本文關(guān)鍵詞：基于變換光學(xué)的新型電磁功能器件的研究與設(shè)計(jì)　出處：《山東大學(xué)》2016年博士論文　論文類(lèi)型：學(xué)位論文

  更多相關(guān)文章： 變換光學(xué) 麥克斯韋方程組 石墨烯 電磁功能器件 漸變折射率

【摘要】：變換光學(xué)是近年來(lái)新興的一種設(shè)計(jì)電磁物質(zhì)的技術(shù),其理論基礎(chǔ)是麥克斯韋方程組在坐標(biāo)變換下形式不變性原理。變換光學(xué)與傳統(tǒng)光學(xué)的區(qū)別在于,傳統(tǒng)光學(xué)是用費(fèi)馬原理來(lái)描述折射率的變化如何影響光的傳播路經(jīng),而變換光學(xué)則是通過(guò)設(shè)計(jì)材料的屬性來(lái)實(shí)現(xiàn)特定的光傳播路徑。在變換光學(xué)中空間形狀起著主導(dǎo)作用,通過(guò)坐標(biāo)變換以增加物質(zhì)參數(shù)的復(fù)雜性為代價(jià),大大簡(jiǎn)化電磁器件的設(shè)計(jì)過(guò)程,也就是說(shuō)在設(shè)計(jì)過(guò)程中把空間的改變等效為空間內(nèi)介質(zhì)參數(shù)的改變,為人們提供了一種全新的調(diào)控電磁波的手段。人們可以根據(jù)對(duì)電磁波的調(diào)控需要來(lái)構(gòu)建空間映射,然后尋找能夠?qū)崿F(xiàn)這種映射的坐標(biāo)變換,再計(jì)算出變換介質(zhì)的參數(shù)。這種方法最初應(yīng)用在電磁隱身方面,通過(guò)一組特定的空間映射,得到了變換介質(zhì)的參數(shù),并借助于超材料設(shè)計(jì)出了電磁隱身斗篷,電磁波在隱身斗篷中會(huì)繞開(kāi)隱藏物體,在斗篷外再回到原來(lái)的傳播路徑上,這樣從斗篷外探測(cè)不到斗篷內(nèi)的物體,斗篷內(nèi)的物體就實(shí)現(xiàn)了“隱身”。經(jīng)過(guò)坐標(biāo)變換以后的光學(xué)結(jié)構(gòu)所需物質(zhì)的本構(gòu)參數(shù)一般是不均勻、各向異性的,但大多情況下這些本構(gòu)參數(shù)都可以通過(guò)超材料技術(shù)來(lái)滿足或者近似滿足,這樣在現(xiàn)實(shí)中利用變換光學(xué)技術(shù)就變的可行,同時(shí)也推進(jìn)了變換光學(xué)技術(shù)的快速發(fā)展。超材料在變換光學(xué)的發(fā)展中起著重要的作用,由此引起的革命正在全世界各個(gè)實(shí)驗(yàn)室的諸多研究方向中進(jìn)行。由于在紅外和可見(jiàn)光范圍內(nèi)能夠支持表面等離子波的傳播,貴金屬中的金和銀一直被廣泛地應(yīng)用在光學(xué)超材料的組成中。但是這些貴金屬材料存在很多缺點(diǎn)：介質(zhì)參數(shù)不可改變,在一定頻率范圍尤其是可見(jiàn)光范圍內(nèi)存在嚴(yán)重的損耗等等,這就限制了由金或銀組成的超材料在變換光學(xué)中的應(yīng)用。然而,近年來(lái)出現(xiàn)的目前世界上已知的最薄的,由六角元胞碳原子組成的蜂巢狀二維晶體-石墨烯,具有強(qiáng)度大、導(dǎo)熱性與導(dǎo)電性極好等特性,另外,石墨烯還具備超大的比表面積,價(jià)格低廉等特點(diǎn)。因此,石墨烯被科學(xué)界認(rèn)為是一種可以大力促進(jìn)科學(xué)研究進(jìn)步的材料,并且預(yù)言其在晶體管、太陽(yáng)能電池、傳感器、超級(jí)電容器、場(chǎng)發(fā)射和催化劑載體等方面都有著良好的應(yīng)用前景。在石墨烯的諸多特性中,石墨烯的材料參數(shù)可以通過(guò)外部條件的改變而改變的特性是石墨烯最為突出的特性,這樣石墨烯就可以克服傳統(tǒng)貴金屬組成的超材料的缺點(diǎn),成為一種新型的變換光學(xué)材料。正是在這樣的研究背景下,本文開(kāi)展了一些基于坐標(biāo)變換的電磁功能器件的研究與設(shè)計(jì)工作,主要包括以下幾個(gè)方面：1.在詳細(xì)分析和敘述了幾種隱身斗篷的基礎(chǔ)上,提出了通過(guò)壓縮空間來(lái)改變物體外觀的思路。首先將原空間的一個(gè)圓形區(qū)域劃分為內(nèi)外兩個(gè)區(qū)域,然后對(duì)內(nèi)區(qū)域進(jìn)行壓縮或者擴(kuò)展變換,外區(qū)域采用相應(yīng)的變換,以保證外區(qū)域與自由空間匹配,減小在此交界面上的反射。當(dāng)物體被放入到這個(gè)圓形區(qū)域的內(nèi)區(qū)域時(shí),空間的改變就轉(zhuǎn)化為介質(zhì)參數(shù)的改變,這樣放入內(nèi)區(qū)域的物體對(duì)外界電磁波的散射就會(huì)增大或者減小,以至于觀察者從外部無(wú)法確定物體的真實(shí)大小。對(duì)內(nèi)區(qū)域繼續(xù)進(jìn)行壓縮或者擴(kuò)展,放入內(nèi)區(qū)域的物體對(duì)外界電磁波的散射會(huì)進(jìn)一步改變,當(dāng)散射變得很小很小以至于可以忽略的時(shí)候,那么這個(gè)圓形區(qū)域就變成了隱身斗篷。變換光學(xué)的具體實(shí)現(xiàn)方法有很多,其中借助于某些軟件直接求解偏微分方程的數(shù)值解得到介質(zhì)參數(shù)的方法,比直接進(jìn)行坐標(biāo)變換的計(jì)算量會(huì)減小很多,利用起來(lái)更方便。因此,本文利用COMSOL軟件中的PDE模塊設(shè)計(jì)了一種平面天線,這種天線具有平面結(jié)構(gòu),同時(shí)又具有傳統(tǒng)拋物天線的特性,這樣不僅達(dá)到了天線小型化的目的,還為以后設(shè)計(jì)超常規(guī)天線提供了一種方法。2.提出基于石墨烯的紅外隱身斗篷的設(shè)計(jì),并對(duì)其功能進(jìn)行了研究與分析。與以往采用傳統(tǒng)材料制成的隱身斗篷不同,本文提出了石墨烯隱身斗篷的設(shè)計(jì)。石墨烯是近幾年出現(xiàn)的一種納米材料,由于其獨(dú)特的單原子層結(jié)構(gòu)而具有很多獨(dú)特的性質(zhì),使得石墨烯成為近幾年物理界和材料界的研究熱點(diǎn),其中石墨烯最突出的特點(diǎn)是其介電常數(shù)的可調(diào)性。在此基礎(chǔ)上,本文將設(shè)計(jì)一個(gè)具有漸變折射率的半球面結(jié)構(gòu)的全向隱身斗篷。在現(xiàn)實(shí)中,真正做到折射率漸變是很困難的,所以在制作過(guò)程中一般采用離散方法,用很多均勻折射率來(lái)近似代替漸變折射率。石墨烯的電導(dǎo)率可以通過(guò)很多方法來(lái)改變,本文用外加電場(chǎng),設(shè)置石墨烯層和硅襯底之間電解質(zhì)的不同厚度的方法,來(lái)改變石墨烯的電導(dǎo)率。用很多具有相同電導(dǎo)率的石墨烯窄帶組成的近似半球結(jié)構(gòu)來(lái)代替具有漸變折射率的半球表面,形成一個(gè)全向的隱身斗篷,并且石墨烯對(duì)表面等離子波具有很好的局限性。當(dāng)表面等離子波經(jīng)過(guò)該石墨烯組成的近似半球結(jié)構(gòu)時(shí),其傳播特性和在平面上傳播時(shí)完全相同,這樣半球面內(nèi)的物體就會(huì)被“隱身”。3.提出基于石墨烯的可調(diào)焦距紅外透鏡的設(shè)計(jì),并對(duì)其功能進(jìn)行研究與分析。當(dāng)施加外電場(chǎng)時(shí),石墨烯層和硅襯底之間的距離可以影響石墨烯表面的載流子濃度,從而在石墨烯表面產(chǎn)生不同的電導(dǎo)率。根據(jù)這個(gè)原理,本文將提出基于石墨烯的可調(diào)焦距的紅外透鏡的設(shè)計(jì),通過(guò)有目的地設(shè)計(jì)石墨烯層和硅襯底之間電介質(zhì)的厚度,可以使石墨烯表面產(chǎn)生不同的電導(dǎo)率以及折射率,這樣入射的電磁波就可以在石墨烯層的不同位置會(huì)聚,同時(shí)該透鏡還具有準(zhǔn)直電磁波的作用,最后將用有限元法驗(yàn)證該透鏡的性能。
[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.

【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：O441

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