Scattering by aggregates with and without an absorbing mantle: microwave analog experiments

Area of Science:

• Physics
• Optics
• Materials Science

Background:

• Studying light scattering from aggregates is crucial for understanding various physical phenomena.
• The Rayleigh size limit and coherent scattering approximations are often used for small particles.

Purpose of the Study:

• To investigate the angular scattering functions of loosely packed aggregates of spheres.
• To analyze the effects of an absorbing mantle on scattering properties.
• To compare scattering behavior before and after coating.

Main Methods:

• Utilized the microwave analog technique for measurements.
• Investigated aggregates of 250 and 500 identical spheres near the Rayleigh size limit.
• Applied successive layers of an absorbing mantle to the aggregates.

Main Results:

• Coherent scattering from independent spheres explains uncoated aggregate scattering, with deviations observed between 60°-80°.
• Scattering functions were generally flat in the backscattering hemisphere.
• The coherent scattering approximation failed for coated aggregates, with an equivalent sphere approximation becoming more suitable.
• Maximum polarization near 90° varied non-monotonically with mantle thickness.

Conclusions:

• The scattering behavior of uncoated aggregates can be approximated by independent sphere scattering.
• Coating aggregates with an absorbing mantle significantly alters their scattering characteristics, necessitating different approximation models.
• Mantle thickness influences polarization, showing a complex dependence.