【作者】 程响响；

【导师】 陈红胜； 章献民； 孔金瓯；

【作者基本信息】 浙江大学 ， 电磁场与微波技术， 2010， 博士

【摘要】 以异向介质为代表的复合电磁材料,是由人工设计的亚波长结构单元经过有序的排列而合成。由于它独特的电磁响应能产生自然界物质中难以观察到的奇异电磁现象,在从首次亮相至今还不到十年的时间里,异向介质迅速发展成为科学和工程领域的多学科分支。本文首先提出了一种全新的双各向异性异向介质结构设计并对其进行了理论分析与实验验证,在随后的篇幅中,重点探索与讨论了各种属性的异向介质的潜在应用。本文具体的工作内容归纳如下：1.深入研究了双各向异性异向介质的电磁特性,发现本构参数中的手征因子(只存在于一个方向上)对色散关系影响很大；基于传统S型谐振环提出了双各向异性S型异向介质的实现方法,使环内某些水平金属臂短路以产生电磁耦合；通过宏观视角的理论分析,将这种新型结构的本构参数在准静态极限下全部表征出来,并从理论上得到了非零的手征因子；其双各向异性亦得到了数值仿真与实验测量的双重验证。2.通过高斯波束在小电磁参数手征介质中的传播,生动地描述了手征虚无介质(chiral nihility)所独具的奇特电磁效应,例如在半平面情况下圆极化波的全反射与全透射,以及在平板介质阻抗或折射率与空气相匹配的情况下所显现的特性,包括圆极化分波、波束展宽和驻波等；之所以用小电磁参数手征介质来取代完美的手征虚无介质,是因为它符合物理定理,因而可以由异向介质来实现。3.求解了PEC球体外包裹着多层各向异性介质的电磁波散射问题,并探讨了当各向异性介质的本构参数值分别接近虚无时的整体后向散射特性；与各向同性的球壳相比,轴向介电常数和磁导率为小电磁参数的各向异性球壳在降低后向散射辐度上具有更大的潜能,此特性可被小电磁参数各向异性异向介质用于单基站雷达系统的隐身。4.根据PEC柱体外四层介质壳的优化参数结果,设计了由九层异向介质组成的柱体隐身衣,并经过计算机仿真的验证；不同于坐标变换法所得到的不均匀的隐身衣参数,它的每一层介质都是均匀的各向异性介质,设计简单,制作容易,且拥有与坐标变换的完美参数近乎相同的隐身效果。5.讨论了当隐身衣的背景介质为双各向异性介质的情况,包括静止的双各向异性介质和高速运动的介质,此时的隐身衣参数具有比其背景介质更为复杂的双各向异性,并且无法由简单的各向同性介质的匀速运动来实现。6.提出了消除反射系数中障碍物影响的一维成像方法,运用传输线理论对障碍物建模,并在模型中虚拟地加入一段电磁属性与障碍物完全相反的传输线,它可以被理解成为与障碍物厚度相同的有源异向介质层,它的电磁参数依赖于障碍物的电磁属性；当障碍物中存在瑕疵而变得不均匀时,采用均匀化过程、基于Drude模型将其等效介电常数表征出来,此方法的有效性经过不同例子的成像效果得到了证明。更多还原

【Abstract】 The emergence of artificially designed subwavelength electromagnetic materials, de-noted "metamaterials", have significantly broadened the range of material responses found in nature. Since its first experimental demonstration less than 10 years ago, metamaterial has developed as a rapidly growing multidisciplinary branch of science and engineering.By engineering the internal structure of metamaterials it is possible to create effective electro-magnetic properties, including some which were previously unavailable.This dissertation presents the design of a novel bianisotropic metamaterial firstly, and then explores the per-tinent applications by taking advantage of all the fascinating and versatile electromagnetic properties.The contents can be summarized as follows:1.The refraction and propagation properties of metamaterials with bianisotropic effects are investigated, the dispersion relation can be strongly influenced by the inclusion of chirality. A realization of the bianisotropic metamaterial based on S-ring resonators is proposed, by subtly shorting some horizontal metallic strips inside it. The structure is theoretically analyzed from a microscopic viewpoint, and the constitutive param-eters are characterized, where a nonzero chirality component is clearly shown.Both the numerical simulation and experiment measurement show strong cross polariza-tion effects when waves are incident onto a slab of this material, further confirming the prediction by our theoretical analysis.2.The chiral nihility effects are illustrated by showing the propagation of a Gaussian beam, both reflected and refracted from an air-chiral interface, and through layered chiral nihility media that are matched to free space.The critical angle for total reflec-tion and the index-matched total transmission in a matched chiral half-space, along with the wave splitting, wave widening, and a wave of "standing phase" in matched chiral nihility slabs, are demonstrated. 3.The backscattering properties of a PEC sphere coated with layered anisotropic me-dia, whose constitutive parameters are close to nihility, are studied.Compared with isotropic case, the anisotropic media with small axial parameters have the poten-tial to yield more reduction of backscattering magnitude, which can be used as an invisibility cloak in monostatic radar system.4.According to cloak parameters from optimization, which are totally different from those given by coordinate transformation approach, a well-designed cloak for a PEC cylinder is simulated to perform almost the same invisibility effect, but with much simpler parameters and may be easier to fabricate.5.The case where the background material of a cloak possesses magnetoelectric cou-pling is discussed, including bianisotropic media or isotropic moving with uniform speed which may be comparable with that of light. The specifically proposed consti-tutive parameters for such cloak own more complicated bianisotropy, which can not be simply produced by an isotropic medium in a uniform-velocity motion.6. The imaging method when an obstacle presents in between the target and the sensor is demonstrated, using the concept of active metamaterial.The obstacle’s impact to the reflection coefficients can be canceled by imaginatively adding an opposite layer, leading to a significant improvement of the target imaging. When the obstacle layer is inhomogeneous due to its small defects, a homogenization procedure based on the Drude model is applied to characterize its effective constitutive parameters. The effectiveness of the proposed method has been proved through our calculation examples.更多还原