Granular segregation studies for retroreflector sensor development

We are developing a three-dimensional sensing system that enables the tracking of localized material movement by recording displacement and rotation of passive radar targets within materials of interest. Ultimately, the development of this system will provide a highly reliable, cost-efficient set of tools for basic and applied granular materials research. However, the size and material density of the passive radar targets will be inevitably different than the material in which they are embedded, and particles of different sizes and densities tend to segregate when jostled, sheared, or otherwise disturbed. In other words, neighboring particles of different sizes and/or densities will likely not have identical movements. Therefore, effective use of the passive radar targets to predict movement of the bulk material will require a systematic understanding of how segregation depends on relative size and density of the tracer particles. We study segregation in two different systems to isolate different segregation driving mechanisms in densely sheared granular mixtures. In this paper, we discuss the results from these experiments and demonstrate how this can be used to relate sensor particle movement with bulk granular materials movement.