The microwave response of square mesh metamaterials
The microwave response of square mesh metamaterials
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方网超材料的微波响应
DOI：
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发表时间：
2012
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通讯作者：
C. M. Butler
中科院分区：
文献类型：
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作者：
C. M. Butler
超材料是一类人造材料，由于其工程亚波长结构，已知可以产生自然界中没有的电磁（EM）响应。本论文利用极薄的亚波长网格来形成层状超材料。研究了这些材料的透射和反射响应的电磁特性，包括极化转换行为，以进一步理解和开发利用和控制微波辐射传播的结构。原始的实验研究分为两个部分；第一个研究了由金属网和介电板组成的电堆的响应；第二个研究探索了一个由方形亚波长阵列中的方形对称元素组成的旋转层状结构，该结构通过近场的倏逝耦合展示了手性。当金属网格受到低于截止频率的电磁辐射激励时，孔内只支持瞬变衰减场。将这些亚波长金属网以不同的排列方式与介质板组合，可以观察到高透射低反射的显著宽波段。非相互作用谐振模式允许通过适当选择金属网格几何形状和电介质特性来调谐响应。此外，所述低频带边缘和带宽不依赖于所述堆栈中的单元格数；而是取决于单晶的性质。第二部分论证了“瞬变手性”作为一种新的手性。两个亚波长方形元素的方阵相对于彼此旋转。当旋转的阵列在传播方向上彼此相距较远时，每个阵列都充当有效的介质层。然而，当放置在近距离时，结构显示出旋转入射辐射的偏振平面。所有这些基于网格的结构都具有通过设计可调谐的电磁响应特性，允许根据特定应用定制结构。
Metamaterials are a class of artificial material, known to produce electromagnetic (EM) responses not found in nature due to their engineered subwavelength structure. In this thesis very thin subwavelength meshes are utilised to form layered metamaterials. The EM characteristics of the transmission and reflection response from these materials, including the polarisation converting behaviour, are explored to further understanding and develop structures to exploit and control the propagation of microwave radiation. Original experimental studies are presented across two sections; the first examines the response of stacks assembled from metallic meshes and dielectric plates; the second explores a rotated layered structure formed of square symmetric elements in a square subwavelength array that demonstrates chirality through evanescent coupling of the near fields. When metallic meshes are excited with EM radiation below the cut off frequency, only evanescently decaying fields are supported in the holes. By combining these subwavelength metallic meshes with dielectric plates in different arrangements, remarkably wide bands of high transmission and low reflection may be observed. The non-interacting resonant modes allow the response to be tuned through a suitable choice of the metallic mesh geometry and the properties of the dielectric. Further the low frequency band edge and the bandwidth are not dependent on the number of unit cells in the stack; but are dependent on the properties of the unit cell. The second section demonstrates “evanescent handedness” proposed as a new type of chirality. Two subwavelength square arrays of square elements are rotated with respect to one another. When the rotated arrays are positioned far from one another in the propagation direction, each acts as an effective medium layer. However when placed in close proximity the structure is shown to rotate the plane of polarisation of the incident radiation. All these mesh based structures share the property of producing an EM response that is tunable by design, allowing a structure to be tailored to a specific application.