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標題: | 非磁性圓柱隱形斗篷散射最小化之設計 Nonmagnetic Cylindrical Cloak with Minimized Scattering Design |
作者: | Cheng- Lin Li 李政霖 |
指導教授: | 陳瑞琳 |
關鍵字: | 轉換光學,隱形斗篷,非磁性,散射最小化,阻抗匹配, transformation optics,invincible cloak,nonmagnetic,minimized scattering,impedance match, |
出版年 : | 2014 |
學位: | 碩士 |
摘要: | 近年來,轉換光學的蓬勃發展,人們可以如其所想的控制光前進的路徑,設計波導元件變得更為容易,並透過超常材料即可實現設計的元件。透過轉換光學的應用,隱形裝置將不再是想像。
藉由空間座標轉換理論,我們可以控制電磁場,並且獲得實踐隱形斗篷的材料組成率。然而所需的材料往往是非均勻、非等向、以及磁性的,這些特性在實作上為不容易的,故如何避免上述這些具這些特性之使用,為利用轉換光學設計波導元件所需注意的。因此,有了磁性材料簡化理論,並且非磁性隱形斗篷蘊育而生,透過此理論雖然避免磁性材料的使用,卻產生不可避免的散射。如何設計空間座標轉換式,使磁性簡化產生之散射降至最低,為設計隱形元件時,關心的重點之所在。 為了給予非磁性隱形斗篷良好的隱形效果,我們提出一種分式型座標轉換,設計一參數δ可調整阻抗曲線,以達到散射最小化之目的。此隱形斗篷在外部邊界阻抗匹配,而內部邊界阻抗有兩種類型:δ= 0.9時為零、δ= 1.05時為無窮大,導致兩種不同的阻抗曲線;而在最佳化參數為δ= 1.05時,內部邊界材料參數 之值不發散且緩和漸變至1(外邊界空氣ε值),而有此性質之非磁性斗篷具有極佳的隱形效果。再者,我們找出此非磁性斗篷之隱形最佳幾何參數,以及最佳操作頻率;並與其他轉換座標之隱形效果相比較,此斗篷擁有最小的標準化之總散射截面積寬度(NTSW)。 In the past few years, transformation optics gave a hit in designing waveguide devices, especially in cloaking, and created a convenient and novel approach to manipulating light’s propagation. By coordinate transformation, we can control electromagnetic fields as well as obtain constitutive equations which can realize design of cloaking devices with metamaterials. However, the desired material are often inhomogeneous, anisotropic and magnetic. The material reduced theory were proposed, which avoids using magnetic material; however, leading to inevitable scattering. Therefore, how to minimize scattering is the main key of cloaking design. We proposed a fractional transformation which matches impedance of outside media at cloak’s outer boundary for a nonmagnetic invisibility cloak with minimized scattering. In comparison with the previous transformation, the transformation designed of a switch parameterδ to minimizing scattering possesses of two kinds of impedance values at inner boundary. When 0<δ<1 , its value is zero; when δ>1 , its value is infinite, which gives two different kinds of impedance curves. At δ=1.05 , the value of εθ at inner boundary won’t diverse as well as εθ curve goes smoothly to 1, so the nonmagnetic cloak has great invisibility. Furthermore, we also find out the operation frequency of the cloak, and it is a narrow frequency range. In the last, the invisibility of fractional cloak comparing with previous transformation cloak at same physical conditions, it has the smallest normalized total scattering width. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/16714 |
全文授權: | 未授權 |
顯示於系所單位: | 應用力學研究所 |
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