A pure dielectric metamaterial absorber with broadband and thin thickness based on a cross-hole array structure

A pure dielectric metamaterial absorber with broadband and thin thickness is proposed, whose structure is designed as a periodic cross-hole array. The pure dielectric metamaterial absorber with high permittivity is prepared by ceramic reinforced polymer composites. Compared with those with low permittivity, the absorber with high permittivity is more sensitive to structural parameters, which means that it is easier to optimize the equivalent electromagnetic parameters and achieve wide impedance matching by altering the size or shape of the unit cell. The optimized metamaterial absorber exhibits reflection loss below -10 dB in 7.93 GHz-35.76 GHz with a thickness of 3.5 mm, which shows favorable absorption properties under the oblique incidence of TE polarization (±45°). Whether it is a measured or simulated value, the strongest absorbing peak reaches below -45 dB, which exceeds that of most metamaterial absorbers. The distributions of power loss density and electric and magnetic fields are investigated to study the origin of their strong absorbing properties. Multiple resonance mechanisms are proposed to explain the phenomenon, including polarization relaxation of the dielectric and edge effects of the cross-hole array. This work overcomes the shortcomings of the narrow absorbing bandwidth of dielectrics. It demonstrates that the pure dielectric metamaterial absorber with high permittivity has great potential in the field of microwave absorption.     

溶胶凝胶法制备TiO2@Cf柔性忆阻器交叉开关

以碳纤维作为柔性衬底和电极材料,通过溶胶凝胶法在其表面镀覆TiO₂阻变活性层,进而通过“十”字搭接制备成柔性纤维忆阻器（TiO₂@C_f）。采用X射线衍射、扫描电子显微镜、X射线光电子能谱等测试手段对TiO₂@C_f结构进行表征并对其忆阻特性及阻变机理进行研究。结果表明：碳纤维上的TiO₂涂层为锐钛矿型晶体结构,其氧空位的浓度约为19.5%;制备的TiO 2@C_f柔性忆阻器为突变型忆阻器,其高低阻态阻值开关比可达10⁴;经过疲劳耐受性测试,忆阻器件的高低阻态开关比稳定在2个数量级左右。TiO₂@C_f忆阻器的机理表现为：在高阻态和低阻态时是以欧姆导电为主导的载流子输运机制,其阻态转变机制与氧空位导电细丝的形成和断裂有关。制备的TiO₂@C_f柔性忆阻器在一定程度上具有柔性弯曲变形,同时满足可编织、穿戴等功能。     

一种基于3D打印技术的结构型宽频吸波超材料

设计了一种三层宽频吸波超材料,其表层和中间层为单元尺寸不同的周期阵列结构,底层为吸波平板结构,优化后的总厚度仅为4.7 mm,并采用三维(3D)打印技术成功制备了该吸波超材料.吸波体反射率测试结果表明,在电磁波垂直入射条件下,宽频吸收峰分别出现在5.3和14.1 GHz,两峰叠加使得其在4-18 GHz频率范围内反射损耗均小于-10 dB.采用S参数反演法计算了每一层的等效电磁参数,并利用多层结构反射率公式推导得出该模型的理论反射率,理论计算结果与实测结果基本一致.通过研究能量损耗、电场分布和磁场分布揭示了吸波机理,分析表明该吸波体的宽频吸收效果源于三层结构产生的吸收带宽叠加.本文提出的吸波超材料具有良好的宽频吸收效果,尤其在低频范围吸波性能较佳,结合3D打印快速成型技术,可获得结构精细的三层吸波超材料,具有重要的实际应用价值和广阔的应用前景.     

基于电阻型频率选择表面的宽带雷达超材料吸波体设计

将多边开缝式电阻型频率选择表面 (frequency selective surface, FSS)与传统的磁性吸波材料(radar absorption materials, RAM)复合, 提出了一种新型吸波体模型. 在分析该模型材料结构和拓扑结构的基础上, 得到等效电路模型; 基于传输线理论获得该模型的反射率及输入阻抗. 采用CST仿真软件对电阻型FSS与无电阻型FSS进行对比仿真, 通过分析吸波效率, 结果表明电阻型FSS在8.7 GHz附近具有更加优良的吸波性能, 实物测试结果与仿真结果一致. 同时FSS复合传统的磁性吸波材料RAM 产生了拓频效果, 在8–15 GHz范围内起到全频段吸收.