Particles within aggregates are commonly in a status of dependent scattering due to the near-field multiple scattering and far-field interferences from neighboring particles. The integral radiative characteristics of fractal aggregates are consequently not only influenced by the monomer size parameter , the refractive index , and the monomer number , but also tied to the fractal dimension . The effective-medium approximation (EMA) simplifies the calculation of aggregate radiative characteristics by treating an aggregate and its surrounding medium as a homogeneous sphere with an effective refractive index, and by applying the Lorenz-Mie theory to this equivalent sphere. The study aims to assess the applicability of EMA to predict the scattering cross-section of fractal aggregates consisting of non-absorbing monomers with , varying from 0.001 to 1.25, ranging from 10 to 500, under different fractal dimensions . The accurate results obtained using the multiple spheres T-matrix were used as a reference. In addition, the RDG-FA (Rayleigh-Deybe-Gans Fractal Aggregates) theory, which is widely used for aggregates with monomer size ≪ 1, was also evaluated for comparison. The finding reveals that both EMA and RDG-FA provide accurate predictions for aggregates satisfying the equivalent aggregate size parameter χ less than , where the dependent scattering is limited. As the dependent scattering effect increases, the fractal dimension emerges as a critical factor influencing EMA's accuracy, with EMA excelling for aggregates with larger fractal dimensions close to 3. Furthermore, 2.1 is a critical value of above which EMA outperforms RDG-FA.

中文翻译：

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有效介质近似在预测非吸收性球形颗粒分形聚集体辐射特性中的适用性评估

由于邻近颗粒的近场多重散射和远场干扰，聚集体内的颗粒通常处于相关散射状态。因此，分形聚集体的整体辐射特性不仅受单体尺寸参数、折射率和单体数量的影响，而且还与分形维数有关。有效介质近似（EMA）通过将聚集体及其周围介质视为具有有效折射率的均匀球体，并将洛伦兹-米氏理论应用于该等效球体，简化了聚集体辐射特性的计算。该研究旨在评估 EMA 在预测不同分形维数下由非吸收性单体组成的分形聚集体的散射截面的适用性，其中 的范围为 0.001 至 1.25，范围为 10 至 500。使用多球体 T 矩阵获得的准确结果用作参考。此外，还对广泛用于单体尺寸<1的聚集体的RDG-FA（Rayleigh-Deybe-Gans Fractal Aggregates）理论进行了评估以进行比较。研究结果表明，EMA 和 RDG-FA 都能准确预测满足等效聚集体尺寸参数 χ 小于 的聚集体，其中相关散射受到限制。随着相关散射效应的增加，分形维数成为影响 EMA 准确性的关键因素，对于分形维数接近 3 的较大聚集体，EMA 表现出色。此外，2.1 是一个临界值，高于该值 EMA 优于 RDG-FA。