Ultrawide bandgap by 3D monolithic mechanical metastructure for vibration and noise control

The all-direction vibration and noise control by metastructures have received high demands in the vibroacoustic community in the recent past to solve multiple vibration and noise-related engineering problems. This class of elastic metamaterial has grasped a strong root in this community due to its versatile wave manipulation characteristics, including frequency bandgap property. Inspired by the idea of metamaterial and computational mechanics in breakthrough research for vibration and noise control technology, the present study proposes a novel 3D phononic metastructure that is capable of generating low-frequency extremely wide three-dimensional complete bandgap with relative bandwidth $${{\Delta \omega } \mathord{\left/ {\vphantom {{\Delta \omega } {\omega_{{\text{c}}} }}} \right. \kern-\nulldelimiterspace} {\omega_{{\text{c}}} }} = 171.5\%$$ . The study is based on analytical modeling, numerical finite element analysis and experiment on 3D printed prototype. The proposed monolithic metastructure is comprised of elastic beams connected orthogonally with rigid spherical masses. The axial compression mode of a complete unit cell structure and the flexural stiffness of beams are manipulated to generate low-frequency extremely wide bandgap. By the principle of modal masses participation/mode separation, the opening and closing of the bandgap is analyzed. The results are corroborated by two different numerical FE solutions on the frequency response spectrum, and the models are validated by performing a vibration test on 3D printed prototype. The wave attenuation over ultrawide frequency range is demonstrated through numerical and experimental approaches, and excellent agreement is reported. The proposed monolithic metastructure design may find potential applications in industrial and infrastructural devices where noise and vibration control over ultrawide frequency range are desirable in all directions.