非球形烟尘粒子后向散射场的光谱分析

Backscattering Spectrum Analysis of Nonspheroid Soot Particle

在利用后向散射法测量烟尘浓度和粒径的过程中,对烟尘粒子模型的后向散射光谱特性进了计算,确定影响后向散射光谱强度的主要因素并进行分析。对实际排放的烟尘进行显微观察表明,利用椭球、圆柱和广义切比雪夫3种非球模型可以较好地模拟烟尘粒子,其等效直径约1μm。通过"T矩阵法"对这3种非球形粒子模型后向散射场的光谱特性进行了分析,结果表明:非球形粒子的可见/红外波段后向散射现象较球形粒子明显,特别是广义切比雪夫粒子的后向散射光强最高可达到前向的3.5倍;对于吸收性非球形粒子(复折射率m=1.57-0.56i),后向散射光强远大于非吸收性非球形粒子(复折射率m=1.57-0.001i);随着粒子等效半径的增大,光源波长也应随之增加。这为在实际测量时光源及方位的选择提供了理论依据。

In the process of measuring soot concentration and grain diameter,the backscattering spectrum of soot particle model was calculated to ascertain and analyze main effective factor of backscattering intenisty.In the present paper,ellipsoid,column and generalized Chebyshev,three nonspheroid models,were selected according to micrograph of practical soot particle,which aims to simulate practical soot particle with equivalent diameter of about 1 μm.T-matrix method was used to caculate backscattering spectrum of the three nonspheriod models,and the main effective factor curves of intensity were obtained,too.Both numerical computer simulations and experimental results illustrate that nonspheroid particle backscattering intensity is stronger than that of spheroid particle in the visible/infrared spectrum band,especially for generalized Chebyshev model,whose backscattering intensity can be even 3.5 times higher than that of forward scattering.Meanwhile,the Absorbency non-spheroid particle （complex refractive index m=1.57-0.56i） backscattering intensity is stronger than that of non-Absorbency nonspheriod particle （complex refractive index m=1.57-0.001i）.Furthermore,with the increase in particle equivalent radius,the light source wavelength also needs to be increase to obtain more light intensity information.The backscattering light spectrum information provides a reasonable basis for selecting light source and measure angle.