Design and manufacturing of monolithic mechanical metastructures governing ultrawide low frequency three-dimensional bandgaps

The design and manufacturing of innovative monolithic mechanical metastructures capable of inducing ultrawide low-frequency subwavelength bandgaps, incorporating simple structure morphology and reliable performance, have received enormous attention amongst the scientific community due to the marvellous dynamic characteristics and their potential industrial application in vibration and noise control technology. Specifically, more emphasis is devoted to the mechanical and dynamical properties and innovative design of phononic structures, which leads to periodic systems with unprecedented mechanical and effective medium properties, including ultrawide bandgaps. The present study proposes two types of easily manufacturable 3-D monolithic mechanical metastructure designs, which possess the ability to induce ultrawide low frequency three-dimensional (3-D) complete bandgaps. Employing the principle of mode separation and numerical modal analysis through two different FEM codes, the generation mechanism of ultrawide bandgaps is examined and discussed. The finite supercell structure for both designs is created and numerical frequency response study is performed to validate the claimed properties. The 3-D prototypes are prepared by additive manufacturing technology and vibration tests are performed to confirm the wave attenuation over a broadband frequency range. Both numerical and experimental results are compared and possible discrepancies are discussed. The proposed monolithic metastructures can undoubtedly be manufactured by the conventional additive manufacturing technology, with potential applications in metadevices, where low frequency ultrawide multi-directional vibrations and noise control is desirable. Furthermore, the proposed designs can be employed for underwater acoustic wave manipulation and design of metasurfaces to be embedded at the water surface for ultrahigh transmission of acoustic waves at the water-air interface.