基于变换光学的新型电磁功能器件的研究与设计

发布时间：2018-01-07 10:16

本文关键词：基于变换光学的新型电磁功能器件的研究与设计　出处：《山东大学》2016年博士论文　论文类型：学位论文

【摘要】：变换光学是近年来新兴的一种设计电磁物质的技术,其理论基础是麦克斯韦方程组在坐标变换下形式不变性原理。变换光学与传统光学的区别在于,传统光学是用费马原理来描述折射率的变化如何影响光的传播路经,而变换光学则是通过设计材料的属性来实现特定的光传播路径。在变换光学中空间形状起着主导作用,通过坐标变换以增加物质参数的复杂性为代价,大大简化电磁器件的设计过程,也就是说在设计过程中把空间的改变等效为空间内介质参数的改变,为人们提供了一种全新的调控电磁波的手段。人们可以根据对电磁波的调控需要来构建空间映射,然后寻找能够实现这种映射的坐标变换,再计算出变换介质的参数。这种方法最初应用在电磁隐身方面,通过一组特定的空间映射,得到了变换介质的参数,并借助于超材料设计出了电磁隐身斗篷,电磁波在隐身斗篷中会绕开隐藏物体,在斗篷外再回到原来的传播路径上,这样从斗篷外探测不到斗篷内的物体,斗篷内的物体就实现了“隐身”。经过坐标变换以后的光学结构所需物质的本构参数一般是不均匀、各向异性的,但大多情况下这些本构参数都可以通过超材料技术来满足或者近似满足,这样在现实中利用变换光学技术就变的可行,同时也推进了变换光学技术的快速发展。超材料在变换光学的发展中起着重要的作用,由此引起的革命正在全世界各个实验室的诸多研究方向中进行。由于在红外和可见光范围内能够支持表面等离子波的传播,贵金属中的金和银一直被广泛地应用在光学超材料的组成中。但是这些贵金属材料存在很多缺点：介质参数不可改变,在一定频率范围尤其是可见光范围内存在严重的损耗等等,这就限制了由金或银组成的超材料在变换光学中的应用。然而,近年来出现的目前世界上已知的最薄的,由六角元胞碳原子组成的蜂巢状二维晶体-石墨烯,具有强度大、导热性与导电性极好等特性,另外,石墨烯还具备超大的比表面积,价格低廉等特点。因此,石墨烯被科学界认为是一种可以大力促进科学研究进步的材料,并且预言其在晶体管、太阳能电池、传感器、超级电容器、场发射和催化剂载体等方面都有着良好的应用前景。在石墨烯的诸多特性中,石墨烯的材料参数可以通过外部条件的改变而改变的特性是石墨烯最为突出的特性,这样石墨烯就可以克服传统贵金属组成的超材料的缺点,成为一种新型的变换光学材料。正是在这样的研究背景下,本文开展了一些基于坐标变换的电磁功能器件的研究与设计工作,主要包括以下几个方面：1.在详细分析和叙述了几种隐身斗篷的基础上,提出了通过压缩空间来改变物体外观的思路。首先将原空间的一个圆形区域划分为内外两个区域,然后对内区域进行压缩或者扩展变换,外区域采用相应的变换,以保证外区域与自由空间匹配,减小在此交界面上的反射。当物体被放入到这个圆形区域的内区域时,空间的改变就转化为介质参数的改变,这样放入内区域的物体对外界电磁波的散射就会增大或者减小,以至于观察者从外部无法确定物体的真实大小。对内区域继续进行压缩或者扩展,放入内区域的物体对外界电磁波的散射会进一步改变,当散射变得很小很小以至于可以忽略的时候,那么这个圆形区域就变成了隐身斗篷。变换光学的具体实现方法有很多,其中借助于某些软件直接求解偏微分方程的数值解得到介质参数的方法,比直接进行坐标变换的计算量会减小很多,利用起来更方便。因此,本文利用COMSOL软件中的PDE模块设计了一种平面天线,这种天线具有平面结构,同时又具有传统抛物天线的特性,这样不仅达到了天线小型化的目的,还为以后设计超常规天线提供了一种方法。2.提出基于石墨烯的红外隐身斗篷的设计,并对其功能进行了研究与分析。与以往采用传统材料制成的隐身斗篷不同,本文提出了石墨烯隐身斗篷的设计。石墨烯是近几年出现的一种纳米材料,由于其独特的单原子层结构而具有很多独特的性质,使得石墨烯成为近几年物理界和材料界的研究热点,其中石墨烯最突出的特点是其介电常数的可调性。在此基础上,本文将设计一个具有渐变折射率的半球面结构的全向隐身斗篷。在现实中,真正做到折射率渐变是很困难的,所以在制作过程中一般采用离散方法,用很多均匀折射率来近似代替渐变折射率。石墨烯的电导率可以通过很多方法来改变,本文用外加电场,设置石墨烯层和硅衬底之间电解质的不同厚度的方法,来改变石墨烯的电导率。用很多具有相同电导率的石墨烯窄带组成的近似半球结构来代替具有渐变折射率的半球表面,形成一个全向的隐身斗篷,并且石墨烯对表面等离子波具有很好的局限性。当表面等离子波经过该石墨烯组成的近似半球结构时,其传播特性和在平面上传播时完全相同,这样半球面内的物体就会被“隐身”。3.提出基于石墨烯的可调焦距红外透镜的设计,并对其功能进行研究与分析。当施加外电场时,石墨烯层和硅衬底之间的距离可以影响石墨烯表面的载流子浓度,从而在石墨烯表面产生不同的电导率。根据这个原理,本文将提出基于石墨烯的可调焦距的红外透镜的设计,通过有目的地设计石墨烯层和硅衬底之间电介质的厚度,可以使石墨烯表面产生不同的电导率以及折射率,这样入射的电磁波就可以在石墨烯层的不同位置会聚,同时该透镜还具有准直电磁波的作用,最后将用有限元法验证该透镜的性能。
[Abstract]:Transformation optics is a technology for the design of electromagnetic material emerging in recent years, the theory is based on the Maxwell equations in the form invariance principle coordinates. The difference lies in the transformation optics and traditional optics and traditional optics is used to describe Fermat's principle of refractive index changes such as propagation path of light effects, and transformation optics is the attribute of design material to achieve the light propagation path. The specific spatial shape plays a dominant role in the transformation of optics, complexity by coordinate transformation in order to increase the cost of material parameters, greatly simplify the design process of the electromagnetic device, that is to say in the design process to change the equivalent of space for medium parameter space change. Provides a new method of controlling electromagnetic wave for people. People can build space mapping according to control electromagnetic waves, and then looking to achieve this The coordinate transformation mapping, and then calculate the parameter transformation medium. This method was first applied in the electromagnetic stealth, through a specific set of space mapping, the parameter transformation medium, and with the help of metamaterials designed electromagnetic cloak, the electromagnetic wave will bypass the hidden object in the invisibility cloak, in the cloak outside the back propagation path of the original, so from the outside to detect cloak cloak objects in the cloak of objects in the realization of "stealth". Through the optical structure of coordinate transformation after the required material constitutive parameters are generally not homogeneous, anisotropic, but in most cases these constitutive parameters can through the metamaterial technology to meet or satisfy approximately, in reality this transformation using optical technology becomes feasible, but also promoted the rapid development of transformation optics technology. The development of ultra light materials in transformation Plays an important role in many research direction caused by the revolution is all over the world in the laboratory. Because the infrared and visible light range can support the propagation of surface plasmon wave, precious metals gold and silver has been widely used in optical metamaterials. But these precious metal materials there are many shortcomings: the parameters can not be changed in a certain frequency range especially serious loss in the range of visible light and so on, which limits the application of metamaterials composed of gold or silver in the transform optics. However, in recent years, the current known as the world's thinnest, two-dimensional honeycomb crystal composed of six angle cellular carbon atoms - graphene, with high strength, high conductivity, thermal conductivity and other properties, graphene also has a large surface area, low price and so on. Therefore, graphene is The scientific community that is a vigorously promote scientific progress of research materials, and predicted its transistors, solar cells, sensors, super capacitors, field emission and catalyst carrier has a good application prospect. In many properties of graphene, graphene material properties parameters can be obtained by external conditions change is the most outstanding characteristic of graphene, graphene such can overcome the shortcomings of traditional metamaterials composed of precious metals, become a new type of transform optical materials. It is in such a background, this paper carried out some research and design of electromagnetic devices based on the coordinate transformation that includes the following aspects: 1. in the detailed analysis and description of the basis of several Cloak, made by compressing the space to change the appearance of an object, the first original ideas. A circular area is divided into two regions, and the regional compression or expansion transformation, using the corresponding transformation region, to ensure regional matching with free space, then turn on the reflecting interface decreases. When the objects are put to the area within the circular area, the change of space transformation for the medium parameters change, so in areas within the object on the electromagnetic wave scattering will increase or decrease, so that the observer from the outside can not determine the true size of the object. The region continues to compress or expand into areas within the object scattering of the electromagnetic wave will further change, when the scattering is very small that can be ignored, so the circular area becomes a cloak. There are many specific methods to achieve transformation optics, and directly to some software with them Methods the medium parameters of the numerical solution of partial differential equations, the amount of calculation than directly coordinate transformation will reduce a lot, use more convenient. Therefore, in this paper, a planar antenna design using PDE module in COMSOL software, this antenna has a planar structure and characteristics at the same time with the traditional parabolic antenna, such not only to achieve the purpose of antenna miniaturization, but also for the future design of the ultra conventional antenna provides a method of.2. proposed design of infrared stealth cloak based on graphene, and the function is made with previous research and analysis. With traditional materials cloak different, this paper presents a design of graphene cloak. Graphene is a kind of nano material in recent years, because of its special single atomic layer has many unique properties, the graphene has become in recent years, physics and material science Of which the most prominent feature of graphene is its dielectric tunability. On this basis, this paper will design a hemispherical structure with graded refractive index of the omnidirectional cloak. In reality, truly graded index is very difficult, so the discrete method in the production process for many, we can replace the uniform refractive index gradient refractive index. The conductivity of graphene can be changed by many methods, this paper use the method of external electric field, different thickness arranged between the graphene layer and the silicon substrate of the electrolyte to change the conductivity of graphene. Approximate hemisphere structure instead with hemispherical surface graded refractive index of graphite many have the same narrow graphene conductivity composition, form an omnidirectional cloak, and graphene has great limitations on surface plasma wave. When the surface of ion Through the wave of graphene approximate hemisphere structure, its propagation characteristics and propagation in the plane are the same, so the hemispherical objects in the "stealth".3. will be designed with adjustable focus infrared lens based on graphene, and study and analysis of its function. When the applied electric field. Between the graphene layer and the silicon substrate distance can affect the carrier concentration of graphene surface, resulting in different conductivity on the surface of graphene. According to this principle, this paper will put forward the design of infrared lens with adjustable focal length of graphene based by the purposeful design between the graphene layer and the silicon substrate thickness of the dielectric. The surface of graphene have different conductivity and refractive index, different positions of such incident electromagnetic wave can be in graphene layer convergence, while the lens also has a collimated electromagnetic wave for In the end, the performance of the lens will be verified by the finite element method.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O441

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