Spiral Rod–Mass 3D Phononic Metamaterial with Tunable Low and Ultra-Wide Bandgap

Elastic metamaterials, renowned for their ability to control elastic waves, have garnered widespread scholarly attention in recent years. In the field of bandgap engineering, designing the unit cell structure of an elastic metamaterial focuses on achieving a lower opening frequency and a higher relative bandwidth for the first local resonance bandgap (LRBG), while maintaining practical structural considerations. This study explores the effect of the spiral rod on the relative bandwidth of the first LRBG and proposes a spiral rod–mass 3D unit cell structure (SMS). Numerical band structure calculations reveal that the corresponding metamaterial possesses an LRBG with an exceptionally low frequency and a relative bandwidth of 150%. Furthermore, the analysis demonstrates that the opening and closing frequencies of the first LRBG in the proposed SMS can be adjusted independently, enriching the bandgap characteristics of the structure. To achieve this, we develop a scheme to independently adjust the opening and closing frequencies of the first LRBG by modifying the two parameters individually without affecting the static effective stiffness of the structure. The SMS unit cell and corresponding meta-structure are fabricated using 3D printing. The transmission spectrum is analyzed through numerical calculations and vibration experiments. These results confirm the isolation of elastic waves within the bandgap. Finally, quasi-static compression tests are performed on the 3D-printed samples. The results demonstrate that the SMS has an acceptable static effective stiffness, further validating its practical potential.