Isotactic and syndiotactic chiral mechanical metamaterials with tunable band gaps

Although chiral mechanical metamaterials have garnered significant interest due to their wave manipulation capabilities, research into designs featuring adjustable dynamic characteristics remains relatively limited. This study presents an innovative design strategy that integrates adjustable rudder oscillators into periodic chiral lattices. A syndiotactic configuration is further proposed to produce multiple band gaps for broadband vibration suppression. Additionally, a programmable mechanism is introduced to actively regulate the band gap formation without compromising the structural integrity, particularly the static load-bearing capacity. To facilitate the analysis and optimization, a theoretical model that incorporates rigid-flexible and compressive-torsional coupling effects is developed to predict the transmittance spectra of such chiral metamaterials. For validation, both experiment tests and finite element simulations are conducted. The results obtained from all the means indicate that the syndiotactic configuration can produce vibration suppression zones over the ranges of 130.3-246.7 Hz, 293.4-369.0 Hz, and 597.7-995.6 Hz, while the isotactic one can only suppress vibrations in the ranges of 292.3-369.4 Hz and 699.1-783.0 Hz. The overall bandwidth of the vibration suppression zones generated by the syndiotactic configuration increases by 266.3 %. Meanwhile, a comprehensive analysis is also performed to uncover the underlying mechanisms behind the band gap formation. Furthermore, we demonstrate the tunability of the proposed chiral metamaterials in terms of vibration suppression capability. This work not only provides new insights into the exceptional dynamic behaviors of syndiotactic chiral metamaterials but also establishes solid methodological foundations for their analysis.