摘要超材料是一种人工材料，通过对单元尺寸远小于工作波长的特征结构的设计，获得某些自然界的物质所没有的独特性质，比如负折射率，反常切伦科夫效应，极端各向异性，反常Doppler效应等。由于超材料的这些独特性能，它被广泛应用在电磁学、光子学和光学等科学研究领域。42163
在电磁学对超材料的研究中，一个重要的发现是超材料吸波体。近年来，研究人员开始将分形与超材料吸波组合起来，并取得了一些研究成果。但是，由于材料尺寸的限制，目前的吸波体主要工作在毫米波段以及光波段。应用于厘米波的吸波体的研究相对较少。分形曲线具有空间填充特性与自相似性，基于分形理念设计的超材料吸波体可以有效的实现吸收频率的低频化，将超材料的工作频率减低至厘米波段甚至米波段。此外，基于分形的超材料吸波体具有很好的亚波长特性与多频带吸收特征。
本文首先对超材料吸波的研究背景与发展现状进行了简单的阐述，理论分析了超材料的电磁波的传播特性与吸波原理。对传统的超材料吸波体进行了CST软件仿真，得到了S参数。运用MATLAB软件，对得到的S参数进行了进一步的处理，得到超材料与入射电磁波发生谐振时的吸波深度以及材料的电磁特性参数，分析了传统超材料的吸波特性。
在理论研究分析的基础上，设计并仿真了一种具有极化不敏感以及宽入射角性质的，基于科赫(Koch)分形的超材料吸波体。研究了影响该超材料吸波体吸波性能的主要因素，并通过与普通四方形吸波结构的对比，证明了基于分形结构超材料吸波体的特性与优势。
最后，为了探究拓展超材料吸收带宽的方法，对超材料吸波体进行了层叠设计与优化，仿真得到了理想的效果。
关键词 超材料 吸波材料 分形几何结构 频率选择表面 厘米波
毕业论文设计说明书外文摘要
Title The design of centimeter wave metamaterial absorber based on fractal structure
Abstract
Metamaterial is a kind of artificial materials which performs some specific properties. Nature material rarely shows the properties found in metamaterial. These properties includes negative refraction effect, inverse Doppler effect and anomalous Cherenkov effect and so on. With these unique properties, metamaterial shows a great potential future application in electromagnetism, optics and some other scientific fields.
The metamaterial absorber (MA), one of the applications stimulates a rising interest of researchers in the study of electromagnetic metamaterial. MA owns the capability of 100% perfect absorption of electromagnetic waves of specific frequency by adjusting the effective permittivity and permeability. In practical cases, there usually be some strict limits to the size of MA. Therefore, most MA usually works in the millimeter wave or optical band.
In recent years, researchers have tried to combine MA and fractal structure and achieved some remarkable progress. Fractal structure is famous due to its self-similar pattern and space-filling property. The MA based on fractal structure can decrease the resonant frequency significantly. In some conditions, the fractal structure could enable the MA to absorb centimeter wave even meter wave. In view of the specific feature of fractal structure, it can be a fantastic direction for the designing of multi-band and miniaturized MA.
In the project, we firstly elaborate the origin and development of MA and theoretically analyzes the propagation characteristics in MA. Then we simulate traditional MA in the condition of normal incident wave by using CST MWS and calculate the effective permittivity and permeability with MATLAB. CST基于分形结构的厘米波超材料吸波体:http://www.751com.cn/tongxin/lunwen_42513.html