Topics in Particle and Dispersion Science

DDA - discrete dipole approximation, a computation method to simulate electromagnetic scattering by a non-spherical and/or inhomogeneous particle (for example, Draine and Flatau 1994). Introduced by Purcell and Pennypacker (1973), this method subdivides a particle into small bits of material and accounts for the interference at an observation plane of waves scattered by all these bits. Each bit can be assigned a different refractive index, which opens a possibility to represent an arbitrarily inhomogeneous particle. Each bit is as assumed not only to be illuminated by the incident wave (as in the Rayleigh-Gans-Debye approximation, for example, Bohren and Huffman 1983) but also by the waves scattered by all other bits. Due to computational limitations, the DDA is suitable for relative particle size, x < ~10, and refractive index |m| < ~2, relative to that of a medium surrounding the particles (Draine and Flatau 1994). [MJ]