TED-AJ03-323 STUDIES ON THE PREDICTION OF LIGHT SCATTERRING AND THE ESTIMATION OF MULTIPLE SCATTERING EFFECT BASED ON A DIRECT NUMERICAL SOLUTION METHOD OF MAXWELL'S EQUATION

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概要

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• As for the prediction of light scattering pattern formed by a particle illuminated by a laser beam, Mie scattering theory is applicable only to a particle of a very simple shape. In addition, when many particles are closely allocated and the multiple scattering effect is strong, it is almost impossible to predict the scattering pattern based on an extension of Mie scattering theory. In order to overcome this difficulty, we try to apply a direct numerical solution method of the Maxwell's equation (FDTD method). At first, the accuracy of direct numerical solution is examined in relation to some two-dimensional problems such as light scattering by an infinite cylinder and twin parallel cylinders by comparing the scattering pattern obtained by the direct numerical solution with the corresponding analytical solution. These comparisons show good agreements. Based on this confirmation of accuracy, the multiple scattering effects are examined in relation to the scattering pattern formed by many parallel cylinders allocated closely like in Fig.1 (a). The multiple scattering effects in strict meaning can be detected by comparing the scattering pattern obtained by the direct numerical simulation with that by the superposition of light waves, each of which is given by an analytical solution based on the assumption that the relevant cylinder is allocated solely. This comparison illustrated that the difference between the direct numerical solution and the corresponding superposition of light waves becomes remarkable as shown in Fig.1 (b) when the cylinders are allocated closely. By the way, when the particle size distribution is estimated from the intensity pattern of Fraunhofer diffraction, the scattering pattern formed by many scattering objects is estimated by superposition of intensity patterns, each of which is evaluated based on the assumption of a single scattering object. Such assumption has to be used because the positions of particles are not known and the phase lags among each scattered light wave. Also the difference is examined between such an approximated intensity pattern and the exact pattern given by the direct numerical simulation. Finally three-dimensional problems are discussed. The accuracy of direct numerical simulation is confirmed by comparing the predicted scattering pattern from a spherical object with the analytical solution. After that, the effect of depth of a scattering object is examined using the direct numerical solution method.[figure]

• 一般社団法人日本機械学会の論文

著者

• Okamoto Tatsuyuki

  Osaka University

• Nakajima Norihiko

  Nidec Corporation

• Takagi Toshimi

  Osaka University

• OHARA Yoshitaka

  Tokyo University

• TAKAGI Toshimi

  Osaka Sangyo University

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