【作者】 李进；

【导师】 季杰； 叶宏；

【作者基本信息】 中国科学技术大学 ， 热能工程， 2011， 博士

【摘要】 红外探测技术已在军事中广泛应用,如何有效避免暴露重要目标红外特征,减少损失,已成为一个亟需解决的问题。因此,红外隐真材料的研发正引起科学家极大的重视。光子晶体(Photonic Crystal)因光谱特性会随结构改变而相应发生变化,在信息处理、光学器件、热光伏系统等领域得到了广泛的应用。而利用光子晶体的特性实现大气窗口红外辐射的抑制则是一个新颖的研究领域。在利用光子晶体材料抑制大气窗口波段(3～5μm与8～14μm)发射辐射的初步研究中,建立了一维光子晶体模型,利用传输矩阵法分析了多种基底材料和光子晶体材料组合及其自发辐射对抑制效果的影响。结果表明,当光子晶体的高低折射率介质分别为Silicon(Si)与Potassium Chloride (KCL),在3～5μm与8～14μm内,基底分别为处于100℃的Aluminium (AL)、Silicon Carbide (SiC)及假想表面(发射率为1的表面)时,表面的发射辐射均得到较好的抑制。对于相同基底,如果光子晶体组成材料的高低折射率比值越大(如选择Germanium (Ge)与KCL),抑制效果越好。其次,在不考虑3～5μm波段发射辐射的情况下,采用传输矩阵法分析了光子晶体对8～14μm波段发射辐射的抑制作用。依据材料的光学特性,选择了Ge与Zinc Sulfide (ZnS)作为光子晶体的组成材料。对光子晶体的结构进行了优化,Ge与ZnS的优化厚度分别为0.63μm和1.11μm,光学厚度比为1：1,周期数为8。利用真空蒸发镀膜法制备了光子晶体,并测定了制得光子晶体的光学性质,从理论与实验两个角度验证了光子晶体对大气窗口发射辐射的抑制作用。然后,针对光子晶体材料对大气窗口发射辐射的抑制作用进行进一步的实验研究,从侧面论证模型的正确性,并探索在不同温度情况下的实际抑制效果。采用真空热蒸镀的方法,在不同材料上制备了多周期的Ge/ZnS光子晶体。通过对底部加热,并采用红外热像仪分别拍摄有无光子晶体覆盖的材料的热图,对比热图来充分展示出该种周期结构材料具有抑制物体表面发射辐射的特性。结果表明,只要能保证基底表面的平整度,就可以通过热图充分展示出光子晶体的禁带特性,当实测温度为100℃时,五组实验中红外热像仪的显示温度最低可达26.5℃。接下来,采用有限时域差分法对Ge/Sodium Fluoride (NaF)光子晶体的光谱特性进行了设计。由该结构的反射/透射谱发现,周期数为7的光子晶体在8～14μm内的反射率可达0.99,能较好地抑制大气窗口发射辐射。为实现大气窗口特定波长(如10.6μm)处的光谱透射峰,探索了引入第三种介质或改变原有膜层厚度的方式来形成结构缺陷,从而实现低反射的方法。发现引入第三种红外透明介质形成缺陷的方式无法在特定波长处形成透射峰,而改变原有膜层厚度形成缺陷的方式可在特定波长处实现透射峰,如10.6μm处透射率高达0.938。最后,建立了采用一维Magnesium Fluoride (MgF2)/ZnS型光子晶体滤波器的硅电池热光伏(Thermo PhotoVoltaic)系统的热物理模型。针对高温辐射器的辐射能量分布与Si电池的响应带隙失配的情况,设计了一种基本结构为|L/2HL/2|s的一维光子晶体滤波器,并通过主禁带中心波长平移的方式得到了改进型滤波器。当黑体辐射器的温度为1800K时,采用主禁带中心波长为1.69μm的滤波器的TPV系统的电池输出功率密度与水冷功率密度分别为1.57和36.30Wcm-2,相对采用主禁带中心波长为1.39μm的滤波器的TPV系统,分别提高了8.3%和降低了10.4%。并针对水冷功率密度较大的问题,在主禁带中心波长为1.69μm的滤波器基础上,提出了依次将多套不同主禁带中心波长的滤波器组合的方案(结构为|L/2HL/2|a|L/2HL/2|sl…|L/2HL/2|sn,使其主禁带首尾相接形成较宽的反射带,在适当牺牲电池输出功率密度的条件下,可较大幅度地降低水冷功率密度。之后,结合氧化镱选择性辐射器对系统性能做了分析。更多还原

【Abstract】 Infrared detective technology has been widely used in military affairs. How to avoid important targets to be detected and reduce the loss is of great urgency. So, the development of infrared stealth materials has been paid much attention by scientists. Since the spectral characteristics of photonic crystal will change with the variation of its structure, it has been used in information process, optical device and thermal photovoltaic system, etc.. However, controlling infrared radiation effectively with photonic crystal is a novel research realm.Firstly, in the preliminary analysis about the suppression effect of photonic crystal on atmospheric window band emission (3～5μm and 8～14μm), the physical model of one dimensional photonic crystal is set up with transfer matrix method. The effects of several combinations of substrates and photonic crystals and their spontaneous emissions on inhibition effect are discussed. It is found that, when the high and low refractive index medias composing the photonic crystals are Silicon (Si) and Potassium Chloride (KCL), respectively, and the substrates are Aluminum (AL), Silicon Carbide (SiC) and an imaginary surface (of emissivity equal to 1) at 100℃orderly, all the surface emissions are inhibited well in both bands (3～5μm and 8～14μm). For the same substrate, the inhibition effect could be increased if the ratio of the high and low refractive indices of the composing materials is higher, such as Germanium (Ge) and KCL.Secondly, without considering the emission between 3 and 5μm, the transfer matrix method is used to analyze the inhibition effect of photonic crystal on atmospheric window emission between 8 and 14μm. According to the optical characteristics of the materials, Ge and Zinc Sulfide (ZnS) are chosen as the composing materials of the photonic crystal. The structure of the photonic crystal is optimized, and the optimal thicknesses of germanium and zinc sulfide are 0.63μm and 1.11μm respectively, while the ratio of optical thickness is 1:1 and the period is 8. The photonic crystal is prepared by vacuum evaporation coating method, and the optical properties of the photonic crystal are measured. The inhibition of the photonic crystal to atmospheric window emission is verified by both experimental and theoretical results.Thirdly, the inhibition of photonic crystal to atmospheric window band emission is investigated by further field experiments. The actual inhibition effect is explored when substrates are at different temperatures. By vacuum evaporation coating method, Ge/ZnS type photonic crystals are prepared on different substrates. The infrared thermographies are photographed by infrared thermal imager at different substrate temperatures, when the substrate is coverd with photonic crystal or not, respectively. And the characteristic of photonic crystal inhibiting the atmospheric window emission can be shown sufficiently by comparing the display temperature of thermography with the actual temperature of the substrate. It is found that, if the smoothness of the substrate can be ensured effectively, the stop band characteristic of photonic crystal can be exhibited sufficiently. For example, when the actual temperature of the substrate is 100℃, the lowest display temperature in infrared thermal imager of the five groups of experiments is 26.5℃.Fourthly, finite difference time domain method is used to design the spectral properties of Ge/Sodium Fluoride (NaF) photonic crystal. With the analysis results of reflection and transmission spectrum of Transverse Magnetic (TM) and Transverse Electronic (TE) waves, it is found that the reflectivity of the photonic crystal of 7 periods can reach 0.99 between 8 and 14μm. For the realization of transmission peak at a given wavelength among the atmospheric window (for example,10.6μm), the methods of introducing a third medium and tuning the original film thickness are explored, respectively. Introducing a third medium which is transparent in the infrared spectrum can not achieve the aim of forming transmission peak at the special wavelength, but tuning the original film thickness does work, for example, the transmittivity at 10.6μm could reach 0.938.Finally, the thermophysical model of Thermo PhotoVoltaic (TPV) system adopting silicon cell is set up while one dimensional Magnesium Fluoride (MgF2)/ZnS type photonic crystal filter is used. In view of the mismatch between the energy distribution of high-temperature radiator and the response band range of silicon cell, one kind of photonic crystal filter is designed and its basic period structure is|L/2HL/2|s. And another improved filter is obtained by tuning the central wavelength of the main stop band. When the blackbody radiator is at 1800K and the central wavelength of main stop band of the filter is 1.69μm, the output power density of cell and the cooling power density in the TPV system are equal to 1.57 and 36.30Wcm-2, respectively. By comparing with the TPV system using the filter whose central wavelength of main stop band is 1.39μm, the output power density of cell and cooling power density are increased by 8.3% and decreased by 10.4%, respectively. In order to solve the problem of large cooling power density, on the basis of the filter structure whose central wavelength of main stop band is 1.69μm, the scheme of combining several filters of different main stop band central wavelengths orderly is proposed (the reformed structure is |L/2HL/2|s|L/2HL/2|sl…|L/2HL/2|sn). And a wide reflection band can be formed by the combination of the main stop band of each filter. It is found that, if the output power density of cell is sacrificed in some extent, the cooling power density will decrease significantly. Then, the performance of TPV system with the ytterbia selective radiator is analyzed.更多还原