散射对煤粉太赫兹光谱定量分析的应用研究

Research on Scattering in the THz Quantitative Analysis of Granulated Coal

在利用太赫兹光谱系统对煤质进行定量分析的过程中,样品压片内部煤粉颗粒和高密度聚乙烯颗粒之间的空气孔隙使太赫兹波产生散射进而导致所测煤样本征吸收光谱产生误差。针对样品压片中煤粉颗粒和空气孔隙存在形式的不同建立了压片等效结构,采用Foldy-Twersky EFA理论和迭代Waterman-Truell EFA理论在2~3.5THz频率区间内对压片内部的散射情况进行了数值研究,建立了煤样本征吸收谱提取模型,并利用该模型分别对六种不同粒径范围的煤粉-高密度聚乙烯颗粒混合物压片样品进行了太赫兹域消光光谱的散射校正处理。实验结果表明当煤粉颗粒直径小于38.5μm时,高密度聚乙烯颗粒间空气孔隙对所测样品消光光谱的影响处于主导地位,当煤粉颗粒粒径处于38.5~55μm时,煤粉颗粒散射与空气孔隙散射导致的消光在数值上较为接近,随着颗粒直径进一步增加,煤粉自身散射对吸收光谱的影响也逐步增强并处于主导地位。散射校正前后煤样吸收谱的相关系数和均方根误差表明文中所述模型能够有效减小105μm以下粒径范围内散射对煤粉-高密度聚乙烯混合物压片样品太赫兹吸收光谱的影响,为太赫兹域煤质吸收光谱的定量分析提供了理论基础。

Spectral distortions are common in quantitative terahertz spectra measurement of granulated coal.These spectra warping in the spectroscopy are caused by electromagnetic wave scattering due to coal particles and HDPE intergranularpore-space developed during tableting process consisted in the tablet.In this paper,an equivalent coal-HDPE mixture tablet is built according to the two substances＆#39; structural differences.The scattering contributions of coal particles and air voids are investigated by using the theories of Foldy-Twersky EFA and iterative Waterman-Truell EFA in the frequency from 2 to 3.5 THz,establishing a quantitative analytical model of intrinsic absorption spectra of coal.The studied 6 samples are mixtures of HDPE powder and granulated coal,whose grain sizes varies from one another while the volume concentration is kept constant.Experimental data are recorded with a THz-TDS setup.The scattering loss caused by air voids is more notable when the size of coal particle is smaller than 38.5 μm.When the coal particle size is between 38.5 and 55 μm,it could be observed that the extinction caused by coal particles is more or less the same with it by the air voids.With the increase of coal particle diameter,the scattering contribution of granulated coal to the total propagation loss becomes evident.The correlation coefficient and RMSE between the original and calibrated spectra indicated that the studied quantitative analytical model could significantly reduce the effect of scattering to the measured THz spectrum of coal sample when coal particle size smaller than 105 μm.This study could provide a theoretical basis for quantitative terahertz spectra measurement of coal.