Bandgap and directional waveguide in tubular chiral elastic metamaterials

This study investigates the elastic-wave bandgap formation and waveguide characteristics of planar and tubular chiral locally resonant metamaterials (P-CLRMs and T-CLRMs). In P-CLRMs, the lower bandgap edge originates from the resonances of the local resonators, whereas the upper edge is governed by the out-of-plane vibrational mode of the chiral matrix, resulting in a relatively narrow bandgap. To overcome this limitation, a T-CLRMs configuration is proposed, in which the curled chiral matrix effectively suppresses out-of-plane motion, thereby elevating the upper bandgap frequency and significantly widening the bandgap. Further bandgap broadening is achieved by increasing the resonator filling ratio. Finite-period simulations demonstrate pronounced elastic-wave attenuation, which is further enhanced with an increasing number of unit cells. By locally tuning the modulus of the magnetorheological elastomer, both point and line defects can be introduced, enabling elastic-wave localization and directional waveguide. Straight, S-shaped, and Y-shaped defect paths facilitate controllable straight, curved, and branched wave propagation, respectively. Overall, the proposed T-CLRMs exhibit excellent adaptability and tunability for low-frequency broadband vibration isolation and elastic-wave manipulation, offering a practical platform for reconfigurable elastic-wave devices.