Extremely low-frequency vibration–rotation converter based on granular crystals

Recent study of granular crystals has provided a unique platform for elastic wave control, facilitating the applications of mechanical functional devices. In this work, we propose a granular-crystal-based motion converter that can convert mechanical vibration into rotation in an extremely low-frequency regime. This converter is composed of two segments of granular chains with distinct angle configurations. The band structures of the two segments exhibit a specific frequency window with the propagation properties of each to be dominated by vibration–rotation-mixed and quasi-pure rotation modes, respectively. This mode-nature difference allows for the propagation of elastic waves through the structure while experiencing a vibration–rotation mode nature conversion. We verified the existence of this vibration–rotation transition effect in the chain through spatiotemporal simulation. Our research provides new possibilities for vibration control and mode conversion at extremely low frequencies.