and the waves propagate along the curved trajectory.After proper design,they can have the functions of bending,deflection or focusing of the waves.The core of the design is to distribute the effective refractive index of the lens reasonably,which can be changed locally by changing the properties of each cell,such as the lattice size of phononic crystals,the filling rate of scatters,the material of scatters,and so on.In addition,Gradient index metamaterials can be designed to accurately focus waves over a wide frequency range for several engineering applications such as traveling wave energy harvesting for self-powered electronic devices.In this review,we firstly introduce the concept of gradient lens in optics and its history during about two hundred years.The relationship between refrac

关 键 词：梯度折射率 透镜 等效介质 声子晶体 超材料 

分 类 号：TB34[一般工业技术—材料科学与工程] TH74[机械工程—光学工程]