人造電磁材料之特性分析與應用研究

Abstract

人造電磁材料的電磁特性是由它的週期以及單晶胞圖案而來，反倒與其組成成分沒有直接關聯。一般來說，人們藉由在主介質中嵌入特殊內容物，例如：週期性結構，來合成超穎材料。近年來，由於超穎材料(或稱人造電磁材料)不尋常且驚人的電磁波傳導特性，像是負折射現象和負群延遲現象，吸引了許多目光。即使這些不尋常的現象已經在數值上和理論上被證實，波在超穎材料中的傳導過程所隱含的物理意義仍然需要詳細的探索。 在本計劃中，我們將目標放在研究如何利用人造電磁材料導引電磁波的傳導與輻射。在第一年，我們將使用Floquet-Bloch理論來探索波在人造電磁材料中傳導的基本原理。如此一來，我們在合成一個具有任意相位關係的人造電磁材料時會有很大的優勢。在第二年，我們將研究使用平面或三维人造電磁材料時，其反射主波束掃描的電磁梯度面。重點將會放在增加頻寬並解決頻率相關造成主波束掃描的問題。在第三年，我們探討將一個線波源嵌入超穎材料中所造成的波束調整特性。近來來，這樣的問題已經被深入的研究。人們提出許多方法來解釋此種超穎材料的波束調整特性，舉例來說：將超穎材料視為一個具有負介電係數及負導磁係數之均勻介質的等效介質理論。然而，當我們在解包含金屬與普遍被使用的介質材料的實際結構的馬克思威爾方程式時，理所當然，我們知道在那樣的環境下，其電能和磁能必然是正實數。在這裡，超穎材料(或稱人造電磁材料)將會被視為一個頻率選擇結構，並且我們將使用全波分析，也就是頻域分析法，來計算頻域中的感應電流。 這項子計畫結合了主計畫發展高速傳收系統的目的。在本計劃中所發展的人造電磁材料將會用來當作一個控制電磁波輻射的元件，而這些電磁波是由其他子計畫發展的天線所產生的。最後但並非最不重要的一點，本計劃的其他目的是促進研究生在理論及工程上的研究，以提升他們在應用電磁學上設計之興趣。

Artificial Electromagnetic Materials (AEMs) is a material gaining its electromagnetic properties form its structure configuration including period and unit cell pattern rather than directly from its composition. In general, a metamaterial is synthesized by embedding specific inclusions, for example, periodic structures, in a host medium. Recently, metamaterial or AEMs attract considerable attentions due to its extraordinary and amazing properties of wave propagating; such as the negative refraction phenomena and negative group velocity. Although those extraordinary phenomena were numerically and theoretically verified, the underlying physics of wave process involved in meta-materials remains to be investigated in detail. In this proposal, we aimed at studying the emission control using AEMs. In Phase 1, we will employ the Floquet-Bloch theory to investigate fundamentals of wave propagating in an AEM; especially for the dispersion- and phase- relation of wave propagating. In doing so, we will have a good position to synthesize an AEM having an arbitrary phase relation. In Phase 2, we will study an electromagnetic gradient surface for reflected beam steering utilizing a 3D or planar AEM. The emphasis will be placed at the bandwidth improvement and resolve the problem of frequency-dependent steering angle. In Phase 3, we will investigate beam-shaping characteristics of a line source embedded in a metamaterial. Such a problem has been intensively studied in recent years. Several methods were proposed to interpret the beam-shaping property of the meta-materials; for example, the effective medium theory considering the meta-material as a uniform medium with negative permittivity or permeability. However, we know that the electric and magnetic energy in such an environment, of course, are positive and real numbers when we solve Maxwell’s equations for the real structure containing a metal and a commonly used dielectric material. Here, the meta-material (or AEMs) will be regarded as a frequency-selective structure and a full-wave method: spectral domain analysis will be employed to calculate the induced current in spectral domain. This subproject joints the main project to develop a high-speed transceiver system. The AEMs developed in this project will be employed as a device to control the emission of electromagnetic wave generated by the antennas developed in the other subprojects. Last but not least, the other objective of this project is to promote theoretical and engineering research for the graduate student, to raise their interest on the design of applied electromagnetics.