Particle shape characterization

In general, the particles comprising the earlier generation of obscurants were spherical. Nonspherical particles have, in some cases, been shown to possess more desirable properties, such as broader spectral effectiveness and more obscuration per unit mass. However, the theoretical problem of predicting the interaction of electromagnetic radiation with a particle of arbitrary size, shape, and index of refraction has not been solved for particles with a size on the order of the wavelength of the radiation. Thus, it is difficult to predict or interpret data from experiments conducted on nonspherical particles. The work reported herein addresses this problem with a phenomenological approach. An electrodynamic balance was built that stably suspends individual micron-sized particles. Individual spheres and nonspheres were suspended and photomicrographs were made of the particles while their scattering cross sections were measured in two orthogonal directions. The photographs and cross sections were then analyzed in a search for correlations between particle size and shape and the scattering cross section. This report is organized as follows. Section II contains a description of the experimental apparatus. Photographs of the particles, measurement methodology, and resulting size parameters are presented in Section III. Differential scattering cross-section plots are shown in Section IV and analysis and results described in Section V. Finally, results and conclusions are summarized in Section VI.