高选择性宽频红外超材料吸收体的机理研究与制备

Metamaterial absorbers are intensively researched in the recent years. The researchers bent themselves to achieving mainly the broadband property of metamaterial absorber, and proposed several implemental schemes. Besides the broadband property, metamaterial absorbers are supposed to possess simultaneously the selectivity of absorption and simplicity of the structure in order to present their superiority over the traditional absorbing materials and apply expediently. .In the present project, we will firstly fulfill the full-wave simulation for all metamaterial structures using a finite-difference time-domain (FDTD) method, analyze the scattering parameters and the field distributions, and then study the physical phenomena of the magnetic couple resonance, surface plasma resonance, Fabry-Perot resonance and their higher order terms results from the changes of material parameter and geometrical size by virtue of electromagnetic field theory, equivalent circuit theory and effective medium theory. Subsequently, we will propose an idea that the selectivity of the broadband metamaterial absorber can be achieved by selecting the pattern which fundamental resonance and higher order resonance could be modulated independently, and the simplicity of the structure of the broadband metamaterial absorber can be realized through adopting complex resonance modes and high impedance metal. Finally, we fabricate infrared broadband metamaterial selective absorber (IBMSA) using lift-off method by means of e-beam lithography, which validate the feasibility of the aforementioned idea..The high selective broadband metamaterial absorber can be used for precisely modifying the blackbody radiation spectrum which conduces to exploring or optimizing the applications related to selective emission, such as infrared stealth technology, thermophotovoltaics (TPVs), etc.; and can also be used for restoring the absorptive band gap of electromagnetic wave spectrum which conduces to developing or improving the applications related to absorption bandwidth, such as solar cell, terahertz detector, etc. Moreover, the simplification of the broadband metamaterial absorber makes its optical applications feasible..

超材料吸收体是当前的热点研究领域，科研人员主要致力于实现它的宽频特性。但要充分体现它相对于传统吸收材料的优势并方便应用，还应同时具备吸收的选择性和结构的简易性。. 本项目首先采用时域有限差法对超材料结构进行全波模拟，分析结构的散射参数与场分布；结合电磁场理论、等效电路理论和有效媒质理论研究结构的磁共振，表面等离子共振，Fabry-Perot共振及其高阶项随结构参数与材料参数的变化规律。然后，提出基于独立控制基本共振与高阶共振的图形单元实现吸收选择性、基于复合共振模式与高阻抗金属实现结构的简易性设计高选择性宽频红外超材料吸收体的理念。最后，采用电子束光刻技术与剥离法制备样品，验证前述设计理念的可行性。. 高选择性宽频超材料吸收体，可用于修复电磁波谱吸收禁带或控制黑体辐射谱，这有助于开拓或优化与吸收带宽、选择发射相关的应用，比如太阳能电池、太赫兹探测器、红外隐身技术等。

高选择性宽频超材料吸收体，可用于修复电磁波谱吸收禁带或精确控制黑体辐射谱，这有助于开拓或优化与吸收带宽、选择发射相关的应用，比如太阳能电池、太赫兹探测器、红外隐身技术、热光伏技术等。本项目拟从机理和技术上实现这种吸收体。工作围绕两个问题开展：如何构造出具有宽带隙的图形单元，以至于能比较独立地调制基本共振与高阶共振，实现吸收的高选择性；如何有效地调制不同共振模式的基本共振与/或高阶共振项到同一频率区域进行叠加融合，以至于将超材料结构的复杂性向机理的复杂性转变，实现简化的吸收体的宽频特征等。围绕上述问题，本项目主要对比研究了方形贴片、方环贴片阵列；正四棱柱、方形波导阵列；梯形孔洞阵列等结构的电磁响应特性。研究发现：（1）方环贴片相比于方形贴片图形单元，磁共振（反对称LSPP模式）的基本共振频率与高阶共振频率能比较独立地调制，有利于增加二者之间的频带宽度，使得实现高选择性的吸收成为可能。（2）正四棱柱和方形波导分别作为方形贴片和方环贴片在轴向的延展物，除了具有后者的局域等离子共振模式以外，还具有Fabry-Perot共振模式以及波导模式等。进一步地，相比于方形波导阵列，梯形孔洞阵列存在递进的波导模式共振频率，更有益于设计宽波段的超材料吸收体。再者，为了引入磁共振模式，用口径渐变的方环贴片堆叠形成梯形波导阵列，实现了基于复合共振模式的宽频段高选择性超材料吸收体，其在整个3 μm -12 μm区间仅对5 μm -8 μm波段吸收，且吸收率占整个区间的80%左右，实现了高选择性吸收。此外，吸收率高于90%的相对吸收带宽达到整个区间的37%，而吸收率高于50%的相对吸收带宽（半高宽）达到46%左右，实现了宽频吸收特性。