Dynamics of Microscale Granular Crystals

Granular media support a rich array of acoustic phenomena that stem from their complex microstructure and highly nonlinear particulate interactions. While such complexity enables granular media's unique properties, it simultaneously makes predicting their dynamic response challenging. An approach that has yielded insights into the dynamics of macroscale granular media is to study ordered and reduced-dimensional granular systems. Such simplified granular systems are commonly referred to as "granular crystals." Granular media composed of micro-and nanoscale particles are predicted to be analogous in many ways to their macroscale counterparts, however, many phenomena that are negligible at macroscales, such as interparticle adhesion, become critical at sub-microscales. In this chapter, we review several recent studies of the contact-based dynamics of microscale granular crystals. This includes measurements of the interactions of guided and bulk acoustic waves with the contact resonances of self-assembled microsphere monolayers. These works have implications for the broader study of microscale granular materials, provide new ways to study microscale contact mechanics, and may result in a new class of materials for passive wave tailoring, which can be rapidly and inexpensively fabricated in large scales via self-assembly.