超材料（Metamaterials）是一种人工搭建的材料，它由尺寸远大于自然物质中粒子的人工单元排列而成。因此我们能够轻易地设计调控人工单元的尺寸和物理化学性质，得到一些特异电磁响应的人工材料。电磁超材料可以利用人工单元在电磁谐振频率附近实现近乎为0或负数的介电常数和磁导率，同时我们可以自由控制这些电磁参数来满足我们的要求。超材料的超常特性吸引了世界各地研究人员的关注，其应用领域也随之扩大，其中吸波超材料和光子晶体的发展尤其迅猛。根据Lewin模型，基于Mie谐振的介质颗粒可作为超材料的人工结构单元，这为吸波超材料的设计提供了新的思路。但是，吸波超材料和光子晶体的频率的单一性一直阻碍其应用，因此可调性成为当今超材料研究的一个热点。本课题致力于利用介质材料设计和制备可调吸波超材料和可调光子晶体。通过仿真与实验证实了一种基于Mie谐振的电可调微波吸波超材料。陶瓷介质颗粒粘附在由磁控溅射制备的特殊形状的铜膜上。当向铜膜通直流电时，由于铜膜升温导致颗粒的温度发生变化，其介电常数也随之改变并实现吸收峰的移动。随着颗粒升温，频率向高频移动，吸收率能够始终维持99%以上。相比于以往的设计，这一模型能够实现小型化的可调吸波超材料器件。同时温度梯度形成的介电常数梯度也为拓宽吸收频带提供了一种通用的手段，并能够扩展到其他的应用中，例如超表面和隐身器件等。设计并通过仿真与实验验证了基于Mie谐振的太赫兹吸波超材料。单层二氧化锆微球被人工设计的网格固定在铜膜上，网格的原料为聚二甲基硅氧烷（PDMS） 硅胶，通过直写技术制作而成。样品在0.4 THz产生电磁谐振并实现近乎完美吸收。与此同时，直写技术能够经济高效地制备不同间距和排列结构的吸波超材料，我们探究并验证了不同间距和排列结构对吸收峰的影响。设计并制备了一种磁场可调太赫兹光子晶体。利用直写技术制备不同几何参数的柔性木堆结构，样品材料是钛酸锶钡纳米颗粒和PDMS硅胶的混合物。将木堆结构浸没在4-正戊基-4’-氰基联苯（5CB）液晶中，液晶分子的取向能够随着外界磁场方向的变化而改变。实验结果显示，随着木堆间距的增大，光子带隙会向低频移动，随着木堆层数的增多，光子带隙的位置不变但峰会变得深而尖锐。除此之外，随着外界磁场方向的变化，光子晶体能够实现约7.5%的可调性。
Metamaterials are a kind of artificially constructed materials, which are made up of artificial unit cells that are much larger than the particles in the natural material. Therefore, we can easily design and regulate the size and physical and chemical properties of artificial cells to obtain artificial materials with specific electromagnetic responses. Electromagnetic metamaterials can achieve zero or negative permittivity and permeability near the electromagnetic resonance frequency of artificial cells and we can freely control these electromagnetic parameters to meet our requirements. The extraordinary properties of metamaterials have attracted great attention from researchers around the world and the field of application of metamaterials has been expanded, with the development of metamaterials absorber and photonic crystals particularly rapid. According to Lewin's model, dielectric particles based on Mie-resonance can be used as artificial unit cell of metamaterials, which provides a new idea for the design of metamaterials absorber. However, the limited work frequency of metamaterials absorber and photonic crystals also hinders these applications and then currently the tunability becomes a hot spot of the metamaterial. This topic is devoted to design and prepare tunable metamaterials absorber and tunable photonic crystals by dielectric materials.An electrically controlled metamaterial perfect absorber (MPA) based on Mie resonance is demonstrated experimentally and modeled numerically. A ceramic dielectric cube is adhered to a specially shaped thin copper film sputtered on a quartz plate. By passing direct current (DC) through the film, the temperature of the cube can be varied, resulting in changing the cube’s permittivity and shifting the absorption resonance frequency. The frequency rises as the increase of temperature and the absorption is over 99% throughout the tuning range. This method for constructing miniaturized tunable MPAs compares favorably to bulky alternative designs. It also provides a versatile route to broaden the absorption bandwidth and potentially expand the range of applications such as metasurfaces and cloaking devices utilizing nonuniform permittivity produced by temperature gradients.Mie-resonance terahertz absorbers by self-assembly method are designed and demonstrated in experiments and simulations. A monolayer of zirconium dioxide microspheres fixed on a copper film with designed grids that were manufactured by direct writing with a composite ink system composed of polydimethylsiloxane (PDMS). Magnetic resonance leads to near-unity absorption at about 0.4 THz in the samples. In addition, different spacing and array configurations are created economically and efficiently and we studied and demonstrated the effects of different spacing and configurations for absorption.Magnetically tunable terahertz photonic crystals (PCs) are designed and prepared. Flexible woodpile structures with different geometry parameters created by the direct-writing technology with a composite ink system composed of barium strontium titanate nanoparticles and PDMS are immersed in 5CB liquid crystals (LCs), where the orientation of LC molecule is modulated by external magnetic field. Experiments show that the photonic gaps of these PCs have a red shift with the spacing of rods increasing and the peaks keep the same position but become deeper with the increase of layer. In addition, there is about 7.5 percent fine tunability of photonic gap appearing with the orientation of magnetic field changing.
