Broadband Membrane-type Acoustic Metamaterial Structures with Polymorphic Anti-resonance Modes 2019-01-1574
The researches indicate that rational design of membrane-type acoustic metamaterial (MAM) can make it have a high sound transmission loss (STL) at the anti-resonant frequency. Based on the principle of local resonance of acoustic metamaterials, this paper studied the coupling interactions between sound field and vibration modes, and designed four lightweight MAM structural units with different distributed harmonic oscillators, and then the anti-resonant behaviors of different units within the low frequency were gradually analyzed. The regulation mechanism of continuous polymorphic anti-resonance modes on broadening STL bandwidth was further revealed, and the STL characteristics have been verified within the low-frequency range by numerical simulation and experiments. The results show that the design of a single cross-shaped resonator can increase the diversity of anti-resonance modes and eliminate the node-circular-type resonance mode, then ensure the wider STL bandwidth. Furthermore, four metal platelets set symmetrically between the swing arms based on the unit above increase the local anti-resonance modes of the new unit, which greatly expand the STL bandwidth by shifting its upper limit to the right. In addition, the distributed oscillators in the unit have strong anti-resonant behaviors simultaneously, and the incident sound energy is limited to the unit region, thus the STL peak is high.