In this letter, we present the design, fabrication, experimental investigation of the low frequency and wide band omnidirectional bandgap (BG) in a 3D coupled-inertial ultra-lightweight elastic metastructure which is made of a single material. The BG of 601-1504 Hz has been achieved, yet the filling ratio is only 22.4% in the unit cell. The coupled-inertial mechanism of the rotational and translational enables the capability that the tunable design of the BG can be realized under the limitation of quasi-constant stiffness and iso-density by rationally regulating the geometric parameters of the mass element (ME) to amplify the equivalent inertial. Interestingly, the relative width can be widened to 7% and the lower boundary of the BG can go down by 9.8% simultaneously by reducing the MEs’ thickness. The design enriches the strategy for tuning the BG with the condition of quasi-constant stiffness and iso-density, as well as strict weight limitation.
 

Mechanical Metamaterials and Metastructures,Elastic Bandgap,3D periodicity,Coupling Inertial of Translation and Rotation,Vibration Attenuation