Tunable evolutions of wave modes and bandgaps in quasi-1D cylindrical phononic crystals

We investigate the tunable characteristics of mechanical waves propagating in quasi-1D phononic crystals composed of horizontally stacked short cylinders at various contact angles and offsets. According to the Hertzian contact theory, elastic compression of laterally-touching cylindrical bodies exhibits a various range of contact stiffness depending on their alignment angles. In this study, we first assemble cylindrical particles in various combinations of inclination angles and systematically examine their forming mechanisms of frequency bandgaps. We also investigate the effect of the rattling motions of cylindrical particles by introducing asymmetric center-of-mass offsets with respect to their contact points. We find that the frequency responses of these quasi-1D phononic crystals evolve into multiple band structures as we employ higher deviations of contact angles and offsets. We calculate the dispersive behavior of propagating waves using a discrete particle model for simple zero-offset cases, while we use a finite element method for simulating the rattling motions of particles under non-zero offsets. We report branching behavior of frequency band structures and the evolution of their vibration modes as we manipulate the contact angles and offsets of the phononic crystals. This study implies that we can leverage the versatile wave filtering characteristics of quasi-1D phononic crystals to construct tunable wave filtering devices for engineering applications.