基于同色同谱特征的模拟绿色植被光谱材料研究进展

随着高光谱侦察技术的快速发展,为满足反侦察需求,对模拟绿色植被光谱材料的要求越来越高。绿色植被是应用极广泛的作战背景之一,它在400～2 500 nm波长区间具有独特的光谱特征,有四个主要特征谱带,分别是“绿峰”“红边”“近红外高原”和“水吸收谱带”,源于叶片的叶绿素、组织结构和植物含水。本文基于高光谱技术的侦察特点,为了实现伪装材料与背景之间“同色同谱”,论述了模拟各个特征反射峰的材料现状及现有材料的综合应用,介绍了现有伪装材料精准模拟绿色植被光谱曲线的同时存在耐候性差等问题,以及通过复合来提升光谱曲线相似度和耐候性的相关工作,并对未来模拟绿色植被光谱材料进行了总结及展望。     

植物叶片仿生伪装结构模型设计

通过对绿色植物的光谱反射特征及其影响因素的分析和实验验证，首次提出了植物叶片仿生伪装结构的概念和设计模型，并初步验证了其可行性和有效性。实验结果表明，这种全新的伪装结构在紫外、可见光和近红外波段具有与绿色植被非常相似的光谱反射特征，其“同色同谱”效果可望有效对抗高光谱侦察。     

绿色材料伪装性能检测技术分析

绿色材料是一种重要的伪装材料。伪装上不仅要求绿色材料的颜色与绿色植物近似，而且要求其近红外反射特性与绿色植物近似。伪装绿色检验镜是一种检验绿色颜料与植物绿色异谱程度的器材，论文提出了伪装绿色检验镜镜片的光谱透射特性要求，分析了其检色原理和检色效果，为绿色材料近红外伪装性能的检验提供了一种简便可行的方法。     

界面聚合法制备耐热型山梨醇水溶液微胶囊

为获得具有植物叶片近红外精细反射光谱特征的伪装材料,采用界面聚合法制备山梨醇水溶液微胶囊。选择聚脲为壁材,设计了两步升温的包覆工艺,通过反应温度的优化得到了水分含量达50%以上的山梨醇水溶液微胶囊。扫描电子显微镜下观察到微胶囊呈表面较为光滑的球形;紫外/可见/近红外分光光度计结果表明,微胶囊的反射光谱在1450 nm和1930 nm处呈现与绿色植被相似的水分吸收谷。微胶囊具有优良的水分保持能力,在25℃、相对湿度50%环境中放置96 h后水分含量变化率不超过3%;热重分析和差示扫描量热结果表明,微胶囊水分的流失起始温度超过200℃。该微胶囊轻质、水分含量高、耐热性强,制备工艺简单,与植物叶片近红外反射光谱匹配度高,在对抗高光谱探测技术领域具有良好应用前景。     

伪装隔热封套材料研究

提出了通过共混改性技术使普通PVC封套材料具有伪装隔热性能的方法。分析了PVC封套材料的伪装隔热改性机理,提出了伪装隔热封套材料的设计方案和加工工艺,测试了材料的光谱反射性能和热反射性能。     

热红外伪装遮障材料的制备

热红外伪装遮障材料的制备是研制超轻型多波段伪装遮障的关键技术之一。阐述了一种优化的制备热红外伪装遮障材料的关键技术、配方与工艺等。采用本体透明型方法制备了绿色和土色低发射率材料。检测结果表明，研制的低发射率防热红外伪装涂层样品具有红外发射率低、红外透明性好、多光谱兼容等特点。     

多波段伪装隐身涂层织物的制备研究与应用

采用着色颜料、红外低发射率填料、水性聚氨酯树脂等制备水性多波段伪装涂料,采用刮涂工艺,制备可见光/近红外/热红外多波段伪装涂层织物。通过双波段发射率测量仪、光谱反射率测试仪、光泽度仪等测试手段对涂层的红外发射率、光谱反射率、镜面光泽度等性能进行了表征,此外还对涂层的理化及环境性能进行了测试。结果表明:涂层的颜色满足《GJB 1082—1991伪装网用颜色》的要求,近红外光谱反射特性在380~1100nm范围内与应用背景基本实现了"同色同谱",不同颜色斑块的发射率梯度在0.13以上,在红外成像下能够形成有效的梯度分割,与应用背景具有较好的融合效果,具有可见光/近红外/热红外隐身性能,各项指标均达到了实用要求。     

天然高分子/PVA可生物降解材料研究

聚乙烯醇(PVA)的化学稳定性及成膜性较好,可以完全生物降解,与天然高分子材料的相容性好,已被广泛应用于与天然高分子材料复合制备可生物降解材料。综述了淀粉/PVA复合材料、纤维素/PVA复合材料、壳聚糖/PVA复合材料、木质素/PVA复合材料及蛋白质/PVA复合材料的研究进展,并对其作为可生物降解材料替代某些通用塑料的应用前景进行了展望。     

无机电致变色材料反射特性研究进展

电致变色材料是一种在外加电场下,颜色可以发生可逆转变的材料。电致变色材料可调的光谱范围广,可以实现从可见到中远红外的宽波段调控,在智能窗、显示、防炫目后视镜、智能热控和伪装等领域具有广泛应用前景。目前对无机电致变色材料的研究大多是关于透过特性的研究,对于反射特性的研究较少,这主要是因为无机变色材料大多颜色单一,且不如有机变色材料容易设计。近年来,通过一些特殊的制备方法和结构设计,无机变色材料反射特性的研究逐渐受到科研人员的重视。本文从无机电致变色材料的反射特性出发,详细介绍了无机电致变色在可见–近红外到中远红外波段的反射光谱调控方法和原理,综述了最新研究进展。在可见波段,反射特性调控主要通过制备五氧化二钒及其掺杂化合物、一维光子晶体微结构、法布里–珀罗纳米谐振腔结构和局域表面等离子共振等方式实现。在红外波段,主要利用氧化钨等材料的分子振动吸收和德鲁德自由电子气体理论等理论设计制备红外反射型电致变色器件。最后,对未来无机电致变色材料反射调节的实际应用进行了展望。     

改性水泥基材料用聚乙烯醇纤维耐碱性能研究

为了考察用于改性水泥基材料的聚乙烯醇纤维在水泥水化过程中的稳定性,模拟水泥水化的碱性环境,研究3种国产聚乙烯醇纤维在强碱性条件下的化学结构稳定性及表观形貌和力学性能的变化,分别采用红外光谱、纤维表面微观形貌和单丝断裂强力来进行表征。结果表明,聚乙烯醇纤维在p H为12.8的强碱性条件下具有较好的耐碱性,浸泡10 d时力学强度几乎不变化,浸泡28 d时强度降低不超过10%,红外光谱和微观形貌表征显示纤维的结构和外观无明显改变。     

Diffuse reflectance and transmittance spectra of an interference layer. 2. Evaluation of tin oxide-coated glass

A model for the calculation of diffuse reflectance and transmittance of a single interference layer on a transparent substrate is applied to pyrolytically deposited tin oxide films on glass. Total as well as diffuse reflectance and transmittance spectra were measured in an integrating sphere, and scattering levels between 0.002 and 0.1 were recorded. The optical constants and the thickness of the films were determined from the total reflectance and transmittance spectra. The wavelength-dependent effective root-mean-square roughness of aluminum-coated tin oxide front surfaces was determined by the application of the scalar scattering theory. Surface roughness values between 5 and 25 nm were obtained. The obtained effective rms roughness values of the air-film interface were used together with the other film parameters to calculate the diffuse reflectance and transmittance spectra of the tin oxide-coated glass substrates. A comparison between calculated and experimental spectra showed good agreement for diffuse reflectance, diffuse transmittance, and total integrated scattering spectra.     

Spectral-reflectance reconstruction in the near-infrared region by use of conventional charge-coupled-device camera measurements

Our aim is to develop a method for obtaining the reflectance spectra of samples in the near-infrared (NIR) region (800-1,000 nm) by using a small number of measurements performed with a conventional CCD camera (multispectral imaging). We experimentally determined the spectral sensitivity of the CCD camera in the NIR range, used a method based on principal component analysis to reconstruct the spectral reflectance of the samples, and analyzed the number and shape of the filters that need tobe used to apply this method. Finally we obtained the reflectance spectra of a set of 30 spectral curves by numerical simulation. The small amount of errors in the spectral reconstruction shows the potential of this method for reconstructing spectral reflectances in the NIR range.     

多晶氧化钨薄膜的制备及其红外反射调制性能研究

通过工艺参数的优化,采用直流反应溅射工艺成功地制备了具有良好的电化学循环稳定性的多晶氧化钨薄膜.Raman散射光谱研究表明:随着锂离子和电子的共同注入,多晶薄膜中的W⁶⁺逐渐被还原为W⁵⁺.红外反射测试表明:电子注入薄膜后,成为自由载流子,使得氧化钨薄膜表现出一定的金属特性,具有一定的红外反射调制能力.采用该工艺制备的WO₃/ITO/Glass结构的发射率可在0.261～0.589的范围内可逆调节.     

Plasmonic back contacts with non-ordered Ag nanostructures for light trapping in thin-film silicon solar cells

In this work, we investigate the light trapping of thin-film silicon solar cells which apply plasmonic Ag back contacts with non-ordered Ag nanostructures. The preparation, characterization and three-dimensional electromagnetic simulations of these back contacts with various distributions of non-ordered Ag nanostructures are presented. The measured reflectance spectra of the Ag back contacts with non-ordered nanostructures in air are well reproduced in reflectance spectra derived from the three-dimensional electromagnetic simulations of isolated nanostructures on Ag back contacts. The light–matter interaction of these nanostructures is given by localized surface plasmons and, thus, the measured diffuse reflectance of the back contacts is attributed to plasmon-induced light scattering. A significant plasmonic light-trapping effect in n-i-p substrate-type μc-Si:H thin-film solar cell prototypes which apply a Ag back contact with non-ordered nanostructures is identified when compared with flat reference solar cells.     

Estimating visible through near-infrared spectral reflectance from a sensor radiance spectrum

We show that surface spectral reflectance can be separated from illumination effects in visible through near-infrared (350 nm-1740 nm) hyperspectral data by using only the information in a single radiance spectrum. The separation method exploits the fact that reflectance and illumination spectra typically lie in distinct subspaces. We present a comparison of a linear and a nonlinear algorithm for the separation. These algorithms compute an estimate of the spectral reflectance up to a scaling factor. In addition, we present an iterative method that is used to determine the starting point for the nonlinear algorithm. We also develop a method for selecting the dimension of the reflectance and illumination subspaces that is appropriate for material identification applications. The accuracy of the separation methods is quantified by application to noisy visible through near-infrared spectral data with a database of 107 materials and 3000 illumination spectra. The utility of the separation method for material identification is demonstrated with the same database. The results show that accurate reflectance recovery and material identification is possible by use of visible through near-infrared spectral data over the outdoor environmental conditions represented in this data set.     

Using the Kramers-Kronig method to determine optical constants and evaluating its suitability as a linear transform for near-normal front-surface reflectance spectra

In this paper, the suitability of using the Kramers-Kronig transform to routinely extract optical constants from near-normal incidence reflectance spectra of solids and liquids is demonstrated. In addition, the possibility of utilizing the Kramers-Kronig transform as a linearizing transform for near-normal incidence reflectance spectra is investigated. Also, several commercial Kramers-Kronig software packages were utilized in determining the optical constants from the near-normal incidence reflectance of Plexiglas. Unexpectedly, the results produced by the various packages differed significantly. The near-normal reflectance of water was measured, the Kramers-Kronig transform was applied to extract the optical constants of water, and the result was compared to values found in the literature. Furthermore, the Kramers-Kronig transforms of near-normal incidence reflectance spectra of various concentrations of sugar in water were calculated to evaluate its use as a linearizing transform for quantitative applications.     

Weighted compression of spectral color information

Spectral color information is used nowadays in many different applications. Accurate spectral images are usually very large files, but a proper compression method can reduce needed storage space remarkably with a minimum loss of information. In this paper we introduce a principal component analysis (PCA) -based compression method of spectral color information. In this approach spectral data is weighted with a proper weight function before forming the correlation matrix and calculating the eigenvector basis. First we give a general framework for how to use weight functions in compression of relevant color information. Then we compare the weighted compression method with the traditional PCA compression method by compressing and reconstructing the Munsell data set consisting of 1,269 reflectance spectra and the Pantone data set consisting of 922 reflectance spectra. Two different weight functions are proposed and tested. We show that weighting clearly improves retention of color information in the PCA-based compression process.     

Magnetic Properties of a Nitronyl Nitroxide Triradical as a Model for Single-Component Molecule-Based Ferrimagnets

IR and Raman spectra of neutral iodine substituted electron donors DIET, DIEDO and DIETS were measured. Their fundamental vibrational modes were calculated and compared with the experimental data. Additionally, we studied IR and Raman spectra of 2:1 charge-transfer salts formed by these donors with paramagnetic [Fe(bpca)(CN)₃] anions. Polarized IR reflectance spectra of DIET and DIEDO salts were also recorded.     

Relating reflectance spectra space to Munsell color appearance space

The goal is to construct a simple model relating the conceptually defined Munsell color space to a physical representation of the relationship among the reflectance spectra obtained from the color chips comprising the Munsell color atlas. In the model both the Munsell conceptual system and the transformed reflectance spectra are shown to be well represented in Euclidean space, and the two spaces are related by a simple linear transformation. A practical implication is that the method allows one to compare the location of an empirical reflectance spectrum with the aiming point in the conceptual structure.